Efficacy and safety of LM-108, an anti-CCR8 monoclonal antibody, in combination with an anti-PD-1 antibody in patients with gastric cancer: Results from phase 1/2 studies.

2504 Background: Targeting tumor-infiltrating regulatory T cells (Tregs) is a potential approach to overcome immunotherapy resistance in the treatment of cancers. LM-108 is a novel Fc-optimized, anti-CCR8 monoclonal antibody that selectively depletes tumor-infiltrating Tregs. Here we report a pooled analysis of results from 3 phase 1/2 studies (NCT05199753; NCT05255484; NCT05518045) to evaluate the efficacy and safety of LM-108 in combination with anti-PD-1 therapy in patients with gastric cancer. Methods: Eligible patients with gastric cancer treated with LM-108 in combination with an anti-PD-1 antibody were included in the analysis. Patients received intravenous LM-108 at dose levels of 3 mg/kg Q2W, 6 mg/kg Q3W, or 10 mg/kg Q3W plus an anti-PD-1 antibody (intravenous pembrolizumab 200 mg Q3W or 400 mg Q6W or toripalimab 240 mg Q3W). The primary endpoint was investigator-assessed ORR per RECIST v1.1. The secondary endpoints included safety, other efficacy outcomes, and biomarkers analysis. Data cutoff date for the pooled analysis was December 25, 2023. Results: Forty-eight patients with gastric cancer (median age: 60.5 years; male: 72.9%) from China, USA, and Australia were treated ≥ 1 dose of LM-108 in combination with pembrolizumab or toripalimab. Most (n = 47, 97.9%) patients had received at least 1 prior anticancer treatment, and 43 (89.6%) had received prior anti-PD-1 therapy. Treatment-related adverse events (TRAEs) occurred in 39 (81.3%) patients, in which the most common events (≥15%) were alanine transaminase increased (25.0%), aspartate transaminase increased (22.9%), white blood cell decreased (22.9%), anemia (16.7%). Grade ≥ 3 TRAEs occurred in 18 (37.5%) patients, the most common events (≥ 4%) were anemia (8.3%), lipase increased (4.2%), rash (4.2%), and lymphocyte count decreased (4.2%). Among 36 efficacy-evaluable patients across all regimens, ORR was 36.1% (95% CI 20.8%–53.8%) and DCR was 72.2% (95% CI 54.8%–85.8%). The median PFS was 6.53 months (95% CI 2.96–NA). Among 11 patients whose disease had progressed on first-line treatment, ORR was 63.6% (95% CI 30.8%–89.1%) and DCR was 81.8% (95% CI 48.2%–97.7%). Of the 11 patients who progressed on first-line treatment, 8 had high CCR8 expression. Among these 8 patients, ORR was 87.5% and DCR was 100%, with 1 CR, 6 PR, and 1 SD observed. Conclusions: LM-108 in combination with an anti-PD-1 antibody showed promising antitumor activity in patients with gastric cancer that was resistance to anti-PD-1 therapy. The combination therapy was well tolerated. These results support further evaluation of LM-108 in CCR8 positive gastric cancer. Clinical trial information: NCT05199753 ; NCT05255484 ; NCT05518045 .