A Thpok-Directed Transcriptional Circuitry Promotes Bcl6 and Maf Expression to Orchestrate T Follicular Helper Differentiation

The generation of high-affinity neutralizing antibodies, the objective of most vaccine strategies, occurs in B cells within germinal centers (GCs) and requires rate-limiting "help" from follicular helper CD4(+) T (Tfh) cells. Although Tfh differentiation is an attribute of MHC II-restricted CD4(+) T cells, the transcription factors driving Tfh differentiation, notably Bcl6, are not restricted to CD4(+) T cells. Here, we identified a requirement for the CD4(+)-specific transcription factor Thpok during Tfh cell differentiation, GC formation, and antibody maturation. Thpok promoted Bcl6 expression and bound to a Thpok-responsive region in the first intron of Bcl6. Thpok also promoted the expression of Bcl6-independent genes, including the transcription factor Maf, which cooperated with Bcl6 to mediate the effect of Thpok on Tfh cell differentiation. Our findings identify a transcriptional program that links the CD4(+) lineage with Tfh differentiation, a limiting factor for efficient B cell responses, and suggest avenues to optimize vaccine generation.