Certain newly established Epstein‐Barr virus‐containing Burkitt's lymphoma cell lines do not express the cytotoxic T‐lymphocyte‐detected membrane antigen (LYDMA) through which EBV infection is normally controlled by the host. When the EB virus recovered from these BL lines was used to transform peripheral blood lymphocytes from seronegative donors, the lymphoblastoid cell lines (LCLs) that arose were all LYDMA positive. This indicates that the LYDMA‐negative nature of the BLs is not the result of a mutation in the resident viral genome but is rather a specific adaptation in those cells, perhaps permitting evasion of the host immune surveillance in tumour development. A comparison of the EBV gene expression in six LYDMA‐negative and two LYDMA‐positive BL lines and in their corresponding LCLs revealed that several of the BL lines did not express all of the viral gene products classically associated with latent transformation by EBV. Four out of eight cell lines showed restricted expression of the latent membrane protein (LMP) and/or the EB nuclear antigen, EBNA 2. A new level of EBV gene regulation therefore appears to be operating in some of the BL cell lines. The patterns of expression of EBV genes in the cell lines did not show any correlation with the known susceptibility of the lines to T cell killing.

Epstein-Barr virus (EBV), a ubiquitous herpesvirus, induces potent HLA class I-restricted cytotoxic T-lymphocyte (CTL) responses. Analyses of target antigen choice have shown that the very strong CTL responses which are often observed through the HLA All allele map are due almost entirely to a single transformation-associated EBV protein, the nuclear antigen EBNA4. Here, we sought to determine the number and relative immunogenicities of HLA All-restricted epitopes within this 938-amino-acid protein. An initial screening with a series of recombinant vaccinia virus vectors encoding progressively truncated forms of EBNA4 was followed by peptide sensitization experiments using overlapping 14-or 15-mers from the entire sequence. These two approaches allowed the identification of five epitope regions located between residues 101 and 115, 416 and 429, 396 and 410, 481 and 495, and 551 and 564 of the EBNA4 molecule. CTL preparations from all seven HLA All-positive donors tested had demonstrable reactivities against the 416-to-429 peptide, whereas reactivities against the other epitopes either tended to be lost on serial passage or, for some of the donors, were never detected. The immunodominance of the 416-to-429 epitope was further supported by peptide dilution assays using polyclonal effectors and by CTL cloning experiments. Analysis of the 416-to-429 region identified the nanomer 416-424 (IVTDFSVIK) as the cognate peptide. This peptide was able to sensitize targets to lysis by All-restricted CTL clones at concentrations as low as 5 x 10-14 M.

The pathogenesis of Epstein-Barr (EB) virus-positive Burkitt's lymphoma (BL) appears to involve the combined actions of virus-induced B-cell proliferation, and a rare chromosomal translocation juxtaposing c-myc and immunoglobulin gene loci in a single B cell; holoendemic malarial infection in some way facilitates the oncogenic process. Outgrowth of the EB virus-positive tumour suggests either breakdown or evasion of those immune controls, in particular cytotoxic T-cell responses against the virus-induced lymphocyte-detected membrane antigen LYDMA, which limit virus-infected B-cell numbers in healthy virus carriers. Immunosuppression, such as that which malarial infection may induce, cannot itself be a sufficient explanation in this regard since our studies have identified a number of BL patients who retain detectable LYDMA-specific T-cell surveillance. The present work shows that in many cases of virus-associated BL, the emerging malignant clone is insensitive to such surveillance. Several EB virus-positive BL cell lines, recently established in vitro and expressing the class I histocompatibility locus antigens (HLAs) which restrict cytotoxic T-cell function, were not killed by HLA-matched LYDMA-specific effector populations in assays where the EB virus-positive lymphoblastoid cell line (LCL), derived from normal B cells of the same patient, sustained high levels of lysis.

In mice the cytotoxic T-cell response to several types of virus is influenced by genes within the major histocompatibility complex; in particular, genetic control is exercised at the effector cell level through a requirement that virus-specific cytotoxic T cells recognise viral antigens in association with H-2K and H=2D region gene products on the surface of infected cells. In man the restriction which the analogous HLA-A, -B and -C-region gene products might place on virus-specific T-cell function is still in dispute. The earliest and most controversial evidence concerns the Epstein-Barr virus (EBV), a B lymphotropic agent which causes infectious mononucleosis (IM) and which induces an unusually vigorous T-cell response; cytotoxic T cells from IM patients' blood were shown to be EBV-specific yet, in contrast to mouse systems, apparently free of any obvious HLA restriction. Since then T-cell recognition of EBV-infected B cells has assumed particular significance as a model system for the study of cytotoxic T-cell function in man. This report describes the results of a new approach clearly indicating that HLA-A and -B region products do indeed have a role in this system.