Assessment of IFNγ responsiveness in patient-derived xenografts.

Patient-derived xenografts are a useful tool in cancer immunology, as they allow researchers to study human cancers in vivo when starting with a relatively small amount of human tumor tissue. These models make it possible to study tumor cell-intrinsic changes that occur in response to external stimuli including cytokines like interferon gamma (IFNγ) that are important for effective anti-tumor immune responses. IFNγ responsiveness can be measured by assessing surface expression of MHC class I on tumor cells, the molecule on which tumor antigens are presented to cytotoxic T cells in the tumor microenvironment. Low levels of MHC class I and lack of responsiveness have been associated with resistance to T-cell directed therapies like immune checkpoint inhibitors. In this chapter, we present a protocol for an assay to screen patient-derived xenografts for their responsiveness to IFNγ. The results of this assay can be used as a starting point for uncovering cancer cell-intrinsic mechanisms of resistance to immunotherapies in patient tumors.