Cancer Cell Intrinsic Expression of MHCII Regulates the Immune Microenvironment and Response to Anti-PD-1 Therapy in Lung Adenocarcinoma

MHC class II (MHCII) expression is usually restricted to antigen presenting cells, but can be expressed by cancer cells. We examined the effect of MHC class II (csMHCII) expression in lung adenocarcinoma on T cell recruitment to tumors and response to anti-PD-1 therapy. The functional significance of altering csMHCII expression was explored using two orthotopic immunocompetent murine models of non-small cell lung cancer: CMT167 (CMT) and Lewis Lung Carcinoma (LLC). We previously showed that CMT167 tumors are eradicated by anti-PD1 therapy, while LLC tumors are resistant. RNA-seq analysis of cancer cells recovered from tumors revealed that csMHCII correlated with response to anti-PD1 therapy, with immunotherapy-sensitive CMT167 cells being csMHCII positive, while resistant LLC cells were csMHCII negative. To test the functional effects of csMHCII, MHCII expression was altered on the cancer cells through loss- and gain-of-function of CIITA, a master regulator of the MHCII pathway. Loss of CIITA in CMT167 decreased csMHCII, and converted tumors from anti-PD-1-sensitive to anti-PD-1-resistant. This was associated with decreased T cell infiltration, lower levels of Th1 cytokines, increased B cell number and decreased macrophage recruitment. Conversely, overexpression of CIITA in LLC cells resulted in csMHCII and . Enforced expression of CIITA increased T cell infiltration and sensitized tumors to anti-PD-1 therapy. csMHCII expression was also examined in a subset of surgically resected human lung adenocarcinomas by multispectral imaging, provided a survival benefit and positively correlated with T cell infiltration. These studies demonstrate a functional role for csMHCII in regulating T cell infiltration and sensitivity to anti-PD-1.