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Cyclical Expression of EBV Latent Membrane Protein 1 in EBV-Transformed B Cells Underpins Heterogeneity of Epitope Presentation and CD8⁺ T Cell Recognition¹

Cancer Research United Kingdom Institute for Cancer Studies, University of Birmingham, Birmingham, United Kingdom

CD8⁺ T cells specific for EBV latent cycle epitopes can be reactivated in vitro by stimulating with the autologous EBV-transformed B lymphoblastoid cell line (LCL). The resultant CD8⁺ clones kill epitope peptide-loaded targets, but frequently do not kill or show only low levels of lysis of the unmanipulated LCL in 5-h cytotoxicity assays. However, they reproducibly show clear LCL recognition in cytokine (IFN-) release assays and inhibit LCL outgrowth in long-term coculture assays. We show that this growth inhibition is not mediated by cytokines, but by slow killing detectable in extended cytotoxicity assays. The paradoxical earlier findings reflect the fact that cytokine assays are more sensitive indicators of Ag-specific recognition in situations in which the target population is heterogeneous at the single-cell level in terms of epitope display. Such heterogeneity exists within LCLs with, at any one time, subpopulations showing large differences in sensitivity to T cell detection. These differences are not cell cycle related, but correlate with differing levels of EBV latent membrane protein (LMP)1 expression at the single-cell level. In this study, LMP1 is not itself a CD8⁺ T cell target, but its expression enhances Ag-processing capacity and HLA class I expression. We propose that LMP1 levels fluctuate cyclically in individual cells and, over time, all cells within a LCL pass through a LMP1^high T cell-detectable phase.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by grants from the Medical Research Council and Cancer Research UK.

² Address correspondence and reprint requests to Prof. Alan B. Rickinson, Cancer Research-U.K. Institute for Cancer Studies, University of Birmingham, Vincent Drive, Edgbaston, Birmingham, B15 2TT, United Kingdom. E-mail address: a.b.rickinson{at}bham.ac.uk

³ Abbreviations used in this paper: EBNA, EBV nuclear Ag; CMA, concanamycin A; CSA, cyclosporin A; dox, doxycycline; LCL, lymphoblastoid cell line; LMP, latent membrane protein; mfi, mean fluorescence intensity; Z-KO, BZLF1 knockout derivative of rB95.8 virus.