RETROVIRUS-MEDIATED TRANSFER OF A HYGROMYCIN PHOSPHOTRANSFERASE THYMIDINE KINASE FUSION GENE INTO HUMAN CD34(-MARROW CELLS() BONE)

Retrovirus-mediated gene transfer into human hematopoietic stem cells has been proposed as a means of therapy for various inherited diseases and as a method of gene marking. The transduction efficiency of an am photropic retroviral vector (PA317/HyTK) containing a hygromycin phosp hotransferase-thymidine kinase fusion gene was examined with human CD3 4(+) bone marrow cells in the presence of interleukin-3 (IL-3), interl eukin-6 (IL-6), and stem cell factor, Transduction efficiencies determ ined from the ability of transduced granulocyte-macrophage colony form ing units (CFU-GM) to grow in hygromycin B and from polymerase chain r eaction analysis of individual transduced CFU-GM growing in the presen ce of hygromycin B were 0.3-3.0% (mean +/- S.D., 1.1 +/- 0.9%) and 0.1 -1.2% (mean +/- S.D., 0.5 +/- 0.4%), respectively. Ganciclovir at a do se of similar to 1 mu M reduced the number of CFU-GM derived from vect or-infected CD34(+) cells by 50%. These findings demonstrate that huma n hematopoietic stem cells infected with this retroviral vector are su sceptible to ganciclovir, offering the potential to control transduced gene expression in vivo.