Determining the Immunologic Effects of Trastuzumab Deruxtecan (T-DXd) in a Novel Chimeric HER2 Tumor Model

Vanderbilt University, Nashville TN

Investigators

Abstract

PROJECT SUMMARY The aHER2 antibody-drug conjugate, trastuzumab deruxtecan (T-DXd}, has revolutionized breast cancer treatment, prompting numerous clinical trials investigating immune checkpoint inhibitors (ICls} in combination with T-DXd. However, few studies have explored T-DXd's immunologic effects, and comprehensive preclinical data supporting ICI combinations is lacking. This challenge stems from trastuzumab's inability to bind to rodent HER2. Consequently, many existing models rely on human-derived cell lines or xenografts transplanted into immune-deficient mice, thus discounting T-DXd's immunologic effects. To address this, we have developed a robust, immunocompetent tumor model to study trastuzumab-based therapies by minimally editing the mouse HER2 trastuzumab binding region, which we termed HER2x. The HER2x tumor model binds trastuzumab, is nonimmunogenic, and is sensitive to TDXd treatment. Preliminary experiments utilizing this model suggest that T-DXd induces immunologic memory formation, potentiates responses in immune-competent compared to athymic nude mice, and increases tumor T cell infiltration. Additionally, combining T-DXd with aPD-L 1 (an ICI) showed additive therapeutic benefits in pilot experiments. Taken together, we hypothesize that T-DXd enhances adaptive antitumor immune responses through modulation of the tumor microenvironment and can be further optimized through combination with ICls. To test this hypothesis, Aim 1 will determine if T-DXd augments T cell-mediated antitumor immune responses in HER2+ breast cancer models, and if this is necessary for treatment efficacy. HER2x tumors will be inoculated into immunocompetent, syngeneic mice, which will then receive either T-DXd treatment or a vehicle control. At set timepoints, tumors will be extracted for immune phenotyping via multiparametric flow cytometry, single-cell RNA sequencing, and immunohistochemistry. In vivo T cell depletion studies will then establish the importance of CD4+ and CD8+ T cells for T-DXd efficacy in the HER2x model. Aim 2 will determine if combining T-DXd with aPD-1 or aPD-L 1 provides improved and more durable responses in HER2+ breast cancer. HER2x tumors will be inoculated as before, and mice will receive treatment with T-DXd, trastuzumab, or a vehicle control, in combination with aPD1, aPD-L 1, or an isotype control. Survival and tumor volume will then be tracked until endpoint. All complete responder mice will undergo a tumor rechallenge experiment to establish if combination therapy enhances tumoral immunologic memory formation. Additionally, combination treated tumors will be extracted at set timepoints for immune phenotyping to assess if ICI treatment alters T cell functional phenotypes in T-DXd treated tumors. Completion of this proposal will deliver urgently needed insights into the immunologic mechanisms of T-DXd, with the potential to provide clinically relevant and translational data supporting ICI combinations in patients. Furthermore, the completion of this project will facilitate the development of my technical, critical thinking, and communication skills that will be crucial to my success as independent translational oncology scientist.