Osiris Therapeutics has been given the green light by regulators in Canada for Prochymal, its treatment for acute graft-versus host disease in children, making it the world’s first approved drug which has a stem cell as its active ingredient.

The US firm has received market authorisation from Health Canada to market Prochymal (remestemcel-L), for acute GvHD, a complication of bone marrow transplantation that kills up to 80% of children affected, many within just weeks of diagnosis. Until now, there has been no approved treatments for the disease and currently steroids are used as first-line therapy with a success rate of only 30%-50%.

Prochymal, which demonstrated a clinically meaningful response at 28 days after therapy began in 61%-64% of patients, can now be used for use in children who have failed to respond to steroids. However, the approval is conditional on Osiris carrying out additional clinical trials to verify the anticipated benefit of the therapy.

Prochymal is an intravenous formulation of mesenchymal stem cells (MSCs), which are derived from the bone marrow of healthy donors between the ages of 18 and 30 years. The MSCs are grown in culture so that up to 10,000 doses of Prochymal can be produced from a single donor which are then stored frozen and infused without the need to type or immunosuppress the child.

Door has been opened

Unsurprisingly, Osiris is delighted and chief executive Randal Mills said the Canada thumbs-up represents "not only a great day for Osiris, but for everyone involved in the responsible development of stem cell therapies". Noting that the decision marks the first approval of a stem cell drug, he claimed that now "the door has been opened, it will surely not be the last".

The company quoted Joanne Kurtzberg of Duke University and lead investigator for Prochymal, as saying that she had seen the therapy "reverse the debilitating effects of severe GvHD in many of my patients and now, after nearly two decades of research, the data demonstrating consistently high response rates, a strong safety profile and improved survival clearly support" its use.

It has been a fairly rocky road to an approval for Prochymal, which missed primary endpoints in two Phase III GvHD trials in 2009, although it showed promise in the subgroup with severe refractory acute GvHD and that data has satisfied the Canadian authorities. The therapy is also in late-stage trials for refractory Crohn’s disease, although it halted a Phase III study in March 2009, while Prochymal is also being evaluated for myocardial infarction and type 1 diabetes.

In 2008, Osiris signed a pact worth potentially $1.38 billion with Genzyme Corp, now part of Sanofi, to develop Prochymal and another stem cell drug, Chondrogen, for osteoarthritis. However, in February, the French drugmaker said it had discontinued its project with Prochymal for GvHD, which surprised Osiris as the decision was made without consultation or indeed notification.

Given Sanofi's stance, Osiris said the agreement was therefore terminated and all rights to Prochymal would revert back without compensation to the Paris-based giant. It could also seek out fresh partners "without restriction".