BLIMP1 negatively regulates IL-2 signaling in T cells

IL-2 signaling sustains immune homeostasis by fine-tuning the balance between effector and regulatory T cells. Our genome-wide CRISPR knockout screen using IL-2-dependent cells derived from a patient with Adult T-cell Leukemia (ATL) showed enriched sgRNAs targeting PRDM1 (encoding BLIMP1). BLIMP1 inhibits IL-2 production in T cells; however, its role in IL-2 signaling remains unknown. Here, we show that Prdm1 overexpression decreased IL-2 signaling in CD4+ T cells, while its deletion enhanced IL-2 signaling during influenza infection. Adoptive transfer of Prdm1 CKO Tregs into Rag2-/- mice elevated IL-2 signaling in T-cell induced colitis. Moreover, CRISPR/Cas9-mediated PRDM1 deletion augmented IL-2 signaling in human CD4+ T cells and natural Tregs with BLIMP1 binding to key genes affecting IL-2 signaling. Furthermore, ATL cells from acute patients exhibited increased IL-2 signaling but reduced BLIMP1 induction. Thus, BLIMP1 represses IL-2 signaling in T cells which is critical in orchestrating normal and pathophysiological immune responses.