Isolation of a normal B cell subset with a Burkitt‐like phenotype and transformation in vitro with Epstein‐Barr virus

Abstract

Epstein-Barr virus (EBV) is causally linked with endemic Burkitt's lymphoma (BL), a tumor whose homogeneous cell surface phenotype suggests derivation from a particular subset of activated germinal centre B cells in vivo. Endemic BL also shows an unusual form of EBV infection with down-regulation of certain of the virus latent proteins which are constitutively expressed when EBV infects and transforms normal resting B cells in vitro. Here we question whether this virus:cell interaction is unique to malignant BL cells or whether it might be reproduced by in vitro infection of those particular germinal centre cells displaying the BL-like phenotype. Firstly, we show by biochemical means that a subset of normal tonsillar B cells does indeed express the globotriaosylceramide glycolipid BLA and the common acute lymphoblastic leukaemia antigen CALLA, 2 important markers of the BL phenotype. Secondly, using 2-colour immunofluorescence labelling with anti-BLA and anti-CALLA monoclonal antibodies (MAbs), 4 subsets of low buoyant density tonsillar B cells (BLA+ CALLA+, BLA+ CALLA-, BLA- CALLA+, BLA- CALLA-) have been separated by means of a FACS and tested for their susceptibility to EBV-induced growth transformation in a limiting dilution assay. The BLA+ CALLA+ (i.e., BL-like) subset contained the highest proportion of cells already actively in cycle in vivo and gave the lowest yield of transformants, perhaps reflecting the greater efficiency with which EBV transforms resting target cells. Of the cell lines established from the BLA+ CALLA+ population, a significant number retained BLA expression but CALLA was always lost. In 2 further respects, these lines resembled conventional in vitro transformants rather than lines of BL type; thus the cells expressed cellular "activation" antigens (CD23, CD39, CD30, Ki-24) characteristic of the lymphoblastoid phenotype and contained the full spectrum of EBV latent proteins.

Epstein-Barr virus infection in vitro can rescue germinal center B cells with inactivated immunoglobulin genes

“…of GC cell preparations in vitro produced lines with a typical LCL phenotype expressing all the latent antigens 18 ; indeed expression of the full spectrum of latent genes appears to be incompatible with retention of the GC phenotype. 19 Interest in viral infection of GC cells was reawakened by the observation that EBV-positive PTLD tumors, many of which had full latent antigen expression, often arise from B cells with atypical, even nonfunctional, IgH alleles.…”

CD40 ligand, Bcl-2, and Bcl-xL spare group I Burkitt lymphoma cells from CD77-directed killing via Verotoxin-1 B chain but fail to protect against the holotoxin

“…Both B cell tumors display a GC phenotype with the exception of follicular lymphoma being constitutively Bcl-2 positive due to the deregulation of the bcl-2 gene arising from the 14 : 18 translocation that characterizes this disease. 14,15,35,36 For any therapeutic modality to succeed against this most common of the lymphoma, it needs to overcome the powerful survival influence afforded to B cells by Bcl-2. Moreover, normally Bcl-2 negative BL cells can be prompted by extracellular signals to express the survival protein.…”

“…12 Based partly on their mutual expression of CD77, BL cells are now deemed to represent phenotypic tumor equivalents of normal GC B cells. 13,14 A large proportion of follicular lymphoma also appears to remain faithful to their normal counterparts by displaying CD77 on the tumor cell surface. 15 VT-1 is composed of an A subunit non-covalently associated with a pentamer of B subunits.…”

Population depletion activates autonomous CD154-dependent survival in biopsylike Burkitt lymphoma cells

“…[2][3][4][5][6] Another tumor bearing a GC B-cell phenotype is Burkitt lymphoma (BL), although here development is not constrained to conventional follicles. [7][8][9][10] Nevertheless, BL presents with a classical "starry sky" histology reflecting the presence of large infiltrating macrophages that are there to scavenge tumor cells entering apoptosis. 9,11,12 This feature of spontaneous apoptosis is a vestige of the tumor's GC origin in which the constitutive B cells need to be selected by antigen during the development of a memory response.…”