Kaluza, Karen M.

Abstract We study mechanisms of tumor escape from adoptive therapy in the mouse melanoma model B16ova. In this model, transfer of OT-I T cells can significantly prolong the survival of mice. However, intense OT-I pressure promotes tumor cell genomic instability, and most mice eventually develop recurrent ova gene-loss tumors. We hypothesized that simultaneous transfer of two CTL clones would limit tumor recurrence by preventing the selection of single gene-loss cells. To accomplish this, we co-transferred OT-I T cells and Pmel T cells. Co-transfer three days following tumor challenge prevented tumor growth, while neither clone alone could. And in mice with established tumors, co-transfer provided significantly better therapy than either clone alone. This improvement was due to both fewer tumors recurring and the delayed appearance of those that did recur. Additionally, we found that recurrent tumors from mice treated with co-transfer continued to express both target antigens, and the mice maintained both T cell populations. We therefore hypothesized that it should be possible to exploit those cells to further prolong the survival of mice. We used cyclophosphamide to stimulate reactivation of the immune system in mice with recurrent tumors and found that this supplemental therapy significantly prolonged the lives of only those mice which had previously received co-transfer. Overall, our results reveal several benefits of targeting multiple tumor antigens.

Abstract Oncolytic virotherapy offers the potential to treat tumors both as a single agent and in combination with traditional modalities such as chemotherapy and radiotherapy. Here we describe an effective, fully systemic treatment regimen, which combines virotherapy, acting essentially as an adjuvant immunotherapy, with adoptive cell transfer (ACT). The combination of ACT with systemic administration of a vesicular stomatitis virus (VSV) engineered to express the endogenous melanocyte antigen glycoprotein 100 (gp100) resulted in regression of established melanomas and generation of antitumor immunity. Tumor response was associated with in vivo T-cell persistence and activation as well as treatment-related vitiligo. However, in a proportion of treated mice, initial tumor regressions were followed by recurrences. Therapy was further enhanced by targeting an additional tumor antigen with the VSV-antigen + ACT combination strategy, leading to sustained response in 100% of mice. Together, our findings suggest that systemic virotherapy combined with antigen-expressing VSV could be used to support and enhance clinical immunotherapy protocols with adoptive T-cell transfer, which are already used in the clinic. Cancer Res; 72(18); 4753–64. ©2012 AACR.

An antitumor T-cell response can lead to tumor control without clearing all tumor cells. As long as residual tumor cells remain, there is a constant risk of escape from that T-cell response. We previously showed that adoptive transfer of anti-ova OT-I T cells into B16ova-bearing mice led to tumor regression followed by escape of tumors that had lost the ova gene, rendering the OT-I T cells ineffective. In this study, we hypothesized that simultaneous transfer of cytotoxic T lymphocytes targeted against two independent antigens would reduce selection for single-antigen-loss cells, thereby limiting tumor escape. Using OT-I and Pmel T cells to treat B16ova tumors, we found that early cotransfer could prevent tumor emergence in most mice, whereas neither T-cell specificity alone was able to do so. When combined with total body irradiation for the treatment of larger 7-day tumors, cotransfer was also better at limiting tumor recurrence, and the tumors that did escape combination therapy continued to express both target antigens. As adoptively transferred T cells also persisted in vivo , even in mice with recurrent tumors, we hypothesized that restimulation of these antitumor T cells would prolong survival of mice with recurrent tumors. Consistent with this hypothesis, administration of a low-dose regimen of cyclophosphamide following tumor escape slowed tumor growth in mice that had previously received T-cell therapy, but not in control-treated mice, an effect that was associated with increased activation of T cells in vitro by low- but not high-dose cyclophosphamide.