Background: Despite recent therapeutic advancements in metastatic renal cell carcinoma (mRCC), only 5-10% of patients will achieve a complete response (CR) to therapy. Cytoreductive nephrectomy removes a large portion of the tumor which may be a source of immunosuppression driven by tumor cell-intrinsic factors in the tumor microenvironment. A pre-clinical orthotopic mouse model of aggressive metastatic triple negative breast cancer showed that neoadjuvant anti-PD-1 checkpoint inhibition generated enhanced and sustained antitumor immune responses with improved survival compared to adjuvant therapy (Liu J et al. Cancer Discov. 2016:1382). Clinical validation of improved outcomes with neoadjuvant compared to adjuvant immune checkpoint inhibitors has been demonstrated in trials for patients with non-small cell lung cancer, advanced melanoma, and recurrent glioblastoma (Forde, P.M., et al. N Engl J Med. 2018:1976; Amaria, R.N., et al Nat Med. 2018:1649; Cloughesy T.F., et al. Nat Med 2019:477). Recent data from a phase III trial in subjects with untreated mRCC, demonstrated the superiority of combination cabozantinib and nivolumab over sunitinib and established a new standard of care for mRCC (Choueiri T.K., et al. Annals of Onc, 2020;31 (suppl; abstr 6960). We hypothesize that if tumor specific immune responses to immunotherapy are greatest prior to nephrectomy, then treatment with nivolumab (nivo) and cabozantinib (cabo) prior to cytoreductive nephrectomy will lead to maximal peripheral and intra-tumoral specific immune responses and higher rates of CR during the course of treatment. Methods: This is an open label phase II, multicenter clinical trial of combination nivo and cabo prior to cytoreductive nephrectomy in patients with mRCC (NCT04322955). 48 treatment- naïve subjects with radiological or histological diagnosis of mRCC will be enrolled with the primary endpoint of CR rate according to RECIST version 1.1. Subjects will receive cabo (40mg) daily and nivo (480mg) every 4 weeks for 12 weeks prior to nephrectomy and a 3+3 design will be used to evaluate the safety of the interval (21 or 14 days) between the discontinuation of cabo and nephrectomy. Post-operatively, subjects will resume treatment with cabo and nivo until evidence of disease progression. Secondary endpoints include median size reduction of the primary tumor, response rate, PFS, OS, and surgical outcomes using the Clavien-Dindo classification system. Tissue based assays will quantify treatment related changes in the renal tumor microenvironment through polychromatic immunofluorescence, single cell RNA sequencing of the biopsy and nephrectomy specimen, and multiplex assessment of circulating serum cytokines. Dynamic contrast-enhanced MRI will be performed in a subset of subjects to assess radiologic correlates of response. The study is currently open to enrollment. Clinical trial information: AAAS6927.