Intra-lesional Nivolumab Therapy for Limited Cutaneous Kaposi Sarcoma

This is a single-center, phase I safety/expansion trial of nivolumab in HIV-infected (with stable, treated HIV on cART) and HIV-uninfected patients with limited cutaneous KS. PRIMARY OBJECTIVES: \- To determine the safety and tolerability of four intra-lesional injections of nivolumab given every two weeks to treat KS. They will be assessed by NCI Common Terminology Criteria for Adverse Events version 5 (NCI CTCAE v. 5). SECONDARY OBJECTIVES: * To determine the changes in cytotoxic T cells and regulatory T cells in the lesions as determined by immunohistochemistry and flow cytometry. * To determine the changes in cytotoxic T cells and regulatory T cells in the peripheral blood as determined by flow cytometry. * To determine the changes in PD-1/PD-L1 expression as determined by immunohistochemistry in lesions. OUTLINE: Participants with treatment-experienced KS will be enrolled into Cohort A (initial safety cohort). If there are no grade 3 or higher adverse events, enrollment into the expansion cohort (Cohort) B will be available to participants with either treatment-experienced or treatment-naïve KS, including those previously enrolled in the safety cohort. Patients will receive one intra-lesional injection of nivolumab into one cutaneous KS lesion every 2 weeks for up to a total of 4 doses until completed or intolerable toxicity, request to withdraw, or withdrawal per the Principal Investigator. Participants will be followed for an additional 5 months after completing the 4 treatment doses.