The role of Tet2-mutant clonal hematopoiesis in solid tumor immunology Free

Background: Clonal hematopoiesis (CH) is an age-related condition wherein somatic mutations in hematopoietic stem and progenitor cells lead to overrepresentation of mature immune cells that harbor the same mutation, affecting approximately 10% of older adults. While CH is primarily associated with increased risk of myeloid malignancy and some cardiovascular disease, recent evidence suggests that it is detectable in more than 20% of patients with solid tumors. In such patients, infiltrating myeloid cells harboring the same CH mutations have been detected at appreciable levels in tumor tissue and correlate with poor patient outcomes across cancer types. The impact of CH in the solid tumor immune microenvironment and response to immune checkpoint therapy (ICT) is unknown.

Methods: To mechanistically study the effects of CH on solid tumor biology in vivo, we established orthotopic models of pancreatic adenocarcinoma (PDAC) and melanoma in bone marrow chimera mice that harbor a CH clone heterozygous for a loss of function mutation in Tet2 (Tet2^+/mut); the second most mutated gene seen in human CH. Briefly, lethally irradiated CD45.1 recipient mice were transplanted with either Tet2^+/mut CD45.2 cells or wild-type (WT; Tet2^+/+) CD45.2. Following complete bone marrow reconstitution, mice were orthotopically implanted with mT4 pancreatic tumor cells (KPC-derived PDAC model) or B16-F10 melanoma cells. CH and WT mice were randomized to receive 3 doses of either a vehicle control or combination immune checkpoint therapy (ICT; αCTLA-4 + αPD-1). Tumor-infiltrating lymphocytes were analyzed by single-cell RNA sequencing (scRNA-seq; n=3/group) and CyTOF (n=5/group), while remaining mice were followed for tumor progression and overall survival (n ≥ 15/group). In vitro, we evaluated the role of Tet2^+/mut mutations in antigen presentation by performing a series of co-culture assays using WTand Tet2^+/mut bone marrow-derived macrophages with wild-type OT-I CD8⁺CD44^- naïve T cells. Finally, we evaluated clinical data from 35,971 non-small cell lung cancer (NSCLC) and 25,064 colorectal cancer (CRC) patients to assess associations between TET2 CH and ICT response.

Results: In vivo, we observed that the Tet2^+/mut myeloid cells were highly abundant in the tumor microenvironment. While there were no significant differences in tumor growth in the untreated setting, Tet2^+/mut CH was associated with a significantly improved response to ICT in both the PDAC and melanoma models. Both CyTOF and scRNA-seq identified an increase in intratumoral antigen-presenting macrophages and more activated T cells in Tet2^+/mut CH mice in response to ICT. Mechanistically, in vitro studies demonstrated that Tet2^+/mut macrophages preferentially polarized into antigen presenting cells in response to IFNγ. Further, while IFNγ-primed Tet2^+/mut and WT macrophages were both capable of cross-priming naïve CD8⁺ T cells, Tet2^+/mut macrophages were significantly more immunogenic as demonstrated by increased CD8⁺ T cell proliferation and effector cytokine production upon restimulation. Clinically, TET2 CH was associated with improved outcomes in both NSCLC and CRC patients specifically among those treated with ICT.

Conclusions: These findings demonstrate that TET2-mutant clonal hematopoiesis can remodel the solid tumor microenvironment by reprogramming macrophages toward an antigen-presenting phenotype that more effectively cross-prime CD8+ T cell and correlates with improved response to immune checkpoint therapy. Although CH has been previously linked to poor prognosis, our data reveal a context-dependent, tumor-extrinsic mechanism by which TET2 CH can enhance immunotherapy efficacy. This work identifies TET2 CH as a potential predictive biomarker for ICT response in solid tumors and highlights the potential of considering other hematologic factors in cancer immunotherapy outcomes.