N 6 -Methyladenosine Directly Regulates CD40L Expression in CD4 + T Lymphocytes.

T cell activation is a highly regulated process, modulated via the expression of various immune regulatory proteins including cytokines, surface receptors and co-stimulatory proteins. N 6 -methyladenosine (m 6 A) is an RNA modification that can directly regulate RNA expression levels and it is associated with various biological processes. However, the function of m 6 A in T cell activation remains incompletely understood. We identify m 6 A as a novel regulator of the expression of the CD40 ligand (CD40L) in human CD4 + lymphocytes. Manipulation of the m 6 A 'eraser' fat mass and obesity-associated protein (FTO) and m 6 A 'writer' protein methyltransferase-like 3 (METTL3) directly affects the expression of CD40L. The m 6 A 'reader' protein YT521-B homology domain family-2 (YTHDF2) is hypothesized to be able to recognize and bind m 6 A specific sequences on the CD40L mRNA and promotes its degradation. This study demonstrates that CD40L expression in human primary CD4 + T lymphocytes is regulated via m 6 A modifications, elucidating a new regulatory mechanism in CD4 + T cell activation that could possibly be leveraged in the future to modulate T cell responses in patients with immune-related diseases.