We have constructed a recombinant vaccine BCG-MUC1-IL2, which expresses high level of human MUC1 VNTR core protein and secretes functional IL2. MUC1 is a breast cancer-associated antigen that is known to stimulate immunological responses in human. Interleukin 2 (IL2) is a lymphocyte activator and growth factor. BCG is a strong immune adjuvant that has been used safely and effectively in preventing tuberculosis and treating multiple human cancers. We hypothesized that, by combining the cancer-associated antigen with immunologic activators, recombinant BCG-MUC1-IL2 will augment the MUC1-specific immune responses and tumor inhibition. A mouse melanoma cell line transfected with human MUC1 (B16/hMUC1) grown in a human MUC1 transgenic mouse (MUC1-Tg) was selected for testing this hypothesis. The mice were immunized subcutaneously with 3×104 CFU of BCG-MUC1-IL2 and boosted four weeks later. The immunized animals were then challenged with 1,000 B16/hMUC1 melanoma cells the day after the last immunization. Control animals received either BCG-vector or PBS according to the same schedule. The tumor growths in all three groups were monitored. The animals were sacrificed when the tumor reached the maximal allowed size or four weeks after control animal died of tumor growth. The splenocytes and serum were collected from individual animals and were used to study the MUC1-specific immunities by ELISPOT and ELISA. We found that mice immunized with BCG-MUC1-IL2 had significant delay in tumor appearance. The mice in PBS group all developed tumors (four out of four) in three weeks and were scarificed by the fifth week because tumor reached the maximum size (1.5 cm3) allowed by the approved protocol. Mice in the BCG-vector group developed tumor one week later than PBS group. In BCG -MUC1-IL2 group, only one mouse developed tumor after fifth week and no tumor was observed in remaining three mice. These mice were sacrificed for immunological study at the end of eighth week after tumor challenge. The BCG-MUC1-IL2 vaccine mediated immunity was determined by ELISPOT and ELISA. The results of ELISPOT indicated that the MUC1-specific INF-γ expressing splenocytes were increased only in mice immunized with BCG-MUC1-IL2, but not in mice treated with BCG-vector or PBS. The IL4 expressing splenocytes were induced by both BCG-MUC1-IL2 and BCG-vector. A high level of MUC1-specific IgG production was detected by ELISA in BCG-MUC1-IL2 group. These results suggest that the recombinant BCG-MUC1-IL2 induces not only MUC1-specific cellular and humoral immune responses but also tumor inhibition and it may serve as a vaccine for breast cancer prevention and treatment.
[Proc Amer Assoc Cancer Res, Volume 45, 2004]