Cdkn2a inactivation promotes malignant transformation of mouse immature thymocytes before the β-selection checkpoint

Abstract

CDKN2A deletion is the most frequent genetic alteration in T-cell acute lymphoblastic leukemia (T-ALL), occurring across all molecular and immunophenotypic subtypes. CDKN2A encodes two functionally unrelated tumor suppressor proteins, ARF and INK4a, critical regulators of cell cycle and proliferation. Arf has been reported to suppress T-ALL development in post-β-selection thymocytes, but whether CDKN2A acts as a tumor suppressor gene in immature, pre-β-selection thymocytes remains to be elucidated. Resorting to a Rag2-deficient model of T-ALL, driven by the ETV6::JAK2 fusion, we report that Cdkn2a haploinsufficiency at early stages of T-cell development facilitates leukemia development. ETV6::JAK2;Rag2-/-;Cdkn2a+/- T-ALL arose from pre-β-selection thymocytes, since the thymocyte differentiation arrest caused by Rag2 deficiency was maintained in pre-leukemic mice. Furthermore, somatic loss of the Cdkn2a wild-type allele was frequently observed in ETV6::JAK2;Rag2-/-;Cdkn2a+/- T-ALL cells, suggesting a selective advantage for total inactivation of Cdkn2a. Both Cdkn2a-sufficient and Cdkn2a-defective T-ALL presented additional genetic alterations, such as Notch1 mutations and gains of chromosomes 13 and 15. These data indicate that Cdkn2a acts as a gatekeeper for leukemogenesis from the most immature stages of thymocyte development.