Retroviral transfer of genes into canine hematopoietic progenitor cells.

Amphotropic retroviral vectors containing either the bacterial neomycin phosphotransferase gene or a mutant dihydrofolate reductase gene (DHFR*) were used to infect canine hematopoietic progenitor cells. Successful transfer and expression of both genes in canine hematopoietic progenitor cells has been achieved as measured by the ability of the viruses to confer resistance to either methotrexate (MTX) or the aminoglycoside G418, respectively. Gene transfer was achieved using helper-free retroviral vectors. The rate of gene expression in canine granulocyte/macrophage colony-forming units (CFU-GM) after cocultivation for 24 hours with virus-producing packaging cells ranged from 6-25%. Autologous marrow cocultivated for 24 hours with virus-producing packaging cells was transplanted into six dogs after lethal total body irradiation. All dogs showed engraftment within two weeks and four dogs survived for 5-7 months without adverse effects. One dog that had been given marrow infected with a DHFR* virus and that received MTX as in vivo selection after marrow transplantation and survived, showed 0.1 and 0.03% MTX-resistant CFU-GM at weeks 3 and 5. The efficiency of gene transfer into canine CFU-GM has been increased threefold by culturing marrow cells for six days in long-term marrow culture after 24 hour cocultivation with virus producing packaging cells.