Neoadjuvant PD-1 and LAG-3-targeting bispecific antibody and other immune checkpoint inhibitor combinations in resectable melanoma: the randomized phase 1b/2 Morpheus-Melanoma trial

Patients with stage III melanoma are at high risk of relapse. The NADINA trial evaluating neoadjuvant nivolumab plus ipilimumab and the SWOG-1801 trial evaluating neoadjuvant pembrolizumab have demonstrated superior clinical outcomes with neoadjuvant versus adjuvant checkpoint inhibition. Morpheus-Melanoma was a phase 1b/2, randomized umbrella trial evaluating tobemstomig (anti-PD-1/anti-LAG-3 bispecific antibody; n = 40), tobemstomig plus tiragolumab (anti-TIGIT monoclonal antibody; n = 20) and atezolizumab (PD-L1-targeting monoclonal antibody) plus tiragolumab (n = 20) versus nivolumab (anti-PD-1 monoclonal antibody) plus ipilimumab (anti-CTLA-4 monoclonal antibody; n = 22) in stage III melanoma. The primary endpoint was pathological response by independent pathological review. Additional endpoints included safety and exploratory biomarkers. Here tobemstomig showed a similar pathological response rate (pRR) versus nivolumab plus ipilimumab (80.0% (32/40) versus 77.3% (17/22)); major pathological responses were less frequent with tobemstomig versus nivolumab plus ipilimumab treatment (62.5% (25/40) versus 72.7% (16/22)). Tobemstomig plus tiragolumab and atezolizumab plus tiragolumab showed a lower pRR versus nivolumab plus ipilimumab (60.0% (12/20) and 45.0% (9/20) versus 77.3% (17/22), respectively). Tobemstomig demonstrated improved safety versus nivolumab plus ipilimumab, with 2.5% (1/40) and 22.7% (5/22) of patients experiencing grade 3 or higher treatment-related adverse events (TRAEs), respectively, and 0% (0/40) and 13.6% (3/22) of patients discontinuing treatment due to TRAEs, respectively. Grade 3 or higher TRAEs were reported by 15% (3/20) of patients in the tobemstomig plus tiragolumab arm and by no patients in the atezolizumab plus tiragolumab arm. Baseline CD8⁺ and CD3⁺ tumor-infiltrating T cell density, IFNγ pathway and effector T cell gene expression, tumor mutational burden and pre-surgery circulating tumor DNA correlated with pathological response across treatments. In conclusion, in the Morpheus-Melanoma study, tobemstomig demonstrated a similar pathological response and improved safety profile versus nivolumab plus ipilimumab in patients with resectable stage III melanoma. ClinicalTrials.gov identifier: NCT05116202 .