Tissue-Biased Expansion of DNMT3A-Mutant Clones Associated with Conserved Epigenetic Alterations

DNA methyltransferase 3A (DNMT3A) is the most frequently mutated gene in clonal hematopoiesis (CH) and serves as a key tumor suppressor in the hematopoietic system. Somatic mutations in DNMT3A arise in hematopoietic stem and progenitor cells (HSPCs) many years before malignancies develop, but how they prime cells for transformation remains unknown, partly due to our inability to compare mutant to equivalent wild-type cells before frank disease. To overcome this challenge, we derived multiple normal and DNMT3A-mutant lymphoblastoid cell clones from a germ-line mosaic individual in whom these cells co-existed for nearly six decades. Although arising early in gestation, mutant cells dominated the blood, but not other tissues. Deep sequencing revealed similar mutational burdens and mutational signatures across normal and mutant clones. In contrast, epigenetic profiling uncovered focal erosion of DNA methylation at oncogenic regulatory regions in mutant clones. These regions overlapped with those sensitive to DNMT3A loss after DNMT3A ablation in HSPCs and with those present in leukemia samples. These results suggest that DNMT3A is responsible for maintaining a conserved DNA methylation pattern that is maintained for decades and across cell types and states. Erosion of this pattern confers a distinct competitive advantage, increasing the likelihood of malignant transformation Analysis of DNA methylation in human umbilical cord CD34+cells after KO of DNMT3A