Modelling the dynamics of spontaneous clonal hematopoiesis in pet dogs during cancer therapy - PROJECT SUMMARY Somatic mutations with leukemogenic potential confer selective cellular advantages leading to clonal expansion of hematopoietic stem cells, a phenomenon termed “clonal hematopoiesis” (CH). CH represents a premalignant lesion associated with aging, as it occurs in >10% of people 70 years of age or older, conferring an approximate 20-fold increased risk for future hematologic malignancy. Importantly, cancer patients with CH that undergo chemotherapy or radiotherapy exhibit a substantially increased risk for secondary neoplasia. In one study of 750+ human cancer patients undertaken by Dr. Bick (mPI), a greater than 5-fold increase in CH was observed for those that underwent radiation treatment (with or without chemotherapy) compared to those that did not receive radiation. Given its expanding role in cancer survivorship, there is a growing need for novel therapeutic strategies that target CH to mitigate risk for future malignancy and modify its potential impact on cancer treatment. However, a major barrier to better understanding the influence of CH on cancer pathophysiology remains the absence of an in vivo model system that recapitulates the development and evolution of CH during aging, tumorigenesis and subsequent cancer treatment. Studies of aged (>25 months) mice reveal that CH is a relatively rare event, suggesting that their comparatively short lifespans preclude its development. Genetically engineered mouse models have been generated in which hematopoietic stem cells typically carry one of the known human CH driver genes, but these typically necessitate bone marrow transplantation (often myeloablative) which induces a variety of systemic changes. Xenograft mouse models employing transplanted human hematopoietic cells have also been used, but these are immunodeficient and thus not ideal. As pet dogs with spontaneous cancers have been increasingly used as a preclinical translational model, we asked whether CH may also occur naturally in this species. We found that within a cohort of 600 dogs without cancer, 12% carried a CH mutation, comparable to the rate of CH in humans. Importantly, CH was not detected in dogs less than 6 months of age and is thus similarly associated with aging. Building upon these findings, the purpose of this proposal is to credential pet dogs as a relevant tool for studying CH in the context of onco-aging. Our interdisciplinary team will leverage completed and ongoing studies in pet dogs with cancer to optimize resources necessary to study CH in this species, interrogate how CH evolves in the context of cancer treatment, and explore the impact of CH on the tumor immune microenvironment. We will also employ single cell whole genome sequencing using the new primary template-directed amplification technique to improve sensitivity and precision of variant calling. Lastly, we will validate findings in dogs using biobanked samples from comparable human studies. These studies will establish a blueprint for incorporation of CH analytics into canine translational cancer work, with a future goal of using this unique model system to evaluate novel CH targeted therapies.
