Abstract A50: Epstein-Barr virus in the putative stem cell fraction of some multiple myeloma cell lines.

Abstract

Abstract Epstein-Barr virus (EBV) associated cancers have traditionally been thought to harbor the viral genomes as nuclear plasmids in all or nearly all of a patient's tumor cells as determined by in situ hybridization (ISH). We discovered EBV in 4 out of 7 standard multiple myeloma (MM) cell lines. In these positive cell lines, EBV was found in only a subpopulation of cells. For example, in MM.1S (a MM cell line) less than 1% of the cells harbored viral DNA as determined by limiting dilution PCR. These rare infected cells carried approximately 20 EBV copies. Fluorescence in situ hybridization (FISH) confirmed the presence of multiple copies of the EBV genome in rare cells. Immunofluorescence similarly detected the presence of viral genomes expressing EBV nuclear antigen (EBNA) - 1 and 2 in rare cells. Reverse transcriptase PCR confirmed EBNA1 and EBNA2 viral RNA expression. The cells that harbor virus are phenotypically distinct CD19+CD138− B cells. The phenotype overlaps with that identified as a MM cancer stem cell population. Viral genomes were not detected in the plasma cell-like population (CD19−CD138+). The results are consistent with the possibility that EBV is present in MM cancer stem cells in some MM cell lines and that virus is lost as these MM cancer stem cells with a B cell-like phenotype differentiate into plasma cells. Introduction of a dominant negative shRNA of the EBV EBNA-1, a protein essential for viral replication, decreased the proliferation of only the MM cell lines which were positive for EBV. Insertion of the dominant negative EBNA-1 shRNA had no effect on EBV negative MM cell lines, suggesting that EBV plays a role in the growth kinetics of cell lines even when present in a tiny percentage of cells. These results suggest that in some MM lines, EBV is harbored in a B cell-like progenitor population that overlaps with the putative cancer stem cell fraction. The loss of EBV inhibits cell proliferation and that EBV is lost during the B-cell to plasma cell differentiation process. The results presented here suggest that identifying the EBV status of MM patients prior to treatment might lead to a more efficient course of therapy. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A50. Citation Format: Sunetra Biswas, Meir Shamay, Courtney M. Shirley, Raluca Yonescu, William H. Matsui, Ivan Borrello, Richard J. Jones, Richard F. Ambinder. Epstein-Barr virus in the putative stem cell fraction of some multiple myeloma cell lines. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A50.