The Moloney murine leukemia retrovirus-derived vector N2 was used to transfer the bacterial NeoR gene (conferring resistance to the neomycin analogue G418) into hematopoietic progenitor cells. Approximately 5% of day seven CFU-GM were resistant to 2,000 micrograms/ml G418, using a supernatant infection protocol in the absence of vector-producing cells. A greater proportion of CFU-GM colonies were recovered relative to uninfected controls as the stringency of selection was diminished. Enzyme activity was detected in drug-resistant colonies, confirming that the resistant colonies obtained after infection with N2 represented cells producing neomycin phosphotransferase. Activity in the CFU-GM colonies approached 50% of that of drug-resistant vector- producing cells on a per cell basis. To test the hypothesis that more rapidly cycling bone marrow cells would be more susceptible to vector infection, we treated progenitor cells obtained from cyclic hematopoietic (CH) dogs with the N2 vector. Despite the increased numbers of hematopoietic progenitor cells obtained from CH dogs, the proportion of G418-resistant CFU-GM did not increase over that obtained with N2-infected normal marrow. These results demonstrate that retroviral vectors can be used to transfer and express exogenous genes in canine hematopoietic progenitor cells.

Granulocytic (colony-forming units in culture, or CFU-c) and erythrocytic (erythropoietin-responsive cells, or ERC) progenitor cells in canine cyclic hematopoiesis (CH) have been shown to fluctuate over the cycle and in the same phases as one another. The ERC cycle is preceded by 3 or 4 days by a rise in serum erythroid-stimulating activity and is followed by a reticulocytosis. During the cycle CFU-c show a differential sensitivity to two sera, one normal and one containing elevated amounts of colony-stimulating activity. The proliferation rate of CFU-c also fluctuates from well above normal to considerably less than normal over the cycle. These results are discussed in the light of present knowledge of the pathogenesis of canine CH. We suggest that these results support the contention that CH is a disorder of hemopoietic stem cells and that the cycling of humoral factors and peripheral blood cells may follow as a consequence.

The Moloney murine leukemia retrovirus-derived vector N2 was used to transfer the bacterial NeoR gene (conferring resistance to the neomycin analogue G418) into hematopoietic progenitor cells. Approximately 5% of day seven CFU-GM were resistant to 2,000 micrograms/ml G418, using a supernatant infection protocol in the absence of vector-producing cells. A greater proportion of CFU-GM colonies were recovered relative to uninfected controls as the stringency of selection was diminished. Enzyme activity was detected in drug-resistant colonies, confirming that the resistant colonies obtained after infection with N2 represented cells producing neomycin phosphotransferase. Activity in the CFU-GM colonies approached 50% of that of drug-resistant vector- producing cells on a per cell basis. To test the hypothesis that more rapidly cycling bone marrow cells would be more susceptible to vector infection, we treated progenitor cells obtained from cyclic hematopoietic (CH) dogs with the N2 vector. Despite the increased numbers of hematopoietic progenitor cells obtained from CH dogs, the proportion of G418-resistant CFU-GM did not increase over that obtained with N2-infected normal marrow. These results demonstrate that retroviral vectors can be used to transfer and express exogenous genes in canine hematopoietic progenitor cells.