Begelomab (BEGESAND®) Salvages Steroid-Resistant Acute GVHD in Pediatric Patients.

Background: Acute graft-versus-host disease (aGVHD) is a leading cause of morbidity and mortality following pediatric hematopoietic stem cell transplantation (HSCT). Approximately half of children achieve complete response (CR) to corticosteroids, whereas steroid-refractory (SR) disease carries a 1-2-year mortality of 41-44%. Mortality risk is 2.6-fold higher in children > 13.9 years, and respiratory failure accounts for 26% of deaths. Existing second-line agents-ruxolitinib, tocilizumab, or extracorporeal photopheresis-have delayed onset or high toxicity. Begelomab (BEGESAND®), a monoclonal antibody targeting CD26/dipeptidyl peptidase-4 (DPP4), inhibits CD26-mediated T-cell activation and has demonstrated 75% response in adults with minimal toxicity. However, pediatric data are lacking. Methods: We retrospectively reviewed five consecutive pediatric patients (ages 3-20 years) treated with Begelomab (BEGESAND®) for SR (n = 4) or steroid-dependent (SD; n = 1) aGVHD between 2017-2021 under emergency IND authorization. Begelomab (BEGESAND®) was administered intravenously at 2.7 mg/m2/day on days 1-5, 10, 14, 17, 21, 24, and 28. GVHD was graded by MAGIC criteria; flow cytometry and immunohistochemistry (IHC) assessed CD26 expression and immune effects. Results: All patients had grade IV disease after ≥2 prior agents. Two with pre-existing sepsis died early, before treatment response could be assessed. Of three evaluable patients, two (67%) achieved CR within 21 days and one achieved durable control by 6 months. All three remain alive; no Begelomab (BEGESAND®)-related toxicity, cytopenia, or new infections occurred. Flow cytometry showed preserved T-cell subsets, and IHC demonstrated CD26 localization at sites of epithelial injury. Conclusions: Begelomab (BEGESAND®) showed promising timely and durable responses with excellent safety in pediatric SR/SD-aGVHD, supporting further evaluation in multicenter pediatric trials.