pre-effector cell response. To enhance the host immune response 
to the B16BL6 tumor, we introduced the gene encoding an 
allogeneic MHC class I antigen (H-2K S ) into tumor cells in vivo . 
This procedure involved the admixture of tumor cells or 
intratumor inoculation with cationic liposomes complexed with 
recombinant plasmid DNA (H-2K S or control b-galactosidase genes) . 
In the first experiment (Expt. 1) , 10 6 B16BL6 tumor cells were 
admixed with H-2K S or /9-gal liposomes before intradermal 
inoculation into syngeneic mice. Nine days later, harvested 
lymph node cells were activated with aCD3 monoclonal antibody (1 
mg/ml) for 2 days followed by culture in IL-2 (10 U/ml) for 3 
days (> 4-fold expansion) . The antitumor reactivity of these 
cells were assessed by adoptive immunotherapy (3 x 10 7 
cells/mouse) of 3-day pulmonary B16BL6 metastases. Mice also 
received a subtherapeutic dose of IL-2 (15,000 U i.p. bid x 8) to 
enhance the therapeutic efficacy of the transferred cells. 
Pulmonary metastases were counted 14 days later. In the second 
experiment (Expt. 2), established B16BL6 tumors were injected on 
days 7, 9, 11, and 13 with 0.05 ml of either H-2K S or /9-gal 
liposomes in vivo . LN harvested on day 15 were activated by 
aCD3/IL— 2 and subsequently assessed in adoptive immunotherapy of 
lung metastases as described. 
Mean no. pulmonary metastases (SEM) 
Gene transfer 
Expt . 1 
Expt . 2 
A None 
B b-gal 
C H-2K S 
248(5) 
>250 
75(53)*+ 
216(12) 
155(36)* 
49(15)*+ 
*p » 0.05 vs. A; +p < 0.05 vs. B (Wilcoxon) 
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Recombinant DNA Research, Volume 15 
