A SIRT7-dependent acetylation switch regulates early B cell differentiation and lineage commitment through Pax5

B lymphopoiesis is orchestrated by lineage-specific transcription factors. In B cell progenitors, lineage commitment is mediated by Pax5, which is commonly mutated in B cell acute lymphoblastic leukemia. Despite its essential role in immunity, the mechanisms regulating Pax5 function remain largely unknown. Here, we found that the NAD⁺-dependent enzyme SIRT7 coordinates B cell development through deacetylation of Pax5 at K198, which promotes Pax5 protein stability and transcriptional activity. Neither Pax5^K198 deacetylated nor acetylated mimics rescued B cell differentiation in Pax5^−/− pro-B cells, suggesting that B cell development requires Pax5 dynamic deacetylation. The Pax5^K198 deacetylation mimic restored lineage commitment in Pax5^−/− pro-B cells and B cell differentiation in Sirt7^−/− pro-B cells, suggesting the uncoupling of differentiation from lineage commitment. The SIRT7–Pax5 interplay was conserved in B cell acute lymphoblastic leukemia, where SIRT7 expression correlated with good prognosis. Our findings reveal a crucial mechanism for B lymphopoiesis and highlight the relevance of sirtuins in immune function.