IFNγ-induced stem-like state of cancer cells as a driver of metastatic progression following immunotherapy

Despite the remarkable success of immune checkpoint blockade (ICB) therapy, most cancer patients still do not respond. We now find that immunotherapy can induce stem-like properties in tumors. Using mouse models of breast cancer, we observe that cancer stem cells (CSCs) show not only enhanced resistance to T cell cytotoxicity, but that interferon gamma (IFNγ) produced by activated T cells directly converts non-CSCs to CSCs. IFNγ enhances several CSC phenotypes, such as resistance to chemo- and radiotherapy and metastasis formation. We identified the branched-chain amino acid aminotransaminase 1 (BCAT1) as a downstream mediator of IFNγ-induced CSC plasticity. Targeting BCAT1 in vivo improved cancer vaccination and ICB therapy by preventing IFNγ-induced metastasis formation. Breast cancer patients treated with ICB exhibited a similar increase in CSC markers expression indicating comparable responses to immune activation in humans. Collectively, we discover an unexpected, pro-tumoral role for IFNγ that may contribute to cancer immunotherapy failure. [Display omitted] •IFNγ increases CSC content by converting non-CSCs to CSCs•BCAT1 is a downstream mediator of IFNγ-mediated CSC plasticity•Targeting BCAT1 improves cancer immunotherapy•CSCs have enhanced resistance to T cell cytotoxicity Beziaud and colleagues report that IFNγ produced by T cells enhances cancer cell plasticity, which promotes metastasis formation in pre-clinical models and correlates with a cancer stem cell signature in cancer patients treated with immunotherapy. Inhibiting BCAT1 blocks this cancer plasticity without affecting the IFNγ pro-inflammatory effects essential for immunotherapy success.