This is a pilot study of infusions of ex vivo expanded, gene marked donor bone marrow stromal cells following allogeneic bone marrow transplantation. The study is a within patient dose escalation safety evaluation. It is believed that this patient population may benefit from these donor stromal cell infusions. As the stromal cells will be obtained from the original stem cell donor, no conditioning is required. Patients will receive two infusions of mesenchymal cells (MSC) approximately 14 to 21 days apart unless there is unacceptable toxicity after the first infusion. The first dose of cells to be given will be 1x10^6 MSC/kg and the second dose of cells will be 5x10^6 MSC/kg. The patients will be followed for approximately 28 days following the second infusion for any toxicity. Only after all six patients have safely completed both infusions will we consider 5 x 10^6 MSC/kg a safe dose of allogeneic mesenchymal stem cells for infusion.