Recombinant DNA Advisoiy Committee - 2/10-11/92 
led to development of the allogeneic mouse model. The investigators incorporated the 
knowledge gained concerning localized inflammatory response resulting from direct 
introduction of a foreign gene, and applied it to tumor-specific responses. A murine colon 
carcinoma, CT26, was injected into the flank of the mouse. When the tumor became 
palpable, DNA/liposome complexes encoding for H2-K s (the foreign MHC gene) were 
injected directly into the tumor. Beta galactosidase was injected into the tumors of control 
animals. These experiments were also performed using retroviral vectors as delivery 
vehicles. Results demonstrated that not only were cytotoxic T lymphocytes capable of 
lysing the tumor cells which contained the introduced H2-K s gene, but unmodified CT26 
tumor cells were also killed. This result suggested that the most likely mechanism of 
action by which this process was occurring was that the immune system was upregulating 
the expression of its tumor antigens. 
Dr. Nabel showed data supporting the conclusion that this action is T lymphocyte and LY2 
cell mediated. Data were presented showing that the LY2 cell activity could be blocked 
almost completely by incubation with the anti-LY2 antibody. Therefore, the mechanism of 
action may be T lymphocyte mediated and LY2 cell-dependent. 
Dr. Nabel summarized the data from a number of mouse experiments. Whether 
preimmunized or not, the H2-K s injected mice responded better than the beta 
galactosidase controls. A responder was defined as having a greater than 50% reduction 
in tumor diameter at three weeks following introduction of the tumor. A greater than 
50% reduction was observed in the weakly immunogenic tumor, MCA 106. The response 
is variable after stopping treatment, tumors recur about 50% of the time. Following 
retreatment, the tumors usually disappear. Other animals exhibit complete regression of 
their tumors with no evidence of recurrence. The incidences where the tumor does not 
regress completely is probably due to the failure of the MHC gene to insert into cells at 
the margin of the lesion. 
Dr. Nabel described his research on nude mice. If the same experiments are conducted 
with either CT26 or MCA 106, there is no protection when using beta galactosidase or H2- 
K s genes. Experiments have been conducted in normal mice where either the CD4 subset 
or the CD8 subset of T lymphocytes have been depleted. Protection is lost when the CD8 
subset is depleted. The final control experiment was designed to ask whether deletion of 
the polymorphic region of the Class I gene would affect protection. Presumably, the 
immune response is found in the polymorphic region. Indeed, deletion of this region 
yielded no protection when compared to the wild type controls. This data confirms that 
the observed response is probably T lymphocyte mediated and that the alpha 1 and alpha 
2 domains of the Class I molecule are required for protection. 
Dr. Nabel described the proposed mechanism. Probably, a foreign Class 1 MHC gene is 
Recombinant DNA Research, Volume 15 
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