Mesoblast and the National Institutes of Health (NIH)-funded Blood and Marrow Transplant Clinical Trials Network (BMT CTN) are collaborating on a pivotal Phase 3 trial of the cell therapy Ryoncil (remestemcel-L-rknd) for adults with severe steroid-refractory acute graft versus host disease (SR-aGvHD).

Ryoncil is an allogeneic (off-the-shelf) bone marrow-derived mesenchymal stromal cell (MSC) therapy that modulates the immune system to counter severe inflammation. It has already been FDA-approved for SR-aGvHD in pediatric patients (ages 2 months and older).

The trial will evaluate Ryoncil as part of a first-line regimen for adults who fail corticosteroid therapy—a population facing high mortality and limited treatment options. The BMT CTN, which represents US centers performing roughly 80% of allogeneic bone marrow transplants nationwide, will spearhead the pivotal Phase 3 study.

"Partnering with Mesoblast in this pivotal trial is an exciting step forward,” said Dr John Levine, Chair of the BMT CTN Steering Committee and Professor of Internal Medicine and Pediatrics at Mount Sinai. “We aim to extend the use of this potentially life-saving therapy, already FDA-approved for children and adolescents, to adults battling severe SR-aGvHD.”

Following recent discussions with the FDA on patient selection and treatment timing, the trial will randomize adult patients as early as possible after corticosteroid failure to receive ruxolitinib alone or combined with Ryoncil. The trial protocol will be submitted to the FDA with enrollment expected to begin in the first quarter of 2026.

Mesoblast CEO Silviu Itescu emphasized the broader significance: “This partnership addresses a critical unmet need in adult SR-aGvHD, a condition with dismal outcomes under current therapies. Expanding Ryoncil to adults represents a market opportunity three to four times larger than the pediatric market.”