Mesoblast (ASX:MSB) will collaborate with the Blood and Marrow Transplant Clinical Trials Network on a pivotal trial of Ryoncil as part of a first-line regimen in adults with severe acute graft versus host disease refractory to corticosteroids, according to a Friday Australian bourse filing.

The patients will be randomized in the trial as early as possible after corticosteroid refractoriness to receive ruxolitinib alone or combined with Ryoncil to give them the best chance of survival.

The trial protocol will be provided to the US Food and Drug Administration to initiate enrollment in the first quarter of 2026. Mesoblast recently met with the US FDA to discuss the most appropriate patient population and timing of treatment in a pivotal trial of Ryoncil for adults with severe acute graft versus host disease.

Ryoncil is already approved by the FDA in children and adolescents.