Anti-tumour effects of a xenogeneic fibroblast activation protein-based whole cell tumour vaccine in murine tumour models

The clinical benefit of cancer immunotherapy, including tumour vaccines, is influenced by immunosuppressive factors in the tumour microenvironment. Among these factors, cancer-associated fibroblasts (CAFs) and their products, such as fibroblast activation protein-alpha (FAP alpha), greatly affect tumourigenesis, development, metastasis and treatment tolerance, which make them promising immunotherapy targets for cancer patients. Our previous study reported that a whole cell tumour vaccine (WCTV) expressing FAP alpha inhibited tumour growth by simultaneously attacking cancer cells and CAFs. This study aimed to improve WCTVs with xenoantigens to end immune tolerance and to further activate the adaptive immune system. In the present study, we designed a WCTV by transducing a vector encoding human FAP alpha (hFAP alpha) into murine tumour cells and evaluated its efficacy in multiple solid tumour models. Immunotherapy with this WCTV effectively delayed tumour growth and prevented recurrence. The anti-tumour responses were clearly linked to antigen-specific cytotoxic T cells, whereas CD4(+) T lymphocytes also played a role. Humoural immune responses were activated because the adoptive transfer of immunoglobulins induced abscopal anti-tumour effects, and autoantibodies against FAP alpha were specifically detected in the sera of immunized mice. Moreover, an increased number of apoptotic tumour cells along with a reduced number of CAFs within the tumours suggest that xenogeneic FAP alpha-based WCTV has the potential to drive T cell and antibody responses against cancer cells and CAFs. This finding could offer an advanced strategy to treat multiple solid tumours with individualized cancer immunotherapy techniques.