Immune responses towards malignant plasma cells have clearly been demonstrated in the course of monoclonal B cell dyscrasias and shown to be mostly specific for idiotypic determinants of the monoclonal immunoglobulin (Ig). These responses are specifically efficient against lymphoma cells expressing a membrane form of the monoclonal Ig. In myeloma, such immune responses are often weak and a number of strategies are currently assayed in order to boost the cell-mediated responses against the secreted monoclonal Ig. The use of cytokines promoting Th1 responses could be helpful for the induction of anti-tumour immunity and the control of residual disease in patients treated with myeloablative therapy, and such strategies need to be evaluated. In a light chain myeloma model where the monoclonal Ig can only be secreted, we tried to induce protective immune responses through immunization of animals with transfected malignant plasma cells. An expression plasmid encoding GM-CSF and IL-12 proved to be highly efficient for the induction of both cytotoxic and proliferative responses after immunization of animals with transfected and irradiated tumour cells. Anti-tumour immunization according to this protocol was successful in protecting 93.4% of the animals against a subsequent tumour challenge.
