A medical treatment that uses stem cells derived from bone marrow has just been approved in Canada. The drug, Prochymal, has already been used to treat children for a type of immune disease arising during bone marrow transplantation. The makers of Prochymal, US-based Osiris Therapeutics Inc., claims that theirs is the first ever stem cell-based drug to be approved.

But this isn’t your typical stem cell therapy. Unlike other treatments being developed that aim to replace dying or damaged cells, Prochymal uses stem cells to suppress a dangerous immune response.

Bone marrow transplants are necessary when a person’s own bone marrow has been destroyed due to chemotherapy or radiation therapy to treat cancer. The donated bone marrow is rich with the stem cells that give rise to all of the body’s blood cells. But anyone receiving bone marrow from a donor runs the risk that the infection-fighting white blood cells in the donor’s marrow will attack the host, a condition called graft-versus-host disease. Steroids can often be used to suppress the attack, but in cases where they are not effective, the disease can cause severe damage to the skin, liver and digestive tract, resulting in death.

Prochymal, which is prepared with bone marrow – or mesenchymal – stem cells, has been used in a small trial to treat children who are suffering from graft-versus-host disease but are not responsive to steroids. The stem cells in Prochymal migrate to areas of white blood cell-induced inflammation to repair the damage, according to Osiris. After extracting bone marrow from donors the stem cells are purified and cultured in the lab to an extent that one donor supplies enough cells for 10,000 doses.

The trial that won Prochymal its approval involved 59 children with graft-versus-host disease who were non-responsive to steroids. Patients were given infusions twice a week for four weeks. Soon after first infusion, 63 percent showed a “clinically meaningful” response (no further details). Researchers then compared survival between responsive and non-responsive groups 28 days following first infusion: 78 percent of the responsive group versus 9 percent of the non-responsive group.

If we do the math we see that 37 of the 59 patients were “responsive” to Prochymal while 22 were not. And of those 37, 29 survived to day 28 while only 2 did from the non-responsive group. The numbers certainly warrant approval of a last resort treatment, even more so since the group showed no adverse health affects.

So why does a company based in Dulles, VA have to go to Canada to get approval? Well, as promising the results are, they no doubt are surprising to some. In 2009 Prochymal suffered a major setback as two separate trials showed that, while the drug was safe, it failed to improve the condition of patients with graft-versus-host disease. An unperturbed Osiris had made a statement that perhaps, while the drug was ineffective for the entire population, it might work for a small subgroup. The latest trial, ended in 2010, showed us that it is indeed effective for children.

But even with the failed 2009 trials, the FDA isn’t dragging its feet. Prochymal is currently being tested in trials that will assess, not only its ability to mitigate graft-versus-host disease, but Crohn’s Disease as well. Chrohn’s disease is an autoimmune disorder that results in inflammation of the gastrointestinal tract. The FDA has granted Prochymal ‘Fast Track’ status which should speed up the approval process. And perhaps in part due to its approval in Canada, the FDA has also made Prochymal available through ‘Expanded Access,’ which allows the use of an investigational drug to treat patients with immediate need and no other options.

Osiris also has plans to develop Prochymal for the repair of heart tissue following a heart attack, the preservation of pancreatic islet cells in type 1 diabetes, and to repair lung tissue in patients with pulmonary disease.

The source of the cells are healthy adult donors, thus avoiding the formidable controversies surrounding embryo-derived stem cells. Once extracted, the cells are then left to divide in a dish until the total population is enormously increased.

One concern on the minds of potential recipients (and their loved ones) might be the source of those stem cells; that is, from other people. The donors are screened for transmittable diseases and even their medical and “social” histories are evaluated to check for behavioral indicators that mark them as high risk for certain diseases. On top of that, the donors are monitored for developing conditions for up to five years after donation.

As the first of its kind, Prochymal’s approval is a landmark victory for stem cell therapies and regenerative medicine as a whole, and I really think Osiris and their collaborators deserve credit. It appears that they have sifted the data from the two 2009 trials and, with their 2010 trial, turned two wrongs into a right.

[image credits: NASDAQ, Nature, and Healblog]

images: NASDAQ, Nature, and Healblog