Transgene expression induces immune response in gene therapy of hematopoietic stem cells. These findings make clear the limitation of this therapeutic alternative under investigation. The level of transgene expression is most critical in terms of induction of immune response in gene therapy of hematopoietic stem cell factor. The finding, published in the latest edition of "http://www.nature.com/mt/index.html" Molecular Therapy, is the result of the trials of one team from the Research Institute of Vall d'Hebron University Hospital in Barcelona (IR-HUVH).