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BACKGROUNDSerologic measurement of antibodies to Epstein–Barr virus (EBV) immunoglobulin A/viral capsid antigen (IgA/VCA) and early antigen (IgA/EA) has been used widely to screen for nasopharyngeal carcinoma (NPC) in China. Recently, it was found that plasma EBV DNA concentration is an indicator for the staging and prognosis of patients with NPC. To determine whether there is a correlation between plasma EBV DNA levels and serum levels of IgA/VCA, the authors measured both in patients with NPC and in a control group.METHODSReal‐time polymerase chain reaction was used for quantitative analysis of plasma EBV DNA concentration, and enzyme‐linked immunoadsorbent assay was used to measure EBV VCA/IgA in patients with primary NPC (n = 120 patients), locally recurrent NPC (n = 8 patients), and distant metastatic NPC (n = 21 patients) among 76 patients with NPC after the completion of radiotherapy, in 60 patients with NPC in clinical remission, in 38 patients with non‐NPC tumors, and in 47 control individuals.RESULTSThe median plasma EBV DNA levels were 6200 copies/mL, 9200 copies/mL, and 2050 copies/mL in patients with primary, locally recurrent, and distant metastatic NPC, respectively, but declined to 0 copies/mL in patients with clinically remissive NPC, in patients who completed radiotherapy, in patients with non‐NPC tumors, and in the control group. In contrast, EBV VCA/IgA titers and detection rates remained high in all NPC groups. Plasma EBV DNA levels were significantly higher in patients who had serum VCA/IgA titers ≥ 1:640 (median, 83,450 copies/mL) compared with the levels in patients who had titers ≤ 1:320 (median, 17,200 copies/mL). Patients with NPC who had advanced TNM stage (Stages III and IV; median, 8530 copies/mL) and T classification (T3 and T4 tumors; median, 8530 copies/mL) had significantly higher plasma EBV DNA levels compared with patients who had early TNM stage (Stages I and II; median, 930 copies/mL) and T classification (T1 and T2 tumors; median, 3700 copies). Patients who had advanced TNM stage NPC had significantly higher mean VCA/IgA titers (1:424) compared with patients who had early TNM stage NPC (1:246), but there was no correlation between IgA/VCA titer and T or N classification of NPC.CONCLUSIONSThe results suggest that plasma EBV DNA detection is a more sensitive and specific marker than the serum IgA/VCA titer for the diagnosis and monitoring of patients with NPC. These findings provide convincing evidence for the use of plasma EBV DNA measurements for the early diagnosis and staging of NPC as well as for monitoring recurrence and metastasis of this tumor. Cancer 2004. © 2004 American Cancer Society.

SummaryEpstein-Barr virus (EBV) is a B lymphotropic herpesvirus of humans that elicits strong HLA class I-restricted cytotoxic T lymphocyte (CTL) responses. An influence of such responses on virus evolution was first suggested by our finding that EBV isolates from the highly HLA Allpositive Papua New Guinea (PNG) population carried a lys-thr mutation at residue 424 of the nuclear antigen EBV-encoded nuclear antigen (EBNA4) that destroyed the immunodominant target epitope for All-restricted CTL recognition. Here we turn to a much larger population, Southern Chinese, where the All aUde is again present in over 50% of the individuals. Each of 23 EBV isolates analyzed from this population were also mutated in the EBNA4 416-424 epitope, the mutations sdectively involving one of the two anchor residues in positions 2 (417 val-leu) or 9 (424 lys-asp, -arg or -thr) that are critical for All-peptide interaction. The majority of the Chinese isolates and all 10 PNG isolates also carried mutations affecting positions 1 and 2 of the next most immunodominant All-restricted epitope, EBNA4 residues 399-408. These changes dearly affected antigenidty since All-positive lymphoblastoid cell lines (LCLs) carrying these mutant EBV strains were not recognized by All-restricted CTLs raised against the prototype B95.8 virus. Furthermore, Chinese donors naturally infected with these mutant viruses did not mount detectable All-restricted CTL responses on in vitro stimulation with autologous LCL cells carrying either the B95.8 or their endogenous EBV strain. In two different highly Allpositive populations, therefore, immune pressure appears to have sdected for resident EBV strains lacking immunodominant All-restricted CTL epitopes.

Similarly to other mammalian and avian retroviruses that lack a transforming gene, moloney murine leukaemia virus (MoMuLV) causes no morphological transformation in infected tissue culture cells. However, following injection in an appropriate animal host, MoMuLV induces mainly thymic lymphomas after a long latency period. A common characteristic of neoplasms induced by retroviruses lacking transforming genes is their clonal origin. Here we have generated MoMuLV-induced rat thymic lymphomas and confirmed their clonal nature. Furthermore, we took advantage of the clonality of these tumours to investigate the specificity of provirus integration in the tumour DNA. We reasoned that if several independently derived thymic lymphomas would contain the provirus integrated in the same region of cellular DNA, this would be a strong indication that this integration event is a contributing factor in oncogenesis. The results indicate that there is indeed a cellular DNA region (termed the MLVI-1 locus) that serves as the substrate for proviral DNA integration in 5 out of 16 tumours we examined.