Breaching the Tumor-Immune Mechanical Barrier for Optimal Antitumor Immunity

Project Summary/Abstract Tumor immune exclusion predicts poor anticancer therapeutic responses and patient outcomes. The mechanical barrier built by intercellular junction connections and extracellular matrix maintains immune exclusion in immune- privileged organs. How such barriers dictate immune infiltration in cancer remains largely unknown. My prior training and career goals are focused on the unmet need to comprehensively understand what mechanical barriers are utilized by tumors, how they instigate immune exclusion to evade immune surveillance, and how to rationally design innovative therapies that break down mechanical barriers and unleash the full potential of antitumor immunity. Since joining the Ellisen Lab at Massachusetts General Hospital/Harvard Medical School, I have focused my mechanical barrier studies on the tight junction related molecule TROP2, which is overexpressed and thought to play a role in progression of multiple cancers including aggressive triple negative breast cancer (TNBC). Like its paralog EPCAM, TROP2 is one of a set of mechanical barrier molecules linked to lack of tumor infiltrating immune cells. Additionally, my preliminary bioinformatic analysis shows that TROP2 has a significant negative correlation with key antitumor immune markers in multiple breast cancer cohorts. Thus, I hypothesized that TROP2 may enforce a mechanical barrier to deter antitumor immune infiltration in breast cancer. Importantly, TROP2 is the target protein of multiple recently developed antibody drug conjugates (ADCs) including Sacituzumab Govitecan (SG). SG, the first FDA approved ADC for TNBC, combines a TROP2-targeted antibody with a topoisomerase 1 (TOP1) inhibitor as cytotoxic payload. While SG is proving to be a highly successful precision therapy, its mechanisms remain poorly understood. Furthermore, the cytotoxic payload of SG is a TOP1 inhibitor, a class of drugs known to elicit immunogenic cell death, thus providing a strong rationale to understand mechanisms by which targeting TROP2 alone and in the context of SG will modulate tumor immune microenvironment, thus sensitizing tumors to immune checkpoint inhibitors. This proposal will employ biochemistry, mouse tumor models, genetic screens, as well as multi-omics and spatial imaging analysis of patient specimens. The study aims to dissect the mechanism of TROP2-mediated immune exclusion in TNBC (Aim 1); discover mechanisms of the SG/anti-PD1 combination (Aim 2), and systematically uncover novel instigators of breast tumor immune exclusion (Aim 3). My extensive background in breast cancer immune microenvironment and the interdisciplinary expertise of my mentor/advisors/collaborator team make me well- suited to carry out this innovative proposal to systematically unravel tumor-intrinsic mechanisms of immune exclusion. Together with the institutional support from Massachusetts General Hospital/Harvard Medical School, this award will help me gain additional knowledge and training in the area of tumor models, spatial multi-omics analysis, and CRISPR screens, as well as career development skills which will ultimately help me to rapidly transition to a fruitful and impactful independent research career.