Background: KN046 is a novel bispecific antibody that blocks both PD-L1 interaction with PD1 and CTLA-4 interaction with CD80/CD86. KN046 has a wild type IgG1 Fc portion that preserves intact effector functions, such as depletion of T_regs in tumor microenvironments. This first-in-human study evaluated the safety, tolerability, PK and preliminary efficacy of KN046 in subjects with advanced solid tumors. Methods: This traditional “3+3” dose-escalation design study enrolled patients (pts) with advanced unresectable or metastatic solid tumors refractory or intolerant to standard therapies. Previous treatment from PD1 or PD-L1 immune checkpoint inhibitors was allowed. KN046 was administered intravenously Q2W. Dose limit toxicity (DLT) evaluation period is 28 days. The planned dose levels (DL) were 0.3, 1, 3, 5 and 10 mg/kg. Efficacy evaluation was performed by RECIST 1.1 every 8 weeks. Results: As of Dec 13, 2018, 10 pts had been enrolled (0.3 mg/kg, n = 1; 1 mg/kg, n = 3; 3 mg/kg, n = 3; and 5 mg/kg, n = 3). Median duration of treatment was 8 (range: 2-24) weeks. 1 DLT was observed at 5 mg/kg dose (a grade 3 immune-related hepatitis without elevation in total bilirubin; reversible in two weeks). The most common (≥30%) treatment-emergent AEs (TEAE) were Fatigue, Diarrhea, Nausea, Vomiting. Six immune-related TEAEs (Abdominal pain lower, Arthralgia, Hepatic function abnormal, Hyperthyroidism, Nausea and Transaminitis) were observed in 3 pts. One pt with NSCLC from 3 mg/kg cohort had confirmed completed response. Two pts (TNBC and nivolumab refractory RCC) from 1 mg/kg cohort had shown long-term stable disease ( > 12 weeks). Faster clearance of KN046 was observed at lower dose might be due to target-mediated clearance. T1/2 is approximately 7~9 days at doses of 3 mg/kg and above when saturation occurs. Conclusions: Single agent KN046 has an acceptable safety profile and is in line with previously reported safety data from other immune checkpoint inhibitors. Preliminary efficacy results are promising. PK data from initial 4 cohorts support Q2W schedule. The study is currently ongoing at dose level of 5 mg/kg Q2W. Clinical trial information: NCT03529526