Specific cTfh frequency correlates with memory B cell responses in HIV controllers.

Background: Follicular helper T cells (Tfh) play an essential role in the affinity maturation of the antibody response by providing help to B cells. To determine whether this CD4+ T cell subset may contribute to the spontaneous control of HIV infection, we analyzed the phenotype and function of circulating Tfh (cTfh) in patients from the ANRS CO21 CODEX cohort who naturally controlled HIV-1 replication to undetectable levels (HIC group), and compared them to treated patients with similarly low viral loads (ART group). Methods: HIV-specific cTfh (Tet+) were detected by Gag MHC-II tetramer labeling in the CD45RA- CXCR5+ CD4+ T cell population. The function of cTfh was analyzed by the capacity to promote IgG secretion in cocultures with autologous memory B cells. Results: HIV-specific cTfh (Tet+) proved more frequent in the controller group than in the treated patient group (P=0.002). The frequency of PD-1 expression in Tet+ cTfh was increased in both groups (median >75%) compared to total cTfh (<30%), but the intensity of PD-1 expression per cell remained higher in the ART group (P=0.02), pointing to the persistence of abnormal immune activation in treated patients. The function of cTfh, analyzed in coculture with memory B cells, did not show major differences between groups in terms of total IgG production, but proved significantly more efficient in the controller group when measuring HIV-specific IgG production. The frequency of Tet+ cTfh correlated with HIV-specific IgG production (R=0.71 for Gag-specific and R=0.79 for Env-specific IgG, respectively). Conclusion: Taken together, these findings indicate that key cTfh/B cell interactions are preserved in controlled HIV infection, resulting in potent memory B cell responses that may play an underappreciated role in HIV control.