Purified canine CD34+Lin- marrow cells transduced with retroviral vectors give rise to long-term multi-lineage hematopoiesis

Human CD34(+) cells have been shown to retain long-term hematopoietic engrafting potential in preclinical and clinical studies. However, recent studies of human and murine CD34(-) stem cells suggest that these are functionally important early progenitors. Using autologous transplantation, we investigated whether canine CD34(+) and CD34(-) marrow cells could be transduced and give rise to long-term hematopoiesis. CD34(+)Lin(-) and CD34(-)Lin(-) cell populations purified by fluorescence-activated cell sorting were separately cocultivatcd with retroviral vectors LN (CD34(+)Lin(-)) and LNY (CD34(-)Lin(-)), which carry the neomycin (neo) gene. After myeloablative total body irradiation (920 cGy), 3 dogs received transplants of both CD34(+)Lin(-) cells and CD34(-)Lin(-) cells and 2 dogs received only CD34(-)Lin(-) cells. Untransduced autologous marrow cells were given to ensure hematopoietic recovery. Using CFU-C assays, transduction efficiencies of CD34(+)Lin(-) cells ranged from 6% to 18% with no CFU-C formation from CD34(-)Lin(-) cells. PCR-based detection of the neo gene from WBCs was used to detect transduced cells weekly after transplantation. Additional PCR studies in 3 dogs given both CD34(+)Lin(-) and CD34(-)Lin(-) cells were performed on monocytes, granulocytes, and T cells (2 dogs, one at 7.5 months and the other at 9 months) and granulocytes (I dog at 12 months). LN was detected up to 12 months posttransplantation in WBCs and mono-myeloid and lymphoid populations from 3 dogs receiving transplants of transduced CD34(+)Lin(-) cells. LINN was not detected at any time after transplantation in 5 dogs that received transduced CD34(-)Lin(-) cells. Whereas canine CD34(+)Lin(-) marrow cells contributed to long-term multilineage hematopoiesis, progeny of CD34(-)Lin(-) progenitor cells were not detected after transplantation in these experiments.