In this research study, we want to learn more about the use of donor-derived cytotoxic T-cells (CTLs) to treat viral infections that occur after allogeneic stem cell transplant. A cytotoxic T cell is a T lymphocyte (a type of white blood cell) that kills cells that are infected (particularly with viruses). Allogeneic means the stem cells come from another person. These CTLs are cells specially designed to fight the virus infections that can happen after a bone marrow transplant.