Srsf2p95h And Tet2 Loss Co-Operate To Promote Chronic Myelomonocytic Leukaemia In Vivo

Sequencing of \u003e3000 MDS and related myeloid neoplasms has provided a detailed picture of the genetic landscape of these cancers. Most harbour mutations in two pathways: the RNA spliceosome (eg. SRSF2, SF3B1, U2AF1) and epigenetic regulators (eg. DMNT3, TET2). Co-mutation of SRSF2 and TET2 are profoundly enriched in MDS and MDS/MPN (p=2.63 × 10-14; q=1.21 × 10-12). In CMML and the related chronic neutrophilic leukaemia and atypical chronic myeloid leukaemia, there is a positive association between mutation of SRSF2 and TET2 (p=0.002). This association is strongest in CMML (p=0.004), where SRSF2 mutations occur in ∼50% of patients and TET2 mutations in ∼60%. SRSF2/TET2 co-mutation influences clinical presentation, with co-mutated CMML having higher leukocyte counts yet less pronounced monocytosis compared to those with wild-type SRSF2/TET2. Based on the human clinical genetics, we crossed the conditional Srsf2P95H/+ mutants with Tet2fl/fl mice to establish animals where we could mutate both concomitantly. At 52 weeks post gene mutation there is a hypocellular bone marrow with increased myeloid bias at the expense of B lymphoid and erythroid lineages in the Srsf2/Tet2 double mutants. Under conditions of native haematopoiesis with aging, a distinct myeloid bias and monocytosis develop in the Srsf2/Tet2 mutants which is not seen in either single mutant or controls. The compound Srsf2/Tet2 mutants display increased granulocytic and monocytic proliferation (myelo-monocytic hyperplasia) with increased immature promonocytes and monoblasts (∼10-15% total nucleated cells) and evidence of binucleate promonocytes. These are features of CMML (CMML-2). Upon secondary transplant, recipients developed leukocytosis, monocytosis and splenomegaly. This demonstrates that our model is able to reproduce SRSF2/TET2 co-operativity in vivo, yielding a disease with core characteristics of CMML, unlike single Srsf2 or Tet2 mutation.