Abstract
Monosodium urate (MSU) crystals have been reported to evoke specific cell immunity and to work as an adjuvant in a mouse model. The crystals also have another unique characteristic to bind with positively charged proteins, which could help to deliver some antigens into human dendritic cells (DC). We focused on the application of MSU crystals as not only an adjuvant but also as a carrier of positively charged antigenic protein to induce human cytotoxic T cells (CTL) efficiently in vitro. We selected human leukocyte antigen (HLA)-A2 expressing the multiple myeloma IM-9 cell line and its product idiotype (Id) protein as one of the best pairs of target cells and positively charged tumor-specific antigen, respectively. Following the sensitization of DC derived from HLA-A2-positive volunteers pulsed with tumor-specific monoclonal immunoglobulin G-Fab fragments (IM-9 Fab) attached to MSU crystals, the DC-stimulated CD8(+) T cells killed significantly more target cells (40.1 +/- 1.7%) than those stimulated by DC pulsed with MSU crystals alone (6.2 +/- 8.6%, P < 0.01) or IM-9 Fab alone (4.7 +/- 8.1%, P < 0.01). These cytotoxic effects of the DC-stimulated CD8(+) cells were reduced when MSU crystals were precoated with fetal bovine serum. In addition, we confirmed that MSU crystals facilitated human DC to express the maturation marker, CD83 and deliver (Fab')(2), attaching to the crystals by flow cytometer analysis. MSU crystals have distinct advantages of a protein carrier binding with positively charged proteins and delivering antigenic protein into DC, as well as an adjuvant promoting DC maturation and inducing CTL.