Single cell RNA sequencing analysis of tumor responses to triple drug oral immunotherapy in dogs with osteosarcoma

Abstract Osteosarcoma constitutes a rare childhood cancer that is associated with dismal outcomes. As such, there is a need to develop non-invasive immunotherapeutic approaches to treat this aggressive malignancy. To address this need, we described the cellular heterogeneity in spontaneously occurring canine osteosarcoma tumors then evaluated how treatment with adjuvant immunotherapy altered the tumor microenvironment. We investigated the effects of a triple drug immunotherapeutic (orally administered losartan, ladarixin, and toceranib) that was designed to deplete immune suppressive macrophages and promote antitumor immunity. The treated cohort of dogs were given the adjuvant immunotherapy for 14 days prior to amputation, while naïve samples were collected from unrelated dogs undergoing amputation to treat a primary osteosarcoma tumor. In total, we completed single cell RNA sequencing on 6 naïve dogs and 6 treated dogs to profile just under 100,000 cells. Unsupervised clustering revealed 30 unique cell populations with T cells, macrophages, and neutrophils making up the majority of immune infiltrates. Evaluation of changes to the cellular proportions following treatment revealed a marked reduction in macrophages, which suggests the combination immunotherapy was able to alter the tumor microenvironment. Overall, this study provides unique insights into the heterogeneity within canine osteosarcoma tumors and highlights the impacts of adjuvant immunotherapy on tumor infiltrating immune cell transcriptional programs. T32 OD012201 U01 CA5341458 Shipley family foundation