Serum soluble CD86 levels correlate with CD86 variant 3 gene expression and are prognostic indicators in myeloma.

We previously showed that cell-surface CD86 expressed on multiple myeloma (MM) cells contributed to not only tumor growth but also antitumor cytotoxic T lymphocyte responses mediated by induction of IL-10-producing CD4+ T cells. The soluble form of CD86 (sCD86) was also detected in serum from patients with MM. Thus, to determine whether sCD86 levels are a useful prognostic factor, we investigated the association of serum sCD86 levels with disease progression and prognosis in 103 newly diagnosed MM patients. Serum sCD86 was detected in 71% of MM patients but only rarely in patients with monoclonal gammopathy of undetermined significance and healthy controls, and the level was significantly increased in advanced-stage MM. When we examined differences in clinical characteristics according to the serum sCD86 level, those in the high (≥2.18 ng/ml, n=38) group exhibited more aggressive clinical characteristics with shorter overall survival times in comparison with those in the low (<2.18 mg/ml, n=65) group. On the other hand, it was difficult to stratify MM patients into different risk groups based on cell-surface CD86 expression levels. Serum sCD86 levels were significantly correlated with the expression levels of CD86 variant 3 mRNA transcripts, which lack exon 6 resulting in a truncated transmembrane region, and its variant transcripts were upregulated in the high group. Thus, our findings suggest that sCD86 can be easily measured in peripheral blood samples and may be a useful prognostic marker in MM.