Distinct dynamics of antigen-specific induction and differentiation of different CD11c+Tbet+ B-cell subsets.

BACKGROUND: CD11c+Tbet+ B cells are enriched in autoimmunity and chronic infections and also expand on immune challenge in healthy individuals. CD11c+Tbet+ B cells remain an enigmatic B-cell population because of their intrinsic heterogeneity. OBJECTIVES: We investigated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen-specific development and differentiation properties of 3 separate CD11c+ B-cell subsets-age-associated B cells (ABCs), double-negative 2 (DN2) B cells, and activated naive B cells-and compared them to their canonical CD11c- counterparts. METHODS: Dynamics of the response of the 3 CD11c+ B-cell subsets were assessed at SARS-CoV-2 vaccination in healthy donors by spectral flow cytometry. Distinct CD11c+ B-cell subsets were functionally characterized by optimized in vitro cultures. RESULTS: In contrast to a durable expansion of antigen-specific CD11c- memory B cells over time, both ABCs and DN2 cells were strongly expanded shortly after second vaccination and subsequently contracted. Functional characterization of antibody-secreting cell differentiation dynamics revealed that CD11c+Tbet+ B cells were primed for antibody-secreting cell differentiation compared to relevant canonical CD11c- counterparts. CONCLUSION: Overall, CD11c+Tbet+ B cells encompass heterogeneous subpopulations, of which primarily ABCs as well as DN2 B cells respond early to immune challenge and display a pre-antibody-secreting cell phenotype.

Parallel detection of SARS-CoV-2 epitopes reveals dynamic immunodominance profiles of CD8+ T memory cells in convalescent COVID-19 donors.

Objectives: High-magnitude CD8+ T cell responses are associated with mild COVID-19 disease; however, the underlying characteristics that define CD8+ T cell-mediated protection are not well understood. The antigenic breadth and the immunodominance hierarchies of epitope-specific CD8+ T cells remain largely unexplored and are essential for the development of next-generation broad-protective vaccines. This study identified a broad spectrum of conserved SARS-CoV-2 CD8+ T cell epitopes and defined their respective immunodominance and phenotypic profiles following SARS-CoV-2 infection. Methods: CD8+ T cells from 51 convalescent COVID-19 donors were analysed for their ability to recognise 133 predicted and previously described SARS-CoV-2-derived peptides restricted by 11 common HLA class I allotypes using heterotetramer combinatorial coding, which combined with phenotypic markers allowed in-depth ex vivo profiling of CD8+ T cell responses at quantitative and phenotypic levels. Results: A comprehensive panel of 49 mostly conserved SARS-CoV-2-specific CD8+ T cell epitopes, including five newly identified low-magnitude epitopes, was established. We confirmed the immunodominance of HLA-A*01:01/ORF1ab1637-1646 and B*07:02/N105-113 and identified B*35:01/N325-333 as a third epitope with immunodominant features. The magnitude of subdominant epitope responses, including A*03:01/N361-369 and A*02:01/S269-277, depended on the donors' HLA-I context. All epitopes expressed prevalent memory phenotypes, with the highest memory frequencies in severe COVID-19 donors. Conclusion: SARS-CoV-2 infection induces a predominant CD8+ T memory response directed against a broad spectrum of conserved SARS-CoV-2 epitopes, which likely contributes to long-term protection against severe disease. The observed immunodominance hierarchy emphasises the importance of T cell epitopes derived from nonspike proteins to the overall protective and cross-reactive immune response, which could aid future vaccine strategies.

Parallel detection of SARS‐CoV‐2 epitopes reveals dynamic immunodominance profiles of CD8+ T memory cells in convalescent COVID‐19 donors

Objectives High‐magnitude CD8+ T cell responses are associated with mild COVID‐19 disease;however, the underlying characteristics that define CD8+ T cell‐mediated protection are not well understood. The antigenic breadth and the immunodominance hierarchies of epitope‐specific CD8+ T cells remain largely unexplored and are essential for the development of next‐generation broad‐protective vaccines. This study identified a broad spectrum of conserved SARS‐CoV‐2 CD8+ T cell epitopes and defined their respective immunodominance and phenotypic profiles following SARS‐CoV‐2 infection. Methods CD8+ T cells from 51 convalescent COVID‐19 donors were analysed for their ability to recognise 133 predicted and previously described SARS‐CoV‐2‐derived peptides restricted by 11 common HLA class I allotypes using heterotetramer combinatorial coding, which combined with phenotypic markers allowed in‐depth ex vivo profiling of CD8+ T cell responses at quantitative and phenotypic levels. Results A comprehensive panel of 49 mostly conserved SARS‐CoV‐2‐specific CD8+ T cell epitopes, including five newly identified low‐magnitude epitopes, was established. We confirmed the immunodominance of HLA‐A*01:01/ORF1ab1637–1646 and B*07:02/N105–113 and identified B*35:01/N325–333 as a third epitope with immunodominant features. The magnitude of subdominant epitope responses, including A*03:01/N361–369 and A*02:01/S269–277, depended on the donors' HLA‐I context. All epitopes expressed prevalent memory phenotypes, with the highest memory frequencies in severe COVID‐19 donors. Conclusion SARS‐CoV‐2 infection induces a predominant CD8+ T memory response directed against a broad spectrum of conserved SARS‐CoV‐2 epitopes, which likely contributes to long‐term protection against severe disease. The observed immunodominance hierarchy emphasises the importance of T cell epitopes derived from nonspike proteins to the overall protective and cross‐reactive immune response, which could aid future vaccine strategies. Fifty‐one convalescent COVID‐19 donors were analysed for their ability to recognise 133 predicted SARS‐CoV‐2‐derived peptides restricted by 11 common HLA‐I allotypes using heterotetramer combinatorial coding. Forty‐nine mostly conserved SARS‐CoV‐2‐specific CD8+ T cell epitopes, including five new, were identified. This study revealed three dominant epitopes (HLA‐A*01:01/ORF1ab1637–1646, B*07:02/N105–113 and B*35:01/N325–333). The magnitude of subdominant epitope responses, including HLA‐A*03:01/N361–369 and A*02:01/S269–277, largely depended on the donors' HLA context. All epitopes had a prevalent memory phenotype, which were significantly higher in severe COVID‐19 donors.