Tumor reactivity of immune T cells in short-term culture

Provision of Granulocyte-Macrophage Colony-Stimulating Factor Converts an Autoimmune Response to a Self-Antigen into an Antitumor Response

Many tumor Ags recognized by T cells are self-Ags. Because high avidity, self-reactive T cells are deleted in the thymus, any residual self-reactive T cells existing in the periphery are likely to be low avidity and nonresponsive due to peripheral tolerance mechanisms. Activation of these residual T cells is critical for targeting tumors for immunotherapy. In this study, we studied immune responses against the murine B16 melanoma using a tyrosinase-related protein 2 (TRP-2) peptide as a model tumor/self-Ag. Our results showed that TRP-2 peptide vaccination alone elicited a weak T cell response and modestly decreased B16 lung tumor nodules. The combination of peptide vaccination and treatment with an Ab directed against the inhibitory receptor CTLA-4 enhanced the immune response against TRP-2 peptide, inducing autoimmune depigmentation and further decreasing lung tumor nodules. However, both vaccination methods failed to protect against orthotopic (s.c.) B16 tumor challenge. The addition of an irradiated GM-CSF-expressing, amelanotic tumor cell vaccine significantly delayed s.c. B16 tumor growth. Subsequent studies revealed that provision of GM-CSF increased dendritic cell numbers in lymph nodes and spleen. Furthermore, addition of CTLA-4 blockade increased the frequency of TRP-2-specific, IFN-secreting T cells in spleen and lymph nodes. Overall, our results indicate that combining enhancement of Ag presentation with removal of CTLA-4-mediated inhibition can convert a "weaker" autoimmune response into a more potent antitumor immune response.

Treatment of subcutaneous tumor with adoptively transferred T cells

Adoptive immunotherapy with T cells directed at tumor antigens has been demonstrated to result in the regression of malignant tumors in humans. These encouraging results have prompted the further exploration of parameters necessary to treat tumor in various locations in animal models. We have demonstrated that T cells that are sensitized to tumor antigens and then ex vivo cultured are capable of eradicating pulmonary metastases. In this report, we demonstrate that these T cells are capable of eliminating subcutaneous tumor deposits. Critical to the successful treatment of subcutaneous tumor was treatment with a large number of adoptively transferred T cells and pretreatment of the mice with irradiation. The transfer of T cells from tumor-bearing mice into irradiated mice failed to inhibit the therapeutic effect of ex vivo cultured T cells, suggesting that irradiation was not acting only as an immunosuppressant. Irradiation resulted in increased expression of the F4/80 and 33D1 epitopes on antigen-presenting cells within the tumor. The therapeutic effect of the adoptively transferred T cells was eliminated if either CD4 cells or CD8 cells were depleted. Naive T cells subjected to the same culture conditions were completely ineffective at eliminating tumor. These results demonstrate that adoptively transferred T cells derived from tumor-bearing hosts can treat subcutaneous tumor deposits, and they define the conditions necessary for the elimination of tumor in this location.