cells (some infected and most uninfected) that contribute to the total pool of 
cells both in the blood and the bone marrow of these animals. 
III. Studies in Dogs: 
Literature review: Another approach to the scaling up of the infection 
protocol has been carried out by developing BMT/gene transfer in dogs. Kwok 
et al.. (1986) used Neo R and DHFR vectors to demonstrate the acquisition by 
canine CFU-GM in vitro of resistance to G418 (16-25%) and methotrexate (MTX) 
(7-16%) respectively (Table lb). More recently, the same group attempted to 
transplant bone marrow infected with a DHFR vector (Stead et al., 1986). While 
3-12% of CFU-GM were MTX-resi stant at the time of infection, three dogs had no 
detectable MTX-resi stant CFU-GM following transplant. Although the 
administration of MTX to three other dogs resulted in the detection 0.03-1% 
MTX-resistant CFU-GM for a brief period about 30 days after transplant, two of 
the animals died as the result of MTX toxicity. 
Studies by our own group: In collaboration with Dr. Clinton Lothrop, Jr.. 
University of Tennessee, we have found that the N2 vector conferred G418 
resistance on up to 12% of canine CFU-GM In vitro. In addition, NPT activity 
could be detected in colonies with the NPT assay (Table lb; Lothrop et al.. 
1986). An initial BMT iji vivo did not result in detectable gene transfer. 
In summary, the use of dogs promises to provide an additional model for 
the development and evaluation of clinically useful retroviral gene transfer 
protocol s. 
IV . Studies in Sheep; 
In collaboration with Drs. Esmail Zanjani. formerly of University of 
Minnesota and now at the University of Reno, and Michael Harrison. UCSF. we 
have successfully introduced functional vectors into fetal lambs (Table lc. 
Kantoff et al.. submitted for publication). Hematopoietic colonies were shown 
Recombinant DNA Research, Volume 12 
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