Dissertations / Theses on the topic 'Memory B cells'

B cells recognise antigens on micro-organisms through their B cell receptor (BCR) and via Toll-like receptors (TLRs), and thus respond in both innate and adaptive manners during the subsequent immune response. Innate recognition through TLRs has the potential to alter the behaviour of whole B cell populations. I show, here, that MyD88-dependent activation of B cells via TLR2 or TLR9 causes the rapid loss of expression of CD62L, by metalloproteinasedependent shedding, resulting in the exclusion of these cells from lymph nodes and Peyer’s patches, but not the spleen. Moreover, systemic infection with Salmonella typhimurium causes shedding of CD62L and the subsequent focussing of B cell migration to the spleen. I reveal that splenic B cells undergo further changes during S. typhimurium infection, including TLR-dependent differentiation of marginal zone B cells into IgM-secreting plasma cells. Together, these TLR-mediated alterations to B cells are likely to influence the development of immunity to pathogens carrying the appropriate ligands. In addition to these innate responses of B cells, endocytosis of cognate antigen through their BCR allows antigen presentation. This, together with their ability to secrete cytokines, means they have the potential to drive T helper cell responses. I investigate the role of B cells in such CD4+ T cell responses by following antigen-specific T cells in vivo, using both a peptide immunisation strategy and the S. typhimurium infection model. I use anti-CD20 B cell depletion antibodies to deplete B cells at various stages of the immune response, and analyse the effects on T follicular helper and memory cell populations. I show that both the generation and maintenance of T follicular helper cells is dependent on the presence of B cells. Furthermore, I demonstrate that B cells are necessary very early in immune responses, during the first 10 days, for efficient generation of memory T cells.

Background: The presence of B cells in early stage non-small cell lung cancer (NSCLC) is associated with longer survival, however, the role these cells play in the generation and maintenance of anti-tumor immunity is unclear. B cells differentiate into a variety of subsets with differing characteristics and functions. To date, there is limited information on the specific B cell subsets found within NSCLC. To better understand the composition of the B cell populations found in NSCLC we have begun characterizing B cells in lung tumors and have detected a population of B cells that are CD79A(+)CD27(-)IgD(-). These CD27(-)IgD(-)(double-negative) B cells have previously been characterized as unconventional memory B cells and have been detected in some autoimmune diseases and in the elderly population but have not been detected previously in tumor tissue. Methods: A total of 15 fresh untreated NSCLC tumors and 15 matched adjacent lung control tissues were dissociated and analyzed by intracellular flow cytometry to detect the B cell-related markers CD79A, CD27 and IgD. All CD79A(+) B cells subsets were classified as either naive (CD27(-)IgD(+)), affinity-matured (CD27(+)IgD(-)), early memory/germinal center cells (CD27(+)IgD(+)) or double-negative B cells (CD27(-)IgD(-)). Association of double-negative B cells with clinical data including gender, age, smoking status, tumor diagnosis and pathologic differentiation status were also examined using the logistic regression analysis for age and student's t-test for all other variables. Associations with other B cell subpopulations were examined using Spearman's rank correlation. Results: We observed that double-negative B cells were frequently abundant in lung tumors compared to normal adjacent controls (13 out of 15 cases), and in some cases made up a substantial proportion of the total B cell compartment. The presence of double-negative cells was also found to be inversely related to the presence of affinity-matured B cells within the tumor, Spearman's coefficient of -0.76. Conclusions: This study is the first to observe the presence of CD27(-)IgD(-)double-negative B cells in human NSCLC and that this population is inversely correlated with traditional affinity-matured B cell populations.

B-Lymphozyten leisten unterschiedliche Beiträge zur Pathophysiologie der Rheumatoiden Arthritis. Sie produzieren Autoantikörper, präsentieren Autoantigene und schütten verschiedene Zytokine, die am proinflammatorischen Prozess beteiligt sind, aus. Aufbauend auf diesen Ergebnissen wurden in den letzten Jahren Therapien entwickelt, die gezielt B-Lymphozyten ansteuern um direkt oder indirekt in den autoimmunen Krankheitsverlauf einzugreifen. Die zeitlich begrenzte B-Zell-Depletion mit Rituximab (anti CD20-Antikörper) hat dabei in den letzten Jahren einen hohen Stellenwert erlangt und wird im klinischen Alltag insbesondere bei der Behandlung von Patienten mit rheumatoider Arthritis angewandt. Rituximab induziert im peripheren Blut bemerkenswerte Veränderungen in der Homöostase der B-Zell-Subpopulationen. Nach Therapie mit dem anti-CD20 Antikörper Rituximab beginnt die Repletionsphase mit der peripheren Aussaat von transitionalen unreifen B-Zellen. Im weiteren Verlauf kommt es zu einer Normalisierung des naiven B-Zell-Pools. Das B-Zell Gedächtnis und in besonderem Maße die IgD+CD27+ Gedächtniszellen erholen sich nach Therapie nur langsam. In einer prospektiven klinischen Studie hat unsere Arbeitsgruppe gezeigt, dass die Gesamtzahl der Gedächtniszellen gut mit der Dauer der klinischen Antwort auf Rituximab korreliert. Es ist wenig über die speziellen molekularen Veränderungen innerhalb der Gedächtnis B-Zellen nach Rituximab Therapie bekannt. Um die Veränderungen im peripheren Blut zu verstehen untersuchten wir die somatische Mutationsfrequenz und das Muster der Ig-VH3 Gen Rearrangements, indem wir prä- und posttherapeutisch bei 18 Patienten einzelne B-Zellen isolierten und den individuellen B-Zellrezeptor durch eine Einzelzell RT-PCR amplifizierten und sequenzierten. Wir verglichen das Mutationsmuster nach erfolgreicher B-Zelldepletion in den neu rezirkulierenden Gedächtnis B-Zellen mit dem Mutationsmuster von vier Gesunden Blutspendern und sechs nicht-RA Patienten, die eine Hochdosis Chemotherapie mit anschließender autologer oder allogener Stammzelltransplantation erhalten hatten. Zunächst haben wir die Zusammensetzung der Gedächtniszellen im peripheren Blut analysiert. Der Phänotyp der peripheren prä-switch (IgD+CD27+) und post-switch (IgD-CD27+) Gedächtniszellen zeigte keine quantitativen Unterschiede in RA-Patienten im Vergleich zu Gesunden. Bei der direkten Analyse des B-Zell Immunglobulin Rezeptors fanden sich jedoch zwischen klassengeswitchten und ungeswitchten Gedächtnis B-Zellen signifikante Unterschiede in der Anzahl der Mutationen in der variablen Region der Ig Rezeptors. Die Population der IgD+CD27+ Gedächtniszellen beinhaltete sowohl nicht mutierte, wenig mutierte und stark mutierte (Median= 9 Mutationen pro Sequenz) rearrangierte Ig- Rezeptoren, wohingegen die IgD-CD27+ Gedächtniszellen einen durchgehend hoch mutierten (Median = 18 Mutationen pro Sequenz) Rezeptor aufwiesen. Der Unterschied zwischen beiden Gruppen war signifikant (Mutationsfrequenzen 3.83±0.19% vs. 7.1±0.53%; P=0.0001). Grundlegende Veränderungen wurden bei den rezirkulierenden ungeswitchten Gedächtniszellen (IgD+CD27+) nach vorübergehender B-Zell Depletion mit Rituximab festgestellt. Diese Zellen wurden bis 6 Jahre nach Rituximab beobachtet und zeigten eine stark verzögerte Zunahme an Mutationen im Ig-Rezeptor. Ein Jahr nach einmaliger Gabe von Rituximab waren 84% der einzelnen zirkulierenden IgD+/CD27+ B-Zellen unmutiert. Zu diesem Zeitpunkt fanden sich keine stark mutierten Ig-VH3 Gen Rearrangements (P=0.0001). Mit zunehmendem Abstand zur B-Zell depletierenden Therapie konnten in der Repopulationsphase zunehmende Zahlen an Mutationen in den B-Zell Ig Rezeptoren festgestellt werden. Beispielsweise waren während des 2. Jahres der Regeneration (P=0.0001) 7.8%, sowie nach 4 Jahren nur 14% der Ig Rezeptoren mutiert. Sogar 6 Jahre nach Behandlung, waren VH Mutationen in IgD+ Gedächtniszellen noch deutlich vermindert. Selbst nach dieser Zeit fanden sich in der prä-switch Gedächtnispopulation nur 27% hochmutierte Sequenzen während vor der passageren B-Zelldepletion 52% ein hohe Zahl an Mutationen trugen (P=0.0001). Die posttherapeutische Analyse der CDR3 Länge der regenerierten IgD+ Gedächtniszellen ergab eine erhöhte CDR3 Länge, die signifikant mit der Anzahl der nicht mutierten VH Genrearrangements während der Repletionsphase korreliert. Interessanterweise regenerierten Patienten nach Hochdosis Chemotherapie und allogener Stammzelltransplantation ihre IgD+ Gedächtniszellen mit einer deutlich höheren Anzahl an Mutationen. Ein Jahr nach Transplantation zeigten die Ig Rezeptoren schon 22% hoch mutierte und 42% unmutierte VH Rearrangements. Das zeigt, dass eine gegen CD20 gerichtete Behandlung nicht nur eine Verzögerung der Produktion der ungeswitchten Gedächtniszellen zur Folge hat, sondern darüber hinaus einen signifikanten Effekt auf die Mutationsrate im präswitch Gedächtnis B-Zellpool besitzt. Im Gegensatz zum Mutationsmuster der IgD+ Gedächtniszellen regenerierten die klassengeswitchten Gedächtniszellen nach anti-CD20 Depletion im peripheren Blut mit quantitativ normalen Mutationen im Ig Rezeptor. Interessanterweise fand sich allerdings eine Änderung der exprimierten Isotypen mit deutlicher Dominanz IgA exprimierender B Zellen. Weitere Analysen der klassengeswitchten Gedächtnis B-Zellen zeigen außerdem eine Therapie induzierte qualitative Veränderung dieses B-Zellpools. So waren posttherapeutisch die Mutationen in bestimmten T-Zell abhängigen Mutationshotspots, dem RGYW/WRCY Motiv, signifikant vermehrt (Mutationstargeting vor Therapie 27% vs. 43% nach Rituximab, P=0.0003). Dies weist darauf hin, dass die Mechanismen der Affinitätsreifung im klassengeswitchten B-Zellgedächtnis vor und nach B-Zelldepletion unterschiedlich funktionieren. Der Mutationsmechanismus selbst ist allerdings in diesen Zellen quantitativ nicht eingeschränkt. Zusammenfassend zeigt unsere Arbeit zum erstem mal, dass es nach einer passageren B-Zelldepletion mit anti-CD20 Antikörpern zu einer über Jahre hinweg nachweisbaren ausgeprägten Verzögerung in der Aquisition von somatischen Mutationen in rearrangierten VH Genen der IgD+ Gedächtniszellen kommt. Demgegenüber erholt sich das klassengeswitchte B-Zellgedächtnis mit uneingeschränkter Zahl von Mutationen im Ig Rezeptor. Diese Resultate zeigen, dass anti-CD20 gerichtete Therapien in besonderem Maße IgD+ Gedächtniszellen beeinflussen. Der Selektionsdruck durch Antigene und/oder die Selektion der Ig Rezeptoren erscheint unter diesen Bedingungen speziell bei IgD-Gedächtnis B-Zellen reduziert. Die Daten unterstützen die Hypothese, dass prä-switch Gedächtnis B-Zellen im Vergleich zu post-switch Gedächtnis B-Zellen andere Bedingungen für die Aktivierung der Mutationsmaschinerie benötigen. Die Resultate eröffnen neue Wege für das Verständnis der Pathophysiologie der B-Zell Gedächtnisentwicklung und können helfen neue zielgerichtete Therapien zur Behandlung von Autoimmunerkrankungen zu konzipieren
Diverse roles of B cells in the pathophysiology of rheumatoid arthritis are now well established. B cells contribute to autoimmunity by producing autoantibodies, processing autoantigen and the production of different cytokines which are involved in the inflammatory cascade. Therefore approaches to target B lymphocytes directly or indirectly are developed for clinical practice to treat autoimmune diseases including rheumatoid arthritis. Transient B cell depletion by rituximab (anti-CD20 antibody) has gained prime importance in recent years. Meanwhile anti-CD20 mediated transient B cell depletion therapy is now used with clinical efficiency in the treatment of patients with rheumatoid arthritis. Rituximab induces noteworthy changes in the homeostasis of peripheral B cell subpopulations during the repletion phase with emerging immature B cells in peripheral blood followed by normalization of the naïve B cell pool and a longterm delay in memory B cell subsets in patients with rheumatoid arthritis. Particularly IgD+CD27+ memory B cells repopulate very slowly during B cell regeneration. In a prospective clinical study, our laboratory has shown that the overall number of memory B cells correlates well to the duration of clinical response to rituximab. Little is known about the particular molecular changes in the memory B cell repertoire after rituximab therapy. To better understand peripheral memory B cell subsets, we explored in detail the somatic mutational frequency and pattern of Ig-VH3 gene rearrangements by using a single B cell sorting technique followed by nested PCR before and up to 6 years after rituximab therapy in 18 RA patients. We compared rituximab inflicted dynamics of mutational acquisition to memory B cell repopulation in 4 healthy donors and 6 non RA patients undergoing high dose chemotherapy followed by autologous or allogeneic stem cell transplantation (SCT). Firstly we analyzed the peripheral composition of memory B cell subsets. The phenotypic analysis of peripheral pre-switch (IgD+CD27+) and post-switch (IgD-CD27+) memory B cells did not reveal any quantitative differences in RA patients prior to B cell depletion therapy compared to healthy donors. However extending those studies in directly analysing the B cell immunoglobulin receptor from individual B cells of RA patients and healthy controls brought interesting results. Pre-switched and post-switched memory B cells showed a highly significant difference in the amount of mutations/sequence. The population of IgD+CD27+ memory B cells is comprised of non-mutated, low and highly mutated (median= 9 mutations/ sequence) rearranged Ig receptors whereas the IgD-CD27+ memory B cell compartment shows quite uniformly highly mutated (median 18 mutations/ sequence) sequences indicating a significant difference between these two groups (mutational frequencies 3.83±0.19% vs. 7.1±0.53%; P=0.0001). Profound changes were noted in the re-emerging pre-switch memory B cells (IgD+/ CD27+) after transient B cell depletion with rituximab. These cells showed over a time period of 6 years after treatment with rituximab significantly delayed acquisition of mutations in Ig receptors on the single B cell level. One year after a single course of rituximab 84% of single repopulating IgD+/CD27+ B cells were unmutated and no highly mutated Ig-VH gene rearrangements were found(P=0.0001). Over time increasing numbers of mutations could be detected i-e 7.8% during 2nd year of regeneration (P=0.0001), 14% after 4 years (n=2). Nevertheless even 6 years after rituximab, VH mutations in IgD+ memory B cells were still reduced with 27% highly mutated sequences compared to 52% pre therapy(P=0.0001). Post-therapy analysis of CDR3 length of regenerated IgD+ memory B cells revealed increased CDR3 length which also correlates well with elevated number of non-mutated VH gene rearrangements observed during repletion phase. In comparison patients undergoing high dose chemotherapy followed by allogeneic stem cell transplantation repopulated IgD+ memory cells earlier with higher numbers of mutations in IgD+ memory B cells. One year after transplantation Ig receptors showed already 22% highly mutated and 42 % unmutated VH rearrangements. These findings indicated that anti-CD20 mediated B cell depletion seems not only to delay the production of pre-switch memory B cells but also significantly affects the acquisition of mutations in the IgD+ memory B cell pool. In contrary to the mutational pattern of IgD+ memory B cells after rituximab class switched memory B cells repopulate in the periphery with quantitatively normal mutations in their Ig receptors. Although the numeric replenishment of these recirculating class-switched memory B cells was also reduced after rituximab, we found no delay in quantitative acquisition of mutations also an increased proportion of IgA expressing B cells in this memory B cell subset was detected. Our data showed that post-therapy mutational targeting in RGYW/WRCY motifs were significantly increased as compared with that of pre-treatment (27% before rituximab vs. 43% after therapy, P=0.0003) indicating that affinity maturation may operate differently in class-switched memory B cells before and after B cell depletion. These results indicate a normal development process with an unimpaired mechanism of mutational acquisition in class-switched memory B cells. These data argue for different requirements to undergo somatic hypermutations in IgD+ memory B cells in comparison to class switched memory B cells. To conclude, our work has demonstrated for the first time a delayed acquisition of somatic hypermutations at single Ig receptor VH gene rearrangements of IgD+ memory B cells in comparison to class-switched memory B cells. These results demonstrate that IgD+ memory B cells are particularly susceptible to anti-CD20 treatment in patients with rheumatoid arthritis. In addition antigenic pressure and/or selection are substantially reduced by rituximab therapy which is basically not seen in the class-switched memory compartment. These data are in line with the hypothesis that IgD+ memory B cells have distinct requirements for activating their mutational machinery compared to class-switched memory B cells which recover normal mutations during regeneration phase. The results have implications in understanding the pathophysiology of memory B cell in rheumatoid arthritis and may be helpful in designing new targeted therapies

We found that IgM+IgD- memory (ME-M) B cells formed a large reservoir of intestinal antigen-selected IgM+ lymphocytes distinct from antigen-naïve IgM+ lymphocytes. Human ME-M B cells colonized the intestine early in life, persisted throughout adulthood and inhabited Peyer’s patches and isolated lymphoid follicles. Intestinal ME-M B cells shared some commonalities with splenic IgM+IgDlowCD27+ marginal zone B cells, including phenotypic traits, multiple IgVH gene families and a pronounced reactivity against microbial carbohydrates and lipids. However, ME-M B cells expressed a gut-specific gene signature and an IgVH gene mutation profile consistent with a germinal center origin from gut inductive sites. Accordingly, ME-M B cells showed strong reactivity against mucus-embedded commensal antigens. Furthermore, ME-M B cells generated IgM+ or IgA+ plasma cells (PC) in response to T cell-dependent or independent signals and organized clonally coordinated IgM and IgA responses in ileum and colon. IgM+ PC emerging from ME-M B cells released IgM antibodies that along with IgA, coated intestinal bacteria and fungi.
Hem descovert que les cèl·lules B de memòria IgM+IgD- (ME-M) formen una gran reserva intestinal de limfòcits preseleccionats diferents dels limfòcits verges. Les cèl·lules ME-M colonitzen l'intestí als inicis de la vida i hi perduren durant l’edat adulta en les plaques de Peyer i els fol·licles limfoides aïllats. Les cèl·lules ME-M comparteixen certes característiques amb les cèl·lules B IgM+IgDlleuCD27+ de la zona marginal esplènica, incloent trets fenotípics, famílies de gens IgVH i reactivitat pronunciada contra hidrats de carboni i lípids microbians. No obstant això, les cèl·lules ME-M expressen una signatura gènica específica del intestí i un perfil de mutació en els gens IgVH consistent amb un origen a centres germinals intestinals. En consequència, les cèl·lules ME-M mostren reactivitat enfront d'antígens comensals del moc intestinal. A més, les cèl·lules ME-M generen cèl·lules plasmàtiques (PC) IgM+ o IgA+ en resposta a senyals dependents i independents de cèl·lules T, i organitzen respostes clonals coordinades IgM i IgA en l'ili i el còlon. PC IgM+ derivades de cèl·lules ME-M, produeixen anticossos IgM que, juntament amb IgA, recobreixen bacteris i fongs del moc intestinal.

Gedächtnis-B-Zellen und Plasmazellen sind essentielle Komponenten der protektiven Immunität. Die Mechanismen ihrer Induktion, ihres Überlebens und der Gedächtnis-B-Zellreaktivierung sind allerding bisher nur unvollständig verstanden. Um unser Wissen diesbezüglich zu erweitern, wurden in der vorliegenden Arbeit zum einen Charakteristika von Primär- und Sekundärimmunantworten nach Immunisierung mit Keyhole Limpet Hemocyanin (KLH) untersucht und zum anderen das Vorkommen sowie der Phänotyp humaner Gedächtnis-B-Zellen in verschiedenen lymphatischen Geweben analysiert. Die primäre parenterale KLH Immunisierung führte auf serologischer und zellulärer Ebene zu einer Reihe unerwarteter Ergebnisse, welche u. a. das Auftreten von IgA Antikörpern und die gleichzeitige Präsenz von hoch- und wenig mutierten primären Plasmablasten beinhalteten. Die Untersuchung der Gedächtnis-B-Zellverteilung in verschiedenen lymphatischen Geweben ergab den größten Gedächtnis-B-Zellpool in der Milz. Blut-, Tonsillen-, Knochenmarks- und Milz-Gedächtnis-B-Zellen wiesen nur wenige phänotypische Unterschiede auf. Einer davon war die CD69 Expression auf tonsillären ruhenden Gedächtnis-B-Zellen, was darauf hindeutet, dass tonsilläre Gedächtnis-B-Zellen tatsächlich sessil sein könnten. Die hier erhaltenen Ergebnisse stellen neue Erkenntnisse über bisher unbeschriebene Mechanismen bei parenteralen Immunantworten wie zum Beispiel die Induktion von IgA Antikörpern sowie die potentielle Rekrutierung kreuzreaktiver Gedächtnis-B-Zellen dar. Es bleibt zu klären, wie die Reaktivierung solcher Gedächtnis-B-Zellen reguliert ist. Derartiges Wissen wäre insbesondere für Therapien von Erkrankungen des Immunsystems, wie Autoimmunität, von Bedeutung. Das potentiell patrouillierende Verhalten der Gedächtnis-B-Zellen ist ein markanter Unterschied zu den nischenabhängigen sessilen Plasmazellen und deutet weitestgehend darauf hin, dass Gedächtnis-B-Zellen nicht auf derartige Nischen angewiesen sind.
Memory B cells (mBC) and antibodies are major mediators of protective immune responses yet the mechanisms of their induction, maintenance and mBC reactivation are poorly understood. Therefore, to enhance knowledge in this regard this study comprehensively characterized a human primary and secondary B cell immune response to Keyhole Limpet Hemocyanin (KLH). Secondly, mBC maintenance was investigated by a systematic analysis of mBC presence, frequency and phenotype within different lymphoid organs. Parenteral primary KLH immunization yielded unexpected results on the serological and B cellular level, including KLH-specific IgA antibody induction, the simultaneous presence of low and highly mutated circulating KLH-specific primary plasmablasts and only little clonal overlap between the primary, memory and secondary KLH-specific B cell repertoires. With respect to the organ distribution of human mBC, the spleen was identified as a major mBC reservoir. Splenic, tonsillar, bone marrow and blood mBC pools exhibited a largely comparable phenotype. Yet, we found tonsillar mBC to express CD69. Due to their resting state tonsillar mBC could therefore constitute a tissue resident cell population. The observations described allow insights into hitherto unknown potential mechanisms behind primary immune responses, i.e. prominent IgA induction by parenteral challenge and inclusion of cross-reactive mBC. The so far unclear regulatory players involved deserve future investigation, as such knowledge may be crucial for therapeutic interventions in immune system disorders. Furthermore, strikingly different to the resident plasma cells in the bone marrow, mBC appear to distribute between lymphoid organs and continuously recirculate in peripheral blood indicative of their potential permanent screening activities, suggesting that human mBC do not require one dedicated niche for their principle survival.

Antikörper gegen Circumsporozoite protein (CSP), ein Oberflächenantigen von Plasmodium falciparum (Pf), können sterile Immunität hervorrufen und dadurch die Entwicklung von Malaria im Tierversuch verhindern. Im Menschen werden protektive B-Zell Gedächtnisantworten gegen CSP durch natürliche Malariaerkrankung bzw. Vakzinierung jedoch nur unzureichend erzeugt. - Für die Entwicklung von Gedächtnis-B-Zellen stellt die Affinitätsreifung, welche durch somatische Immungobulin Hypermutation sowie der nachfolgenden Selektion von B-Zellen mit verbesserter Antigenaffinität charakterisiert ist, eine Schlüsselfunktion in der Generierung von protektiven Immunantworten dar. Wie Affinitätsreifung gegen CSP im Menschen stattfindet ist jedoch nicht bekannt. In dieser Arbeit wird die Affinitätsreifung von CSP Gedächtnis B-Zellen auf Einzelzellebene im Menschen über drei kontrollierte Infektionen mit Pf Sporozoiten unter Chemoprophylaxe untersucht. Durch Hochdurchsatz-Einzelzell-Sequenzierung der Immunoglobulin (Ig) gene loci und der Produktion von rekombinanten monoklonalen Antikörpern gewährt diese Arbeit Einsicht in die Selektion und Affinitätsreifung von humanen Gedächtnis-B-Zell Antworten gegen komplexe Proteinantigene und identifiziert Keimbahn kodierte Immunglobulin Charakteristika, die mit hoher CSP-Affinität und Pf-Inhibition einhergehen. Überraschenderweise zeigen die Daten, dass initiale klonale Selektion von hochaffinen B Zellen eine weitaus wichtigere Rolle als Affinitätsreifung in dieser Infektion spielt. Diese Arbeit zeigt fundamentale Eigenschaften von humanen Gedächtnisantworten in einer komplexen Parasiteninfektion und liefert die Grundlage für ein mögliches Design von neuartigen Immunogenen um hoch-affine B-Zellen gegen CSP effizienter zu induzieren.
Antibodies against the major Plasmodium falciparum (Pf) sporozoite surface protein, circumsporozoite protein (CSP), can mediate sterile immunity thereby preventing malaria disease symptoms as shown by passive transfer in animal models. However, protective anti- CSP memory antibody responses are not efficiently induced by natural Pf exposure or vaccination. Affinity maturation, i.e. the diversification of antigen-activated naïve precursor B cells by a somatic immunoglobulin (Ig) gene mutation process and the subsequent selection of B cells expressing antigen receptors with improved antigen affinity in germinal center reactions is considered key to the formation of protective memory B cell responses. However, how the anti-PfCSP memory B cell response matures in humans is not known. To address this question, the clonal evolution of the human anti-Pf CSP memory B cell response over three successive controlled Pf infections under chemoprophylaxis was assessed at single cell level by high throughput paired full-length Ig gene sequencing and recombinant monoclonal antibody production. The work provides basic insights in the longitudinal development of human memory B cell responses and identified germline-encoded Ig gene features that were associated with high anti-CSP affinity and Pf inhibitory antibody activity. The clonal selection of germline B cells expressing such antibodies, rather than affinity maturation, was associated with high quality anti-PfCSP memory B cell responses. The data provide insights into the evolution of antibody response to a complex protein antigen during infection and a strong rational for the design of novel CSP immunogens to target naïve B cell precursors expressing potent anti-CSP antibodies for the induction of protective memory B cell responses by vaccination.

Streptococcus pneumoniae is a significant cause of mortality and morbidity in both children and older adults, with infection resulting in invasive disease, pneumonia and otitis media. The inclusion of pneumococcal conjugate vaccines in routine infant immunisation programmes has had a major impact on disease rates. Vaccine-induced protection against pneumococcal infection is thought to be mediated by the generation of persistent serotype-specific functional antibodies and antigen-specific memory B cells, the latter capable of generating a rapid secondary antibody response on re-exposure to antigen. Although many studies have investigated the immunogenicity of pneumococcal vaccines in different age groups by measuring serotype-specific antibodies, there is more limited information about the B cells underlying such an immune response. Important areas to investigate include the identity of the B cell subsets involved in antibody production and the potential link between memory B cells (B_MEM) and persistent antibody production by long-lived plasma cells. In this thesis I have investigated in detail the immune response to pneumococcal vaccines given to children and adults by a variety of different methods. By examining the variability of a B_MEM ELISpot method, it was shown that this assay is robust and reproducible and can be performed on fresh or frozen samples and in different laboratories. Using this technique, in a study of pre-school children, it was demonstrated for the first time that the level of pre-existing serotype 3-specific antibody is negatively correlated with, and may directly impair the B_MEM response to a booster dose of 13-valent pneumococcal conjugate vaccine (PCV-13) containing serotype 3 glycoconjugate. In the same study, it was shown that antibody persistence against most vaccine serotypes can be expected until the age of 3.5 years. A novel antigen-labelling technique was used in a detailed kinetics study of antigen-specific B cell subsets in response to either PCV-13 or 23-valent pneumococcal polysaccharide vaccine in adults. The results of this study revealed distinct B cell subset response patterns that were observed in all study participants indicating that IgM B_MEM seem to play a major role in the immune response to pneumococcal vaccines. In addition, in the same study, genome wide analysis of gene expression was performed and it was shown that vaccination with either a pneumococcal conjugate or polysaccharide vaccine results in a marked difference in numbers of differentially expressed genes 8 days following vaccination. A further tool likely to be of use in investigating B cell responses is the analysis of the antibody repertoire using next-generation sequencing techniques. In order to test the ability of these methods to detect vaccine responses, a large dataset of high-throughput B cell receptor sequences was analysed and revealed convergence of antigen-specific complementary-determining region (CDR)₃ amino acid (AA) sequences following vaccination and identified antigen-specific sequences. It was further demonstrated that for sequences directed against the H. influenzae type b (Hib) polysaccharide, diversity of immunoglobulin gene rearrangements is much greater than previously recognised. Frequencies of Hib-specific CDR₃ AA sequences were linked with anti-Hib avidity indices highlighting the potential of this method as an alternative (functional) measure of vaccine immunogenicity. These data suggest that studying the B cells and antibody repertoire post-vaccination can give novel insights into the biology that underlies the immune responses.

Les lymphocytes T CD8+ spécifiques de l'antigène sont impliqués dans la réponse immunitaire adaptative et jouent un rôle essentiel dans la protection de l'hôte contre l'infection par des pathogènes intracellulaires. Cette protection de longue durée dépend de la génération de réponses lymphocytaires T CD8+ mémoires, hautement fonctionnelles en termes de fréquence et de fonctionnalité, après réinfection.Après présentation de l'antigène, une cellule T CD8 naïve subit une forte expansion clonale, générant une population hétérogène de cellules activées qui est dominée, au sommet de l'expansion, par des effecteurs CD8 de courte durée (SLEC). Cette expansion est suivie d'une phase de contraction massive par apoptose. Quelques cellules survivent à cette phase de contraction et finissent par se différencier en cellules mémoire hautement compétentes. Les processus par lesquels et le moment où se différencient les précurseurs de mémoire (MPECs) restent largement inconnus, tout comme les étapes ultérieures de leur maturation en cellules mémoire pleinement fonctionnelles. Les signaux d'aide provenant des cellules T CD4+ sont clairement requis tout au long du processus de maturation des MPEC.Notre équipe a montré que les lymphocytes T CD4+ régulateurs FoxP3+ (Tregs) favorisent la maturation des MPEC en limitant l'exposition à l'IL-2 et en fournissant des signaux inhibiteurs, mais ce n'est probablement qu'une facette de l'aide complexe et multiforme apportée par les cellules T CD4+ au MPEC. Les Tregs agissent sur des MPEC préexistants. Les réponses mémoire B et CD8+ partagent des caractéristiques communes, telles que l'expression du facteur de transcription Bcl-6. Les lymphocytes T CD4+ folliculaires (Tfh) sont les principaux producteurs de la cytokine IL-21. Bien que les mécanismes par lesquels les Tfh induisent l’expression de Bcl-6 dans les cellules B doivent être clarifiés, ils pourraient inclure l’IL-21 et l’interaction CD40-CD40L.Dans ce projet de thèse, nous avons étudié le rôle potentiel des Tfh dans l'initiation de la différenciation mémoire T CD8+, dans des modèles de souris transgéniques permettant une déplétion transitoire et sélective des Tfh, infectées par la bactérie recombinante Listeria monocytogenes-OVA.Nous avons montré que dès 2 jours après l'infection, les MPECs très précoces peuvent être identifiés par l’expression du récepteur de chimiokine CXCR5. Ces précurseurs précoces, qui ont un phénotype effecteur, se développent et migrent temporairement à la jonction des zones T et B, où ils interagissent avec les Tfh puis perdent leur expression CXCR5.Cette interaction avec les Tfh, considérés jusqu'à présent comme des auxiliaires exclusifs des cellules B, est nécessaire pour que les MPECs CD8+ deviennent des cellules mémoire compétentes sensibles à l'IL-21, capables de générer des réponses effectrices secondaires efficaces.Cette étude dévoile les premières étapes cruciales dans la génération de la mémoire CD8+, identifie CXCR5 comme le premier marqueur connu des MPECs CD8+, révèle l’implication fondamentale des Tfh dans le CD4 help et indique une coordination possible, via les Tfh, entre les voies de différentiation mémoire CD8+ et B. Ces résultats peuvent avoir des implications pour la conception du vaccin et de l'immunothérapie
Antigen-specific CD8 T cells are involved in the adaptive immune response and play a critical role in protecting the host from infection by intracellular pathogens. This long-lasting protection depends on the generation of memory CD8+ T cell responses, which are highly functional in terms of frequency and functionality, after secondary infection.Following antigen activation, a naive CD8 T cell undergoes strong clonal expansion, generating a heterogeneous population of activated cells that is dominated, at the peak of expansion, by short-lived CD8 effectors (SLECs). This expansion is followed by a phase of drastic contraction through massive apoptosis. A few cells survive this contraction phase and eventually become highly competent memory cells. Precisely when and how these memory precursors (MPECs) are generated is largely unknown, and so are the subsequent steps of their maturation into fully functional memory cells. Help signals from CD4+ T cells are clearly required throughout the MPEC maturation process.Our team has previously shown that FoxP3+ regulatory CD4+ T cells (Tregs) favor MPECs maturation by limiting exposure to IL-2 and by providing inhibitory signals, but this is probably only one facet of the complex and multifaceted help provided by CD4+ T cells to MPEC, and Tregs act on pre-existing MPECs.B-cell memory and CD8+ T cell memory share some common features, such as the expression of the transcription factor Bcl-6. Tfh are major producers of the cytokine IL-21. The mechanisms by which Tfh induces Bcl-6 in B-cells need to be clarified, they might include IL-21 and CD40-CD40L.In this PhD project, we have investigated the potential role of Tfh on the initiation of CD8 memory differentiation, in transgenic mice models, allowing transient and selective depletion of Tfh cells, infected by recombinant Listeria monocytogenes-OVA.We have shown that as early as 2 days after infection, very early memory precursors can be identified by their expression of the chemokine receptor CXCR5. These early precursors, which have an effector phenotype, expand and temporarily migrate to the junction of T-cell and B-cell zones, where they interact with follicular CD4 T cells (Tfh) then lose their CXCR5 expression.Remarkably, this interaction with Tfh, hitherto considered as exclusive B-cell helpers, is required for memory precursors to become competent memory cells responsive to IL-21 and capable of mounting efficient cytotoxic secondary effector responses.This study thus unveils critical early steps in the generation of CD8 memory, identifies CXCR5 as the earliest known marker of CD8 memory precursors, reveals a major helper role for Tfh, and points to possible coordination, through Tfh, between the pathways of CD8 and B-cell memory generation. These findings may have implications for vaccine and immunotherapy design

Respiratory syncytial virus (RSV) infections are the major contributor to acute lower respiratory syndrome in newborns. Infections generally result in hospitalization and sometimes in death. A vaccine is not available yet, despite decades of research. Vaccine development is hampered in consequence of a failed vaccine trial in the 1960s which entailed fatal outcomes. An alternative to direct vaccination of children is maternal vaccination for passive immunization of babies before birth. RSV infects every person repeatedly throughout life which implies that pregnant woman carry RSV-directed memory B cell (MBC) repertoires. A successful maternal vaccine would therefore elicit high titer RSV-neutralizing IgGs by reactivation of pre-existing MBCs which would protect newborns during the first months of life. RSV has two neutralizing antigens, of which the fusion protein (RSV F) is the most promising vaccine candidate. RSV F mediates the fusion process of viral and cellular membranes, wherefore it exists in a pre-fusion (pre F) or post-fusion (post F) conformation. Even though there is more interest in the pre F conformation as immunogen, the post F conformation may be equally considered as successful vaccine antigen. The pre F conformation is very metastable and readily switches to the highly stable post F conformation, which implies that a post F-based vaccine would be more cost-efficient to produce. More importantly, several neutralizing epitopes are preserved on the post F conformation and a substantial amount of RSV F-directed MBCs induced by natural infection are actually pre/post F cross-reactive. Since most of the pre/post F cross-reactive MBCs were previously shown to have higher affinities for the post F conformation, a post F-based vaccine may be ideal for reactivation and clonal expansion of MBCs which express neutralizing B cell receptors (BCRs). Every antigen, also RSV post F protein, has its own signatures within BCR repertoires because of preferential selection of BCR characteristics for B cell clonal expansions. In order to understand how RSV F protein shapes BCR repertoires, RSV F-directed BCRs were isolated from a healthy blood donor and three vaccinees who received an RSV post F vaccine. BCR repertoire analysis confirmed the assumption that the pre and post F protein have their own signatures within RSV F-directed BCR repertoires. The different characteristics indicated longer affinity maturation of pre F-reactive MBCs. Furthermore, estimation of clonal relatedness between the pre and post F-binding BCR repertoires from the healthy donor provided indications that a substantial number of the isolated BCRs are actually pre/post F cross-reactive, which confirmed a previous study. Analysis of the BCR repertoires isolated from the RSV post F-vaccinees showed that the vaccine induced a biased MBC response with preferential BCR characteristics. There were several implications that the post F-vaccine expanded primarily pre/post F cross-reactive MBCs. In contrast to the high variability of pre/post F cross-reactive BCRs induced by natural infection, the vaccine-induced MBC response indicated a skewed selection of VH4 gene family-encoded BCRs for clonal expansion and affinity maturation. More importantly, estimation of clonal relatedness revealed convergent MBC responses between the three analyzed subjects, while several MBC lineages shared stereotypic characteristics with pre F-binding BCRs or RSV-neutralizing antibodies. Some of the supposedly pre/post F cross-binding or neutralizing BCR sequences were expressed as mAbs and functionally characterized. RSV pre/post F cross-binding and neutralization activities could be demonstrated for all of the expressed mAbs. This project demonstrated the potential of ‘clonal’ grouping as novel reverse approach to screen BCR repertoires for functional antibodies.

The diversity of virus-specific antibodies and of B cells among different individuals is unknown. Using single-cell cloning of antibody genes, we generated recombinant human monoclonal antibodies from influenza nucleoprotein-specific memory B cells in four adult humans with and without preceding influenza vaccination. We examined the diversity of the antibody repertoires and found that NP-specific B cells used numerous immunoglobulin genes. The heavy chains (HCs) originated from 26 and the kappa light chains (LCs) from 19 different germ line genes. Matching HC and LC chains gave rise to 43 genetically distinct antibodies that bound influenza NP. The median lengths of the CDR3 of the HC, kappa and lambda LC were 14, 9 and 11 amino acids, respectively. We identified changes at 13.6% of the amino acid positions in the V gene of the antibody heavy chain, at 8.4 % in the kappa and at 10.6 % in the lambda V gene. We identified somatic insertions or deletions in 8.1% of the variable genes. We also found several small groups of clonal relatives that were highly diversified. Our findings demonstrate broadly diverse memory B cell repertoires for the influenza nucleoprotein. We found extensive variation within individuals with a high number of point mutations, insertions, and deletions, and extensive clonal diversification. Thus, structurally conserved proteins can elicit broadly diverse and highly mutated B-cell responses.

Influenza A virus (IAV) is a major cause of serious respiratory illness worldwide, leading to approximately 5 million severe cases and 500,000 deaths per year. Given the disease severity, associated economic costs, and recent appearance of novel IAV strains, there is a renewed interest in developing novel and efficacious “universal” IAV vaccination strategies as well as therapeutic remedies. Previous studies from our laboratory have concentrated on IAV-specific CD8 T cell-mediated protection against IAV infection as IAV-specific CD8 T cells are needed for efficient clearance of virus. Recent studies highlight that immunizations capable of generating local (i.e., nasal mucosa and lung) tissue-resident memory T and B cells in addition to systemic immunity offer the greatest protection against future IAV encounters. Current IAV vaccines are designed to largely stimulate IAV-specific antibodies, but do not generate the lung-resident memory T and B cells induced during IAV infections. In order to effectively generate lung-resident memory populations, it is believed a local antigen depot is needed as tissue-resident memory formation is enhanced by the presence of local antigen. Recently, polyanhydride nanoparticles have been demonstrated to slowly release their contents at the site of inoculation serving as an antigen depot. However, the ability of an intranasal vaccination with polyanhydride nanoparticles to induce IAV-specific lung-resident immune responses and provide protection against subsequent IAV infection has not been determined. Here, I report on the intranasal administration of a biocompatible polyanhydride nanoparticle-based IAV vaccine (IAV-nanovax). IAV-nanovax is capable of providing protection against subsequent homologous and heterologous IAV infections in both inbred and outbred populations. My findings demonstrate that vaccination with IAV-nanovax promotes the induction of germinal center B cells within the lungs that are associated with both systemic IAV-specific IgG as well as local lung IAV-specific IgG and IgA antibodies. Furthermore, intranasal IAV-nanovax vaccination leads to a significant increase in IAV-specific CD4 and CD8 T cells within the lung vasculature as well as in the lung tissue. Most importantly, my studies demonstrate that IAV-nanovax induced lung-resident IAV-specific CD4 and CD8 T cells express canonical tissue-resident memory markers. This dissertation further explores a novel regulation pathway previously identified by our laboratory where plasmacytoid dendritic cells (pDCs) eliminate IAV-specific CD8 T cells early during high-dose and high-pathogenic IAV infections in a FasL:Fas (pDCs:CD8 T cell) dependent manner. However, recent studies suggest that B cells are the predominate lymphocyte to express FasL in mice. Here, I demonstrate that FasLpos B cells greatly outnumber FasLpos pDC within the lung draining lymph nodes (dLNs) during IAV infections. Interestingly, my results demonstrate the presence of two subsets, CD11cpos and CD11cneg, of FasL-expressing B cells that differentially influence the IAV-specific CD8 T cell response during high-dose IAV infections. While CD11cneg B cells kill IAV-specific CD8 T cells, contributing to lethality during high-dose IAV infections, CD11cpos B cells may instead be protective. In addition to the negative impacts of high-dose IAV infections, I also demonstrate that chronic ethanol (EtOH) consumption detrimentally impacts existing IAV-specific CD8 T cell memory responses. Here, my results reveal that chronic EtOH consumption causes a numerical loss in existing IAV-specific CD8 T cell memory responses. This numerical loss in existing IAV-specific CD8 T cell memory is associated with a reduction in cytotoxic activity within the lungs as well as an increase in morbidity and mortality during a secondary IAV challenge. Together, the results presented herein demonstrate the ability of a novel polyanhydride nanovaccine to induce robust pulmonary IAV-specific T and B cell responses and further our understanding of factors that can negatively impact IAV-specific CD8 T cells as well as protection against IAV infection. Overall these findings highlight the importance of IAV-specific CD8 T cells, as well as CD4 T cells and B cells, in providing protection against IAV infections.

Anticorpos monoclonais (AcMos) para uso terapêutico correspondem a uma área importante na indústria de biofármacos, em especial os AcMos humanos, que apresentam menor probabilidade de elicitar imunogenicidade. O objetivo deste trabalho consistiu em obter AcMos humanos antitetânicos através da separação de linfócitos B produtores de anticorpos específicos utilizando o antígeno ou de plasmablastos. As células foram coletadas de doadores após vacinação e separadas por equipamento de cell sorter. As regiões variáveis dos anticorpos foram amplificadas e clonadas em vetores de expressão, que foram usados para transfectar transitoriamente células HEK293-F. O uso da toxina tetânica conjugada independentemente com dois marcadores, biotina e Alexa Fluor® 647, possibilitou a separação específica de linfócitos B produtores de AcMos antitetânicos, que foram avaliados por ELISA, western blotting e pela inibição da ligação da toxina ao gangliosídio GT1b. O ensaio in vivo mostrou proteção total dos animais contra a toxina tetânica quando três AcMos foram usados em conjunto.
Monoclonal antibodies (mAbs) for therapeutic use correspond to a major area of the biopharmaceutical industry, especially human mAbs that are less prone to elicit immunogenicity. The objective of this work was to obtain anti-tetanus human mAbs through separation of memory B lymphocytes producing specific antibodies stained with the antigen or plasmablasts. Cells were collected from peripheral blood of donors after vaccination and separated through cell sorting. The variable regions of the antibodies were amplified and cloned in expression vectors for transient transfection of HEK293-F cells. The staining with the tetanus toxin labeled independently with two markers, biotin and Alexa Fluor® 647 allowed the separation of specific B lymphocytes producing anti-tetanus mAbs. The antibodies expressed were evaluated by ELISA, western blotting and the inhibition of the binding of the tetanus toxin to the ganglioside GT1b. The in vivo neutralization assay showed that a pool of three different mAbs were able to protect mice against the tetanus toxin.

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A malária constitui um dos maiores problemas de saúde pública mundial, sendo responsável por aproximadamente meio milhão de mortes anuais. Por isso, e devido à crescente resistência dos parasitos aos antimaláricos usuais e aumento do número de casos graves, sobretudo os ocasionados por P. vivax, grandes esforços têm sido dispensados no desenvolvimento de vacinas. Até o momento, a única vacina licenciada mostrou-se capaz de conferir algum grau de imunidade contra P. falciparum, porém a inabilidade de manutenção de resposta protetora ao longo do tempo tem sido um grande desafio a ser superado. Indivíduos naturalmente expostos à doença desenvolvem graus variados de proteção, que parece ser perdida na ausência de reestímulos. Essas observações apontam para falhas na memória imunológica mediada por células B. No Brasil, onde cerca de 85% dos episódios de malária são atribuídos a P. vivax, estudos acerca do desenvolvimento e manutenção de memória imunológica são escassos. O entendimento de fatores que possam modular as respostas imunes durante e após a malária são importantes no desenvolvimento de vacinas. Esse estudo teve como objetivo avaliar aspectos clínicos e hematológicos, verificar a geração e persistência de anticorpos e células B de memória (MBCs) direcionadas aos peptídeos sintéticos (PvAMA-1(S290-K307) e PvMSP-9(E795-A808)), bem como à proteína recombinante PvAMA-1DII e averiguar a ocorrência de flutuações no compartimento de células B em indivíduos durante a malária aguda e em 30, 60 e 180 dias decorridos do diagnóstico (convalescença) por P. vivax. Os resultados obtidos mostraram que alterações hematológicas ocorerram predominantemente na fase aguda, destacando-se plaquetopenia, linfopenia e leucopenia. Na fase aguda da infecção, indivíduos exibiram MBCs e anticorpos específicos para PvAMA-1(S290-K307) e PvMSP-9(E795-A808), bem como para a PvAMA-1DII, os quais persistiram, de maneira geral, por > 180 dias na ausência de reinfecções/recaídas. Não foram observadas associações positivas entre respostas de anticorpos e MBCs ao longo do tempo para todos os antígenos avaliados. Além disso, este estudo corroborou a relação entre exposição/infecção malárica e ocorrência de flutuações no perfil fenotípico de subpopulações de células B no sangue periférico, com destaque para a expansão de imaturas e plasmáticas durante a fase aguda da doença. No tocante às MBCs atípicas, independentemente do grupo avaliado (controles expostos, fase aguda ou convalescença) estas células se encontraram expandidas em relação ao observado em indivíduos não expostos à malária. Os dados desse estudo ainda sugerem que a expansão de células B atípicas observada em indivíduos provenientes de área endêmica é influenciada pela ocorrência de episódios pregressos da doença. Estudos posteriores são de fundamental importância para determinar o impacto de tais alterações em estratégias de imunizações voltadas ao combate da malária vivax em populações expostas em regiões de baixa transmissão de malária na Amazônia Brasileira.
Malaria is one of the greatest public health problems in the world, accounting for approximately half a million annual deaths. Therefore, due to the increasing resistance of the parasites to the usual antimalarials and an increase in the number of severe cases, especially those caused by P. vivax, great efforts have been dispensed with in the development of vaccines. To date, the only licensed vaccine has been shown to confer some degree of immunity against P. falciparum, but the inability to maintain a protective response over time has been a major challenge to be overcome. Individuals naturally exposed to the disease develop varying degrees of protection, which seems to be lost in the absence of re-stimulation. These observations point to failures in B cells-mediated immune memory. In Brazil, where about 85% of malaria episodes are attributed to P. vivax, studies on the development and maintenance of immune memory are scarce. Understanding of factors that can modulate immune responses during and after malaria are important in the development of vaccines. This study aimed to evaluate clinical and hematological aspects, to verify the generation and persistence of antibodies and memory B cells (MBCs) directed to synthetic peptides (PvAMA-1(S290-K307) and PvMSP-9(E795-A808)), as well as to the recombinant protein PvAMA-1DII and to investigate the occurrence of fluctuations in the B cell compartment in individuals during acute malaria and at 30, 60 and 180 days after the diagnosis (convalescence) of P. vivax. The results showed that hematological alterations occurred predominantly in the acute phase, especially thrombocytopenia, lymphopenia and leucopenia. In the acute phase of infection, individuals exhibited MBCs and antibodies specific for PvAMA-1(S290-K307) and PvMSP-9(E795-A808) as well as for PvAMA-1DII, which generally persisted > 180 days in the absence of reinfections/relapses. No positive associations between antibody responses and MBCs over time were observed for all antigens evaluated. In addition, this study corroborated the relationship between exposure/malarial infection and occurrence of fluctuations in the phenotypic profile of B-cell subpopulations in peripheral blood, with emphasis on immature and plasma expansion during the acute phase of the disease. Regarding atypical MBCs, regardless of the group evaluated (exposed controls, acute phase or convalescence), these cells were expanded in relation to that observed in individuals not exposed to malaria. The data from this study still suggest that the expansion of atypical B cells observed in individuals from the endemic area is influenced by the occurrence of previous episodes of the disease. Subsequent studies are of fundamental importance to determine the impact of such changes on immunization strategies aimed at combating vivax malaria in populations exposed in regions of low malaria transmission in the Brazilian Amazon.

Malaria, caused by the apicomplexan parasite Plasmodium, is a major cause of morbidity and mortality throughout the world. This study has focused on the role of the spleen in the control of the blood stage of infection. Three aspects have been examined specifically: the effect of infection on the architecture of the spleen, the role of the spleen in parasite clearance and the formation of B cell memory. Firstly, the effect of infection on the splenic microarchitecture was examined. An essential component of the splenic architecture is the marginal zone (MZ), an area of the spleen that separates the reticuloendothelial red pulp of the spleen from the lymphoid white pulp compartment. Two unique populations of macrophages are found in the marginal zone: marginal zone macrophages (MZM) and marginal metallophilic macrophages (MMM). In the current study, parasitised red blood cells (pRBC) as well as normal RBC located to the MZ thirty minutes after intravenous injection and formed close associations with both MMM and MZM. Eight days after infection, at the time of peak parasitemia, a complete loss of both MMM and MZM was observed. Assays to detect cell death revealed that the loss of both MMM and MZM appeared to occur as a result of apoptosis. The apoptosis was not induced by up regulation of the inflammatory cytokines tumour necrosis factor or interferon-γ and could not be blocked by over expression of the apoptosis inhibitor Bcl2. Significantly, MMM were retained in the absence of CD8+ T cells implicating CD8+ T cells in the loss of MMM. Finally, infection of CD95-/- mice demonstrated that CD95/CD95-ligand (Fas/Fas-ligand) interactions were responsible for some of the CD8+ T cell-mediated loss of MMM. These data provide evidence for a novel interaction between MMM and CD8+ T cellsfollowing infection with Plasmodium. Secondly, the role of the spleen in the control of parasitemia and disease was monitored with an emphasis on determining the role of splenic macrophage populations (MMM, MZM and red pulp macrophages [RPM]) in parasite clearance. A clodronate liposome-mediated macrophage depletion technique was used, and caused a complete loss of all three macrophage sub-populations, as well as 50% of splenic dendritic cells, within 24 hours of administration. Each of the macrophage populations, as well as splenic DC, demonstrated different repopulation kinetics following their depletion from the spleen and these kinetics were utilised to examine each cell population in isolation. RPM depleted mice had significantly higher peak parasitemias than the controls. This peak returned to the level observed in undepleted control animals only after the repopulation of RPM was complete, suggesting that RPM play a role in the control of peak parasitemia following infection. Neither MMM nor MZM played a role in the control of parasitemia. The role of non-splenic macrophages and splenic dendritic cells also was investigated and shown to be insignificant in the absence of splenic macrophages. Finally, the role of RPM in mice immune to infection was investigated and their role shown to be dispensable, with immune mice clearing parasitemia efficiently in the absence of RPM. RPM therefore are important for the innate control of infection with P. chabaudi but are dispensible once adaptive immunity is established. Finally, the role of the spleen in the development of parasite-specific B cell memory was examined. Initial studies demonstrated that germinal centre (GC) development was compromised following infection with P. chabaudi, with an involution of B cell follicles noted early in infection. Adoptive transfer of memory B cells from immunised to naïve mice demonstrated that some protection was conferred on recipient mice by parasite-specific memory B cells. But, the memory B cells could not protect the host from developing parasitemia and did not produce significant amounts of parasite-specific immunoglobulin within seven days of challenge infection. Memory B cells could not be detected ten weeks after infection, indicating that the development, or survival, of parasite-specific memory B cells was compromised. The development of bystander memory B cells was not affected by infection. Finally, long-lived plasma cells were shown to develop in response to infection, although re-exposure of the cells to parasites in the form of recrudescent parasitemia resulted in their loss. This study therefore has identified a defect in the development of long-term, B cell-mediated, protection against infection with P. chabaudi. Each of these factors has significant implications for the understanding of how the spleen contributes to the control of infection with Plasmodium and potential applications for the further development of malaria vaccines and treatment regimens.

Malaria, caused by the apicomplexan parasite Plasmodium, is a major cause of morbidity and mortality throughout the world. This study has focused on the role of the spleen in the control of the blood stage of infection. Three aspects have been examined specifically: the effect of infection on the architecture of the spleen, the role of the spleen in parasite clearance and the formation of B cell memory. Firstly, the effect of infection on the splenic microarchitecture was examined. An essential component of the splenic architecture is the marginal zone (MZ), an area of the spleen that separates the reticuloendothelial red pulp of the spleen from the lymphoid white pulp compartment. Two unique populations of macrophages are found in the marginal zone: marginal zone macrophages (MZM) and marginal metallophilic macrophages (MMM). In the current study, parasitised red blood cells (pRBC) as well as normal RBC located to the MZ thirty minutes after intravenous injection and formed close associations with both MMM and MZM. Eight days after infection, at the time of peak parasitemia, a complete loss of both MMM and MZM was observed. Assays to detect cell death revealed that the loss of both MMM and MZM appeared to occur as a result of apoptosis. The apoptosis was not induced by up regulation of the inflammatory cytokines tumour necrosis factor or interferon-γ and could not be blocked by over expression of the apoptosis inhibitor Bcl2. Significantly, MMM were retained in the absence of CD8+ T cells implicating CD8+ T cells in the loss of MMM. Finally, infection of CD95-/- mice demonstrated that CD95/CD95-ligand (Fas/Fas-ligand) interactions were responsible for some of the CD8+ T cell-mediated loss of MMM. These data provide evidence for a novel interaction between MMM and CD8+ T cellsfollowing infection with Plasmodium. Secondly, the role of the spleen in the control of parasitemia and disease was monitored with an emphasis on determining the role of splenic macrophage populations (MMM, MZM and red pulp macrophages [RPM]) in parasite clearance. A clodronate liposome-mediated macrophage depletion technique was used, and caused a complete loss of all three macrophage sub-populations, as well as 50% of splenic dendritic cells, within 24 hours of administration. Each of the macrophage populations, as well as splenic DC, demonstrated different repopulation kinetics following their depletion from the spleen and these kinetics were utilised to examine each cell population in isolation. RPM depleted mice had significantly higher peak parasitemias than the controls. This peak returned to the level observed in undepleted control animals only after the repopulation of RPM was complete, suggesting that RPM play a role in the control of peak parasitemia following infection. Neither MMM nor MZM played a role in the control of parasitemia. The role of non-splenic macrophages and splenic dendritic cells also was investigated and shown to be insignificant in the absence of splenic macrophages. Finally, the role of RPM in mice immune to infection was investigated and their role shown to be dispensable, with immune mice clearing parasitemia efficiently in the absence of RPM. RPM therefore are important for the innate control of infection with P. chabaudi but are dispensible once adaptive immunity is established. Finally, the role of the spleen in the development of parasite-specific B cell memory was examined. Initial studies demonstrated that germinal centre (GC) development was compromised following infection with P. chabaudi, with an involution of B cell follicles noted early in infection. Adoptive transfer of memory B cells from immunised to naïve mice demonstrated that some protection was conferred on recipient mice by parasite-specific memory B cells. But, the memory B cells could not protect the host from developing parasitemia and did not produce significant amounts of parasite-specific immunoglobulin within seven days of challenge infection. Memory B cells could not be detected ten weeks after infection, indicating that the development, or survival, of parasite-specific memory B cells was compromised. The development of bystander memory B cells was not affected by infection. Finally, long-lived plasma cells were shown to develop in response to infection, although re-exposure of the cells to parasites in the form of recrudescent parasitemia resulted in their loss. This study therefore has identified a defect in the development of long-term, B cell-mediated, protection against infection with P. chabaudi. Each of these factors has significant implications for the understanding of how the spleen contributes to the control of infection with Plasmodium and potential applications for the further development of malaria vaccines and treatment regimens.

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Fundação Oswaldo Cruz. Centro de Pesquisas Gonçalo Moniz. Salvador, Bahia, Brasil
Foi anteriormente demonstrado que as células NK (Natural Killer) estão relacionadas às bases para resistência à infecção por Trypanosoma cruzi, pois a depleção de células positivas para NK1.1+ resulta em alta parasitemia de camundongos C57BI/6 infectados pelo T. cruzi. Estudos de nossa equipe indicaram ainda que as células T NKH-t- poderiam induzir a formação de células T efetoras/nnemória, e que a resistência à infecção foi correlacionada com a quantidade de células T CD4-<- CD45RB"®^ presentes antes da infecção. No presente estudo avaliamos a função regulatória de células T NK1.1+ durante a infecção experimental pelo T. cmzi, na ausência de linfócitos B. Utilizamos os seguintes animais: C57BI/6 controles, ^MT C57BI/6, nMT reconstituídos (com células B de C57BI/6 ou B de C67BI/6 IL-10KO) ou tratados com imunoglobulinas. Neste modelo experimental, observamos que os animais p.MT apresentaram menores números de células T efetoras/memória no baço comparados aos controles (C57BI/6), na fase aguda de infecção. A reconstituição com células B ou o tratamento com Ig em animais ^iMT infectados resultou em aumento de células T efetoras/memória, comparado ao controle (jiMT infectado). Da mesma maneira e até fase crônica de infecção, a transferência adotiva de células B em animais ^MT causa persistência de células T efetoras/memória no baço. Como a molécula de CD1 (encontrada sobre células B e dendríticas) é reconhecida por células NK1.1, a expressão desta molécula foi também avaliada durante a infecção. Após a infecção, houve diminuição de células CD1+ no baço de animais C57BI/6, e ausência destas células nos jxMT. A recuperação desta população celular no baço de {aMT infectados após reconstituição com linfócitos B foi concomitante á reposição de células T CD4+ NK1.1 no músculo esquelético destes mesmos animais. Houve ainda aumento de CD4+NK1.1 também no músculo esquelético dos animais ^MT reconstituídos com linfócitos B provenientes de C57BI/6 IL-10KO. De modo interessante, a depleção de NK1.1 durante a fase crônica, causou aumento de células T efetoras/memória encontradas no músculo esquelético de animais |uMT. Esses resultados estão relacionados aos dados de histopatologia, onde foi evidenciado maior infiltrado inflamatória no tecido HfKiscular de animais fxMT tratados com anti-NK1.1, durante a fase crônica da infecção. Nossos resultados indicam desse modo que a presença da célula B estaria ligada à formação de células T CD45RB"^ na fase aguda e manutenção/aumento de memória imune na fase crônica de infecção, conferindo ao grupo de animais reconstituídos com células 6, maior sobrevida. Sugere-se, portanto que as células T CD4+ NK1.1+ poderiam ser regulatórias no sentido de apresentar atividade antiinflamatória e que as células aP+NK1.1+ exerceriam função auxiliar na geração de células T efetoras/memória em nosso sistema experimental.
We have previously demonstrated that NK (Natural Killer) cells have been related to resistance to T. cruzi infection and the depletion of NK1.1+ cells resulted in high mortality and increased parasitemia in C57BI/6 Infected mice. Recently, we suggested that the NK1.1 T cells were involved on memory T cell generation, and resistance to infection was correlated with increased numbers of 004^“'*''^ CD45RB"®^®“'^ T cells, present before infection. In this study we evaluated the regulatory function of NK1.1+ T cells during 7. cruzi infection in ^iMT C57BI/6 infected mice. The following mice were used; C57BI/6, ^MT C57BI/6 and nMT C57BI/6 Imunoglobulin (lg)-treated or adoptively transferred with B cells (obtained from C57BI/6 or from C57BI/6 IL-10KO). In this experimental model. yMT infected mice have show decreased numbers of effector memory T cells, compared to C57BI/6 infected controls, during acute infection. The adoptive transfer of B cells or the treatment with immunoglobulins (Igs), induced increased numbers of effector memory splenic T cells, compared to C57BI/6 controls. Furthermore, Ig administration to p,MT uninfected mice is able to increase ap+NK1.1+ splenic cell population. As NK1.1 cells recc^nize C01 molecule which is expressed on B and dendritic cells, CD1 expression was evaluated in spleens of nMT and C57BI/6 mice to estimate whether the expression of CD1 was modified after infection. When compared to uninfected controls, CD1-presenting cells decreased from both nMT and C57BI/6 mice and were increased following B cell-transfer to laMT recipient mice. Interestingly, the depletion of NK1.1 cells also increased effector memory T cells found on skeletal muscles infiltrates from jiMT, and this was correlated to the increased inflammatory response found in these ^iMT NK1.1-depleted mice, during the chronic phase of infection. In this inflammatory compartment, ^iMT infected mice presented low numbers of CD4+NK1.1 T cells, when compared to C67BI/6. Previous observations from our laboratory suggest that CD4+NK1.1+ T cells (which are decreased in skeletal muscle from infected laMT mice), may be related to the enhanced inflammatory response during the early chronic infection. Finally, these studies suggest that CD4+NK1.1+ T cells may be regulatory with an antiinflammatory activity and that ap+NK1.1+ T cells may be involved on effector memory T cell-generation in our experimental system.

Les alloanticorps anti-HLA sont dirigés vis-à-vis de différents épitopes des molécules du système HLA. Cette immunisation survient lors d'une transplantation d'organe, de transfusions sanguines ou d'une grossesse. On retrouve aussi ces anticorps, lorsque les techniques de détection sont sensibles, en l'absence de tout évènement immunisant. En transplantation d'organe, rénale en particulier, la présence d'anticorps anti-HLA, du fait des lésions de rejet humoral qu'ils induisent, constitue une des premières causes de perte de fonction des greffons à moyen et long terme. Néanmoins, les cellules lymphocytaires qui sont la source de ces anticorps anti-HLA demeurent mal identifiées.Dans la première partie de ce travail, nous avons étudié, dans une cohorte de patients en attente de transplantation rénale, la distribution des différentes sous-populations lymphocytaires B circulantes par cytométrie de flux en relation avec la nature des évènements immunisants vis-à-vis du système HLA, la présence et la diversité des anticorps anti-HLA. Nous avons étudié en parallèle les concentrations sériques de BAFF ("B cell activating factor belonging to the TNF family"), principal facteur impliqué dans la survie et la différenciation des lymphocytes B matures. Nous avons retrouvé une association entre la présence et la diversité des anticorps anti-HLA, et l'augmentation de la proportion de lymphocytes B naïfs activés Bm2, par rapport aux autres sous-populations lymphocytaires B, et indépendamment de l'existence d'évènements immunisants. Les concentrations sériques de BAFF étaient également associées positivement à la présence et à la diversité des anticorps anti-HLA. Ces données suggèrent que l'augmentation des lymphocytes B naïfs activés et des concentrations sériques de BAFF favorise le développement des anticorps anti-HLA à la suite d'un événement immunisant. A l'instar du mécanisme évoqué en auto-immunité, BAFF pourrait intervenir en présence de l'alloantigène en favorisant la survie de clones B alloréactifs.Dans la deuxième partie de notre travail, nous nous sommes intéressés plus particulièrement à l'implication des lymphocytes B mémoire alloréactifs dans la réponse humorale anti-HLA. Pour détecter les lymphocytes B mémoire circulants, nous avons utilisé un test de stimulation polyclonale permettant leur différenciation en plasmablastes puis nous avons recherché et étudié la spécificité des anticorps anti-HLA produits dans les surnageants de culture. Un premier résultat important a été la possibilité de détecter, chez les patients présentant des anticorps anti-HLA, des lymphocytes B mémoire alloréactifs circulants plusieurs années après un événement immunisant. En deuxième lieu, la présence de ces lymphocytes B mémoire était associée au nombre d'évènements immunisants. En effet, les patients ayant développé, en l'absence d'événement immunisant des anticorps anti-HLA - dont nous montrons par ailleurs le caractère potentiellement pathogène - n'ont pas présenté de lymphocytes B mémoire alloréactifs circulants. Enfin, à l'aide du logiciel HLAMatchmaker, nous avons montré que les anticorps produits par les lymphocytes B mémoire étaient dirigés contre un nombre restreint d'épitopes partagés par plusieurs antigènes HLA, ce qui suggère une oligoclonalité du contingent B mémoire alloréactif. Chez les mêmes patients, les anticorps anti-HLA circulants présentaient une diversité de spécificité plus large, étant dirigés contre de multiples épitopes HLA. Ces résultats suggèrent l'existence d'au moins deux types de réponse humorale vis-à-vis des alloantigènes HLA : l'une aboutissant à la production de lymphocytes B mémoire et de plasmocytes à la suite d'une réaction de centre germinatif T-dépendante, l'autre impliquant seulement des plasmocytes, possiblement issus de réponses extra-folliculaires. Les facteurs orientant vers l'un ou l'autre type de réponse sont encore mal définis mais pourraient impliquer la dose et la voie d'exposition aux alloantigènes.

Le pemphigus est une maladie auto-immune spécifique de la peau et des muqueuses provoqué par des auto-anticorps (Ac) spécifiques des desmogléines (Dsg) 1 ou 3. Ces Ac pathogéniques inhibent l'adhésion cellulaire des kératinocytes. Le pemphigus se déclenche par la conjonction d’événements rares impliquant l’émergence puis la coopération de lymphocytes B (LB) et de lymphocytes LT auto-réactifs dans un contexte génétique et environnemental particulier. Jusqu’à présent, la première ligne de traitement du pemphigus était constituée de fortes doses de corticoïdes, qui sont de puissants immunosupresseurs systèmiques. Le Rituximab (RTX), un Ac monoclonal chimérique anti-CD20, constitue une thérapeutique innovante aboutissant à l’élimination des LB. L’étude clinique RITUX 3 a été conçue pour évaluer l’efficacité et l’innocuité du traitement utilisant le RTX associé à une courte corticothérapie dans le traitement de première intention du pemphigus par rapport au traitement de référence par la corticothérapie standard (CS). Dans un premier temps, notre analyse clinico-biologique des patients après 24 mois a démontré que l’utilisation du RTX associé à de la prednisone à court terme en traitement de première intention chez les patients atteints de pemphigus foliacé et vulgaire modéré à sévère est à la fois plus efficace et mieux toléré que le traitement de référence par la prednisone seule (89% de patients versus 34%). Cette efficacité a été confortée à plus long terme après la reconstitution du répertoire lymphocytaire B avec un risque de rechute de 2% à 36 mois. La présence d’une forme sévère de pemphigus au diagnostic (PDAI ≥ 45) et d’un taux d’Ac anti-Dsg à 3 mois supérieur aux valeurs seuils (anti-Dsg1 ≥ 20 ou anti-Dsg3 ≥ 120) sont associés à un risque de rechute précoce de 50%. Ces deux facteurs prédictifs permettent d'identifier un sous-groupe de patients présentant un risque élevé de rechute nécessitant une perfusion d'entretien de RTX au 6ème mois. Dans un deuxième temps, nous avons étudié l’impact des traitements par RTX et par CS chez les patients atteints de pemphigus afin de mieux appréhender la réponse auto-immune. La caractérisation phénotypique des LB auto-réactifs et l’analyse de la fréquence des LB capables de sécréter des immunoglobulines (Ig)G anti-Dsg par une approche ELISPOT a permis d’établir que l’efficacité du traitement par RTX dans le pemphigus semble liée à l’élimination des LB mémoires CD27+IgG+ spécifiques des Dsg. Des LB auto-réactifs Dsg restent détectables après RTX suite à la reconstitution lymphocytaire B, mais ces LB ont un phénotype naïf et non commuté (IgM) et ne secrètent plus d’IgG. En revanche, la persistance des LB auto-réactifs capables de sécréter des IgG anti-Dsg après traitement par CS est certainement à l’origine des rechutes fréquentes. L’analyse de l’expression génique ciblée à l’échelle unicellulaire a démontré qu’initialement, les LB spécifiques des Dsg ont un profil pro-inflammatoire avec l’expression de trois gènes codant pour les interleukines (IL)-1β, IL-12p35 et IL-23p19 et pour le gène de l’IRF5 (Interferon regulatory factor 5) par rapport aux LB non auto-réactifs. Le RTX et la CS ont des effets différents sur l'expression de ces gènes mais les deux réduisent l’expression génique d’IL-1β qui semble jouer un rôle important dans la physiopathologie du pemphigus. Parallèlement, l’analyse transcriptomique puis protéique des LB isolés des patients en rémission complète ou incomplète 6 ans après l’étude RITUX 1 a mis en évidence une augmentation d'expression de KCNN4 (Potassium calcium-activated channel subfamily N member 4) à la surface des LB chez les patients atteints de pemphigus en rémission complète pouvant influencer la maturation des LB
Pemphigus is an autoimmune disease of the skin and mucous membranes caused by autoantibodies (Ab) specific to desmoglein (Dsg) 1 or 3. These pathogenic Ab inhibit cell adhesion of keratinocytes. The development of pemphigus is associated with the conjunction of many uncommon events involving the emergence and then the cooperation of auto-reactive B cells and T cells link to genetic and environmental factors. Until now, the first line of treatment consisted of high doses of corticosteroids. Rituximab (RTX), an anti-CD20 chimeric monoclonal antibody, is an innovative therapy that results in B cells depletion. The RITUX 3 clinical trial was designed to evaluate the efficacy and safety of RTX combined with a short-course glucocorticoid therapy as a first-line treatment of pemphigus versus the standard treatment with standard corticosteroids (CS). As a first step, our clinico-biological analysis of patients after 24 months has shown that the use of RTX combined with short-term prednisone as a first-line treatment in patients with moderate to severe pemphigus is both more effective and better tolerated than the reference treatment with prednisone alone. Respectively, 89% of patients versus 34% in each group and both pemphigus foliaceus and pemphigus vulgaris patients responded. This efficacy was confirmed in the longer term after reconstitution of the B lymphocyte repertoire with a risk of relapse of only 2% at 36 months. The presence of a severe form of pemphigus at diagnosis (PDAI ≥ 45) and an anti-Dsg Ab level at 3 months above threshold values (anti-DSG1 ≥ 20 or anti-DSG3 ≥ 120) are associated with 50% risk of early relapse. These two predictive factors make it possible to identify a subgroup of patients at high risk of relapse requiring a maintenance infusion of RTX at the 6th month. In a second step, we studied the impact of RTX and CS treatments in patients with pemphigus in order to better understand the autoimmune response. The phenotypic characterization of auto-reactive B cells and the analysis of the frequency of B cells able of secreting anti-Dsg immunoglobulin (Ig) G by an ELISPOT approach demonstrated that the efficacy of RTX treatment in pemphigus seems related to the elimination of IgG-switched Dsg memory B-cells. Dsg specific B cells remain detectable after RTX when B cells return, but these B cells have a naïve and non-switched (IgM) phenotype and no longer secrete IgG. On the other hand, the persistence of self-reactive Dsg B cells capable of secreting IgG anti-Dsg after treatment with CS is certainly at the origin of the frequency of relapses. The unicellular targeted gene expression analysis demonstrated that initially, Dsg-specific B cells have a pro-inflammatory profile with the overexpression of three genes encoding Interleukin (IL) -1β, IL-12p35 and IL-23p19 and for the IRF5 gene (Interferon regulatory factor 5) compared to non-self-reactive B cells. RTX and CS have different effects on the expression of these genes, but both reduce the gene expression of IL-1β, which seems to play an important role in the pathophysiology of pemphigus

Les lymphocytes T CD4 (LT CD4) jouent un rôle central dans la régulation des réponses immunitaires vis-à-vis des agents infectieux et des vaccins. Cependant, leur différenciation in vivo est encore mal comprise et les caractéristiques des LT CD4 capables de persister à long terme tout en assurant une réponse immunitaire protectrice sont mal définies. L’approfondissement de ces connaissances est indispensable pour le développement de nouveaux vaccins.

Pour approcher cette question, nous avons utilisé deux approches expérimentales. La première est un suivi de la différenciation des LT CD4 au cours de la réponse immune primaire chez des sujets vaccinés contre l’hépatite B ;la deuxième est la caractérisation phénotypique et fonctionnelle des LT CD4 mémoires antigène(Ag)-spécifiques pendant la phase d’état. Cette analyse a été réalisée au sein des LT CD4 spécifiques d’Ag vaccinaux, l’Ag de surface du virus de l’hépatite B (HBs) et la toxine tétanique (TT), ainsi que ceux spécifiques des Ag du cytomégalovirus (CMV). Les LT CD4 Ag-spécifiques ont été mis en évidence par cytométrie de flux après marquage intracytoplasmique du ligand du CD40 (CD40L) exprimé en réponse à une stimulation de courte durée par l’Ag. Des expériences basées sur la stimulation par la toxine du syndrome du choc toxique et le marquage du segment Vbeta2 du récepteur des LT ont démontré la bonne sensibilité et spécificité de cette méthode.

Le suivi de la réponse primaire chez 11 donneurs jusqu’à plus d’un an après immunisation par le vaccin anti-hépatite B a permis d’établir un modèle de différenciation des LT CD4 Ag-spécifiques in vivo chez l’homme. Nous avons mis en évidence des LT CD4 spécifiques d’un nombre limité de peptides immunodominants de la protéine HBs suggérant une réponse de type oligoclonale. Grâce à l’utilisation d’un cytomètre neuf couleurs, nous avons mené une analyse détaillée de l’hétérogénéité de la population mémoire HBs-spécifique. L’expression du CCR7 permet de distinguer des cellules de type mémoire centrale (LTCM, CCR7+) et effectrice (LTEM, CCR7-) se distinguant notamment par leur capacité à migrer vers les ganglions lymphatiques ainsi que par leurs propriétés fonctionnelles. Nous avons montré l’existence de ces deux sous-populations au sein des cellules HBs-spécifiques mais par opposition à leur définition initiale, ces LTCM sont capables de produire des cytokines effectrices. La proportion importante de LTCM exprimant le Ki67 témoigne d’une activité proliférative persistante in vivo et suggère la capacité de ces cellules à s’auto-renouveler et éventuellement à alimenter le pool des LTEM. La proportion importante de LTCM exprimant la chaîne alpha du récepteur à l’IL-7 (CD127) suggère que ces cellules sont sensibles aux signaux émanant de l’IL-7, une cytokine dont le rôle dans le maintien de la mémoire lymphocytaire T est connu. Compte tenu de la relevance potentielle de ces caractéristiques uniques pour le développement de vaccins et de l’accumulation de travaux montrant l’avantage sélectif des LTCM à conférer une immunité protectrice, nous avons focalisé la dernière partie de ces recherches sur cette sous-population. Une étude transversale des LTCM spécifiques de plusieurs types d’Ag (éliminés (HBs et TT) ou persistants (CMV)) a été menée. Nos résultats montrent une hétérogénéité, variable selon l’Ag, de la capacité de ces cellules à produire des cytokines effectrices et de leur phénotype de différenciation. Cette donnée nouvelle soulève la possibilité que les LTCM soient hétérogènes dans leur capacité à conférer une immunité protectrice. L’acquisition du marqueur KLRG1 par une fraction des LTCM s’associe à une capacité accrue à produire des cytokines effectrices et à une expression élevée du CD127. La possibilité que ces cellules soient particulièrement aptes à conférer une immunité protectrice et durable est discutée, tout comme les mécanismes menant à leur génération et l’intérêt de ces connaissances pour la conception de nouveaux vaccins.

Doctorat en Sciences médicales
info:eu-repo/semantics/nonPublished

A contribuição de células B para a memória imunológica se dá por duas distintas populações: células B de memória e células produtoras de anticorpos de longa vida (ASC). A inter-relação entre estas células bem como os mecanismos envolvidos para a manutenção destas tem sido pouco entendida. O veneno de Thalassophryne nattereri tem se mostrado capaz de induzir uma intensa resposta imune de memória. Nós avaliamos o efeito das Natterinas, que são as toxinas majoritárias e inéditas, na indução e manutenção da resposta imune de memória de células B. Este estudo, além de permitir um maior esclarecimento da resposta humoral de memória induzida pelo veneno do peixe T. nattereri, permitiu o estudo da complexa organização do compartimento de células B de memória e ASCs. Também evidenciamos a importância da atividade proteásica para a manutenção da cronicidade de resposta de células B no peritônio, no baço e na medula, como verificamos que a ativação de receptores inatos como osTLRs é decisiva para a geração e manutenção de ASCs B220pos/neg em resposta às Natterinas, dependentes das vias de sinalização MyD88 ou TRIF. Estas sinalizações controlam a magnitude, a qualidade e a longa duração da resposta humoral de memória.
The contribution of B cells for the immunological memory feels for two different populations: memory B cells and long-lived antibodies secreting cells (ASC). The interrelation among these cells as well as the mechanisms involved for the maintenance of these it has been little understood. The venom of Thalassophryne nattereri possesses the ability to induce an intense memory immune response. We evaluated the effect of Natterins that are majority toxins in the venom, in the induction and maintenance of the immune memory response of cells B. The study, besides allowing a larger explanation of the humoral memory response induced by the venom of the fish, it allowed the understanding of the complex organization of the memory B cells compartment, mainly of the subtype of long-lived cells (ASC). Also, we showed the importance of the protease activity of Natterins in the maintenance of the chronic B cell responses in the three analyzed compartments. We verify that the activation of Toll like receptors is decisive for the generation and maintenance of ASCs B220pos/neg in response to Natterins, dependent on the MyD88 or TRIF signaling that control the quality and the duration of the humoral memory response.

La transplantation rénale est le meilleur traitement de l’insuffisance rénale chronique terminale, que ce soit en termes d’espérance ou de qualité de vie. Malgré les progrès réalisés en immunologie de la transplantation et dans la gestion globale des patients transplantés, la principale étiologie de perte de greffon reste le rejet, et en particulier le rejet humoral.L’évaluation du risque de rejet humoral repose principalement sur le dosage des anticorps anti-HLA dirigés contre le greffon. Pourtant, il apparait que ces anticorps ont un faible pouvoir prédictif de l’incidence et du pronostic du rejet, ce qui pourrait être expliqué par une hétérogénéité de leurs caractéristiques intrinsèques. Ces caractéristiques dépendent des cellules responsables de leur sécrétion, plasmocytes à courte et longue durée de vie, et donc indirectement des cellules responsables du maintien du pool de ces cellules sécrétrices d’anticorps : les lymphocytes B mémoires. Il a été montré en pathologies infectieuses que ces lymphocytes B mémoires sont hétérogènes en termes de phénotype, de fonction, de degré de clonalité et de diversification de leur BCR (B-cell receptor). Néanmoins, ceci n’a pas encore été analysé en transplantation rénale. Un des objectifs de cette thèse était d’étudier le degré d’hétérogénéité des lymphocytes B mémoires HLA-spécifiques chez des patients immunisés en attente de transplantation rénale. Pour ce faire, une analyse en cellule unique de lymphocytes B mémoires HLA-spécifiques de patients présentant différents contextes et degré d’immunisation a été réalisée, dans le but d’identifier leurs caractéristiques phénotypiques et transcriptomiques et la diversification de leur répertoire BCR.La deuxième partie des travaux s’est concentrée sur les modalités diagnostiques du rejet de greffe rénale. Depuis quelques années, des outils de biologie moléculaire sont disponibles, permettant d’évaluer des centaines de transcrits exprimés dans le tissu de biopsie. Ces outils donnent la possibilité de décrire de nouvelles voies physiopathologiques, et potentiellement d’améliorer le diagnostic du rejet, en particulier le rejet humoral. Néanmoins, leur utilisation en pratique courante est restreinte du fait de leur faible disponibilité, des difficultés à interpréter les données produites, et de leur coût. De plus, du fait de cette sous-utilisation en pratique clinique, leur impact exact dans la prise en charge des patients n’est pas déterminé. Au cours de cette thèse, un outil de diagnostic moléculaire ayant des caractéristiques compatibles avec une utilisation en pratique clinique a été développé. Celui-ci permet de diagnostiquer le rejet et de le classer en rejet humoral ou cellulaire. Dans un second temps, cet outil a été confronté à des situations cliniques litigieuses, afin d’évaluer son intérêt en pratique courante.À travers ces travaux, cette thèse vise d’une part à améliorer la compréhension de la réponse humorale en transplantation rénale, afin de contribuer à terme à mieux stratifier le risque immunologique en transplantation, et d’autre part à améliorer les modalités diagnostiques du rejet en aidant à la généralisation des outils de biologie moléculaire appliqués aux biopsies de greffons rénaux
Kidney transplantation is the best treatment of end-stage renal disease, improving life quality and quantity. Despite advances in pathophysiological knowledge of kidney transplant immunology, kidney transplant rejection remains the major cause of allograft dysfunction, especially antibody-mediated rejection.Antibody-mediated rejection risk assessment is based on the evaluation of donor-specific anti-HLA antibodies. However, these antibodies have a poor predictive value for incidence and prognosis of rejection. This could be explained by the heterogeneity of their intrinsic characteristics. These characteristics depend on cells responsible for their secretion, which include short- and long- lived plasma cells. Consequently, they indirectly depend on the cells responsible for maintaining the pool of these antibody-secreting cells, such as memory B cells. In infectious diseases, it is known that memory B cells are heterogeneous in terms of phenotype, function, degree of clonality, and diversification of their B-cell receptor (BCR). However, this heterogeneity has not been examined in the context of kidney transplantation.The aim of the first part of this thesis was to study the heterogeneity of HLA-specific memory B cells in sensitised patients on kidney transplant waiting list. To this end, single-cell analysis of HLA-specific memory B cells from patients with various aetiologies and degrees of immunisation was performed. This led to their phenotypic and transcriptomic characterisation and to the assessment of their BCR repertoire.The second part of this thesis was dedicated to the diagnosis of kidney transplant rejection.In recent years, biopsy-based transcriptomics has emerged, enabling the assessment of hundreds of transcripts in kidney biopsy tissue. These tools provide the opportunity to elucidate new physiopathological pathways and potentially enhance the diagnosis of rejection, especially humoral rejection. However, their application in clinical practice is still limited due to their restricted availability, required expertise for data processing and interpretation, and cost. Furthermore, their exact impact on patient management remains undetermined. Here, a molecular diagnostic tool with characteristics suitable for clinical use was developed. This tool enables the diagnosis of rejection and its classification between antibody-mediated and T-cell mediated rejection. Subsequently, this tool was assessed in ambiguous clinical situations to evaluate its impact in clinical practice.Through these studies, this thesis focused on enhancing our understanding of the humoral response in renal transplantation, which could help improving immunological risk stratification in transplantation. Additionally, it aimed to improve biopsy-based transcriptomics in the diagnosis of kidney transplant rejection

In C. difficile infection (COl), the antibody-mediated immune response to secreted toxins A and B appears to be important in determining the nature of clinical disease. The aim of this study was to evaluate multiple aspects of the humoral immune response to C. difficife toxins A and B in patients with C. difficile-associated disease (COAO), among which included subjects with inflammatory bowel disease. Humoral immune measurements were also quantified for healthy controls and patients with cystic fibrosis (CF) who have been reported to rarely develop COl. Isolated peripheral blood mononuclear cells (PBMCs) were fluorescently labelled with Alexa Fluor® 488 and other B cell markers to identify transiently circulating toxin A-specific antigen-activated B cells during clinical disease by flow cytometry. PBMCs were also polyclonally stimulated in vitro for 6 days to induce proliferation and differentiation of memory B cells (MBCs) to antibody-secreting cells (ASCs). ELiSPOT assays were used to quantify toxin A- and B-specific IgG ASCs. Toxin A- and B-specific antibody levels in sera and supernatant samples of cultured PBMCS were studied by ELISA. A small proportion of toxin A-specific, antigen-activated B cells were detected in the circulation soon after COl. Differential antibody and MBC responses to C. difficile toxins A and B were detected over many months following CDl and in CF patients. The magnitude of these responses did not significantly differ between patients with single and recurrent CDAD. A greater proportion of toxin B-specific MBCs were present in the peripheral circulation in the CDAD and CF groups. No correlation was seen between the frequency of circulating toxin-specific antigen-activated or MBCs and contemporaneous serum anti-toxin IgG levels in either group. These data suggest that serum anti-toxin antibodies can underestimate the breadth of humoral immunity and strongly support the use of toxin-specific B (memory) cell analyses to complement serological studies.

The development of vaccines directed against polysaccharide capsules of S. pneumoniae, H. influenzae and N. meningitidis have been of great importance in preventing potentially fatal infections. Bacterial capsular polysaccharides are T-cell-independent antigens that induce specific antibody response characterized by IgM immunoglobulins, with a very low IgG class switched response and lack of capability of inducing a booster response. The inability of pure polysaccharides to induce sustained immune responses has required the development of vaccines containing polysaccharides conjugated to a carrier protein, with the aim to generate T cell help. It is clear that the immunogenicity of glycoconjugate vaccines can vary depending on different factors, e.g. chemical nature of the linked polysaccharide, carrier protein, age of the target population, adjuvant used. The present study analyzes the memory B cell (MBC) response to the polysaccharide and to the carrier protein following vaccination with a glycoconjugate vaccine for the prevention of Group B streptococcus (GBS) infection. Not much is known about the role of adjuvants in the development of immunological memory raised against GBS polysaccharides, as well as about the influence of having a pre-existing immunity against the carrier protein on the B cell response raised against the polysaccharide component of the vaccine. We demonstrate in the mouse model that adjuvants can increase the antibody and memory B cell response to the carrier protein and to the conjugated polysaccharide. We also demonstrate that a pre-existing immunity to the carrier protein favors the development of the antibody and memory B cell response to subsequent vaccinations with a glycoconjugate, even in absence of adjuvants. These data provide a useful insight for a better understanding of the mechanism of action of this class of vaccines and for designing the best vaccine that could result in a productive and long lasting memory response.

The development of vaccines directed against polysaccharide capsules of S. pneumoniae, H. influenzae and N. meningitidis have been of great importance in preventing potentially fatal infections. Bacterial capsular polysaccharides are T-cell-independent antigens that induce specific antibody response characterized by IgM immunoglobulins, with a very low IgG class switched response and lack of capability of inducing a booster response. The inability of pure polysaccharides to induce sustained immune responses has required the development of vaccines containing polysaccharides conjugated to a carrier protein, with the aim to generate T cell help. It is clear that the immunogenicity of glycoconjugate vaccines can vary depending on different factors, e.g. chemical nature of the linked polysaccharide, carrier protein, age of the target population, adjuvant used. The present study analyzes the memory B cell (MBC) response to the polysaccharide and to the carrier protein following vaccination with a glycoconjugate vaccine for the prevention of Group B streptococcus (GBS) infection. Not much is known about the role of adjuvants in the development of immunological memory raised against GBS polysaccharides, as well as about the influence of having a pre-existing immunity against the carrier protein on the B cell response raised against the polysaccharide component of the vaccine. We demonstrate in the mouse model that adjuvants can increase the antibody and memory B cell response to the carrier protein and to the conjugated polysaccharide. We also demonstrate that a pre-existing immunity to the carrier protein favors the development of the antibody and memory B cell response to subsequent vaccinations with a glycoconjugate, even in absence of adjuvants. These data provide a useful insight for a better understanding of the mechanism of action of this class of vaccines and for designing the best vaccine that could result in a productive and long lasting memory response.

Die beständige Autoantikörperproduktion in Patienten mit Systemischem Lupus Erythematodes (SLE) suggeriert die Existenz eines autoreaktiven humoralen Gedächtnisses; die Häufigkeit selbstreaktiver Gedächtnis-B-Zellen in SLE wurde jedoch noch nicht ermittelt. Unter normalen Umständen exprimieren neu gebildete B-Zellen im Knochenmark Autoantikörper mit hoher Frequenz, darunter auch antinukleäre Antikörper. Diese autoreaktiven B Zellen unterliegen einer strengen Überwachung an zwei Kontrollpunkten für Selbsttoleranz, einer im Knochenmark und einer in der Peripherie. Im Gegensatz dazu steht SLE mit einem Defekt in Zusammenhang, der die Etablierung von B-Zell-Toleranz an diesen beiden Kontrollpunkten verhindert und somit einer hohe Anzahl selbstreaktiver naiver B-Zellen in der Peripherie. Das Ziel dieser Studie war die Bestimmung der molekularen Eigenschaften und Reaktivitäten von IgG Gedächtnis-B-Zell-Antikörpern in SLE. Mittels einer Einzelzell-PCR basierten Methode wurden 200 monoklonale Antikörper von einzelnen IgG+ Gedächtnis-B-Zellen vier unbehandelter SLE Patienten kloniert. Die generelle Häufigkeit an polyreaktiven und HEp-2 selbstreaktiven Antikörpern in dieser Population war vergleichbar mit der in gesunden Vergleichspersonen. 15% der Antikörper aus IgG+ Gedächtnis-B-Zellen eines Patienten mit Serum-Autoantikörpertitern derselben Spezifität waren hochreaktiv und spezifisch gegen die SLE-assoziierten löslichen Kernantigene Ro52 und La; nicht jedoch in den übrigen drei Patienten oder gesunden Vergleichspersonen. Die Keimbahnkonfigurationen dieser Antikörper gegen Kernantigen waren nicht-selbstreaktiv oder polyreaktiv mit schwacher Ro52-Bindung und untermauern die Theorie, dass somatische Mutationen zur Reaktivität und Spezifität von Autoantikörpern beitragen. Die Häufigkeitsvarianz, mit der Gedächtnis-B-Zellen SLE-assoziierte Antikörper exprimieren, legt nahe, dass dies eine wichtig Variable für den Erfolg von Therapien sein kann, die diese Population beseitigen.
Persistent autoantibody production in patients with systemic lupus erythematosus (SLE) suggests the existence of autoreactive humoral immunological memory, but the frequency of self-reactive memory B cells in SLE has not been determined. Under normal circumstances, autoantibodies including antinuclear antibodies (ANAs) are frequently expressed by newly generated B cells in the bone marrow, but these autoreactive B cells are tightly regulated at two checkpoints for self-tolerance, in the bone marrow and the periphery, before maturation into naïve immunocompetent B cells. In contrast, SLE is associated with a failure to establish B cell tolerance at the two checkpoints leading to high numbers of autoreactive naïve B cells in the periphery. The aim of this study was to determine the molecular features and reactivities of IgG memory B cell antibodies expressed in SLE. A single-cell PCR based strategy was applied that allowed the cloning of the Ig heavy and Ig light chain genes of a single purified B cell and the in vitro expression of 200 recombinant monoclonal antibod-ies from single IgG+ memory B cells of four untreated SLE patients. The overall frequency of polyreactive and HEp-2 self-reactive antibodies in this compartment was similar to healthy controls (HC). 15% of IgG memory B cell antibodies were highly reactive and specific for SLE-associated extractable nuclear antigens (ENAs) Ro52 and La in one patient with serum autoantibody titers of the same specificity but not in the other three patients or healthy individuals. The germline forms of the ENA antibodies were non-self-reactive or polyreactive with low binding to Ro52 supporting the idea that somatic mutations contribute to autoantibody specificity and reactivity. Heterogeneity in the frequency of memory B cells expressing SLE-associated autoantibodies suggests that this variable may be important in the outcome of therapies that ablate this compartment.

Rapid waning of antibody and vaccine effectiveness is observed following infant immunisation with protein-polysaccharide conjugate vaccines. This is despite the demonstrable presence of immunological memory. However, disease can develop within a few days of carriage acquisition of encapsulated bacteria. Persistence of functional antibody, therefore, appears to be the key determinant of long-term protection against invasive bacterial diseases. Antibody persistence is thought to depend on the survival of long-lived plasma cells and memory B cells generated in germinal centres (GC). Using the ELISpot method, the kinetics of the B cell response following a booster dose of MenC conjugate vaccine (MenCV) at one year of age, and following a 2 dose-primary course of a new tetravalent meningococcal vaccine (MenACWY-CRM197) given at 2 and 4 months of age, were determined. It was found that priming with these vaccines induced protective antibody levels in the majority of children but detectable memory B cells only in a subset of children. A strong association was found between the level of polysaccharide-specific antibody and memory B cells produced after priming, and the persistence of functional antibody at one year of age. The kinetics of a primary B cell response were determined in healthy adults after immunisation with rabies vaccine, and compared to the B cell response following primary immunisation with MenCV in 2 months old infants. The timing of appearance of the B cells in peripheral blood was similar in infants and adults, although the magnitude of the response was slightly lower in infants. These observations suggest that long-term humoral immunity induced by immunisation with protein-polysaccharide conjugate vaccines in early infancy depends on the production of adequate GCs during priming. The children who generate efficient GCs during priming (identified by higher production of memory B cells, plasma cells and Abs) may best maintain protective antibody levels in the long-term, while those children generating less efficient GCs, have a smaller B cell pool, lower antibody response during priming, and might not maintain protective antibody levels in the long-term.

Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2007.
Title from electronic title page (viewed Mar. 26, 2008). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Microbiology and Immunology." Discipline: Microbiology and Immunology; Department/School: Medicine.

Tick-borne encephalitis virus (TBEV) is a serious viral infection that affects the central nervous system. It was estimated that between 1990 and 2009 a total of 169,937 cases of TBE were recorded in Europe. TBEV belongs to genus Flavivirus that comprises over 70 viruses, many of them are important human pathogens. Most members are either transmitted by mosquitoes e.g. West Nile virus (WNV), Dengue virus (DENV) or ticks e.g. TBEV. Due to the extensive antigenic cross-reactivity among flaviviruses serological diagnosis of TBE infections is commonly difficult in areas where more than one virus type circulates. Particularly, a situation now exists in Europe, where TBEV and WNV are endemic in many countries Thus, this thesis focused on the one hand on optimization of serological test systems using recombinant envelope protein domain III (rED3). It represents domain 3 of the major antigen, the surface protein E, which additionally has been shown to induce flavivirus specific neutralizing antibodies. Therefore rED3 was expressed and purified and its application as antigen in ELISA for TBEV diagnosis was verified. On the other hand a memory B-cell assay was established to analyse antiviral immunity after TBEV-vaccination. Here rED3 was used as antigen to determine the frequency of rED3 specific antibody-secreting cells (ASCs). Vaccination is the most effective method of preventing TBE disease and is currently recommended for all those who live and work or travel to areas of TBE endemicity. An essential requirement of any vaccine is the induction of long-term protective immunity. Several vaccines have defined levels of serum antibody (as measured by ELISA, haemagglutination inhibition test, or neutralisation test) that serve as correlates or surrogates of protective immunity. But this does not take account of vaccine induced memory B cells. Although, not providing direct protection against infection, they represent an important second line of immune defence that is initiated only if pre existing antibody levels are too low to prevent infection or if the invading pathogen is able to circumvent the pre-existing antibody response. A thorough understanding of the frequencies of antigen-specific memory B cells and their relationship with the antibodies in serum serological memory is likely to be critical to give information about the long-term efficacy of vaccine as well as its correlates of protection. This thesis focuses on the establishment of a recombinant protein based ELISA and of a memory B cell assay for analysis of specific antiviral immunity after vaccination with the following two objectives: (1) Expression and purification of recombinant envelope protein domain 3 (rED3) and verification of its application as antigen in ELISA for TBEV diagnosis; (2) Establishment of a memory B cells assay using rED3 for determination of frequency of rED3 specific antibody-secreting cells (ASCs) in individuals vaccinated against TBE. In this study, TBEV- and WNV-specific antigen ED3 was expressed in E. coli as MBP fusion proteins with C-terminal histidine tag using pMAL-c2x vector. By purification with amylose affinity chromatography followed by nickel affinity chromatography, highly purified TBEV rED3 and WNV-rED3 were obtained. Nevertheless, using TBEV-rED3 protein in Western Blot unspecific reaction with serum antibodies of negative serum was detected and a differentiation between WNV infection and TBEV was impossible, probably due to the MBP moiety. However, using the purified rED3 protein as antigen in ELISA, TBE virus-specific antibodies were detected specifically. Twenty-three serum samples predefined as TBEV positive were tested positive by rED3-based ELISA and commercial IgG ELISA. Five predefined negative serum samples were tested negative by rED3-based IgG ELISA as well as commercial IgG ELISA. But cross reactivity of WNV and DENV positive sera was detected in 15 of 18 sera by commercial ELISA. On the other hand, these samples were found negative in TBEV rED3-based ELISA. Thus, TBEV-rED3-based ELISA allows a differentiation of infections caused by TBE serogroup and mosquito-borne flaviviruses but not the inactivated virus based commercial ELISA. Interestingly, compared to neutralisation test the specificity of rED3-based ELISA obtained 100% with a sensitivity of 91.6%. In contrast, the commercial ELISA obtained 100 % sensitivity but a low specificity with only 42.8%. In order to determine frequency of antigen-specific antibody secreting cells (ASCs) produced by individuals who received the vaccination against TBE, peripheral blood mononuclear cells (PBMCs) were isolated from blood samples. Subsequently, memory B cells were activated with R848 (Resiquimod) and human recombinant IL-2 (hrIL-2) for 72 hours in 37°C, 5% CO2, 90% humidity. After 72 hours of incubation, Enzyme-Linked Immunospot (ELISPOT) detected antigen-specific memory B cells. In order to evaluate specificity of TBEV-rED3 in ELISPOT, other antigens including WNV-rED3, Maltose binding protein (MBP) and Influenza Nucleoprotein (NP) were included. Study subjects could be separated into two groups: last vaccination before 5 years or longer than 10 years. TBEV-rED3 specific ASCs could be detected in 11 of 12 TBE vaccinated individuals with different vaccination history and even low serum anti-TBE antibodies levels. TBEV-rED3 specific ASCs were found with frequency of ranging 0.016-0.188 % per total IgG ASCs and lower than frequency of Influenza-NP specific ASCs (between 0.012-0.51%). But TBE-specific memory B cells could be maintained for more than 20 years of post-vaccination. There was a significant difference in number of ASCs between vaccinated and non-vaccinated group (p<0.05). Interestingly, there was no significant difference between TBE vaccinated groups between 1-5 years (mean of 2.5 years) and >10 years (mean of 16.5 years) since vaccination (p>0.05). These finding proved that memory B cells have been stable for years and are maintained up to 25 years since last vaccination. A statistic analysis showed that there was no significant correlation between serum levels of anti-TBEV antibodies and the frequency of rED3 specific IgG ASCs (p>0.05, Spearman’s coefficient r = 0.36). A similar result was also indicated for influenza-vaccinated individuals (p>0.05, Spearman’s coefficient r = 0.27). These findings revealed that memory B cells and plasma cells maybe play an independently role in maintaining of immunological memory. Anyway, neutralizing antibodies have been found in all vaccines (a Geometric mean titre (GMT) of 96.04, 95% confident interval (CI): 52.76-174.8) and thus were maintained for a long time since last vaccination. Interestingly, the quantitative determination of specific IgG in TBE post-vaccination sera by rED3-based ELISA exhibits a good correlation with neutralizing antibody titres. The presence of specific antibodies in rED3-based ELISA is therefore highly predictive for the presence of neutralizing antibodies, and this correlation can probably be used in the future to establish guidelines for recommendations of booster vaccinations. Additionally, it became apparent that the number of previous booster vaccinations correlated strongly with the frequency of circulating memory B cells. As expected, individuals who received a booster increased both the specific antibody titre and frequency of antigen specific memory B cells. This suggests that immunological long-term memory induced by booster immunizations is better reflected by the circulating memory B cells than the amount of the antibody titre. Thus, memory B cells seem to be a more reliable parameter for the assessment of long-term immunity. Taken together, a highly antigenic rED3 using the bacterial expression system was produced and it is a promising alternative to whole inactivated virus in ELISA. Notably, rED3 was a reliable antigen for detecting antigen-specific memory B cells in individuals who have been previously TBEV vaccinated. This study provides data on immunological memory for TBE vaccination and might be useful for reconsideration of recommendations for booster dose. In conclusion, boosters of vaccination should be recommended for all individuals who live and work or travel to areas of TBE endemicity. As consequently, vaccine-induced protection is enhanced by both strong humoral and cell-mediated immune responses. If pace of pathogenesis is rapidly growing, pre-existing virus-specific antibodies represent the first line of defence against infection before the memory response is fully activated and implemented. They clearly function best together to efficiently protect against disease.

Despite the outstanding progress made in the understanding of the immune response against viral pathogens as well as on the care-management of transplant patients since the beginning of organ transplantation, hCMV infection still represents a major adverse complication among solid organ and hematopoietic cell transplant patients directly threatening both allograft and patient survival. While the advent of new and more potent anti-viral therapies used either as anti-viral treatments during active infection or as part of a preventive strategy, has lead to a significant reduction of the incidence of hCMV infection and its related complications, the occurrence of viral infection after transplantation is still considered as a rather unpredictable event. Certainly, this is the reflection of the considerably poor clinical monitoring of the viral immune susceptibility of each individual, which is merely based on the serological immune status combination between recipient and donor IgGantibody levels in sera and the direct assessment of the virus itself replicating in peripheral blood. The work constituting this doctoral thesis, researches further into how assessing hCMV-specific memory T and B-cell subsets, using a highly sensitive technique such as the ELiSPOT assay, which allows an accurate enumeration of antigen-specific immune responses at the single cell level, may help to better identify cellular and humoral immunized patients against the hCMV and thus, ultimately helping identifying kidney allograft recipients at high risk of hCMV infection after kidney transplantation. Importantly, an accurate and reliable knowledge of the immune-protection level against hCMV of transplant patients would allow individualization for anti-viral decision-making, thus personalizing this therapy. To date, an important body of evidence has been generated within the transplant scientific community, demonstrating the key role of the adaptive immunity, and particularly the cellular immune response in preventing, controlling and restricting viral replication. In contrast to previous reported data, in which have analyzed different types of organ transplant patients, receiving distinct type of anti-viral therapies and have fundamentally focused on the post-transplant setting, we here focused for the first time on the evaluation of hCMV-specific memory T and B cells against different immunogenic hCMV antigens prior to kidney transplantation in very clean and homogenous cohorts of kidney transplant recipients. In the first part of this thesis, it is shown that high frequencies of hCMV-specific T-cell responses, particularly against the IE-1 dominant hCMV antigen, may significantly improve the current serological identification of those kidney allograft recipients at high-risk for hCMV infection. Importantly, this approach was capable to discriminate such patients before transplantation with high sensitivity, regardless the type of preventive anti-viral strategy used based on the classical risk factors for the estimation of CMV risk after transplantation. Furthermore, the high negative predictive value of the test highlights the usefulness of such diagnostic tool among the kidney transplant population. In the second part of this study, we provide further insight about the cross-talk between the humoral and cellular memory adaptive immune response against hCMV, by monitoring baseline hCMV-specific memory T and B-cell responses, which significantly increases the capacity to discriminate "true" immunized kidney transplant recipients against hCMV as compared to current evaluation of hCMV-specific antibody titers in the sera. Our study points to the direction that monitoring IE-1 hCMV-specific T-cell frequencies before transplantation would help transplant physicians on the one hand to better discriminate patients with no need of hCMV prophylactic treatment from those in whom prophylaxis should preferentially be indicated and on the other, to better predict those patients in whom prophylaxis treatment could safely be discontinued.
El treball que constitueix aquesta tesi doctoral, investiga més a fons com avaluar cèl·lules T IB de memòria CMVh específiques, utilitzant una tècnica altament sensible, com l'assaig ELISPOT, que permet una enumeració precisa de respostes immunes antigen específiques a nivell individual cel·lular, pot ajudar a identificar millor els pacients cel.lulars i humorals immunitzat contra la CMVh i, per tant, en última instància, ajudar a la identificació de receptors d'al·loempelts renals amb alt risc d'infecció per CMVh després del trasplantament renal. És important destacar que un coneixement exacte i fiable del nivell de protecció immunitària contra CMVh dels pacients trasplantats permetria individualització per a la presa de decisions anti-viral, personalitzant així aquesta teràpia. A la primera part d'aquesta tesi, es demostra que les altes freqüències de les respostes de cèl·lules T CMVh específics, en particular contra l'antigen CMVh dominant IE-l, pot millorar significativament l'actual identificació serològica dels receptors de al·loempelts renals d'alt risc per infecció per CMVh. És important destacar que aquest enfocament era capaç de discriminar aquests pacients abans del trasplantament amb una alta sensibilitat, sense importar el tipus d'estratègia antiviral preventiva utilitzada està basada en els factors de risc clàssics per a l'estimació del risc de CMV després del trasplantament. D'altra banda, l'alt valor predictiu negatiu de la prova posa de manifest la utilitat d'aquesta eina de diagnòstic entre la població trasplantament de ronyó. Ala segona part d'aquest estudi, es proporcionarà més informació sobre la diafonia entre la resposta immune adaptativa memòria humoral i cel·lular contra de HCMV, mitjançant el control de la memòria T i de cèl·lules 8 respostes HCMV específics de la línia de base, el que augmenta significativament la capacitat de discriminar "veritable" immunitzat receptors de trasplantament renal en contra CMVh en comparació amb l'avaluació actual dels títols d'anticossos CMVh específics en els sèrums. En els punts d'estudi a l'adreça que el monitoratge-l IE freqüències de cèl.lules T específiques de CMVh abans del trasplantament seria ajudar els metges de trasplantament, per una banda per discriminar millor els pacients sense necessitat de CMVh tractament profilàctic d'aquells a qui la profilaxi preferentment s'han d'indicar i en l'altra, per predir millor els pacients en els quals amb seguretat podria interrompre la profilaxi tractament.