Epstein-Barr virus (EBV) antigens in tumor tissue define associations of virus with human malignancies and provide clues as to mechanisms of viral oncogenesis. In Burkitt's lymphoma, EBV markers are absent from 85% of sporadic cases and 4% of endemic (African) cases, raising questions as to the exact role EBV in the disease. Standard screening criteria may be insufficient to determine the EBV status of all tumors. One of 9 tumors from American patients expressed EBV nuclear antigen 1 (EBNA1) and contained standard episomal EBV DNA, making this series consistent with the 15% EBV association traditionally ascribed to sporadic Burkitt's lymphoma. Surprisingly, 3 tumors without detectable EBNA1 contained partial EBV genomes. Identification of defective, integrated viral DNA in some tumors indicates greater involvement of virus in sporadic Burkitt's lymphoma than previously documented and suggests a process of viral DNA rearrangement and loss during malignant progression most consistent with an initiating role for EBV in tumorigenesis.

Varicella-zoster virus (VZV) expresses at least six viral transcripts during latency. One of these transcripts, derived from open reading frame 63 (ORF63), is one of the most abundant viral RNAs expressed during latency. The VZV ORF63 protein has been detected in human and experimentally infected rodent ganglia by several laboratories. We have deleted >90% of both copies of the ORF63 gene from the VZV genome. Animals inoculated with the ORF63 mutant virus had lower mean copy numbers of latent VZV genomes in the dorsal root ganglia 5 to 6 weeks after infection than animals inoculated with parental or rescued virus, and the frequency of latently infected animals was significantly lower in animals infected with the ORF63 mutant virus than in animals inoculated with parental or rescued virus. In contrast, the frequency of animals latently infected with viral mutants in other genes that are equally or more impaired for replication in vitro, compared with the ORF63 mutant, is similar to that of animals latently infected with parental VZV. Examination of dorsal root ganglia 3 days after infection showed high levels of VZV DNA in animals infected with either ORF63 mutant or parental virus; however, by days 6 and 10 after infection, the level of viral DNA in animals infected with the ORF63 mutant was significantly lower than that in animals infected with parental virus. Thus, ORF63 is not required for VZV to enter ganglia but is the first VZV gene shown to be critical for establishment of latency. Since the present vaccine can reactivate and cause shingles, a VZV vaccine based on the ORF63 mutant virus might be safer.Acute infection with varicella-zoster virus (VZV) causes chickenpox. The virus spreads throughout the body and infects the nervous system. Latent infection is established in dorsal root and cranial nerve ganglia, and the virus can subsequently reactivate and cause zoster (shingles). Several VZV gene products have been shown to be expressed during latency. Transcripts encoding VZV open reading frame 4 (ORF4), ORF21, ORF29, ORF62, ORF63, and ORF66 (3, 4, 10, 21) have been detected in latently infected human ganglia. ORF63 transcripts are among the most abundant VZV mRNAs expressed during latency in some studies and have been detected in 47 to 86% of human ganglia (4, 10). ORF63 mRNA is also one of the most frequently expressed viral genes in latently infected rodent ganglia (11,25).The ORF63 protein has been detected in neurons of latently infected human (10,18,20) and rodent (6, 11) ganglia. The protein is present in the cytoplasm of neurons during latency; however, during reactivation and in cell culture, the protein is present in both the nucleus and cytoplasm (18,20,25). VZV ORF63 is expressed as an immediate-early protein and is present in virions (13). While earlier studies reported conflicting results about the transregulatory activity of ORF63 (8, 14), Bontems et al. (1) found that in transient-expression assays ORF63 repressed the VZV thymidine kinase and DNA polymerase promoters. Repression of viral ...

Life-long viral persistence is a hallmark of human herpesvirus infection. In the Epstein-Barr virus (EBV)-positive Burkitt's lymphoma (BL) cell line, Mutu, spontaneous loss of all viral episomes accompanied productive viral DNA replication. The molecular configuration of intracellular EBV DNA evolved from monoclonal episomes in cells retaining the original tumor phenotype to predominantly replicating linear DNA and, subsequently, only integrated forms in BL cells that had acquired the lymphoblastoid cell phenotype. Transient appearance of deleted, rearranged WZhet EBV DNA capable of disrupting viral latency, along with the integration of viral DNA into human chromosomes, indicates a genetic instability in the host cell which, if duplicated in vivo, may affect configuration and persistence of the viral genome in expanding malignant cell clones.

A series of nonnucleoside, N-␣-methylbenzyl-N-arylthiourea analogs were identified which demonstrated selective activity against varicella-zoster virus (VZV) but were inactive against other human herpesviruses, including herpes simplex virus. Representative compounds had potent activity against VZV early-passage clinical isolates and an acyclovir-resistant isolate. Resistant viruses generated against one inhibitor were also resistant to other compounds in the series, suggesting that this group of related small molecules was acting on the same virus-specific target. Sequencing of the VZV ORF54 gene from two independently derived resistant viruses revealed mutations in ORF54 compared to the parental VZV strain Ellen sequence. Recombinant VZV in which the wild-type ORF54 sequence was replaced with the ORF54 gene from either of the resistant viruses became resistant to the series of inhibitor compounds. Treatment of VZV-infected cells with the inhibitor impaired morphogenesis of capsids. Inhibitor-treated cells lacked DNA-containing dense-core capsids in the nucleus, and only incomplete virions were present on the cell surface. These data suggest that the VZV-specific thiourea inhibitor series block virus replication by interfering with the function of the ORF54 protein and/or other proteins that interact with the ORF54 protein.Varicella-zoster virus (VZV) causes a disseminated primary infection, chickenpox, and later may reactivate to cause herpes zoster, commonly known as shingles (3,26). Herpes zoster can result in pain lasting over 1 month from the onset of the rash, termed postherpetic neuralgia (PHN). PHN is often a debilitating condition that is quite difficult to treat (15,32,33).Acyclovir (ACV), valaciclovir, and famciclovir are the primary antivirals used for treating VZV infections in both immunocompetent and immunocompromised individuals (25). Unfortunately, despite these medications, PHN remains a major problem, and the currently available drugs have a limited effect on prevention of this condition. Thus, there is a need for additional, more effective medications to treat herpes zoster in adults.The development of antiviral resistance remains a concern, particularly when treatment relies on only a small number of approved drugs with common modes of action (13,14,25,26). ACV, valaciclovir (which is metabolized to acyclovir), and famciclovir (the prodrug of penciclovir) are all phosphorylated by the viral thymidine kinase as an initial step for intracellular activation. They are subsequently phosphorylated by cellular kinases, and the activated compounds inhibit the viral DNA polymerase. Sorivudine and brivudine are also potent inhibitors of VZV, and although they represent a different class of nucleoside analogues from ACV, they also require phosphorylation by the viral thymidine kinase for activation (18,31). While thymidine kinase-deficient VZV can be treated with foscarnet, a direct inhibitor of the viral DNA polymerase (25), this drug requires intravenous administration and has a marked potential for...