Clinical Utility of Slam Family Member CD229 in Identifying Tumor Cells and High-Risk Disease Markers, CD86 (B7-2) and CD126 (IL-6 receptor), Using Flow Cytometric Analysis in Multiple Myeloma

Introduction: The immunophenotypic analysis of plasma cells using flow cytometry (FCM) is useful for the diagnosis for multiple myeloma (MM) and the detection of MM cells after treatment. CD138 is a well-known surface marker identifying plasma cells, although decreased CD138 expression on plasma cells is frequently observed in MM patients with relapsed or progressive disease. Thus, more stable MM antigens are needed. The SLAM family molecule CD229 has recently been reported to be specifically overexpressed on MM cells including their clonogenic precursors, suggesting that it may be a good marker to identify MM cells. Furthermore, some surface antigens, i.e., costimulatory molecule CD86 (B7-2), its receptor CD28, IL-6 receptor (CD126), insulin-like growth factor-1 (CD221), and coinhibitory molecule B7-H1 (PD-L1, CD274), were reported to be associated with poor prognosis. This study aimed to validate the potential of CD229 as a new MM cell marker and the efficacy of immunophenotypes on MM cells as prognostic markers in a multicenter study.