Background: YH003, a recombinant, humanized agonistic anti-CD40 IgG2 monoclonal antibody (mAb) specifically recognizes and agonizes CD40 on the antigen-presenting cells to enhance immune responses. Preclinical data have shown potent anti-cancer activity when combined with anti-PD-1 antibodies. Methods: This is an ongoing phase 1 dose-escalation study. Patients with advanced solid tumors receive YH003 by IV administration Q3W as monotherapy at 0.03 to 3.0 mg/kg for the first cycle (21 days) then in combination with Toripalimab at 240 mg Q3W for the 4 subsequent cycles in an accelerated “3+3” design. The safety, tolerability and preliminary efficacy data will be analyzed. Results: As of 31 Dec 2020 data cutoff, 9 patients (pts) were enrolled and treated at 0.03 mg/kg (n = 3), 0.1mg/kg (n = 3), and 0.3mg/kg (n = 3). The median age was 63 years (range 33-68). Baseline ECOG scores were 0 (7 pts) and 1 (2 pts) with a median of 2 prior lines therapy (range 1-7). 5 pts had received prior immunotherapy (PD-1/PD-L1 or PD-1+CTLA-4). As of data cutoff, no dose limiting toxicities (DLT) were observed. No Serious Adverse Event (SAE) or AEs leading to treatment discontinuation were reported. Four drug related AEs were reported including one Grade 1 (G1) choroidal thickening (related to YH003) at 0.03 mg/kg, one G1 fatigue (related to YH003) at 0.1 mg/kg, two G1 febrile episodes (one related to YH003 and the other related to combination treatment) at 0.3 mg/kg. Among 5 patients assessable for response, there were 2 SD (one with anti-PDL1 refractory Merkel cell carcinoma at 0.03 mg/kg and one with anti-PD1 refractory NSCLC at 0.1 mg/kg) and 1 PR with anti-PD1/anti-CTLA4 refractory ocular melanoma at 0.1 mg/kg. Conclusions: YH003 was well tolerated up to 0.3 mg/kg dose levels when combined with Toripalimab and has shown encouraging antitumor activity in patients with advanced solid tumors. Clinical trial information: NCT04481009