Background: Cancer cells can inhibit effector T cells through both immunomodulatory receptors and alteration of the tumor microenvironment as a result of cancer metabolism. A majority of patients treated with immune checkpoint inhibitors recently approved by the FDA fail to exhibit a clinical response. The extent to which metabolic conditions within the tumor impede T cell activation and anti-tumor effector function in renal cell carcinoma (RCC) are unknown. Methods: Under the IACUC protocol M1600005-00, BALB/c or Rag mice were subcutaneously injected with 100,000 Renca cells obtained from ATCC and growth monitored by caliper measurements in 3 dimensions every 3 days. In vivoPD-1 blockade was performed by 200 mcg/i.p. injection every 3 days using purified mPD-1 (BioXcell, J43). Deidentified tissue donations from patients with RCC were collected under the IRB protocol #151549 and processed into single cell suspensions following mechanical dissociation for the functional assays indicated below. Results: Through work with Rag deficient mice lacking functional B and T cells, we have established that tumor growth is regulated in a T cell dependent manner as evidenced by earlier formation and faster tumor growth. In a syngeneic mouse model of RCC (RenCa), we find that inhibition of PD-1 delays tumor growth and size. Tumor infiltrating lymphocytes (TILs) were abundant in patient-derived RCC, but are phenotypically distinct and are impaired both functionally and metabolically from healthy control. Instead of efficient use of aerobic glycolysis, TILs fail to increase glucose metabolism, and instead display increased reactive oxygen species (ROS) and mitochondrial dysfunction. CD8 effector cells found in tumors have notable differences in mitochondrial morphology compared to healthy control CD8 T cells by electron microscopy and immunofluorescence where CD8 TIL are punctate and dispersed throughout the cell while healthy control CD8 mitochondria are fused in networks. Thus bypassing metabolic defects may partially restore TIL activation. Conclusions: Preclinical data suggests that improved understanding of metabolic dysfunction in TILs of RCC may allow for combined therapies to improve response rates of checkpoint inhibition in this disease.