Mapping the lineage relationship between CXCR5+ and CXCR5- CD4+ T cells in HIV infected human lymph nodes

CXCR5 is a key surface marker expressed on follicular helper T (TFH) cells. We report here B cell help functionality in a population of CD4+ T cells isolated from primary human lymph nodes (LN) that lacked CXCR5 expression. This CXCR5- subset is distinguished from other CXCR5- CD4+ T cells by high PD-1 expression. Accumulation of CXCR5-PD-1+ T cells correlated with peripheral CD4+ T cell depletion and an increase in T-bet+ B cells in the LN, highlighting these atypical CD4+ T cells as a key component of lymphoid dysregulation during chronic HIV infection. By interrogating the phenotypic heterogeneity, functional capacity, TCR repertoire, transcriptional profile, and epigenetic state of CXCR5-PD-1+ T cells, we showed that CXCR5-PD-1+ T cells are related to CXCR5+PD-1+ T cells and provided evidence for the down regulation of CXCR5 following cell division as one mechanism for the absence of CXCR5 expression. Notably, CXCR5-PD-1+ T cells exhibited a migratory transcriptional program and contributed to circulating CXCR5-PD-1+ T cells with B cell help functionality in the peripheral blood. Thus, these data link LN pathology to circulating T cells and expand the current understanding on T cell diversity in the regulation of B cell responses during chronic inflammation.