Effectiveness of combined interleukin 2 and B7.1 vaccination strategy is dependent on the sequence and order: A liposome-mediated gene therapy treatment for bladder cancer

We have developed a novel liposome-mediated immuno-gene therapy using inter leukin 2 (IL-2) and B7.1 in a murine bladder cancer model. A carcinogen-ind uced murine bladder cancer cell line, MBT-2, was transfected with cationic Liposome 1,2-dimyristyloxypropyl3-dimethyl-hydroxyl ammoniun bromide/dioleo lylphosphatidylethanolamine and IL-2 plasmid, The optimized transfection co ndition generated IL-2 levels of 245-305 ng/10(6) cells/24 h, 100-fold high er than the levels seen with retrovirus transfection, Ninety percent of the peak level of IL-2 production was maintained for up to 11 days after trans fection, Animal studies were conducted in C3H/HeJ female mice with 2 x 10(4 ) MBT-2 cells implanted orthotopically on day 0. Multiple vaccination sched ules were performed with i.p. injection of 5 x 10(6) IL-2 and/or B7.1 gene- modified cell preparations. The greatest impact on survival was observed wi th the day 5, 10, and 15 regimen. Control animals receiving retrovirally ge ne-modified MBT-2/IL-2 cell preparations had a median survival of 29 days. Animals receiving the IL-2 liposomally gene-modified cell preparation alone had a median survival of 46 days, Seventy-five percent of animals receivin g IL-2 followed by B7.1 gene-modified tumor vaccines were the only group to show complete tumor-free survival at day 60, All of these surviving animal s rejected the parental MBT-2 tumor rechallenge and survived at day 120 wit h a high CTL response. In conclusion, liposome-mediated transfection demons trates a clear advantage as compared with the retroviral system in the MBT- 2 model. Multi-agent as opposed to single-agent cytokine gene-modified tumo r vaccines were beneficial, These "targeted" sequential vaccinations using IL-2 followed by B7.1 gene-modified tumor cells significantly increased a s ystemic immune response that translated into increased survival.