Stimulation of Herpesvirus saimiri expression in the absence of evidence for type C virus activation in a marmoset lymphoid cell line

The superantigen-homologous viral immediate-early gene ie14/vsag in herpesvirus saimiri-transformed human T cells

Herpesvirus saimiri C488 transforms human T lymphocytes to stable growth in culture. The growth-transformed human T cells harbor the viral genome in a nonintegrated episomal form without production of virus particles. In these cells, virus gene expression was previously found to be confined to the transforming genes stpC and tip. In order to analyze virus gene expression in more detail, we applied a subtractive hybridization technique and compared stimulated virus-transformed cells with uninfected parental T cells of the same donor. A number of known T-cell activation genes were isolated. Viral stpC/tip cDNAs were enriched after subtraction. In addition, the viral immediate-early, superantigen-homologous gene ie14/vsag was represented by numerous cDNA clones that comprised the entire spliced transcript. Whereas a weak basal expression of ie14/vsag was detected by reverse transcription-PCR only, the phorbol ester-induced transcripts were readily shown by Northern blotting. ie14/vsag, which before had been classified as a major immediate-early gene of herpesvirus saimiri, is localized within a highly conserved region with extensive homologies to the cellular genome. Mutant viruses without the ie14/vsag gene are replication competent and fully capable of transforming human and marmoset T cells. Since ie14/vsag is transiently expressed after stimulation, it may increase T-cell proliferation in an activation-dependent and superantigen-like but apparently Vbeta-independent way.

Regulation of the herpesvirus saimiri oncogene stpC, similar to that of T-cell activation genes, in growth-transformed human T lymphocytes

Herpesvirus saimiri strain C488, a T-cell tumor virus of New World primates, transforms human T lymphocytes to stable interleukin-2-dependent growth without need for further stimulation by antigen or mitogen. The transformed cell lines show the phenotype of activated mature T cells and retain many essential features of the primary parental cells, e.g., antigen specificity. In contrast to transformed New World monkey T cells, the human lines do not support lytic growth of the virus, even after chemical stimulation. Here we show that many viral genes remain silent during episomal persistence. However, the viral oncogene stpC is predominantly transcribed and translated to a stable cytoplasmic protein of 20 kDa that is heterogeneously expressed in individual cells. This 1.7-kb mRNA is bicistronic, encoding also Tip, a viral protein interacting with the T-cell-specific tyrosine kinase Lck. stpC/tip transcripts are heavily induced upon stimulation by mitogen or phorbol ester. Block of protein synthesis does not abolish transcription: treatment with cycloheximide greatly induces stpC/tip mRNA levels. Thus, this gene complex is regulated similarly to early T-cell activation genes. Constitutive and induced expression engage different transcription start sites. The T-cell regulation of the viral genes stpC and tip may contribute to the T-cell tropism of growth transformation by herpesvirus saimiri.

Characterization of a spontaneous undifferentiated carcinoma from an African green monkey (Cercopithecus aethiops)

An adult male African green monkey (Cercopithecus aethiops) with an undifferentiated carcinoma, probably originating from the nasal mucosa, was received from the Akron, Ohio zoo. Cultivation of this tumor in vitro resulted in a mixture of fibroblastic and epithelial cells which was subsequently separated using differential trypsinization. The neoplastic nature of the cultured epithelial cells was verified by their ability to transplant into athymic nude, or antithymocyte serum-treated mice, where poorly differentiated carcinomas were produced, and cultures of the tumors that arose in nude mice were morphologically similar to pretransplantation cultures. Early cultures showed a normal male karyotype characteristic of the species; however, in long-term cultures, a clearly defined, small submetacentric Y chromosome was not observed. Electron microscopic examination of tumor tissue and cultured tumor cells revealed desmosomes and the presence of cytoplasmic (keratin-type) fibrils, which tended to be organized around the nucleus. In addition to the keratin-type fibrils, the cultured tumor cells also contained a large amount of cytoplasmic inclusion material that may represent keratohyalin granules. There was no evidence of a viral association with tumor material or cultured cells. The cultures were susceptible to infection by vesicular stomatitis virus, Herpesvirus hominis type 1, and H. saimiri, but were resistant to the Epstein-Barr virus.

Augmentation of lymphocyte cytotoxicity by antibody to herpesvirus saimiri associated antigens

Sera from owl monkeys infected with Herpesvirus saimiri (HVS) mediated antibody-dependent lymphocyte cytotoxicity (ADLC) against virus-infected owl monkey kidney cells. Peripheral blood lymphocytes from rhesus monkeys served as effector cells in this cytotoxic assay. ADLC titers increased along with membrane immunofluorescence (MF) titers but among some sera, the ADLC titers were much higher than expected from the MF titers, suggesting that multiple serum factors were involved in mediating ADLC in this system. Absorption of both low and high titered sera with HVS-infected owl monkey kidney cells removed all ADLC activity. Preliminary results from serial serum samples from two infected monkeys that developed leukemia and/or lymphoma demonstrated that ADLC but not MF titers increased to high titers with progression of disease and followed essentially a different kinetic pattern than that noted by MF. The possible significance of these findings in relation to malignant disease induced by this virus is discussed.