Immunotargeting of the xCT Cystine/Glutamate Antiporter Potentiates the Efficacy of HER2-Targeted Immunotherapies in Breast Cancer
Laura Conti, Elisabetta Bolli, Antonino Di Lorenzo, Valentina Franceschi, Francesca Macchi, Federica Riccardo, Roberto Ruiu, Luca Russo, Elena Quaglino, Gaetano Donofrío, Federica Cavallo
Abstract
Abstract Despite HER2-targeted therapies improving the outcome of HER2+ breast cancer, many patients experience resistance and metastatic progression. Cancer stem cells (CSC) play a role in this resistance and progression, thus combining HER2 targeting with CSC inhibition could improve the management of HER2+ breast cancer. The cystine–glutamate antiporter, xCT, is overexpressed in mammary CSCs and is crucial for their redox balance, self-renewal, and resistance to therapies, representing a potential target for breast cancer immunotherapy. We developed a combined immunotherapy targeting HER2 and xCT using the Bovine Herpes virus-4 vector, a safe vaccine that can confer immunogenicity to tumor antigens. Mammary cancer–prone BALB-neuT mice, transgenic for rat Her2, were immunized with the single or combined vaccines. Anti-HER2 vaccination slowed primary tumor growth, whereas anti-xCT vaccination primarily prevented metastasis formation. The combination of the two vaccines exerted a complementary effect by mediating the induction of cytotoxic T cells and of HER2 and xCT antibodies that induce antibody-dependent cell-mediated cytotoxicity and hinder cancer cell proliferation. Antibodies targeting xCT, but not those targeting HER2, directly affected CSC viability, self-renewal, and migration, inducing the antimetastatic effect of xCT vaccination. Our findings present a new therapy for HER2+ breast cancer, demonstrating that CSC immunotargeting via anti-xCT vaccination synergizes with HER2-directed immunotherapy.