Neonates are more susceptible to influenza virus infection than adults, resulting in increased morbidity and mortality as well as delayed clearance of the virus. Efforts to improve influenza infection outcomes in neonates typically center on prevention, although current vaccines fall short of complete protection and can only be administered in humans after 6 months of life. We propose that as the neonatal immune system responds differently than the adult immune system, interventions that are efficacious or tolerable in adults cannot be guaranteed to perform the same in neonates. T cell vaccines that target conserved influenza virus epitopes have been proposed for conferring protection to multiple influenza virus strains, but if T cell vaccines will be used in infants and adults, neonates must be able to respond to the same T cell antigens as adults. Mouse pups responded to influenza virus peptide PA224-233 but not NP366-374 during influenza virus infection in contrast to the codominant adult response. Mice infected as pups also generated diminished T cell memory compared to mice infected as adults and displayed skewed immunodominance during secondary infection. Adult bone marrow derived dendritic cells (BMDCs) improved viral clearance when loaded with influenza virus and promoted NP366-374-specific CD8+ T cell responses in infected pups. BMDC peptide vaccination could stimulate PA224-233-specific but not NP366-374-specific CD8+ T cell responses in pups, but, PA224-233 vaccination offered no protection to pups during lethal infection. These data suggest that altered immunodominance must be considered when stimulating CD8+ T cell responses in adults and neonates. Immaturity and active suppression of immune responses are both factors in neonatal vulnerability to disease. Specifically, active suppression of neonatal immunity by regulatory T cells (Tregs) has been proposed as a driving factor in diminished neonatal immunity, but removing these cells can compromise viral defense or increase deleterious inflammation. Mice that lacked Tregs displayed compromised anti-influenza antibody responses and decreased lymph node responses during influenza virus infection. A high proportion of pup Tregs also expressed Gata3. Transgenic pups with a Treg specific Gata3 knockout displayed an increase in Tbet expression in both conventional and regulatory T cells and an increase in IFNγ producing CD4+ T cells in the lungs during infection. These data suggest that Tregs are required for effective humoral responses to influenza virus and that Gata3 expression influences Treg suppressive function in neonates.

De nombreux antigènes de tumeur ont été identifiés depuis la découverte du premier antigène de tumeur humain il y a une vingtaine d’années, et plusieurs d’entre eux ont été utilisés comme antigène cible pour l’élaboration de vaccins thérapeutiques anti-Cancer. Cependant, les résultats des essais cliniques visant à évaluer l’efficacité de ces vaccins se sont la plupart du temps révélés décevants. Aussi, il reste indispensable d’identifier de nouveaux antigènes de tumeur cibles capables d’induire des réponses anti-Tumorales fortes et durables. Parmi les antigènes de tumeur considérés comme cibles potentielles pour un vaccin anti-Tumoral se trouve la Cycline B1, une protéine endogène impliquée dans la régulation du cycle cellulaire. Normalement exprimée de façon transitoire dans les cellules saines en division, cette protéine est surexprimée dans diverses tumeurs et est indispensable au développement tumoral. De plus, des réponses immunitaires spontanées spécifiques de cette protéine ont été observées chez des patients atteints de cancer. L’objectif de ma thèse était de caractériser la réponse en lymphocytes T CD4+, qui jouent un rôle capital dans la réponse immunitaire anti-Tumorale, spécifique de la Cycline B1 humaine chez des sujets sains et chez des patients atteints de cancer. Nous avons mis en évidence l’existence, chez des individus sains, de deux populations de lymphocytes T CD4+ préexistants spécifiques de cette protéine, à savoir des lymphocytes T CD4+ naïfs et des lymphocytes T CD4+ mémoires, cette seconde population lymphocytaire se retrouvant également chez des patients atteints de cancer. De multiples épitopes T CD4+ ont été identifiés dans cette protéine, et étaient différemment reconnus par ces deux populations de lymphocytes T CD4+. En outre, des anticorps IgG anti-Cycline B1 ont été détectés chez des patients atteints de cancer comme chez des individus sains, sans différence significative dans les taux d’anticorps entre ces deux catégories de sujets. Ainsi, cette étude montre que la Cycline B1 est un antigène de tumeur caractérisé par un profil singulier de réponses immunitaires, et confirme le potentiel vaccinal de cette protéine pour l’élaboration d’un vaccin anti-Cancer. / Many tumor antigens have been identified since the discovery of the first human antigen about twenty years ago, and some of them have been used as targets for the development of therapeutic cancer vaccines. However, most of the time, the results of clinical trials designed to assess the efficacy of these vaccines proved to be disappointing. Thus, it is still necessary to identify new tumor antigens able to induce strong and long-Lasting anti-Tumor responses that could be used as targets for cancer vaccine. Cyclin B1, an endogenous protein involved in cell cycle regulation, is one of the tumor antigens which are currently considered as potential targets for a cancer vaccine. Usually expressed transiently in healthy dividing cells, this protein is overexpressed in numerous tumors and is necessary for tumor development. Moreover, Cyclin B1 specific spontaneaous immune responses have been observed in cancer patients. My PhD work aimed at characterizing the response of CD4+ T cells, which play a major role in anti-Tumor immune responses, specific to human Cyclin B1 both in healthy individuals and cancer patients. We showed that, in healthy individuals, there exists two pre-Existing Cyclin B1 specific CD4+ T cell populations, namely naive CD4+ T cells and memory CD4+ T cells, the latter lymphocyte population being also found in cancer patients. Multiple CD4+ T cell epitopes have been identified in this protein, and were differently recognized by these two CD4+ T cell populations. Besides, anti-Cyclin B1 IgG antibodies have been detected both in healthy individuals and in cancer patients, without significant differences in antibody levels between these two groups of donors. Therefore, this work shows that Cyclin B1 is a tumor antigen characterized by a singular pattern of immune responses, and confirms the potential of this protein as a target for a cancer vaccine.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Multi-Antigen-Komplexe wurden in der Vakzinologie als effizientes Modell genutzt, um eine breite Impfstoffabdeckung gegen mehrere Stämme desselben Pathogens zu erzielen. Hier werden die Ergebnisse zur menschlichen B-Zell-Reaktion auf einen Multi-Antigen-Komplex (Bexsero) in drei Impfstoffen (Vax1, Vax2 und Vax3) dargestellt. Bexsero ist ein Impfstoff, der aus vier Antigenen (fHbp-GNA2091, NHBA-GNA1030, NadA und OMV (NZ98-254)) für Neisseria meningitidis (Nm) B besteht. Bei allen drei Impfstoffen konnten außerordentlich diverse Immunglobuline (Ig) beobachtet werden, die als Reaktion auf Bexsero mit einzigartigen Ig-Genselektionsmustern erzeugt wurden. Die Daten zeigen auch Igs, die eine Reihe von Spezifitäten aufweisen (Bexsero-spezifisch-reaktive Igs (nur Vax3) oder polyreaktive Igs (Vax2, Vax3 und Vax4)) und Affinitäten (hochbindende, mäßig bindende, schwach bindende und nicht reaktive Igs). Es wurde keine eindeutige Korrelation zwischen spezifischen Ig-Genmerkmalen und Ig-Reaktivitätseigenschaften beobachtet, obwohl Igs von allen Impfstoffen kollektiv unterschiedliche Affinitäten innerhalb/zwischen Cluster-Igs und zwischen Nicht-Clustern von Bexsero aufweisen, was potenzielle Vorteile für einen breiten Schutz mit sich bringt. Ig-Gen-Merkmale und Antigen-Reaktivitätseigenschaften von Igs, die gegen NHBA (22 Igs), fHbp (2 Igs) und NadA (2 Igs) erzeugt wurden, sind ebenfalls gezeigt. Diese Ig zeigten schwache Bindungsaffinitäten, wenn sie an endogen exprimierten Antigenen auf Nm mc58 getestet wurden, möglicherweise aufgrund eines ungeordneten N-Terminus von NHBA. Es wurde eine Anreicherung von hochmutierten polyreaktiven Ig beobachtet. Es werden unterschiedliche Immunoselektivitätsgrade für die verschiedenen Antigene beobachtet, was auf eine Antigenimmunodominanz sowie auf Hinweise auf eine Epitopmaskierung hindeutet. Mit einem kontrollierbaren System von 4 Antigenen eröffnen die Daten die Möglichkeit die menschliche B-Zell-Reaktion auf Multi-Antigen-Komplexe zu verstehen und zeigen, dass ein umfassendes Verständnis über die feinen zellulären und humoralen Einzelheiten der Immunantworten des Impfstoffs während klinischer Studien erforderlich ist. / Multi-antigen complexes have been exploited in vaccinology as an efficient model, to achieve broad vaccine coverage against multiple strains of the same pathogen. Here, the findings on the human B cell response to a multi-antigen complex (Bexsero) in three vaccinees (Vax1, Vax2 and Vax3) are shown. Bexsero is a vaccine comprising of four antigens (fHbp-GNA2091, NHBA-GNA1030, NadA and OMV (NZ98-254)) for Neisseria meningitidis (Nm) B. Immensely diverse (isotype distribution, IgVH and IgJH gene usage, CDR3 length distribution and clonal selection) immunoglobulins (Igs) generated in response to Bexsero with unique Ig gene selection patterns in all three vaccinees was observed. The data also shows Igs that exhibit a range of specificities {Bexsero-specific-reactive Igs (Vax3 Only) or polyreactive Igs (Vax2, Vax3 and Vax4)} and affinities (highly binding, moderately binding, weakly binding and unreactive Igs). No unique correlation between specific Ig gene features and Ig reactivity properties was observed, albeit Igs from all vaccinees collectively exhibit varied affinities within/between cluster Igs, and amongst non-clusters to Bexsero, with potential advantages for broad protection. Ig gene features and antigen-reactivity properties of Igs generated against NHBA (22 Igs), fHbp (2 Igs) and NadA (2 Igs) are also shown. These Igs exhibited weak binding affinities when tested on endogenously expressed antigens on Nm mc58, potentially due to disordered N-terminal of NHBA. Enrichment of highly mutated polyreactive Igs was observed. Varying degrees of immunoselectivity to the different antigens, suggesting antigen immunodominance as well as evidence of epitope masking are observed. With a controllable system of 4 antigens, the data opens a potential window to understanding the human B cell response to multi-antigen complexes and evinces the need for expansive understanding of the fine cellular and humoral details of vaccine immune responses during clinical trials.