Phenotypic and transcriptomic profiles of tumor-conditioned macrophages in dogs, and the translational value of canine cancer immunology research.

Abstract

Tumor-associated macrophages (TAMs) are heterogeneous and abundantly present in the tumor stroma. They derive from tissue-resident macrophages and recruited monocytes and play a central role in several aspects of cancer. In murine models, TAMs promote invasion, intravasation, circulatory survival and extravasation of tumor cells. TAMs also promote tumor progression and angiogenesis, remodel the tumor microenvironment, and modulate the adaptive immune system. Evidence suggests TAMs are vital for establishing the premetastatic niche. Historically, family-owned dogs have proven to be reliable cancer models. In contrast to laboratory animals, dogs develop cancer naturally and commonly, co-inhabit our environment, are genetically outbred and immunologically experienced. We hypothesized that canine tumor conditioned monocyte-derived macrophages (TCMs) share many characteristics with M2 macrophages and have a tumor-promoting phenotype as in humans. We collected blood from healthy dogs, isolated peripheral blood monocytes and differentiated them in vitro using tumor conditioned media from three canine cancer lines and M-CSF. Three TCM populations were generated and compared with M1 and M2 macrophages. We assessed the macrophages using multicolor flow cytometry and RNA-sequencing. All TCM showed an increased expression of two M2 markers (CD209a and FcɛRI), while 2/3 TCM populations had increased expression of two additional M2 markers (CD206 and CD11d). Transcriptomic analysis is ongoing. Results so far support the hypothesis that canine TCMs share many similarities with human TCMs, further warranting the use of dogs as cancer immunology models. Supported by grant from Agria Animal Insurances (N-2020-0061) and The Research fund for cancer in dogs (Oslo, Norway)