Combined intratumoral injection of bone marrow-derived dendritic cells and systemic chemotherapy to treat pre-existing murine tumors.

Dendritic cells (DCs) are attractive candidates for innovative cancer immunotherapy by virtue of their potential to function as professional antigen-presenting cells for initiating cellular immune responses. In this study, we evaluated a possible synergy of conventional chemotherapy together with intratumoral injection of syngeneic bone marrow-derived DCs for the treatment of preexisting tumors. Using murine CT26 colon adenocarcinoma cells (parental or modified to express beta-galactosidase as a model tumor antigen) to produce s.c. tumors in syngeneic BALB/c mice, the data demonstrate that direct injections of DCs at the tumor site result in partial eradication of established tumors. Strikingly, the addition of systemic chemotherapy (cyclophosphamide) combined with local intratumoral injection of DCs led to complete tumor regression in the treated animals. The tumor-free mice were able to resist a repeat challenge with the same tumor, suggesting that the animals had acquired long term antitumor immunity. Supporting evidence for the paradigm of systemic chemotherapy and intratumoral administration of DCs was obtained using melanoma B16 syngeneic tumor treated with Adriamycin plus DCs. These novel findings raise the possibility of using this potent strategy of combined intratumoral injections of DCs and systemic chemotherapy for cancer treatment.