Induction of anti-tumor immunity by lyophilized myeloma cells secreting GM-CSF.

We have previously demonstrated that a low dose of live myeloma FO cells induced a cellular immunity against tumor without additional modulating factors. In the present study, lyophilized myeloma FO cells were used to induce anti-tumor immunity. In a myeloma vaccination model, immunization with lyophilized myeloma FO cells alone induced a slight response. However, the immunity was dramatically enhanced by myeloma FO cells transfected with a recombinant adenovirus, Adv-1/GM-CSF. The immunocytochemical staining of Adv-1/GM-CSF transfected myeloma FO cells confirmed that more than 90% of cells were positive with GM-CSF expression. Results of sandwich ELISA showed the amount of secreted GM-CSF was 240 ng/24 h per 10(6) cells. Immunization with lyophilized myeloma FO cells secreting GM-CSF prevented the tumor growth in 60% of BALB/c mice. Antibodies against myeloma FO cells were found in the sera of immunized mice. Tumor-specific T-cell response was also evaluated using cytotoxic T lymphocyte assay. In conclusion, lyophilized myeloma FO cells secreting GM-CSF can be used as a potent vaccine to induce strong and protective anti-tumor immunity.