Background: Melanoma has a high response rate to anti-PD-1 alone. More than 50% of melanoma on anti-PD-1 progress within one year. IL-10 inhibits inflammation and stimulates the cytotoxicity and proliferation of tumor infiltrating CD8+ T cells at higher concentrations. IL-10 receptors and PD1 are induced on activated CD8 T cells, providing a mechanistic rationale for combining AM0010 and anti-PD1. AM0010 alone has established tolerability and anti-tumor activity in a phase 1 study. Objective responses were observed in 4 of 15 pts with RCC, one patient with uveal melanoma and cutaneous T cell lymphoma, each. Methods: 25 melanoma pts who had progressed on prior anti-CTLA4 and on prior anti-PD-1 containing regimen were treated with AM0010 (20mg/kg qd, SQ) and pembrolizumab (2mg/kg, q3wk IV). Patients had a median of 3.5 prior therapies (range 2-6) and a median of 2 prior immune therapies (range 1-6). Tumor responses were monitored following irRC. Immune responses were measured by analysis of serum cytokines, activation of blood derived T cells and peripheral T cell clonality. Results: AM0010 plus pembrolizumab was well tolerated. All treatment related adverse events (TrAE) were reversible. DLTs and SAEs leading to study discontinuation were not observed. G3/4 TrAEs were observed in 11 of 25 pts and included fatigue (8) thrombocytopenia (6), anemia (4), rash (1) and hypertriglyceridemia (1). There were no objective tumor responses. 9 of 20 evaluable pts had stable disease (DCR = 45%). As of Jan. 31 2017, the mPFS was 2.0 mo. and the mOS was not reached, with a mFU of 15.5 mos (range 10.0-18.4). AM0010 plus pembrolizumab increased Th1 cytokines as well as the number and proliferation of PD1+ Lag3+ activated CD8 T cells in the blood while reducing inflammatory cytokines and TGFb. A de-novo oligoclonal expansion of T cell clones in the blood and an increase of tumor infiltrating Granzyme+ PD1+ CD8+ T cells in tumor biopsies of treated patients was observed. Conclusions: AM0010 in combination with anti-PD1 is well-tolerated in refractory melanoma pts. The clinical activity and the observed CD8+ T cell activation may suggest to study AM0010 in combination with an anti-PD-1 in melanoma patients with less prior treatments. Clinical trial information: NCT02009449