Exosomes Derived from Burkitt’s Lymphoma Cell Lines Induce Proliferation, Differentiation, and Class-Switch Recombination in B Cells

Abstract

Exosomes, nano-sized membrane vesicles, are released by various cells and are found in many human body fluids. They are active players in intercellular communication and have immune-suppressive, immune-regulatory, and immune-stimulatory functions. EBV is a ubiquitous human herpesvirus that is associated with various lymphoid and epithelial malignancies. EBV infection of B cells in vitro induces the release of exosomes that harbor the viral latent membrane protein 1 (LMP1). LMP1 per se mimics CD40 signaling and induces proliferation of B lymphocytes and T cell–independent class-switch recombination. Constitutive LMP1 signaling within B cells is blunted through the shedding of LMP1 via exosomes. In this study, we investigated the functional effect of exosomes derived from the DG75 Burkitt’s lymphoma cell line and its sublines (LMP1 transfected and EBV infected), with the hypothesis that they might mimic exosomes released during EBV-associated diseases. We show that exosomes released during primary EBV infection of B cells harbored LMP1, and similar levels were detected in exosomes from LMP1-transfected DG75 cells. DG75 exosomes efficiently bound to human B cells within PBMCs and were internalized by isolated B cells. In turn, this led to proliferation, induction of activation-induced cytidine deaminase, and the production of circle and germline transcripts for IgG1 in B cells. Finally, exosomes harboring LMP1 enhanced proliferation and drove B cell differentiation toward a plasmablast-like phenotype. In conclusion, our results suggest that exosomes released from EBV-infected B cells have a stimulatory capacity and interfere with the fate of human B cells.

Exosomal Communication Goes Viral

“…Computational analysis of the differentially expressed proteins predicted that LMP1-modified exosomes would affect molecular and cellular functions of cell growth and proliferation, cellular movement, cell death and survival, development, and cell-to-cell signaling (2). These predictions were corroborated by three independent studies demonstrating that LMP1-modified exosomes do indeed enhance proliferation, migration, invasion, and B cell differentiation toward a plasmablast-like phenotype when incubated with noninfected cells (13)(14)(15). Together, these data suggest that EBV-infected cells can manipulate the tumor microenvironment and contribute to the pathogenesis of EBV-associated cancers through the transfer of LMP1-modified exosomes.…”

Uptake of lymphoma-derived exosomes by peripheral blood leukocytes

“…In our study model, B cells showed a high level of uptake, possibly due to the B cell origin of the lymphoma exosomes, supporting the idea of uptake specificity given the exosomes were collected primarily from cells originating from B cell lymphoma disease. These findings are in line with those of Hazan-Halevy et al 45 and Gutzeit et al 54 concerning B cells and Riches et al 55 in their work with breast tissue. In this study, we observed that DLCL2 exosomes were taken up rapidly and preferentially into CD19+ B lymphocytes and CD14+ monocytes.…”

The cell survival pathways of the primordial RNA-DNA complex remain conserved in the extant genomes and may function as proto-oncogenes

“…In contrast, it is a widely accepted view that exosomes derive from cytoplasmic vesicles. Be a Burkitt's lymphoma cell or a prostatic adenocarcinoma cell, their exosomes are visibly generated in cytoplasmic vesicles [113,116,119]. However, exosome genomics are characterized by the presence of all classes of microRNAs that must have derived from the nucleolus, the physiological site where ribosomes are generated.…”

“…All cells, but excessively the dedifferentiated cancer cells, release exosomes. Examples here are Burkitt's lymphoma [113], glioblastoma [114,115] (Fig. 5), and prostatic adenocarcinoma [116] exosomes.…”