Functional heterogeneity exceeds genetic heterogeneity in chronic myelomonocytic leukemia

The respective role of genetic and epigenetic heterogeneity in the functional diversity of cells that compose human malignancies remains poorly understood. This question is addressed in chronic myelomonocytic leukemia (CMML), a myeloid neoplasm in which clinical diversity contrasts with a limited genetic heterogeneity. By reprogramming CMML-patient and healthy donor CD34-positive cells, we generated induced pluripotent cell clones (iPSC). In one of the patients, we captured a part of the genetic heterogeneity of the leukemic clone and analyzed five iPSCs with two distinct genetic backgrounds, i.e. with and without KRASG12D mutation. Hematopoietic differentiation of these clones recapitulated the main features of the patient disease, including overproduction of granulomonocytes and dysmegakaryopoiesis. These analyses also disclosed significant discrepancies in the behavior as well as the DNA methylation pattern of hematopoietic cells derived from iPSCs with similar genetic background. Introduction of SRSF2P95H mutation in a KRAS-mutated iPSC partially suppressed the functional and epigenetic gap with the other KRAS-mutated clone. Despite the similar functional behavior of these two clones, only the SRSF2P95H clone responded to low doses of the hypomethylating agent decitabine by restoration of a more balanced production of hematopoietic cells. These analyses unravel additional levels of intraclonal heterogeneity beyond the coding mutations, which may also modulate individual cell response to treatment. Twenty-five ng of high-molecular weight genomic DNA of CD34+ from control or patient A iPS clones were used to perform the ERRBS assay as described (Park et al. 2014) and sequenced on a HiSeq 3000 Illumina sequencer. 11 samples were analyzed, 6 iPS clones derived from a CMML patient and 5 derived from 2 different healthy control individuals.