Gp120-Activated Allogeneic Regulatory T cells for Prevention of Graft-versus-Host-Disease: A First-in-Human Trial

Acute graft-versus-host disease (aGvHD) remains a major complication after allogeneic hematopoietic cell transplantation (alloHCT). Adoptive regulatory T-cell (Treg) therapy may suppress alloreactive T-cell responses, but clinical implementation has been limited by donor-specific manufacturing, prolonged ex vivo expansion, and logistical complexity. We developed ATreg, a cell therapy product consisting of gp120-activated, polyclonal Tregs derived from HLA-unmatched third-party donors. The primary objective was to assess the safety, tolerability and toxicity of ATreg, hypothesizing that this would be feasable and safe for aGvHD prevention early after alloHCT in patients with hematologic malignancies. ATreg-001 is a first-in-human, prospective, open-label, single-arm, multi-center phase 1/2 trial (EU CT number 2024-516599-14-00) conducted at 4 German centers (Mainz, Dresden, Münster, and Dortmund). ATreg was generated from standard non-mobilized apheresis products by Treg isolation followed by 16 hours of gp120-mediated activation in the presence of IL-2, without ex vivo expansion, thereby enhancing suppressive function and (potentially) enabling a therapeutic effect at substantially lower Treg doses. Ten patients received ATreg at 0.1 to 1.0 × 10⁶ cells/kg body weight on day +10 ± 5 after alloHCT, in addition to standard GvHD prophylaxis, in a dose-escalation design across 3 cohorts. ATreg was administered within 24 hours after manufacturing. The primary endpoint was the type, incidence, and severity of ATreg-related serious adverse events within 14 days after administration. Secondary endpoints included manufacturing feasibility, aGvHD incidence/severity within 100 days, engraftment, and infections. ATreg administration was well tolerated, with no infusion-related toxicities or other safety signals attributable to ATreg. All treated patients achieved hematopoietic engraftment and full donor chimerism. Within 100 days after alloHCT, no grade 3 to 4 aGvHD occurred, the cumulative incidence of grade 2 to 4 aGvHD was 10%, and no nonrelapse mortality was observed. These first clinical data support the feasibility and favorable safety profile of ATreg, a third-party, gp120-activated Treg product requiring no ex vivo expansion, and warrant further evaluation in larger prospective clinical trials. (1) HLfv and (2) ATreg therapy showed early clinical signals for GvHD prevention, with no cases of grade 3 to 4 aGvHD observed.