During the past year, we have continued collaboration with Dr. John Tisdale in monitoring stem cell engraftment in children and young adults transplanted to treat sickle cell anemia. To minimize potentially life-threatening graft versus host disease (GVHD) in this population, Dr. Tisdale has employed a very low intensity conditioning regimen (which includes rapamycin and low intensity whole body irradiation). Our studies indicate this approach produces high grade hematopoietic stem cell engraftment with minimal engraftment of donor T cells in the recipient. To date, Dr. Tisdale has transplanted matched allogeneic stem cells into 5 patients. Three of these patients rapidly engrafted sufficient hematopoietic precursors to eliminate circulating sickle cells and prevent additional crises. One patient suffered an initial graft failure but engraftment was achieved using a second stem cell infusion. In only one did engraftment fail. The clinical course in patients successfully transplanted has been excellent, with minimal GVHD. We will continue our collaboration with Dr. Tisdale as he extends his very promising studies. We also are working closely with Dr. Barrett who has a longstanding interest in using allogeneic donor grafts which have been selectively depleted of potentially allo-reactive T cells. In the past year, Dr. Barrett has begun a protocol using a new method (photodepletion) for selective depletion of alloreactive donor T cells. Early clinical data has been extremely encouraging, and we await the results with larger numbers and longer followup over the coming year.
