Dnmt3a-dependent DNA methylation enforces lineage commitment and preserves functionality of memory Th1 and Tfh cells.

Following acute viral infection, naïve CD4+ T cells differentiate into T follicular helper (Tfh) and T helper 1 (Th1) cells that generate long-lived memory cells. However, it is unclear how memory Tfh and Th1 cells maintain their lineage commitment. We demonstrate that Tfh and Th1 lineages acquire distinct Dnmt3a-dependent DNA methylation programs that are preserved into memory. deletion impairs lineage commitment and functionality of memory Th1 and Tfh cells, resulting in aberrant upregulation that represses germinal center Tfh cell differentiation. In contrast, transient pharmacological DNA methyltransferase inhibition during priming impairs repression of Tfh-associated genes while properly silencing , and results in enhanced Tfh cell functionality in primary and secondary responses to viral infections. Together, these findings demonstrate that Dnmt3a-mediated epigenetic programing is required to enforce T helper lineage commitment and preserve Tfh and Th1-specific functions during the recall response to infection, and reveal novel strategies to improve long-lived adaptive immunity against infectious diseases.