Spatiotemporal resolution of germinal center Tfh cell differentiation and divergence from central memory CD4(+) T cell fate

Follicular helper T (Tfh) cells are essential for germinal center (GC) B cell responses. However, it is not clear which PD-1(+)CXCR5(+)Bcl6(+)CD4(+) T cells will differentiate into PD-1(hi)CXCR5(hi)Bcl6(hi) GC-Tfh cells and how GC-Tfh cell differentiation is regulated. Here, we report that the sustained Tigit expression in PD-1(+)CXCR5(+)CD4(+) T cells marks the precursor Tfh (pre-Tfh) to GC-Tfh transition, whereas Tigit(–)PD-1(+)CXCR5(+)CD4(+) T cells upregulate IL-7Rα to become CXCR5(+)CD4(+) T memory cells with or without CCR7. We demonstrate that pre-Tfh cells undergo substantial further differentiation at the transcriptome and chromatin accessibility levels to become GC-Tfh cells. The transcription factor c-Maf appears critical in governing the pre-Tfh to GC-Tfh transition, and we identify Plekho1 as a stage-specific downstream factor regulating the GC-Tfh competitive fitness. In summary, our work identifies an important marker and regulatory mechanism of PD-1(+)CXCR5(+)CD4(+) T cells during their developmental choice between memory T cell fate and GC-Tfh cell differentiation.