Background: Nemvaleukin alfa (nemvaleukin, ALKS 4230) is a novel, engineered cytokine that selectively binds the intermediate-affinity interleukin-2 (IL-2) receptor complex to preferentially activate CD8⁺ T cells and natural killer cells with minimal expansion of regulatory T cells, designed to leverage antitumor effects of the IL-2 pathwaywhile mitigating potential toxicity that would limit use. Methods: ARTISTRY-1 (NCT02799095) is a phase 1/2 study. Parts A (dose escalation 0.1-10 µg/kg) and B (6 µg/kg [recommended phase 2 dose]) are monotherapy; pts receive intravenous nemvaleukin for 5 days every 14 or 21 days. In Part C, pts receive nemvaleukin (3 or 6 µg/kg) every 21 days in combination with pembrolizumab (200 mg on day 1). We present safety and antitumor activity (RECIST v1.1, iRECIST) data as of 12/02/2020. Results: In Part A, 39 pts received nemvaleukin. No dose-limiting toxicities were observed; maximum tolerated dose was not reached. Part B enrolled immune checkpoint inhibitor–pretreated pts into melanoma or renal cell carcinoma (RCC) cohorts. 18 pts with melanoma enrolled; 10 were evaluable, 2 (both with metastatic mucosal melanoma) achieved a partial response (PR; 1 unconfirmed). 24 pts with RCC enrolled; 1 of 16 evaluable pts achieved a PR (awaiting confirmation). 12 pts in each cohort continue on study. In Parts A and B, treatment-related adverse events in ≥40% included chills (74.4% and 52.4%, respectively) and pyrexia (74.4% and 47.6%, respectively). In Part C (83 evaluable pts), 12 objective responses (OR) were observed; an additional 5 pts had stable disease (SD) >6 months (1 pt with breast cancer, 2 with ovarian cancer, and 2 with non-small-cell lung cancer). Nemvaleukin did not demonstrate any additive toxicity to that already established with pembrolizumab alone. OR data are summarized in the table. Conclusions: Nemvaleukin was generally well tolerated and demonstrated antitumor activity as monotherapy and in combination with pembrolizumab. Pharmacodynamic studies to identify biomarkers are ongoing. Future research of monotherapy and combination therapy with nemvaleukin is warranted. Clinical trial information: NCT02799095

^aCPI pretreated or naïve pts.^bTNBC, ER+Her2-.^cInvestigator assessed.^dAdditional pts experienced SD >6 months.CR, complete response; iPR, immune partial response; PR, partial response; uPR, unconfirmed PR.