Pre-Leukemic Hematopoietic Stem Cell Clonal Selection by the Adaptive Immune System

/ABSTRACT A lack of proven interventions to prevent leukemia in aged populations leaves a growing demographic vulnerable to this devastating disease. While leukemic cells are subject to immune selection which influences disease progression, we lack knowledge of the stages at which T cells shape the hematopoietic stem and progenitor cell (HSPC) pool from the initiation of clonal hematopoiesis (CH) through to the progression to leukemia, which limits our ability to intervene in this process. The long-term goal of this project is to identify immuno-preventative strategies to intercept leukemogenesis at its earliest stages. The overall objective of this application is to determine the mechanisms by which, and at which stages of pre- leukemic development, HSPC clones are detected and selected by the adaptive immune system. The central hypothesis is that reduced IFNγ responsiveness enables immune evasion of CH-mutant (Dnmt3amut) HSPCs thereby promoting clonal expansion and pre-leukemic evolution. The rationale is grounded in the observation that HSPCs from humans and mice with recurrent CH driver mutations in Dnmt3a have reduced transcript and protein expression of MHC-II machinery, and reduced presentation of exogenous and endogenous antigens via MHC-II. Mechanistically, MHC-II is potently induced by IFNγ on wild-type HSPCs but to a lesser extent on Dnmt3amut HSPCs. In vitro and in vivo, we observe less activation and proliferation of CD4+ T cells by Dnmt3amut HSPCs compared to control HSPCs, supporting that Dnmt3amut HSPCs have reduced immunogenicity. The central hypothesis will be tested by pursuing two specific aims: 1) to define the stages of pre-leukemic HSPC selection that are controlled by CD4+ T cells, and 2) to evaluate decreased IFNγ response of pre-leukemic Dnmt3amut HSPCs as a mechanism of immune evasion. This research is innovative because it introduces a novel framework for understanding how adaptive immunity shapes clonal evolution of pre-leukemic HSPCs. While considerable attention has been given to genetic and cell-intrinsic drivers of CH, the role of immune surveillance—particularly adaptive immune selection—in governing HSPC clonality remains largely unexplored. Ultimately, the proposed work is significant because it will define the role of CD4⁺ T cells in HSPC clone selection during early disease phases in CH and pre-leukemia which has major therapeutic implications for immunoprevention of leukemia. Project Number: 1R01CA311181-01 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Jennifer Trowbridge (+1 co-PI) | Institution: JACKSON LABORATORY, BAR HARBOR, ME | Award Amount: $704,636 | Activity Code: R01 | Study Section: Basic Cancer Immunobiology Study Section[BCIB] View on NIH RePORTER: https://reporter.nih.gov/project-details/11338506