Real-world outcomes of the mesenchymal stromal cell product tomostrocel in heavily pretreated pediatric patients with refractory acute graft-versus-host disease

Patients with acute graft-versus-host disease (aGvHD) not responding to steroids or further-line treatment, including ruxolitinib, face a poor prognosis. We conducted a multi-center, retrospective analysis of real-world data from 140 treatment episodes in 139 pediatric patients with steroid- or treatment-refractory aGvHD receiving the random-donor mesenchymal stromal cell (MSC) preparation tomostrocel. Most patients received 4-6 infusions of 1-2 million MSCs/kg body weight after a median of 3.5 prior therapies, including ruxolitinib in 76 patients. At baseline, over two-thirds had grade III/IV aGvHD, mostly with lower gastrointestinal involvement. At day 28, overall response (OR) rate was 62.9% (74.1%, 75.0% and 53.2% for grade II, III and IV aGvHD, respectively). OR was similar with versus without ruxolitinib pre-treatment. Organ stage with skin, liver, lower gastrointestinal and upper gastrointestinal involvement improved at day 28 in 69.4%, 57.5%, 58.6% and 39.5% of patients, respectively. Most responses were sustained. Six-month overall survival was 64.1%. Favorable survival factors were younger age, lower grade aGvHD and OR at day 28. The favorable safety profile of tomostrocel was consistent with prior MSC reports. Treatment with tomostrocel resulted in good responses with a favorable safety profile in heavily pre-treated pediatric patients, including those pre-treated with ruxolitinib.