Li Lily Wang - US grants

DESCRIPTION (provided by applicant): Protective anti-tumor immunity is impaired by immunosuppressive mechanisms. Immune checkpoint proteins, including CTLA-4, PD-1, and B7-H4, function as effector molecules to disable T-cell responses against cancer. Although checkpoint blockade using monoclonal antibodies (mab) have shown positive outcomes in clinical trials, the overall response rate has been disappointingly as low as 6-21%. Therefore, identifying novel checkpoint proteins is critically needed. We have discovered and functionally characterized a new Ig-superfamily inhibitory ligand, designated V-domain Immunoglobulin Suppressor of T cell Activation (VISTA). We hypothesize that VISTA functions as an additional and crucial immune-checkpoint ligand that controls anti-tumor immunity. The goal in this grant proposal is to determine the molecular and cellular mechanisms of VISTA-mediated immune suppression, both via its direct effect on T effector cell activation, and via its regulatory functon on other immunosuppressive cell types, which in turn control T effector cell responses against cancer. Accordingly, the specific Aims are: (1) Determine the molecular mechanisms whereby VISTA suppresses T-cell activation, and how it collaborates with another immune-checkpoint pathway PD-L1/PD-1 to suppress tumor-specific T-cell responses. (2) Determine the role of VISTA on the development and function of Foxp3+CD4+ Tregs. (3) Define the role of VISTA on the development, differentiation, and function of mononuclear phagocytes in the normal physiological state and during tumorigenesis. A collection of novel reagents and models including VISTA mab, VISTAKO mice, and VISTA conditional KO mice will be used for this study. In addition to a transplantable melanoma B16F10 model, we will employ a clinically relevant inducible-melanoma model for mechanistic studies and assessing VISTA-based therapeutic strategies. Impact: Any successful cancer immunotherapeutic strategy must consider the negative immune regulators that prevent the development of optimal anti-tumor immunity. As a novel immune checkpoint pathway, VISTA provides a new target for the immune intervention in cancer. This study will provide answers regarding VISTA- mediated immune regulation during tumorigenesis. It will establish a novel paradigm in which VISTA and PD- L1/PD1 synergize to control T-cell responses, thus providing a rationale for targeting VISTA either alone or in combination with other immune checkpoint pathways for cancer immunotherapy. Further, this study will establish a new paradigm regarding how tumors utilize VISTA to alter the differentiation and functions of Tregs and monocytes, thus providing novel strategies for targeting these prominent immune-suppressors in cancer immunotherapy.

PROJECT SUMMARY Lung cancer is the leading cause of cancer mortality worldwide (1). More than 80% of lung cancers consist of non-small cell lung cancer (NSCLC) and activating mutations within EGFR occur in ~50% of Asian patients and ~20% of Western patients with NSCLC (1). Contrary to prevailing notions, EGFR mutations in NSCLC occur in both males and females and in both nonsmokers and nonsmokers (1). Thus, targeting EGFR against development of NSCLC will have significant impact to control this disease. In order to maximize efficacy of preventive approaches in NSCLC, the initial focus will be directed toward patients with premalignant lesions or those with previously treated lung cancer. Two promising therapeutic approaches in preventing development of NSCLC are with interventions designed to attenuate tumor development (chemoprevention) or modulate immune recognition of tumor (immunoprevention). This multi-PI proposal will test innovative chemoimmunopreventive strategies for lung cancer, combining the expertise from Dr. You's and Dr. Wang's research groups in chemoprevention and cancer immunotherapy, respectively. Prior work in Dr. You's laboratory has established retinoid X receptor (RXR) agonists (bexarotene and an analog UAB30) as potent chemopreventive agents in mouse models of lung cancer (2, Table 1). Dr. You's group was also the first to demonstrate remarkable efficacy of an immunopreventive multi-peptide EGFR vaccine against EGFR-driven lung tumorigenesis (3). Dr. Wang's prior work has established a novel immune checkpoint protein VISTA as a critical regulator of anti-tumor immunity (4-9), an important contribution given that blockade of immune checkpoint receptors has been identified as a major breakthrough in cancer treatment (10). Dr. Wang's group has shown that VISTA-blocking mAb enhances T cell-mediated tumor rejection in multiple preclinical mouse models (4-9). Given the established efficacy of these aforementioned approaches in controlling tumor growth, we hypothesize that combinatorial approaches of chemoimmunoprevention will enhance anti-tumor immunity within the tumor microenvironment (TME), which will inhibit lung tumor progression and recurrence. Three specific aims are proposed to test this hypothesis. Aim 1 will investigate the immune regulatory role of RXR agonists in preventing establishment of a tumor microenvironment that suppresses T cell activation against developing lung cancer. Aim 2 will determine the preventive efficacy of combined treatment of RXR agonists and a MHCII-restricted EGFR multi-peptide vaccine on EGFR-driven lung tumor progression. Aim 3 will test the hypothesis that blocking immune checkpoint proteins VISTA and PD-L1 will synergize with RXR agonists/EGFR vaccine to prevent acquired resistance and tumor recurrence. This proposal is highly significant because of the potential of chemoimmunoprevention to become a breakthrough preventive approach for lung cancer.