Scientific Objective and Rationale: Our recent study has discovered a novel immune-suppressive ligand protein called V-domain Immunoglobulin Suppressor of T cell Activation (VISTA). By directly suppressing T cell-mediated adaptive immune response, VISTA critically impairs anti-tumor immune responses. Our ongoing research demonstrates the efficacy of VISTA antibody mono-therapy in murine tumor models, against pre-established tumors. Remarkably, VISTA monoclonal antibody-mediated blockade synergizes with a peptide vaccine using TLR agonists as adjuvants to potently reject established tumor, as well as promote tumor-specific memory T cell response for long-term protection. Based on these preliminary data, we hypothesize that VISTA dominantly suppresses the TLR-mediated immune activation via its action on multiple cell types that are directly stimulated by TLR agonists. VISTA-mediated suppression of TLR pathway underlines the synergistic effects of VISTA blockade combined with TLR agonists-based cancer vaccine. Importantly, VISTA blockade maximally synergized with this vaccine platform when compared to the blockade of other related immune checkpoint molecules such as PD-L1, indicating that VISTA is a unique and promising target for cancer immunotherapy.

Three specific aims are proposed to address the interplay between VISTA pathway and TLR signaling in multiple cell types, namely effector T cells, Foxp3+CD4+ regulatory T cells (Tregs), and myeloid cells (i.e., myeloid dendritic cells and myeloid-derived suppressor cells). By using a clinically relevant inducible melanoma model, we will examine the role of VISTA in establishing the immune-suppressive tumor microenvironment and how a combinatorial therapeutic platform of VISTA-blockade and TLR agonist-based vaccine is effective for treating established melanoma.

Career Goals in Cancer Research: I plan to develop my career in the field of cancer immunotherapy, particularly melanoma immunotherapy. To facilitate my career goal, my research will focus on understanding the immune-suppressive mechanisms of immune checkpoint pathways, designing and testing checkpoint blockade strategies either as monotherapy or in combination with vaccines and additional forms of therapies for cancer treatment. My career development will follow the trajectory of developing independent academic research programs, as well as actively collaborating with a host of research groups that share the mission of melanoma research both within and outside of the institute. Furthermore, I will integrate my research plan with the programmatic effort of melanoma research within the cancer center. The melanoma focus of the Fiscal Year 2013 Peer Reviewed Cancer Research Program award provides an extremely valuable resource and opportunity to allow my research program to grow, particularly at this early stage when novel ideas and preliminary findings need to be substantiated by further research.

Clinical Applicability, Benefits, and Risks: Owing to our established alliance with Jassen Biotech to develop human VISTA-blocking antibodies, we predict the initiation of VISTA-targeting early-phase clinical trials within the next 2-3 years. Therefore, our study provides a timely and critical reference that will facilitate near-future clinical applications. Our study will deliver a powerful preclinical treatment protocol, by using the clinically relevant tumor model and evaluating relevant dosage, administration method, pharmacokinetics, and the toxicity of reagents during the combinatorial treatment. The relative ease of applying antibody-based and TLR agonist-based reagent, when in comparison to any forms of adoptively transferred-cell therapies, provides an opportunity for both therapeutic, as well as prophylactic treatment. In this context, a potent "melanoma vaccine" that combines the VISTA-targeting antibody with TLR-agonists and tumor antigens could be developed for treating established metastatic disease as well as for the prevention of recurrence in the surgically resected high-risk population.

Military Benefits: Melanoma has been recognized as one of the rising cancers developed among military personnel, especially field agents who were exposed to harsh environmental elements. Our studies seek to develop novel therapeutic strategies for the treatment of melanoma and therefore directly benefit military personnel and the American public who have suffered from this disease.

Summary: Our proposed study focuses on developing an innovative therapeutic platform for the treatment of melanoma. Using murine melanoma models, we discovered a powerful treatment regime that combines the blockade of a novel immune-checkpoint protein VISTA together with a peptide vaccine using TLR-agonists as adjuvants. Such a "melanoma vaccine platform" could potentially be developed not only for treating established metastatic melanoma, but also for the prevention of recurrence in the surgically resected high-risk population.