Changes in Regulatory T Cells in Dogs with Cancer and Associations with Tumor Type

Background: Regulatory T cells (Treg) have been shown to suppress antitumor immunity and often are increased in humans and rodents with cancer. However, Tregs have not been well studied in dogs with cancer and it is not known if certain tumor types are associated with increased Tregs. Hypothesis: We hypothesized that Treg percentages would be increased in dogs with cancer and that Treg percentages would be higher in dogs with certain types of cancer. Animals: The percentages and numbers of Tregs and nonregulatory T cells and B cells were assessed in 34 dogs with cancer and 9 age‐matched control dogs. Dogs evaluated included 14 dogs with sarcoma, 7 dogs with carcinoma, 7 dogs with lymphoma, and 6 dogs with mast cell tumor. Methods: Numbers and percentages of Tregs, CD4+, and CD8+ T cells and B cells were determined using flow cytometry and compared between control dogs and dogs with cancer. Results: The percentage of Tregs was significantly increased overall in dogs with cancer compared with control dogs. When tumor types were compared, Treg percentages were significantly increased in dogs with carcinoma. The Treg/CD8 T cell ratio was significantly higher in dogs with cancer compared with control dogs and was also significantly increased in 2 dogs with T‐cell lymphoma. Conclusions: Treg percentages in blood were increased in dogs with cancer, particularly in dogs with carcinoma. The Treg/CD8 ratio also identified tumor‐specific abnormalities in dogs with cancer. These findings indicate that tumor‐specific factors may affect Tregs in dogs.