THERAPY OF MURINE TUMORS WITH TUMOR PEPTIDE-PULSED DENDRITIC CELLS - DEPENDENCE ON T-CELLS, B7 COSTIMULATION, AND T-HELPER CELL 1-ASSOCIATED CYTOKINES

Antigen presentation by host dendritic cells (DC) is critical for the initiation of adaptive immune responses. We have previously demonstrat ed in immunogenic murine tumor models that bone marrow (BM)-derived DC pulsed ex vivo with synthetic tumor-associated peptides, naturally ex pressed by tumor cells, serve as effective antitumor vaccines, protect ing animals against an otherwise lethal tumor challenge (Mayordomo, J. I., T. Zorina, W. J. Storkus, C. Celluzzi, L. D. Falo, C. J. Melief, T. Ildstad, W. M. Kast, A. B. DeLeo, and M. T. Lotze. 1995. Nature Med . 1:1297-1302). However, T cell-defined epitopes have not been identif ied for most human cancers. To explore the utility of this approach in the treatment of tumors expressing as yet uncharacterized epitopes, s yngeneic granulocyte/macrophage colony-stimulating factor-stimulated a nd BM-derived DC, pulsed with unfractionated acid-eluted tumor peptide s (Storkus, W. J., H. J. Zeh III, R. D. Salter, and M. T. Lotze. 1993. J. Immunother. 14:94-103) were used to treat mice bearing spontaneous , established tumors. The adoptive transfer of 5 X 10(5) tumor peptide -pulsed DC dramatically suppressed the growth of weakly immunogenic tu mors in day 4 to day 8 established MCA205 (H-2(b)) and TS/A (H-2(d)) t umor models, when applied in three biweekly intravenous injections. Us ing the immunogenic C3 (H-2(b)) tumor model in B6 mice, tumor peptide- pulsed DC therapy resulted in the erradication of established d14 tumo rs and long-term survival in 100% of treated animals. The DC-driven an titumor immune response was primarily cell mediated since the transfer of spleen cells, but not sera, h-om immunized mice efficiently protec ted sublethally irradiated naive mice against a subsequent tumor chall enge. Furthermore, depletion of either CD4(+) or CD8(+) T cells from t umor-bearing mice before therapy totally suppressed the therapeutic ef ficacy of DC pulsed with tumor-derived peptides. Costimulation of the host cell-mediated antitumor immunity was critical since inoculation o f the chimeric fusion protein CTLA4-Ig virtually abrogated the therape utic effects of peptide-pulsed DC in vivo. The analysis of the cytokin e pattern in the draining lymph nodes and spleens of tumor-bearing mic e immunized with DC pulsed with tumor-eluted peptides revealed a marke d upregulation of interleukin (IL) 4 and interferon (IFN) gamma produc tion, as compared with mice immunized with DC alone or DC pulsed with irrelevant peptides. DC-induced antitumor effects were completely bloc ked by coadministration of neutralizing monoclonal antibody directed a gainst T helper cell 1-associated cytokines (such as IL-12, tumor necr osis factor alpha, IFN-gamma), and eventually, but not initially, bloc ked by anti-mIL-4 mAb. Based on these results, we believe that DC puls ed with acid-eluted peptides derived from autologous tumors represents a novel approach to the treatment of established, weakly immunogenic tumors, and serves as a basis for designing clinical trials in cancer patients.