Mettl3-dependent mA modification is essential for effector differentiation and memory formation of CD8 T cells.

Efficient immune responses rely on the proper differentiation of CD8 T cells into effector and memory cells. Here, we show a critical requirement of N-Methyladenosine (mA) methyltransferase Mettl3 during CD8 T cell responses upon acute viral infection. Conditional deletion of Mettl3 in CD8 T cells impairs effector expansion and terminal differentiation in an mA-dependent manner, subsequently affecting memory formation and the secondary response of CD8 T cells. Our combined RNA-seq and mA-miCLIP-seq analyses reveal that Mettl3 deficiency broadly impacts the expression of cell cycle and transcriptional regulators. Remarkably, Mettl3 binds to the Tbx21 transcript and stabilizes it, promoting effector differentiation of CD8 T cells. Moreover, ectopic expression of T-bet partially restores the defects in CD8 T cell differentiation in the absence of Mettl3. Thus, our study highlights the role of Mettl3 in regulating multiple target genes in an mA-dependent manner and underscores the importance of mA modification during CD8 T cell response.