VII. Tumor regression with the MCA 106 fibrosarcoma. 
To evaluate whether direct introduction of MHC class I genes 
into tumors other than the CT26 was effective, MCA 106 (H-2K b ) , a 
fibrosarcoma of C57BL/6 mice was used. Using methods similar to 
those described previously, tumors were inoculated by 
subcutaneous injection into the flank. When palpable tumors 
appeared, they were injected with a vector derived from PLJ H- 
2K S , called vector I, as described in Section 2.b.a. of the 
"Points To Consider." This vector was modified from a previous 
version, and the polyoma T antigen and the 3' long terminal 
repeat were removed with inclusion of a different polyadenylation 
site. Introduction of this plasmid into the MCA 106 tumor caused 
significant reduction in tumor growth (n=4) , in contrast to a 
galactosidase control (n=5) . The H-2K S injected tumors were <50% 
of the size of the control group. In at least one instance, 
complete regression was observed. Representative tumor diameters 
from four animals are shown in the figure below (Fig. 1) . 
Figure 1. Introduction of H-2K S vector I plasmid into MCA 106 
tumors in vivo inhibits tumor growth. MCA 106 bearing C57BL/6 
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Recombinant DNA Research, Volume 15 
