Increased expression of inducible HSP70 in apoptotic cells is correlated with their efficacy for antitumor vaccine therapy

Apoptosis is a physiologic process in normal development, tissue remodeling and cell turnover. This cell death is noninflammatory and nonimmunogenic, but when associated with a danger signal, it can activate the immune system. However, the capacity of apoptotic cells to activate the immune system is not clearly established, although dead tumor cells have been largely exploited as a source of TAA in cellular therapy against cancer. From these cellular preparations, contradictory results have been reported on the effect of apoptotic cells as an effective source of TAA and their immunologic properties. These conflicting data strongly suggest that the optimal preparation of apoptotic cells derived from tumor cells remains to be determined. In this work, we studied and compared the efficacy of antitumor immune responses derived from repeated injections using different preparations of apoptotic cells. We investigated the importance of HSP70 and TGF-beta expression in apoptotic cells used in the treatment of an established and nonimmunogenic rat carcinoma. UVB-mediated apoptosis did not affect TGF-beta expression in tumor cells, whereas HS treatment sharply downregulated it. Thus, downregulation of TGF-beta permits normal DC activation and maturation and the induction of tumor immunity. We conclude that HS followed by UVB irradiation is a superior source of tumor antigen for the treatment of established tumors. Future work will determine whether HS independently upregulates HSP70, thereby suppressing expression of active TGF-beta, or whether the 2 are linked via a still undefined mechanism.