Characterized by the accumulation of somatic mutations in blood cell lineages, clonal hematopoiesis of indeterminate potential (CHIP) is frequent in aging and involves the expansion of mutated hematopoietic stem and progenitor cells (HSC/Ps) that leads to an increased risk of hematologic malignancy. However, the risk factors that contribute to CHIP-associated clonal hematopoiesis (CH) are poorly understood. Obesity induces a proinflammatory state and fatty bone marrow (FBM), which may influence CHIP-associated pathologies. We analyzed exome sequencing and clinical data for 47,466 individuals with validated CHIP in the UK Biobank. CHIP was present in 5.8% of the study population and was associated with a significant increase in the waist-to-hip ratio (WHR). Mouse models of obesity and CHIP driven by heterozygosity of Tet2, Dnmt3a, Asxl1, and Jak2 resulted in exacerbated expansion of mutant HSC/Ps due in part to excessive inflammation. Our results show that obesity is highly associated with CHIP and that a proinflammatory state could potentiate the progression of CHIP to more significant hematologic neoplasia. The calcium channel blockers nifedipine and SKF-96365, either alone or in combination with metformin, MCC950, or anakinra (IL-1 receptor antagonist), suppressed the growth of mutant CHIP cells and partially restored normal hematopoiesis. Targeting CHIP-mutant cells with these drugs could be a potential therapeutic approach to treat CH and its associated abnormalities in individuals with obesity.

Acute myeloid leukemia (AML) patients present with CD8 exhaustion signatures, and pharmacologic inhibition of checkpoints can have therapeutic benefit. The alarmin IL-33 and its receptor STimulation-2 (ST2) promote activation of tissue-regulatory T cells (T_reg cells) and accelerate malignant progression in solid tumors, but their role in leukemia remains unclear. Here, we show that ST2⁺ T_reg cells are enriched in bone marrow (BM) of humans and mice with AML and promote CD8⁺ T cells depletion and exhaustion. ST2 deficiency in T_reg cells restores CD8⁺ T cell function, decreasing AML growth via retention of ST2⁺ T_reg cells precursors in lymph nodes. AML-activated ST2⁺ T_reg cells lack T-bet, IFN-γ and Bcl-6, and kill intratumoral CD8⁺ T cells by amplified granzyme B-mediated cytotoxicity compared to non-AML primed T_reg cells. Engineered anti-ST2 antibodies induce ST2⁺ T_reg cells apoptosis to extend survival in AML models. Together, our findings suggest that ST2 is a potential checkpoint target for AML immunotherapy.

Bone marrow (BM) is a tissue that is of great importance to several areas of basic and translational research, including hematology, oncology, bone biology, and immunology. It is unique in that it is gelatinous in nature but housed in a hard casing of bone. Traditionally, flow cytometry and immunofluorescence (IF) techniques have been employed to study the composition of cellular interactions and elements of the BM. However, it has been challenging to study the BM in an unperturbed state using multiple fluorescent probes at a time to fully appreciate the diverse cell populations and their interactions and relative positioning with each other. This protocol addresses how Phenocycler 2.0^TM, which uses co-detection by indexing (CODEX) in conjunction with HALO 4.0^TM image analysis software, can overcome the obstacles faced by traditional techniques used to study the BM in an unperturbed state.

Clonal hematopoiesis of indeterminate potential (CHIP) is characterized by age-related somatic mutations in hematopoietic stem and progenitor cells (HSC/Ps) and is correlated with an increased risk of myeloid malignancies, elevated inflammatory pathways in circulating myeloid cells, higher all-cause mortality, chronic kidney disease, and cardiovascular disease. The pathophysiology of inflammatory bowel disease (IBD) is intrinsically linked to heightened inflammation. Nevertheless, the presence of CHIP in IBD and its role in the pathophysiology of IBD remains poorly elucidated. In the UK Biobank, CHIP was associated with an increased incidence of IBD. Females with CHIP had a 1.33-fold higher risk, which was further validated in the All of Us database (ßodds ratio, 1.29). For Crohn's disease, DNA methyltransferase 3A (DNMT3A) mutations conferred a 1.81-fold increased incidence in females compared with non-DNMT3A carriers, which rose to 2.09 for large clones (variant allele fraction of ≥10%). In contrast, for ulcerative colitis, TET2 large clones were significantly associated, and only among individuals aged <45 years. These associations were further identified using 2-sample Mendelian randomization. In a mouse model of CHIP-IBD, HSC/Ps with Dnmt3a mutation demonstrated significantly worse pathophysiology compared with controls, due, in part, to heightened expression of apurinic/apyrimidinic endonuclease 1 (APE1) in the bone marrow and colon. Treatment with the APE1/redox factor 1 inhibitor APX3330 ameliorated CHIP-IBD driven by the Dnmt3a mutation.

Obesity is increasingly implicated in hematopoietic malignancies, yet its role in mutation-driven myeloid leukemias remains unclear. Using UK Biobank data from over 440,000 individuals, we found obesity traits including elevated BMI and waist-to-hip ratio were associated with type 2 diabetes, increased plasma IL-17A (interleukin-17A), reduced GLP-1R (glucagon like peptide 1 receptor) expression, and heightened risk of myeloid malignancies. Transplantation of protein tyrosine phosphatase non-receptor type 11, PTPN11 ( Shp2 ^E76K/+ ) mutant hematopoietic stem/progenitors into obese mice demonstrated that metabolic inflammation accelerates leukemogenesis via myeloid cell expansion, lipid metabolic rewiring, IL-17A activation, and accumulation of M2-like tumor-associated macrophages (TAMs), accompanied by T-cell exhaustion and impaired antigen presentation. Notably, dual therapy with an anti-IL-17A antibody and a GLP-1R agonist reversed these effects, by reducing M2-like TAMs, restoring Ciita -dependent antigen presentation, Tyk2 -mediated IFNγ signaling, reactivated T-cell responses, and reducing leukemic burden. These findings establish IL-17A driven, metabolism-coupled immunosuppression as a mechanistic link between obesity and SHP2-mutant myeloid leukemias, highlighting a tractable therapeutic strategy for high-risk obese patients.

Ex vivo expansion of hematopoietic stem cells (HSCs) is limited by mitochondrial stress-induced loss of stemness. To identify protective mechanisms resembling the hypoxic bone marrow niche, we performed single-cell transcriptomics on hypoxia-collected HSCs, revealing significant downregulation of Rho-associated kinase 1 (ROCK1). This observation suggested ROCK1 as a potential regulator of HSC homeostasis. We tested this by genetically or pharmacologically inhibiting ROCK1 with shRNA or Y27632, which reduced mitochondrial reactive oxygen species, mitochondrial mass, and membrane potential while promoting expansion of phenotypic HSCs (Lin⁻CD34⁺CD38⁻CD45RA⁻CD49f⁺CD90⁺). Mechanistically, ROCK1 inhibition attenuated DRP1-mediated mitochondrial fission by decreasing p-DRP1(Ser616) and increasing p-DRP1(Ser637), thereby reducing mitochondrial fragmentation. Additionally, ROCK1 inhibition elevated BCL2 expression and reduced active Caspase-3 levels, indicating suppressed apoptosis. Limiting dilution transplants demonstrated a fourfold increase in functional HSC frequency following ROCK1 inhibition, with enhanced long-term engraftment in secondary recipients. Our findings identify ROCK1 as a critical regulator of mitochondrial dynamics in HSCs and provide a mechanistic basis for targeting ROCK1 to enhance functional HSC expansion, offering a promising strategy to improve outcomes in HSC transplantation by mimicking hypoxic niche signals ex vivo.