The present study demonstrates that immunization with a low dose of unmodified live myeloma tumor cells (FO) elicited tumor-specific immunity. BALB/c mice were vaccinated with 104 live dendritic cells (DC)-FO fusion cells or 103 live FO cells. 80% of vaccinated mice survived from the later challenge with 1x106 FO cells, whereas all control mice developed tumors. Additionally, vaccination with live FO cells gave no protection against the growth of Lewis lung carcinoma cells in C57BL/6 mice. Cellular immunity was found to be primarily responsible for anti-tumor responses. In an adoptive immune model, the development of myeloma was greatly reduced by transfusion of lymphocytes but not sera from mice immunized with FO. T cells from immunized mice also induced lysis of FO cells in the cytotoxic T lymphocyte (CTL) assay. After co-culture with FO, IFN-γ released from immunized T helper cells increased >10-fold, while IL-4 remained unchanged in comparison with control T cells. These findings provided the first evidence that immunization with a low dose of unmodified live FO cells was safe to mice and capable of eliciting specific protective immunity against tumor growth.

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