SLAMF7 in Primary Effusion Lymphoma, Target for Individualized Therapy?

Primary effusion lymphoma (PEL) is a rare, aggressive form of B-cell lymphoma. With a median survival time of around six months the prognosis for PEL patients is poor. Therefore, there is a medical need for novel therapeutic strategies.

We performed expression array analysis to find potential targets for antibody-based therapy. Unsupervised clustering analysis revealed that PEL cell lines grouped separate from cell lines derived from other B-non Hodgkin lymphoma (B-NHL) entities. Notably, PEL and Hodgkin Lymphoma (HL) cell lines clustered on one arm, separate from all cell lines representing less-differentiated B-NHL variants.

PEL and HL cell lines were characterized by a set of common up- and downregulated genes. Typical for PEL and HL was the expression of CCND2 and the absence of Brutons tyrosine kinase and of B-cell markers including CD19, CD20, CD79A and CD79B.

Highly expressed in PEL - but not in HL - were CD138, IL-10, SLAMF7 and PRDM1. PRDM1/BLIMP1 is a master regulator of terminal B-cell differentiation. Originally described as repressor, BLIMP1 can also enhance transcription of SLAMF7 in multiple myeloma (MM) and of IL-10 in type 1 regulatory T-cells. Thus, coexpression of the three genes suggests a causal relationship between transcriptionally active PRDM1/BLIMP1 and its targets SLAMF7 and IL-10 also in PEL.

Expression of SLAMF7 in PEL is especially noteworthy because a monoclonal antibody targeting SLAMF7 (elotuzumab) has been approved for treatment of patients with MM. We observed that SLAMF7 is comparably expressed in PEL and in MM cell lines. If the results on cell lines can be translated to primary PEL, i.e. if PEL tumor cells express SLAMF7, the patients might benefit from an antibody-based targeted therapy against this antigen.