SETD5 regulates leukemic initiation and infiltration in T-cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy characterized by aberrant epigenetic regulation. Although SET domain-containing 5 (SETD5) is structurally classified as a member of the histone methyltransferase family, it lacks canonical methyltransferase activity and functions primarily through nonenzymatic mechanisms. While recognized as a modulator in normal hematopoiesis, the role of SETD5 in T-ALL remains undefined. Here, we show that SETD5 contributes to efficient T-ALL initiation and progression in the models examined. Using ICN1-driven murine T-ALL models (Vav-Cre;Setd5fl/fl and Mx1-Cre;Setd5fl/fl), we show that genetic ablation of Setd5 impairs efficient leukemia initiation. In transplantation assays, Setd5 depletion reduces leukemia burden, prolongs survival, and impairs leukemic infiltration into the spleen, liver, and thymus. Mechanistically, transcriptomic profiling of Setd5-deficient CD3+ T-ALL cells reveals selective repression of transcriptional programs governing cell migration, motility, and cytoskeletal organization. Key regulators of actin cytoskeleton remodeling and extracellular matrix interaction-including Plxnb2, Mmp14, Ceacam1, and Clstn1-are among the most downregulated genes, as validated by RT-qPCR. Furthermore, SETD5 knockdown in the human T-ALL cell lines Jurkat and MOLT-4 results in a marked reduction in proliferation and migration. Our findings demonstrate that SETD5 contributes to T-ALL progression by regulating transcriptional programs that contribute to leukemic cell migration and infiltration, suggesting that SETD5-associated transcriptional programs warrant further investigation as potential vulnerabilities in T-ALL.