Clonal composition and persistence of antigen-specific circulating T follicular helper cells

T follicular helper (TFH) cells are localized in secondary lymphoid organs and play an essential role in promoting B cell responses and antibody affinity maturation in germinal centres (GC). A subset of memory CD4+ T cells expressing the TFH-signature chemokine receptor CXCR5 has been described in human blood as being phenotypically and clonally related to GC TFH. However, the antigen specificity and the relationship of these circulating TFH (cTFH) cells with other circulating memory CD4+ T cells remain poorly defined. In this study, we combined antigenic stimulation and high-throughput T cell receptor (TCR) Vβ sequencing to define the repertoire of human memory cTFH cells specific for different microbial antigens. We found that CXCR5+ cTFH subsets comprised cells that responded to tetanus toxoid (TT), influenza vaccine (Flu) or Candida albicans (C.alb) but endowed with different effector functions compared to cells in CXCR5– non-cTFH subsets. Interestingly, cTFH and non-cTFH cells specific for C.alb or TT had a largely overlapping TCR Vβ repertoire while the repertoire of cTFH and non-cTFH cells specific for Flu was distinct. Furthermore, in-depth immune phenotyping showed that Flu-specific but not C.alb-specific PD-1+ cTFH cells had a “GC TFH-like” phenotype, with overexpression of IL21, CXCL13, BCL6. Longitudinal analysis of multi-year serial blood donations showed that Flu-specific cTFH and non-cTFH cells persisted as phenotypically stable repertoires for years. Collectively, our study contributes to the understanding of the relationship of cTFH with non-cTFH cells and provide insights on the heterogeneous origin and persistence of human cTFH cells specific for different antigens.