Abstract CT067: Preliminary safety and efficacy results of an anti-CD25 monoclonal antibody (BA1106) in patients with advanced solid tumors: The first-in-human study

Abstract Introduction: BA1106 is a first-in-human anti-CD25 monoclonal antibody developed by Boan biotech, which demonstrated significant anti-tumor activity by depleting Treg cells and expanding CD8+ and CD4+T cells in tumor microenvironment in preclinical studies, without IL-2 signaling pathway suppression. A phase 1 study was conducted to evaluate the safety, pharmacokinetics and preliminary efficacy of BA1106 in solid tumors. Methods: Eligible patients with refractory, advanced or metastatic solid tumors were included in the dose escalation part of this study, which followed an accelerated-titration and a Bayesian optimal interval design. The primary endpoints included the safety, maximum tolerated dose (MTD) and dose-limiting toxicities (DLTs). The secondary endpoints included pharmacokinetics, immunogenicity and preliminary efficacy. Results: As of December 23rd, 2024, 31 patients (3 and 12μg/kg, n=1 each; 36, 108μg/kg, n=3 each; 216, 432, 720μg/kg, n=6; 1200ug/kg, n=5) have been treated with BA1106. One DLT (grade 3 hyponatremia) was observed at the dose level of 432μg/kg, and MTD was not reached. Treatment-related adverse events (TRAEs) of any grade were reported in 21 patients (67.7%). 9 (29.0%) patients suffered immune-related adverse events (irAEs) (grade 1 to 2), with rash (n=4, 12.9%), myoglobin blood increased (n=2, 6.5%), and lipase increased (n=2, 6.5%) being the most commonly observed. 3(9.7%) patients suffered grade 3 TRAEs. No patient was dead or premature withdrawal for TRAEs. Out of 26 patients with at least one efficacy assessment, 9 achieved stable disease (SD), with a disease control rate (DCR) of 34.6%. Tumor shrinkage and durable disease control were noted in 4 patients, including a small-cell neuroendocrine carcinoma (treatment duration 76 weeks, still ongoing), a pleural mesothelioma (treatment duration 33.9 weeks), a small bowel adenocarcinoma (treatment duration 22.9 weeks), and a hepatocellular carcinoma (treatment duration 22.1 weeks, still ongoing). The exposure of BA1106 increased with the dose escalation. No positive ADA was detected. A rapid and durable decrease in peripheral blood Treg cells and an increase in the Teff/Treg ratio were observed after first dose. Conclusion: BA1106 was well-tolerated and showed preliminary anti-tumor activity in solid tumors. Simultaneously, a clear decrease of Treg cells and increased Teff/Treg ratio were observed, what show the potential to combined with PD-1 inhibitors. This trial was registered in clinicaltrial.gov, NCT05650242. Citation Format: Dan Liu, Qingyuan Zhang, Zhijie Wang, Junye Wang, Ming Zhou, Deyong Song, Changlin Dou, Lin Shen. Preliminary safety and efficacy results of an anti-CD25 monoclonal antibody (BA1106) in patients with advanced solid tumors: The first-in-human study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr CT067.