Abstract A37: CTLA-4 blockade improves the balance of CD8+ effector and CD4+ regulatory T cells following adoptive cell transfer melanoma immunotherapy.

Abstract

Abstract Background: Clinical trials have shown efficacy for CTLA-4 blockade and adoptive cell transfer (ACT) immunotherapy in the treatment of melanoma. We hypothesized that the addition of CTLA-4 blockade to a non-lymphodepleting regimen of ACT could enhance the control of melanoma tumor growth in a murine model. Methods: A B16F10 melanoma cell line was stably transfected to express low levels of the lymphocytic choriomeningitis virus (LCMV) peptide GP33 (B16GP33). Immunocompetent Ly5.2+/C57BL/6 mice were inoculated with subcutaneous flank injections of 106 B16GP33 cells on day 0. GP33-specific CD8+ T cells were harvested from syngeneic Ly5.1+/C57BL/6 donor mice 8 days after LCMV infection. Mice received no treatment, CTLA-4 blockade (intraperitoneal injections of 200 μg anti-CTLA-4 mAb on days 2, 5, and 8), ACT (intravenous injections of 5x104 GP33-specific CD8+ T cells on day 1), or both. Tumor growth was measured every three days. Subsets of mice were euthanized between days 9 and 18 for TIL and splenocyte analyses. Mice exhibiting minimal B16GP33 tumor growth > 30 days after immunotherapy were challenged with contralateral flank injections of 106 B16F10 and B16GP33 cells. Results: Combination CTLA-4 blockade and ACT immunotherapy resulted in significantly greater inhibition of B16GP33 tumor growth compared to CTLA-4 blockade or ACT alone. TIL analysis identified stronger CD8+ T cell infiltration in tumors treated with combination immunotherapy. This augmented TIL response was due to the induction of endogenous populations of CD8+ T cells, as there were no differences in Ly5.1+/CD8+ T cell infiltration between mice treated with combination immunotherapy versus ACT alone. Significantly fewer CD4+CD25+FoxP3+ regulatory T cells were observed within TIL populations after combination immunotherapy. Splenocyte response to in vitro stimulation with GP33 peptide was stronger after combination immunotherapy compared to single agent immunotherapy. A subset of mice treated with CTLA-4 blockade alone and combination immunotherapy showed minimal B16GP33 tumor growth after prolonged observation. Both groups of mice showed immunity against B16GP33 challenge tumors, but only mice treated with combination immunotherapy exhibited immunity against B16F10 challenge tumors as well. Discussion: The combination of CTLA-4 blockade with non-lymphodepletion ACT may represent a novel and effective form of melanoma immunotherapy. Our findings suggest that the additive benefit of CTLA-4 may be due to the enhanced recruitment of endogenous melanoma-directed effector T cell responses and the induction of smaller populations of regulatory T cells. Moreover, the promotion of a durable and generalized protection from recurrent tumors suggests that this combination may have synergistic immunological effects against melanoma. Citation Format: Lucy Wentworth, David A. Mahvi, Justin V. Meyers, Samantha Durbin, Clifford S. Cho. CTLA-4 blockade improves the balance of CD8+ effector and CD4+ regulatory T cells following adoptive cell transfer melanoma immunotherapy. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr A37.