Mesoblast (ASX:MSB) has received approval from the US Food and Drug Administration (FDA) for Ryoncil (remestemcel-L), making it the first mesenchymal stromal cell (MSC) therapy to be approved in the United States for any indication.
Ryoncil is the only FDA-approved therapy for treating steroid-refractory acute graft-versus-host disease (SR-aGvHD) in children.
The disease
"Allogeneic stem cell transplant" involves a patient receiving stem cells from a donor. The procedure is used to treat blood cancers (like leukaemia), inherited blood disorders (like sickle cell disease), and immune system deficiencies.
However, such transplants carry a risk of graft-versus-host disease (GvHD), where the donor's immune cells attack the patient’s body. First-line treatment for GvHD is corticosteroids, which suppress the immune system.
Steroid-refractory (SR) GvHD occurs when a patient's GvHD does not improve, or in fact worsens, after three to seven days of high-dose corticosteroids.
Once GvHD becomes steroid-refractory, the condition becomes much harder to treat, and patients face a higher risk of death.
Enter Ryoncil
Ryoncil is a therapy using cells from bone marrow (mesenchymal stromal cells). It's typically administered via intravenous infusion. The MSCs modulate the immune system, inhibiting the activation of T-cells, a type of white blood cell that attacks infected and foreign cells. They also reduce the release of cytokines, which are small proteins that control inflammation.
This mechanism allows Ryoncil to target conditions linked to excessive immune responses, such as aGVHD.
Significant clinical results
The FDA’s approval follows a Phase 3 trial of paediatric patients with SR-aGvHD, of which 89% had severe Grade C or Grade D disease. The trial showed that 70% of patients achieved an overall response by Day 28 of treatment with Ryoncil, a rate that's predictive of survival in cases of aGVHD.
More than 85% of patients completed the full course of Ryoncil treatment without interruption, with no discontinuations due to laboratory abnormalities.
Transplant physician Dr Joanne Kurtzberg, Director of the Marcus Center for Cellular Cures at Duke University Medical Center, commented: “Steroid-refractory acute graft-versus-host disease is a devastating condition with an extremely poor prognosis. From today, we are able to offer Ryoncil, the first FDA-approved treatment which will be life-saving for so many children and will have a great impact on their families."
Commercial significance
The global graft-versus-host disease market has been valued at around US$3bn in 2024 and is projected to reach around US$10bn by 2031.
Chief Executive Dr Silviu Itescu commented: “With Ryoncil’s approval by the FDA, Mesoblast has demonstrated the ability to bring the first MSC product to market. We will continue to work closely with the FDA to obtain approval of our other late-stage products, including REVASCOR for cardiovascular diseases and rexlemestrocel-L for inflammatory pain indications.”
With approval secured, Ryoncil will be made available at US transplant centres and other treating hospitals.
Mesoblast also aims to expand Ryoncil’s use to address the adult GvHD market.
Shares in Mesoblast closed 54.04% higher at $3.05 yesterday.
