Safety and efficacy from the phase 1 SURPASS trial of ADP-A2M4CD8, a next-generation T-cell receptor T-cell therapy, in patients with advanced esophageal, esophagogastric junction, or gastric cancer

349 Background: ADP-A2M4CD8 is a specific peptide enhanced affinity receptor mixed CD4+ and CD8+ T-cell therapy targeting the cancer testis antigen MAGE-A4 and modified with addition of a CD8α co-receptor designed to provide additional functionality to CD4+ T-cells. ADP-A2M4CD8 has demonstrated a favorable benefit to risk profile in the Phase 1 SURPASS trial (NCT04044859) in HLA A*02–eligible patients (pts) with unresectable or metastatic tumors positive for MAGE-A4 (Hong DS, et al. E-poster 540P: ESMO 2021; Virtual). Here we report updated clinical outcomes in pts with esophageal, esophagogastric junction (EGJ), or gastric cancer. Methods: SURPASS is a first-in-human trial consisting of a modified 3+3 dose-escalation design and an expansion cohort. Autologous T-cells are obtained by leukapheresis, transduced with a self-inactivating lentiviral vector expressing the MAGE-A4-specific T-cell receptor and the CD8α co-receptor, and infused back to the pts as ADP-A2M4CD8 following lymphodepleting chemotherapy. Primary and secondary objectives are safety and anti-tumor activity, respectively. Results: As September 6, 2022, 13 pts (11 male, 2 female) with esophageal (3), EGJ (8), and gastric cancer (2) received ADP-A2M4CD8 (range: 1.02–9.9x109 transduced T-cells). All pts had adenocarcinoma, median age was 55 years (range: 31–71), median MAGE-A4 expression H-score was 245 (range: 160–300), and pts received median of 2 lines of prior therapy (range 1–5). Adverse events (AEs) were consistent with those typically associated with lymphodepleting chemotherapy, cellular therapy, and/or disease. One pt had a Grade 5 (fatal) AE of pancytopenia. Overall response rate per RECIST v1.1 by investigator review was 15% (2 partial response [PR]). Disease control rate was 77% (2 PR+8 stable disease). This trial is ongoing, and additional data will be presented. Conclusions: Results indicate an acceptable benefit to risk profile and encouraging anti-tumor activity of ADP-A2M4CD8. An additional treatment cohort has been included in the updated SURPASS trial protocol to evaluate ADP-A2M4CD8 combined with nivolumab. A Phase 2, open-label trial in advanced esophageal and EGJ cancers has been initiated (SURPASS-2; NCT04752358). Clinical trial information: NCT04044859 .