Here, we demonstrate that lung tumors which possess inherent or acquired resistance to PD-1/PD-L1 blockade have higher collagen deposition, resulting in tumor immune suppression characterized by decreased total intratumoral CD8+ T cells—the lymphocytes primarily responsible for immune-mediated tumor cell death8,12,23—and increased TIM-3+ exhausted CD8+ T cell subpopulations in murine and human lung tumors. The gene discussed is CD8A; the disease is neoplasm.