Bio-Thera Solutions, Ltd. (SH: 688177), a Guangzhou, China-based commercial-stage pharmaceutical company, has dosed the first patient in a Phase I trial of BAT8013, an antibody-drug conjugate (ADC) directed against CD25, in patients with advanced solid tumors. The milestone marks the clinical entry of an ADC designed to deplete regulatory T cells within the tumor microenvironment rather than to kill tumor cells directly — a mechanistic departure from the HER2- and Trop2-directed ADCs that dominate the current landscape.
The announcement is limited to trial initiation: no safety, pharmacokinetic, or efficacy data have been disclosed. The Phase I study is a multicenter, open-label, dose-escalation trial enrolling 42 patients with advanced solid tumors, according to AllSci trial records. The scientific title indicates the broader protocol also anticipates evaluation of BAT8013 in combination with BAT3306, with or without BAT7205, though Bio-Thera's release specifies that only the single-agent dose-escalation phase is currently active, with combination cohorts subject to further regulatory consultation.
The trial's stated objectives are to characterize safety and tolerability, determine the maximum tolerated dose and recommended Phase II dose, and generate pharmacokinetic and preliminary efficacy data. No dosing schedule, interim readout timeline, or primary completion date was disclosed in the release.
Most clinical-stage ADCs are engineered to bind antigens overexpressed on tumor cells themselves — HER2, Trop2, folate receptor alpha — and rely on internalization by the cancer cell to release a cytotoxic payload. BAT8013 instead targets CD25 (interleukin-2 receptor alpha, encoded by IL2RA), a marker enriched on regulatory T cells within the tumor microenvironment. Bio-Thera's rationale is that eliminating Tregs should relieve local immunosuppression and potentiate the activity of checkpoint inhibitors such as PD-1 and PD-L1 antibodies, rather than exert a tumor-intrinsic cytotoxic effect.
The ADC pairs Bio-Thera's proprietary anti-CD25 antibody with a cleavable linker and a small-molecule topoisomerase I inhibitor payload — the same payload class used in trastuzumab deruxtecan (Enhertu) and several other next-generation ADCs. According to the company, the payload's membrane permeability allows it to diffuse from a killed Treg into adjacent Tregs, producing a localized bystander effect intended to amplify Treg depletion beyond cells that directly bind the antibody.