Single-cell profiling guided combinatorial immunotherapy for breast cancer resistance to Her2/neu and CDK4/6 targeted therapy

Trastuzumab (Herceptin™), a humanized monoclonal antibody targeting the extracellular domain of human epidermal growth factor receptor-2 (HER2), is one of the most successful examples of targeted therapies for HER2-positive breast cancer. However, drug resistance remains daunting challenges. New combinatorial regimen of CDK4/6 inhibitors plus trastuzumab is currently under active clinical investigations. In this study, we seek to prospectively model the in vivo response to CDK4/6 inhibitor Palbociclib (Pal) plus trastuzumab (Ab) using transgenic Her2/Neu mouse model in parallel with the current clinical trial scenario. We performed single cell RNA-seqencing (Drop-seq) to profile and compare tumor cells and infiltrated immune cells derived from control, Ab+Pal sensitive/residual (APS) and resistant/progressive (APR) tumors. We revealed that although Ab+Pal treatment enhanced antigen processing, presentation and interferon signaling on tumor cells, a distinct immunosuppressive immature myeloid cells (IMCs) infiltrated in the resistant tumor microenvironment to promote resistant phenotype. Based on single cell gene set enrichment analysis (profiling) guided drug screening, we identified and evaluated a combinatorial immunotherapy regimen. We found that combinatorial immunotherapy with receptor tyrosine kinase inhibitor Cabozantinib and immune checkpoint blockades overcome Ab+Pal resistance by inhibiting IMCs and enhancing anti-tumor immunity. Moreover, our rationally designed sequential combinatorial regimens enabled durable response and sustained controlling of the emergence of acquired resistance, thus significantly improved outcomes of rapidly evolving Her2/Neu positive breast cancers. Our results implicate that single-cell RNA sequencing profiling guided combinatorial immunotherapy as a strategy to mitigate the emergence of resistance and to achieve long-term therapeutic benefit merits clinical translation. Drop-seq of tumor cells and tumor infiltrating immune cells derived from FVB/N MMTV-neu202Mul mice with different treatment/phenotypes (sensitive and resistant tumors).