Germline noncoding risk variants influence clonal hematopoiesis through altered hematopoietic enhancer activity.

Clonal hematopoiesis of indeterminate potential (CHIP) is a precursor condition characterized by the expansion of mutant hematopoietic stem and progenitor cell (HSPC) clones that increases the risk of hematologic malignancies. Although genome-wide association studies have identified multiple non-coding loci associated with CHIP susceptibility, their mechanisms remain unclear. We hypothesized that CHIP risk variants alter enhancer activity in HSPCs. To test this, we screened 1,374 non-coding variants from 51 CHIP-associated loci using a Massively Parallel Reporter Assay (MPRA) in the CD34+ fraction of MUTZ-3 cells. We identified 87 regulatory variants across 32 loci. Targeted genome editing in hematopoietic cells and complementary reporter assays in primary human HSPCs validated enhancer activity for variants regulating NKD2, FLT3, and MSI2. Functional studies demonstrated that increased MSI2 expression, modeling the effect of the CHIP risk allele, promotes clonal expansion of TET2-deficient HSPCs, providing a mechanistic link between inherited non-coding variation and CHIP clonal expansion.