FDA Grants Orphan Drug Exclusivity to Mesoblast's Ryoncil for Pediatric GVHD

The FDA has granted Mesoblast’s stem cell therapy, Ryoncil (remestemcel-L), seven years of orphan drug exclusivity for the treatment of steroid-refractory acute graft-versus-host disease (SR-aGVHD) in children ages 2 months and older, the company announced May 14. The exclusivity designation means the FDA will not approve another mesenchymal stromal or stem cell product for the same condition until 2032.

SR-aGvHD is a serious and potentially fatal complication of allogeneic stem cell transplants, which are often used to treat blood cancers, inherited blood disorders and immune system diseases. In this condition, donor immune cells attack the recipient’s body. When patients do not respond to steroids, the standard first-line treatment, options are limited.

It is made from bone marrow-derived mesenchymal stromal cells (MSCs) donated by healthy adults and administered as a series of intravenous infusions. These cells have been shown to regulate immune activity and reduce inflammation, offering a novel option for children who do not respond to conventional therapy.

The approval was supported by results from a multicenter trial involving 54 children with SR-aGvHD. After four weeks of treatment, 70.4% of participants had a clinical response. A complete response was seen in 29.6%, while 40.7% showed a partial response. Some patients received additional doses based on how they responded to the initial treatment.

The most common side effects seen in the trial were infections, fever, bleeding, abdominal pain and high blood pressure. Rare but serious adverse reactions such as infusion-related events and allergic responses may also occur.

Ryoncil’s approval followed two earlier rejections by the FDA, which had raised concerns about how Mesoblast measured potency and ensured consistent quality. The company later revised its manufacturing and testing protocols before receiving approval in 2024.

Mesenchymal stromal cells were first described in the late 1960s, when researchers observed that certain bone marrow cells could give rise to bone, cartilage and fat. Later studies revealed their immunomodulatory abilities, which opened the door to their use in inflammatory and immune-related diseases. One of the earliest clinical successes occurred in 2004, when MSCs were used to treat a child with steroid-resistant GVHD.

Globally, other MSC therapies have seen mixed success. Temcell is approved in Japan for GVHD. A small study of 12 patients published in Blood Cell Therapy in 2024 showed positive results for Temcell in pediatric patients. In Europe, Takeda’s Alofisel (darvadstrocel) was once authorized for Crohn’s-related complications, but the European Medicines Agency withdrew its approval in 2024 after a clinical trial failed to show a clear benefit over placebo. A sm

The wholesale acquisition cost price of Ryoncil is $194,000 per intravenous infusion. Based on the recommended dosing schedule — twice-weekly infusions over four weeks — the full course of treatment can reach over $1.5 million. Mesoblast has launched financial assistance and support programs to help with patient access.

Despite the significant cost, Ryoncil brings a long-awaited new, potentially life-saving treatment option and renewed hope for children and families facing stem cell transplants.