Comparison of dendritic cell-mediated immune responses among canine malignant cells.

Dendritic cell (DC) vaccination is one of the most attractive immunotherapies for malignancies in dogs. To examine the differences in DC-mediated immune responses from different types of malignancies in dogs, we vaccinated dogs using autologous DCs pulsed with keyhole limpet hemocyanin (KLH) and cell lysate prepared from squamous cell carcinoma SCC2/88 (SCC-KLH-DC), histiocytic sarcoma CHS-5 (CHS-KLH-DC), or B cell leukemia GL-1 (GL-KLH-DC) in vitro. In vivo inductions of immune responses against these tumor cells were compared by the delayed-type hypersensitivity (DTH) skin test. The DTH response against SCC2/88 cells were observed in dogs vaccinated with autologous SCC-KLH-DC, while the response was undetectable against CHS-5 and GL-1 cells in dogs vaccinated with autologous CHS-KLH-DC and GL-KLH-DC. Skin biopsies taken from DTH challenge sites were then examined for immunohistochemistry, and recruitment of CD8 and CD4 T cells was detected at the site where SCC2/88 cells were inoculated in dogs vaccinated with SCC-KLH-DC. By contrast, neither CD8 nor CD4 T cell infiltration was found at the DTH challenge site in the dogs vaccinated with CHS-KLH-DC or GL-KLH-DC. These findings may reflect that the efficacy of immune induction by DC vaccination varies among tumor types and that immune responses could be inducible in squamous cell carcinoma. Our results encouraged further investigation of therapeutic vaccination for dogs with advanced squamous cell carcinoma in clinical trials.