Monosodium Urate Crystal as a Carrier for Idiotype Tumor Vaccine.

Monosodium urate (MSU) crystal works as a danger signal to evoke specific cell immunity. It stimulates dendritic cells (DCs) maturation and enhances the generation of cytotoxic T cells (CTL), so that it could help specific immune therapy for tumor. On the other hand, MSU crystals are found to attach IgG in gouty arthritis and has been reported that the site of attachment is the Fab moiety of IgG. We focused on the application of MSU as a carrier of IgG idiotype protein to induce cytotoxic T cells to cell line producing the idiotype protein. Multiple myeloma cell line, IM-9, which is characterized by having HLA-A2 and producing monoclonal IgG-k protein, was used as a target cell. Monoclonal Fab fragments were used as idiotype protein; those were made by digesting with papain of IgG collected from the medium harvesting IM-9 cells. MSU crystals were made by sitting at refrigerator of uric acid dissolved by sodium hydroxide solution with boiling. Allogenic dendritic cells were derived from monocytes in peripheral blood of HL-A matched volunteer by treatment with GM-CSF and IL-4. They were pulsed by MSU attached with Fab fragments (MSU-Fab), by Fab fragments (Fab), or by none. Following education by pulsed DCs to CD3⁺ T cells collected from peripheral blood of same volunteer, CD8⁺ T cells were collected and were used as effector cells. Cell cytotoxic ability of the effector cells was determined by lactate dehydrogenase release assay under mixed culture of the target cells and the effector cells (CD8⁺ cells: IM-9 cells = 5: 1). Compared to Fab, MSU-Fab were easily phagocytosed by DCs. DCs pulsed with MSU-Fab or MSU were induced to express CD83 molecule, a marker for mature human blood dendritic cells, whereas neither Fab-pulsed nor untreated-control DCs did not express CD83 molecule. CD8⁺ T cells educated by DCs pulsed with MSU-Fab significantly killed more IM-9 myeloma cells than CD8⁺ T cells educated by DCs pulsed with MSU, DCs pulsed with Fab or DCs alone. These cytotoxic effect of CD8⁺ T cells educated by DCs pulsed with MSU-Fab were reduced when MSU crystals were bathed 10% fetal bovine serum solution before mixing with Fab in order to block MSU to be attached with Fab. The present study revealed that MSU crystals work as carrier of idiotype tumor vaccine not only by facilitating the utilization of the vaccine protein in DCs but also by enhancing the ability to induce tumor specific CTL. The safety and efficacy of MSU-Fab idiotype vaccine will be determined by clinical setting in patients with multiple myeloma.