Mechanisms and Therapeutic Strategies to Reverse TET2 Mutant Clonal Hematopoiesis and the Risk of MDS, AML, and Atherosclerotic Cardiovascular Disease
Authors: Prutsch Nicole , Vromman Amélie , Leeper Brittaney , Chen Mengyu , He Shuning , Ren Siyang , Walker Christopher J. , Zimmerman Mark W. , Janini Gomes Mariana , Folco Eduardo J. , Rauch Philipp J. , Gokhale Prafulla C. , Abraham Brian J. , Neuberg Donna S. , Ebert Benjamin L. , Libby Peter , Look A. Thomas 
Published: December 2023

Inactivating mutations of the epigenetic modifier TET2 are frequent in myeloid malignancies and clonal hematopoiesis of indeterminate potential (CHIP). These mutations in hematopoietic stem and progenitor cells (HSPCs) impart a clonal advantage with increased self-renewal. CHIP is associated with an increased risk of hematological malignancies and, surprisingly, with atherosclerotic cardiovascular disease, supported by studies in mice and humans. The heightened cardiovascular risk in CHIP patients may result from a pro-inflammatory slant of the mutant HSPC progeny, particularly monocytes and macrophages, independent from the risk imparted by elevated LDL cholesterol levels. Targeting molecules like IL-1β may provide a strategy to lower the risk of cardiovascular morbidity in patients with CHIP. However, as an alternative strategy, administration of drugs that selectively suppress the growth of mutant CHIP clones in the bone marrow (BM) might reduce the risk of both i) progression to MDS or hematologic malignancy and of ii) atherosclerotic cardiovascular disease. This study focused on identifying drugs that reverse the inflammatory and atherosclerotic properties of TET2-mutant macrophages. Our previous investigations demonstrated that the nuclear export inhibitor eltanexor selectively kills Tet2-mutant HSPCs in zebrafish embryos and reduces the number of mutant colonies in murine colony formation assays. A murine competitive repopulation model of CHIP tested the in vivo efficacy of eltanexor. We found that eltanexor selectively reduces Tet2-mutant circulating monocytes while having no effect on overall total white blood cell counts. Moreover, a second trial using Ldlr-/- atherosclerosis-prone mice consuming a high-cholesterol diet, showed that treatment with eltanexor selectively reduces the amount of aortic atherosclerotic plaque formation as well as spleen weight in mice injected with Tet2+/- (mutant) BM cells, whereas eltanexor had no significant effect in mice injected with Tet2+/+ (wild-type) BM cells. Single-cell CITE-seq analysis of Ldlr-/- mice injected with a mix of Tet2+/- and Tet2+/+ BM cells showed that eltanexor selectively reduces the percentage of Tet2+/- HSPCs. Additionally, CITE-seq analysis revealed a significant reduction in pro-inflammatory macrophages in the arterial wall after eltanexor treatment, along with a decrease in IL-1β expression by these cells. As TET2 functions in mechanistically regulating gene regulation through epigenetic DNA methylation, we employed ChIP-seq and CUT&RUN-Seq technologies to investigate the mechanisms underlying enhancer dysregulation caused by loss of Tet2. Enhancer profiling of bone marrow-derived macrophages showed that the negative regulator of the macrophage inflammatory response, ATF3, is associated with a super-enhancer. Notably, the ATF3 super-enhancer emerged as the largest super-enhancer in wild-type macrophages but was reduced in Tet2-mutant macrophages. Our investigation also revealed that ATF3 binds with IL-1β at H3K27ac modified regions, and this binding was significantly diminished in Tet2-mutant macrophages. Remarkably, treatment with eltanexor restored the binding of ATF3 to IL1β, providing a mechanism to explain the anti-inflammatory effect of eltanexor concordant with our in vivo results. In summary, this study proposes eltanexor treatment as a novel therapeutic approach to specifically target TET2-mutant cells in individuals with CHIP and sheds light on the underlying mechanisms of the pro-inflammatory slant of TET2-mutant macrophages. These findings offer potential new avenues for precise therapies in humans with CHIP and associated cardiovascular risks from atherosclerosis.