A UC Davis study published online in Molecular Therapy shows that methods using human bone marrow-derived stem cells to deliver gene therapy to cure diseases of the blood, bone marrow and certain types of cancer do not cause the development of tumors or leukemia. Jan Nolta, the study's senior author and director of the UC Davis Stem Cell Program, and her colleagues tested the safety of gene transfer into bone-marrow stem cells from human donors in more than 600 mice. None of the transplanted mice developed leukemia or solid tumors caused by the gene therapy treatment during the evaluation period of up to 18 months.