Tumor recognition and acquisition of protecting adaptive anti-tumor immune response in vivo against CIITA-driven MHC class II expressing Oral Squamous Cell Carcinoma Cells

Background: We have previously demonstrated that cells from MHC class II-negative solid tumors can function as surrogate Antigen Presenting Cells (APCs) for their own tumor antigens, provided they optimally express MHC class II (MHC-II) molecules as a function of genetic transfer of the MHC class II transactivator CIITA. CIITA positive tumors became potent stimulators of a protective adaptive antitumor immune response, triggered by CD4+ T helper (Th) cells and mediated by both Th cells and tumor specific CD8+ cytolytic (CTL). Here we extend our approach to Oral Squamous Cell Carcinoma (OSCC), the most common malignant neoplasm of the oral cavity for which, despite advances in detection and standard therapeutic approaches, the prognosis is poor due to a high rate of locoregional recurrence and development of distant metastasis. Methods: Syngeneic C57BL/6 mice were injected subcutaneously (s.c.) with either parental Mouse Oral Cancer 2 parental (MOC2pc) or MOC2-CIITA tumor cells and tumor growth was checked at least twice a week, using a manual caliper. Mice which have rejected MOC2-CIITA tumor cells were challenged s.c. with MOC2pc. The size for the tumor was measured weekly as described above. For Adoptive Cells Transfer (ACT) experiments, mice were injected s.c. MOC2 cells plus total naïve splenocytes, or total immune splenocytes, or immune CD4+ or CD8+ lymphocytes previously isolated from spleens of mice vaccinated with MOC2-CIITA tumor cells and challenged with MOC2pc that showed no tumor growth. Results: CIITA-driven MHC-II+ MOC2 tumor cells were rejected or strongly retarded in their growth in vivo. When challenged with MOCpc, these animals strongly delayed tumor growth, indicating the acquisition of an anamnestic response. ACT experiments showed that total spleen cells from tumor protected mice, as well as CD8+ and, more importantly, CD4+ spleen cells significantly protected from MOC2pc tumor take, demonstrating the ability of CIITA-transfected tumor cells to stimulate an adaptive immunity based on the triggering of tumor specific Th and CTL cells. Conclusions: These results validate our vaccination approach also in OSCC emphasizing the importance of the expression of MHC-II molecules driven by CIITA, to render tumor cells surrogate APC for their own tumor antigens in vivo and thus open the way to characterize the specific antigenic peptides valuable for possible novel formulations of anti-tumor vaccines.