Improved gene transfer into canine hematopoietic repopulating cells using CD34-enriched marrow cells in combination with a gibbon ape leukemia virus-pseudotype retroviral vector.

We have used dogs to study gene transfer into hematopoietic stem cells, because of the applicability of results in dogs to human transplantation and the availability of canine disease models that mimic human diseases. Previously we reported successful gene transfer into canine marrow repopulating cells, however, gene transfer efficiency was low, usually below 0.1% (Kiem et al, Hum Gene Ther 1996; 7: 89). In this study we have used CD34-enriched marrow cells to study different retroviral pseudotypes for their ability to transduce canine hematopoietic repopulating cells. Cells were divided into two equal fractions that were cocultivated for 72 h with irradiated packaging cells producing vector with different retroviral pseudotypes (GALV, amphotropic or 10A1). The vectors used contained small sequence differences to allow differentiation of cells genetically marked by the different vectors. Nonadherent and adherent cells from the cultures were infused into four dogs after a myeloablative dose of 920 cGy total body irradiation. Polymerase chain reaction (PCR) analysis of DNA from peripheral blood and marrow after transplant showed that the highest gene transfer rates (up to 10%) were obtained with the GALV-pseudotype vector. Gene transfer levels have remained stable now for more than 18 months. Southern blot analysis confirmed the high gene transfer rate. Interference studies on canine D17 cells revealed that 10A1 virus behaved like an amphotropic virus and was not able to use the GALV receptor. In summary, our results show improved gene transfer into canine hematopoietic repopulating cells when CD34-enriched cells are transduced by cocultivation on a GALV-pseudotype packaging cell line in combination with a GALV-pseudotype vector. Furthermore, these results demonstrate that the monoclonal antibody to canine CD34 used in this study is able to enrich for hematopoietic repopulating cells.