Long-Term Persistence of Canine Hematopoietic Cells Genetically Marked by Retrovirus Vectors

Abstract

In 1991 we reported gene transduction into autologous long-term repopulating marrow cells in dogs using amphotropic helper-free retrovirus vectors containing the bacterial neomycin phosphotransferase gene (neo) and the human adenosine deaminase gene (ADA). Two of the dogs are still alive and healthy now more than 5 years after transplantation of transduced autologous marrow cells. In one of the surviving dogs, polymerase chain reaction (PCR) analysis showed the neo and ADA genes to be present in peripheral blood granulocytes and lymphocytes up to the present time. The estimated percentage of neo-positive cells ranged from neo gene has been documented in peripheral blood myeloid and lymphoid cells along with G418-resistant colony-forming unit-granulocyte/macrophage (CFU-GM) for now more than 2 years. These findings represent the longest follow-up of retrovirus-mediated gene transduction in any animal species. Long-term transduction efficiency, though, has remained low and will need to be improved for therapeutic application to be possible. In an effort to develop improved transduction protocols in large animals, we tested two different transduction protocols in our canine model. Results of that study were first reported in 1991 and showed gene transduction in autologous long-term repopulating marrow cells in dogs using amphotropic retrovirus vectors containing the neo and human ADA genes. In this report, we present an update of the two dogs that became long-term survivors. One of the two dogs showed the presence of the neo and ADA gene in peripheral blood granulocytes and lymphocytes for more than 5 years, whereas the other dog failed to show persistence of the transduced gene after 50 months. Three additional dogs have been transplanted on the same transduction protocols and showed similar results with a follow-up of more than 2 years. Our data show successful, low-level gene transduction into marrow cells for more than 5 years after transplant.