Native anti-tumor responses elicited by immunization with a low dose of unmodified live tumor cells.

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 10(4) live dendritic cells (DC)-FO fusion cells or 10(3) live FO cells. 80% of vaccinated mice survived from the later challenge with 1 x 10(6) 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-gamma 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.