Background: Lymphocyte-activation gene 3 (LAG-3) is an immune checkpoint receptor protein that functions to control T cell response, activation and growth. Dual inhibition of PD-1 and LAG-3 may improve anti-tumor effect synergistically. A phase Ia/Ib dose-escalation study evaluated IBI110 ± sintilimab in patient with advanced solid tumors; initial efficacy and safety data were previously presented (C Zhou et al. ASCO 2021; NCT04085185). Here, we reported the updated results. Methods: Eligible patients were ECOG PS 0-1 and had locally advanced, recurrent or metastatic solid tumors for whom standard therapy had failed. Patients received escalating doses of IBI110 (0.01/0.1/0.3/1/3/10/20mg/kg) IV Q3W in phase Ia and escalating doses of IBI110 (0.3/0.7/1.5/3/5/8/10 mg/kg) in combination with sintilimab 200 mg IV Q3W in phase Ib. Crossover from monotherapy to combination therapy was allowed at progression. The primary objectives were safety, tolerability, and anti-tumor activity of IBI110 alone or IBI110+sintilimab (per RECIST v1.1). Results: Phase Ia: 28 patients (median age of 60.5 years [range 35-72], ECOG PS of 0 [n = 14] and 1 [n = 14]) were enrolled. Dose escalation was completed and no dose-limiting toxicity (DLT) was observed in all dose cohorts. The safety profile was generally consistent with the initial. By investigator-assessment, best response was 1 confirmed partial response (PR) and 6 stable diseases (SD) with monotherapy. After crossing to combination therapy at progression, 8 patients who failed prior anti-PD-(L)1 mAb therapy achieved SD. Phase Ib: Overall, 45 patients (median age: 60.0 yr [range 33-74]; ECOG PS: 0 [n = 14], 1 [n = 31]) were enrolled in all dose levels. Dose escalation was completed and no DLT was observed. The most common treatment-related adverse events (TRAEs) were aspartate aminotransferase increased (28.9%), anaemia (24.4%), and alanine aminotransferase increased (22.2%). TRAEs ≥ grade 3 occurred in 10 (22.2%) patients. Immune-related AE (irAE) incidence was 31.1%, and the most common irAE was hypothyroidism (15.6%). In 43 patients who had undergone at least 1 post-baseline tumor assessment, the investigator-assessed best response included 6 PRs (1 endometrial cancer, 4 NSCLC, and 1 SCLC patients) and 23 SDs. Three patients showed a progression-free survival > 1 year and continued treatment. Conclusions: IBI110 alone or plus sintilimab demonstrated acceptable safety profile and promising antitumor activity in patients with advanced solid tumors. Clinical trial information: NCT04085185.