Potential Therapeutic Targets in Plasma Cell Disorders: A Flow Cytometry Study

The discovery of new targets for tailored therapy is a major improvement in oncology, and tools for the rapid and reliable detection of these targets are essential. Clinical trials demonstrated the benefit of recently developed antibodies against antigens on malignant B-cells. The aim of this study was to assess patients with plasma cell (PC) disorders for expression of antigens on malignant PCs that have exhibited promise in targeted cancer therapy. We retrospectively analyzed the expression of CD20, CD22, CD27, CD30, CD38, CD52, CD81, CD138, and SLAMF7 on PCs by flow cytometry in 103 patients with PC disorders. Furthermore, we studied cytogenetic data to correlate immunophenotyping and genetic parameters. The expression frequency of CD22, CD30, and CD52 was similar to other studies (12-35%, 0-19%, and 0-8%, respectively). Unexpectedly, we observed a high CD20 expression frequency in 37% of all AL-amyloidosis cases. The presence of t(11;14) correlated positively with CD20 expression on PCs in AL-amyloidosis (p=0.018). Furthermore, the expression level of SLAMF7 was decreased in advanced PC disorders (p=0.025) and a diminished expression of SLAMF7 is associated with low expression of CD27 and CD81 on malignant PCs in newly diagnosed multiple myeloma. This study provides a contribution to targeted therapy options in PC disorders. Particularly, the results put an emphasis on CD20 as therapeutic target in AL-amyloidosis. Regarding the therapeutic options of the SLAMF7 antibody elotuzumab, these data advise that analysis of SLAMF7 expression before application of elotuzumab might help to estimate the efficacy of elotuzumab in clinical trials. (C) 2015 International Clinical Cytometry Society