Osiris made the decision to file for the Phase II trial after discussions with the FDA regarding positive preliminary results. Based upon our early experience with the drug, it appears that these stem cells may be beneficial to critically ill patients who have failed other treatments for GVHD, said Gary Kleiner, MD, PhD, a pediatric immunologist at the University of Miami. The trial will be open to both pediatric and adult patients who have failed standard therapy for GVHD.

Graft vs. host disease is a life threatening complication of bone marrow transplantation and can affect the skin, liver, and intestines. Patients with any form of severe acute GVHD who meet the eligibility criteria may participate. For ethical reasons related to the severity of the disease, there will be no placebo arm and all patients will receive the active drug. Visit www.GVHDhelp.com for more information about the trial.

We are pleased that we have been able to work swiftly with the FDA on the development of this program, said C. Randal Mills, Ph.D., President and CEO of Osiris. There is a clear need for better treatment options for patients suffering from GVHD. In particular, mortality rates are exceedingly high for patients who fail first-line treatment with steroids.

Prochymal is an intravenous formulation of mesenchymal stem cells that is currently being evaluated for safety and effectiveness in human clinical trials. Osiris obtains these cells from the bone marrow of adult volunteer donors between the ages of 18 and 32 years. Earlier in the year, Prochymal became the first stem cell drug to be granted FDAs Fast Track status for the treatment of the gastrointestinal form of acute GVHD. Osiris is currently enrolling patients in a separate Phase II trial to evaluate this indication.

Osiris Therapeutics, Inc. is the leader in adult stem cell therapy. The stem cells produced by Osiris are obtained from adult volunteer donors, avoiding the technical problems and controversy surrounding other stem cell technologies. Using proprietary methods, these cells are grown in culture to very high numbers, allowing a single donor's cells to treat thousands of patients. These cells can be used in patients unrelated to the donor, without rejection, eliminating the need for donor matching and recipient immune suppression. Once transplanted, the cells promote healing of damaged or diseased tissues. The Company's current focus includes the use of adult stem cells to improve outcomes in bone marrow recipients being treated for leukemia, to repair damage following a heart attack, and to prevent and treat arthritis.

For additional information, please contact Lisa Rodemann at 410.522.5005, extension 610, or visit our website at www.Osiristx.com.

Osiris Therapeutics