suggests that clone-to-clone variation in in vivo growth and 
tumorigenic capacity may result in other modifications of cells, 
caused by transfection or the subcloning procedure, which affects 
their tumorgenicity . These types of clonal differences would 
likely be minimized by transducing a population of cells directly 
in vivo. 
Because the H-2K class I MHC antigen is strongly expressed 
on most tissues and can mediate an allogeneic rejection response, 
we chose it in our animal model studies designed to enhance the 
immunogenicity of tumors in vivo. These studies extended 
previous efforts to modify tumor cells by developing a system for 
the direct introduction of genes into tumors by in vivo infection 
using retroviral vectors or by DNA/ liposome mediated 
transfection. This technology can also be used to deliver 
specific recombinant cytokines into the tumor microcirculation 
and to understand the immunologic basis for tumor rejection in 
vivo. 
[704] 
Recombinant DNA Research, Volume 17 
