Many tumor-associated antigens are derived from nonmutated “self” proteins. T cells infiltrating tumor deposits recognize self-antigens presented by tumor cells and can be expanded in vivo with vaccination. These T cells exist in a functionally tolerant state, as they rarely result in tumor eradication. We found that tumor growth and lethality were unchanged in mice even after adoptive transfer of large numbers of T cells specific for an MHC class I–restricted epitope of the self/tumor antigen gp100. We sought to develop new strategies that would reverse the functionally tolerant state of self/tumor antigen-reactive T cells and enable the destruction of large (with products of perpendicular diameters of >50 mm2), subcutaneous, unmanipulated, poorly immunogenic B16 tumors that were established for up to 14 d before the start of treatment. We have defined three elements that are all strictly necessary to induce tumor regression in this model: (a) adoptive transfer of tumor-specific T cells; (b) T cell stimulation through antigen-specific vaccination with an altered peptide ligand, rather than the native self-peptide; and (c) coadministration of a T cell growth and activation factor. Cells, vaccination, or cyto-kine given alone or any two in combination were insufficient to induce tumor destruction. Autoimmune vitiligo was observed in mice cured of their disease. These findings illustrate that adoptive transfer of T cells and IL-2 can augment the function of a cancer vaccine. Furthermore, these data represent the first demonstration of complete cures of large, established, poorly immunogenic, unmanipulated solid tumors using T cells specific for a true self/tumor antigen and form the basis for a new approach to the treatment of patients with cancer.

The promising, but modest, clinical results of many human cancer vaccines indicate a need for vaccine adjuvants that can increase both the quantity and the quality of vaccine-induced, tumor-specific T cells. In this study we tested the immunological and antitumor effects of the proinflammatory cytokine, IL-23, in gp100 peptide vaccine therapy of established murine melanoma. Neither systemic nor local IL-23 alone had any impact on tumor growth or tumor-specific T cell numbers. Upon specific vaccination, however, systemic IL-23 greatly increased the relative and absolute numbers of vaccine-induced CD8+ T cells and enhanced their effector function at the tumor site. Although IL-23 specifically increased IFN-γ production by tumor-specific T cells, IFN-γ itself was not a primary mediator of the vaccine adjuvant effect. The IL-23-induced antitumor effect and accompanying reversible weight loss were both partially mediated by TNF-α. In contrast, local expression of IL-23 at the tumor site maintained antitumor activity in the absence of weight loss. Under these conditions, it was also clear that enhanced effector function of vaccine-induced CD8+ T cells, rather than increased T cell number, is a primary mechanism underlying the antitumor effect of IL-23. Collectively, these results suggest that IL-23 is a potent vaccine adjuvant for the induction of therapeutic, tumor-specific CD8+ T cell responses.

Camptothecins constitute a novel class of chemotherapeutics that selectively target DNA topoisomerase I (Top1) by reversibly stabilizing a covalent enzyme-DNA intermediate. This cytotoxic mechanism contrasts with that of platinum drugs, such as cisplatin, which induce inter-and intrastrand DNA adducts. In vitro combination studies using platinum drugs combined with Top1 poisons, such as topotecan, showed a schedule-dependent synergistic activity, with promising results in the clinic. However, whereas the molecular mechanism of these single agents may be relatively well understood, the mode of action of these chemotherapeutic agents in combination necessitates a more complete understanding. Indeed, we recently reported that a functional homologous recombination pathway is required for cispla- TPT and CPT-11 have been approved for first and second line treatment of advanced colorectal cancer and second line treatment for ovarian cancer (7-9). As with most chemotherapeutics, these CPT analogs are administered in combination with other agents (10 -13). Although the molecular mechanisms of single agents may be well understood, the combination of two or more agents often induces surprising interactions, which necessitates a more complete understanding of the cytotoxic lesions induced by such combinations for optimal efficacy. For example, in vitro combination experiments using platinum agents, such as cisplatin (cDDP), carboplatin, or oxaliplatin, with a Top1 poison, TPT or CPT-11, demonstrated a sequencedependent synergy in various human tumor cell lines (14 -16). The most cytotoxic sequence was a platinum drug followed by a Top1 poison. Moreover, chemotherapeutic regimens that combine TPT/CPT-11 with platinum drug are showing some promise in the clinic (see Refs. 17-19 and references therein). However, the lack of insight into the mechanism of synergy hampers the optimal design of clinical studies based on the combination of platinum drugs and Top1 poisons.We recently reported genetic evidence that homologous recombination (HR) is responsible for the synergistic cytotoxicity of certain drug/Top1 poison combinations (20). Indeed, a functional HR pathway was required for the synergistic activity of platinum or X-irradiation in combination with TPT yet acted to suppress the synergistic combination of 1-␤-D-arabinofuranosyl cytidine

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