Determining mechanisms of T cell leukemogenesis using E2A −/−mice

Abstract

Abstract T cell acute lymphoblastic leukemia (T-ALL) is a hematological malignancy caused by the transformation of T-lymphocytes during their development. 60% of pediatric T-ALLs have ectopic expression of Tal1, a gene that promotes leukemogenesis in part by altering the function of E2A. Consistent with this, mice with germline deletion of E2A develop T-ALL that mirrors human Tal1 +T-ALL. In this study, we used mice that delete E2A at different stages in T cell development to investigate the mechanisms causing T-ALL. Mice carrying a VavCre transgene and floxed alleles of E2A (VcKO) delete E2A early in T cell development, have reduced numbers of thymocytes prior to transformation, and develop T-ALL with an average latency of 18 weeks. Mice with an LckCre transgene (LcKO) delete E2A later than VcKO mice, have replete thymi, and rarely develop T-ALL. From this, we hypothesized that 1) E2A regulates a gene program in early T cell development that is antagonistic to transformation, or 2) Having a replete, competitive thymus suppresses transformation. Pre-leukemic VcKO thymocytes showed significantly more differentially expressed genes than LcKO thymocytes, including Notch1 and Myc, and are enriched for cancer associated pathways. To determine if the lack of competition in the VcKO thymus contributes to leukemogenesis, we reconstituted VcKO thymi by transplanting wild type bone marrow into sublethally irradiated VcKO mice. BM transplant significantly increased the number and frequency of DP thymocytes and increased leukemia latency. Together, these data suggest that intrinsic loss of E2A promotes leukemogenesis by changing the gene program of early developing thymocytes and by creating a non-competitive environment that supports transformation.