Two-step schedule of anti-tumor immunotherapy: anti-inflammatory treatment and dendritic cell-based vaccination

CHIARELLA, PAULA; BRUZZO, JUAN; FERNANDEZ, GABRIELA; VERMEULEN, MóNICA; VULCANO, MARISA; ISTURIZ, MARTíN A.; BUSTUOABAD, OSCAR D.; RUGGIERO, RAúL A.

Atenas, Grecia

Congreso; Recent advances in cancer immunotherapy with an emphasis on vaccines; 2008

Although animals can be prophylactically immunized against the growth of tumor implants, most of the attempts to use immunotherapy to cause the regression of animal and human tumors once they have become established have been unsuccessful, even when strongly immunogenic tumors were used as target. The aim of this work was to understand the nature of this refractoriness in order to elaborate an efficient immunotherapeutic schedule. By employing a strong immunogenic murine fibrosarcoma (MC-C), we demonstrated that MC-C tumor-bearing mice can generate a T-cell mediated anti-tumor immune response which disappears when MC-C grows over 500 mm3. This tumor-associated immunosuppression was coincidental with the emergence of a systemic inflammatory condition characterized by: a) an high number of circulating and splenic granulocytes most of them displaying activation and high expression of Gr1+ Mac1+ markers (n=6, p<0.01) and  b) an increasing serum concentration of the pro-inflammatory cytokines TNF-á, IL-1â, IL-6 and SAA (serum A amyloid) and CRP (C reactive protein) phase acute proteins (n=3-5), A transient increase of circulating corticosterone and the anti-inflammatory IL-10 at the time when tumor volume was about 500 mm3 was observed, after which the serum concentration of both, corticosterone and IL-10 was down regulated. Splenic Treg CD4+CD25+ cells were not increased throughout tumor growth. Treatment of tumor-bearing mice with a single low dose (0.75 mg/Kg) of the synthetic corticoid dexamethasone significantly reduced all the sistemic inflammatory parameters and simultaneously reversed the tumor associated immunosuppression, as evidenced by the restoration of specific T-cell dependent concomitant immunity, ability of spleen cells to transfer anti-tumor activity and recovery of T-cell signal transduction molecules. Two other anti-inflammatory treatments using indomethacin or dimeric TNF-alfa receptor, also partially reversed the immunosuppression although the effect was not as striking as that observed with dexamethasone. The reversion of the tumor-associated immunosuppression was not enough on its own to inhibit the established growing tumor. However, when we used the two-step strategy of inoculating dexamethasone and then dendritic cells loaded with tumor antigens as an immunization booster, a significant inhibition of the growth of a large MC-C tumor (600 mm3) was observed (p<0.001) despite the fact that the vaccination alone was ineffective. The two-step strategy of tumor immunotherapy that we present is based on the rationale that it is necessary to eliminate or ameliorate the tumor-associated immunosuppression as a precondition to allow an otherwise ineffective anti-tumor immunological therapy to have a chance to be successful.