Development and pre-clinical evaluation of a BCG-MUC1-based novel breast cancer vaccine

Despite aggressive therapy, breast cancer still has a mortality rate of 25%. Therefore, the development of an effective vaccine may be beneficial for the prevention or adjuvant treatment of this malignancy. We have constructed a novel breast cancer vaccine, BCG-hIL2MUC1, that was designed to preferentially stimulate a Th1 immune response. BCG-hIL2MUC1 consists of BCG that express a truncated form of MUC1 and human interleukin-2 (hIL2). In vitro analysis of BCG-hIL2MUC1 by restriction enzyme mapping, DNA sequencing, and Western blot analysis confirmed the expression of MUC1 and hIL2. The immune response to BCG-hIL2MUC1 was evaluated in SCID mice. SCID mice reconstituted with 50 × 106 human peripheral lymphocytes (hu-PBL-SCID) received three biweekly injections of BCG-hIL2MUC1 (0.5 cfu) and the serum and lymphocyte populations analyzed two weeks after the third immunization. Control animals received PBS, MUC1 peptide (100μg) or BCG-261 (0.5 cfu) vaccination. Flow cytometry documented the increased lymphocyte expression of IL2α receptor on lymphocytes obtained from BCG-hIL2MUC1 immunized animals. These lymphocytes expressed IL2 when exposed to MUC1 peptide. There was minimal MUC1 antibody production. These results suggested that our vaccine had stimulated a Th1 immune response. The ability of BCG-hIL2MUC1 to inhibit breast cancer growth was then evaluated in hu-PBL-SCID mice. After immunization with 3 biweekly vaccinations of BCG-hIL2MUC1, hu-PBL-SCID mice were xenografted with 4 × 106 ZR75-1 human breast cancer cells. Control animals received PBS, MUC1 peptide or BCG-261 vaccination. Outcomes of interest were time to tumor detection and rate of tumor growth. All the animals receiving the control vaccines developed a tumor; only 75% of BCG-hIL2MUC1 immunized animals developed a palpable tumor. The rate of tumor growth was slower in the BCG-hIL2MUC1 immunized animals as compared to the control groups (p < 0.05). Histological analysis of the primary tumors in BCG-hIL2MU1 animals revealed areas of apoptosis and reduced MUC1 expression. Our results suggested that BCG-hIL2MUC1 immunization inhibited breast cancer growth in hu-PBL-SCID mice. This inhibition may be due to its ability to stimulate a Th1 immune response. BCG-hIL2MUC1 may be a promising candidate as a breast cancer vaccine.