Background: Aldesleukin (recombinant human interleukin-2) has been an FDA-approved treatment for mRCC since 1992, based on a 5-10% rate of durable complete remissions. Autophagy is a protective mechanism that enables cells to survive the metabolic stress of cancer therapy. Hydroxychloroquine (HCQ) inhibits cellular autophagy and has shown synergy with interleukin-2 in animal tumor models. We hypothesized that this combination would be tolerable and active in patients with mRCC. Methods: The Cytokine Working Group initiated a study of high-dose aldesleukin in combination with oral HCQ for patients with mRCC. Subjects receive up to 6 cycles of aldeskleukin, 600,000 International Units per kg, on a standard schedule. HCQ is administered orally starting 2 weeks prior to the first dose of aldesleukin and continuing up to one year. The initial HCQ dose was 600 mg daily, with a planned dose escalation to 1200 mg daily after safety was demonstrated in five subjects. Subjects were monitored for safety and tolerability as well as response per RECIST 1.1. Results: Five subjects were treated at the first dose level of 600 mg daily HCQ plus aldesleukin with no unexpected toxicity. Thirteen subjects were then treated at HCQ 1200 mg daily with aldesleukin. Of these, two experienced hypotension and tachycardia and 1 patient died from pulmonary emboli. The cardiac events were consistent with aldesleukin toxicity, but were observed earlier in the course of treatment than anticipated for aldesleukin alone. HCQ dose was therefore de-escalated to 600 mg daily, and 8 additional subjects have been enrolled with no unexpected toxicity. In 26 of 39 planned subjects, there has been 1 complete response (CR) and 1 partial response (near CR), both in the 600 mg cohort. As of Oct 24, 2016, after a median of 36.6 months of follow-up, seven out of 26 subject have died, with median overall survival not yet obtained (95% C.I. = (29.6 months,unknown)). Conclusions: HCQ in combination with aldesleukin was found to be tolerable at a dose of 600 mg daily, with expected toxicities. Clinical responses have been observed. Clinical trial information: NCT01550367