Induction of remission results in spontaneous enhancement of anti-tumor cytotoxic T-lymphocyte activity in dogs with B cell lymphoma

Characterization of the tumor microenvironment, particularly the immune cells that infiltrate tumors, provides important predictive and prognostic information in humans with lymphoma and other types of cancer. Tumor associated T lymphocytes have not been previously described in dogs with lymphoma. Therefore, we investigated the phenotype and function of T cells in the lymph nodes of dogs with B cell Non-Hodgkinʹs lymphoma (NHL), as well as the function of T cells in circulation of these dogs. We found that CD4+ and CD8+ T lymphocytes were few in number and minimally responsive to mitogenic stimuli compared to T cells in lymph nodes of normal dogs. Additionally, regulatory T cells (Treg) were significantly increased in tumor tissues compared to lymph nodes of healthy dogs. To better understand cell mediated antitumor immune responses we developed a non-radioactive assay to measure cytotoxic T lymphocyte (CTL) mediated killing of autologous tumor cells. Using this assay, we found that spontaneous CTL activity in the blood of dogs with lymphoma improved significantly following induction of tumor remission using doxorubicin. Coincident with the improvement in CTL activity, circulating Treg numbers were significantly decreased compared to pretreatment levels. We conclude from these studies that CTL activity in dogs with lymphoma can be significantly improved following induction of tumor remission using chemotherapy, as assessed using a new non-radioactive CTL assay.