We want to see if we can use a kind of white blood cell called T cells that we have grown from the stem cell donor instead of the regular treatment with Ganciclovir or Foscarnet to prevent CMV from "flaring up". These cells have been trained to attack CMV virus infected cells. We will grow these T cells from blood taken from the donor before the patients transplant. These cells are called CMV-specific cytotoxic T-lymphocytes or CMV CTL, and they will be given to the patient around 30 days after their transplant.