Transient cell-in-cell formation underlies tumor relapse and resistance to immunotherapy [B16F10]

Despite the remarkable successes of cancer immunotherapies, the majority of patients do not exhibit durable responses. While treatment resistance has frequently been attributed to clonal selection and immunoediting, currently, little evidence directly demonstrates this process in epithelial cancers. Here, we demonstrate in both mouse models and human cells, that tumor cells evade immunotherapy by generating transient cell-in-cell structures, which are impenetrable to immune-derived cytotoxic compounds and to chemotherapies. This formation is mediated predominantly by DLL4/DLL1 which are elevated on activated T cells and along with IFNg induces STAT3 phosphorylation in tumors cells. In contrast to previous reports on cell-in-cell formations, here both cells remain alive and disseminate into single tumor cells once T cells are no longer present. Overall, this work highlights a previously unknown resistance mechanism which enable tumor cells to survive immune pressure and provides a new theoretical framework to cancer immunotherapies. comparison of gene expression profile of B16F10 cells following different treatments.