Cytomegalovirus replication in cells pretreated with 5-iodo-2'-deoxyuridine

Stimulation of cellular DNA synthesis by human cytomegalovirus

Human cytomegalovirus (CMV) is able to induce cellular DNA synthesis in both permissive (human embryonic lung) and nonpermissive (Vero) cells. The induction of cell DNA synthesis was assayed by the incorporation of [methyl-(3)H]thymidine into macromolecules having the buoyant density characteristics of cell DNA. The DNA synthesis induced by CMV infection appears to represent normal semiconservative replication as opposed to repair synthesis. Both strains of CMV tested were capable of inducing cell DNA synthesis. Virus exposed to heat or UV light prior to infection lost the ability to induce DNA synthesis, indicating that a virus-coded function expressed after infection is responsible for stimulation of cell DNA synthesis.

Characterization of an antisense transcript spanning the UL81-82 locus of human cytomegalovirus

In this study we present the characterization of a novel transcript, UL81-82ast, UL81-82 antisense transcript, and its protein product. The transcript was initially found in a cDNA library of monocytes from a seropositive donor. mRNA was obtained from monocytes isolated from a healthy donor with a high antibody titer against human cytomegalovirus (HCMV). The mRNAs were cloned into a lambda phage-derived vector to create the cDNA library. Using PCR, UL81-82ast was amplified from the library. The library was tested for the presence of numerous HCMV genes. Neither structural genes nor immediate-early genes were found. UL81-82ast was detected in five bone marrow samples from healthy antibody-positive donors. This same transcript was also found in in vitro-infected human fibroblasts early after infection but disappears at the same time that UL82 transcription begins. Not only was the transcript amplified using reverse transcription-PCR and sequenced but its protein product (UL82as protein) was detected by both Western blot and immunofluorescence. Phylogenetic studies using UL82as protein were conducted, showing a high degree of conservation in clinical isolates, laboratory strains of HCMV, and even in chimpanzee CMV. The transcript could be involved in the posttranscriptional regulation of the UL82 gene, affecting its mRNA stability or translation. Since the UL82 product, pp71, functions as an immediate-early transactivator, its posttranscriptional control could have some effect over latency reactivation and lytic replication.

In vitro infection of megakaryocytes and their precursors by human cytomegalovirus

Apart from congenital human cytomegalovirus (HCMV) infection, manifest HCMV disease occurs primarily in immunocompromised patients. In allogeneic bone marrow transplantation, HCMV is frequently associated with graft failure and cytopenias involving all hematopoietic lineages, but thrombocytopenia is the most commonly reported hematologic complication. The authors hypothesized that megakaryocytes (MK) may be a specific target for HCMV. Although the susceptibility of immature hematopoietic progenitors cells to HCMV has been established, a productive viral life cycle has only been linked to myelomonocytic maturation. The authors investigated whether HCMV can also infect MK and impair their function. They demonstrated that HCMV did not affect the thrombopoietin (TPO)-driven proliferation of CD34+ cells until MK maturation occurred. MK challenged with HCMV showed a 50% more rapid loss of viability than mock-infected cells. MK and their early precursors were clearly shown to be susceptible to HCMV in vitro, as evidenced by the presence of HCMV in magnetic column-purified CD42+ MK and 2-color fluorescent staining with antibodies directed against CD42a and HCMV pp65 antigen. These findings were confirmed by the infection of MK with a laboratory strain of HCMV containing the β-galactosidase (β-gal) gene. Using chromogenic β-gal substrates, HCMV was detected during MK differentiation of infected CD34+ cells and after infection of fully differentiated MK. Production of infectious virus was observed in cultures infected MK, suggesting that HCMV can complete its life cycle. These results demonstrate that MK are susceptible to HCMV infection and that direct infection of these cells in vivo may contribute to the thrombocytopenia observed in patients infected with HCMV.

Combinations of 3'-azido-3'-deoxythymidine (zidovudine) and phosphonoformate (foscarnet) against human immunodeficiency virus type 1 and cytomegalovirus replication in vitro

Combinations of 3'-azido-3'-deoxythymidine and phosphonoformate produced a moderate synergistic inhibitory effect against human immunodeficiency virus type 1 in vitro at concentrations that are easily achieved in humans. The synergistic effect was more pronounced with increasing concentrations and was not secondary to toxic effects of the drugs. 3'-Azido-3'-deoxythymidine neither inhibited the replication of human cytomegalovirus in human embryonic lung fibroblasts nor interfered with the anticytomegalovirus effect of phosphonoformate. By using partially purified reverse transcriptase of human immunodeficiency virus type 1 and human cytomegalovirus DNA polymerase, various combinations of 3'-azido-3'-deoxythymidine-5'-triphosphate and phosphonoformate produced strong indications of additive interactions. The synergistic interactions in infected cells and the additive effects observed at the reverse transcriptase level indicate that mechanisms other than the reverse transcriptase may be of importance for the inhibition of human immunodeficiency virus replication by these two compounds. A concomitant treatment of cytomegalovirus infections, such as cytomegalovirus retinitis, with phosphonoformate in patients with acquired immunodeficiency syndrome receiving 3'-azido-3'-deoxythymidine may be appropriate, and this combination may also be useful in controlling human immunodeficiency virus infection.

Analysis of a region of the human cytomegalovirus (AD169) genome coding for a 25-kilodalton virion protein

In a previous study, we reported the isolation of a lambda gt11 cDNA clone (C3) for a virus message that mapped to the HindIII R fragment (human cytomegalovirus [AD169]). In this report, we further analyze transcription from this region of the genome. C3 was used to probe Northern (RNA) blots of RNA isolated from infected cells. Two abundant messages, 1.3 and 1.6 kilobases (kb) in size, were detected at 62 h postinfection (p.i.). Examination of different time points determined that the 1.6-kb mRNA accumulated in infected cells between 24 and 48 h p.i. and was classified as a late message. The 1.3-kb message was transcribed early in infection and was initially detected around 12 h p.i. Both transcripts were suppressed when infected cells were treated with inhibitors of DNA synthesis. Sequencing and S1 analysis identified the 5' ends of these two messages within 240 nucleotides of each other. Two CAAT-TATA motifs were found upstream of the 1.3- and 1.6-kb mRNA initiation sites, which suggested that the promoters were also closely associated. Antisera made to the fusion protein, synthesized from the C3 clone, detected a 25-kilodalton (kDa) virus protein found in infected cells and purified virions. Western blot (immunoblot) analysis of infected-cell proteins at various times after infection demonstrated that the accumulation of the 25-kDa protein coincided with the appearance of the 1.6-kb message. Therefore, we conclude that the 25-kDa virion protein is translated from the 1.6-kb message.

Restriction to human cytomegalovirus replication in vitro removed by physiological levels of cortisol

Since viral infection is in most cases contrary to the survival of the host cell, it is reasonable to assume that cells possess innate viral replication inhibitory mechanisms. Even between strains of permissive cells, degrees of permissiveness are observed. Restriction to human cytomegalovirus (CMV) replication in vitro is well known, especially in epithelioid cells or cells derived from certain organs. We have studied restriction in a fibroblastic strain of human embryonic kidney cells. By treatment of cell cultures with maximum physiologic concentration of the hormone cortisol (25 micrograms%) both pre and post virus inoculation, susceptibility to laboratory strain Ad169 CMV and low-passaged clinical isolate JSS CMV was enhanced by factors of 6.4 +/- 0.7 and 11.1 +/- 0.4, respectively; effectively converting these cells to a totally permissive state. A linear dose response, which peaks at 25 micrograms% and declines thereafter up to 300 micrograms%, is evident for both virus strains in this enhancement system. Breakdown of restriction increases in linear fashion with increasing time of cortisol pretreatment of cells. The characterization of cortisol effects converting restrictive human fetal cells in vitro to the permissive state further indicates that human hormones may play a significant role in CMV susceptibility in vivo.

Viral replication in HeLa/fibroblast hybrid cells infected with human cytomegalovirus

Three human hybrid cell lines were generated by the fusion of D 98OR, a HeLa cell variant, and TIG human diploid fibroblasts. Chromosome numbers of the hybrid cells fell between that of D 98OR cells and the combined chromosome number of the two cell lines, with three marker chromosomes identical to those of D 98OR cells. One hybrid, B-3, produced large amounts of human fibronectin as analyzed by immunohistochemistry. Only human cytomegalovirus (HCMV) infected B-3 cells showed positive fluorescence as detected by human antiserum to HCMV. Further cloning of B-3 by limiting dilution resulted in two cloned hybrids with markedly enhanced virus production as compared with B-3 cells. Treatment of these two clones with phorbol ester further enhanced virus production. These cloned hybrids may provide a tool to analyze host cell factors controlling the transcription and replication of HCMV.

Organization and expression of the major genes from the long inverted repeat of the human cytomegalovirus genome

The long inverted repeat (TRL:IRL) of the human cytomegalovirus (CMV) genome is a major transcription unit in productively infected human fibroblasts. Cloned DNA fragments of the CMV IRL and complementary DNA (cDNA) copies of RNAs transcribed from the TRL:IRL were used as probes in RNA filter hybridization experiments to characterize and map the RNAs transcribed from this region of the virus genome. In human fibroblasts, three poly A+ RNAs of 2.7, 2.0, and 1.2 kb were detected during the early (E) and late (L) phases of virus gene expression. Analysis of cloned cDNAs and RNA mapping studies indicate that the TRL:IRL can be divided into three transcriptionally active regions. The most highly transcribed region lies between 0.805 and 0.816 map units and encodes a major abundant poly A+ RNA of 2.7 kb that is expressed at E and L times postinfection (p.i.). The second region spans map coordinates 0.792-0.797 and encodes a 1.2-kb poly A+ RNA that is relatively low in abundance at E times p.i. but achieves nearly the same abundance as the 2.7-kb transcript at L times p.i. The third region encompasses map units 0.796-0.804 and encodes a less abundant poly A+ RNA of 2.0 kb that attains maximum expression at E times. The 1.2- and 2.7-kb RNAs are transcribed in the same direction, while the 2.0-kb RNA is transcribed in the opposite direction. The 2.7-, 2.0-, and 1.2-kb RNAs, as well as 5.7- and 1.8-kb transcripts were detected at immediate early times p.i. when human fibroblasts were treated with cycloheximide, but not in cells treated with anisiomycin.

Molecular cloning and analysis of three cDNA clones homologous to human cytomegalovirus RNAs present during late infection

Three virus-specific clones were isolated from a cDNA library synthesized from human cytomegalovirus (AD169)-infected cell RNA and cloned into the expression vector lambda gt11. These clones, designated C3, D10, and H10 were each found to express a human cytomegalovirus/beta-galactosidase fusion protein that was reactive with antibody prepared against purified virions. By using the cloned cDNA, we were able to identify the transcripts that code for each gene product and study the kinetics of expression during permissive infection. Our results suggest that at least two of the RNAs undergo posttranscriptional processing and appear in infected cells at immediate-early times. The authentic C3 gene product was identified by probing Western blots with antibody prepared against fusion protein fpC3.

Human cytomegalovirus: demonstration of permissive epithelial cells and nonpermissive fibroblastic cells in a survey of human cell lines

To more clearly define the characteristics which render a cell permissive for human cytomegalovirus (HCMV), we screened a panel of human cell lines differing in morphology, ploidy, and extent of differentiation for the ability to sustain productive HCMV replication. Cells were exposed to HCMV at 5 to 20 PFU per cell and examined at 4 to 14 days postinfection to detect the production of infectious virus by a plaque assay and the assembly of progeny virions by electron microscopy. By these criteria, high-titer HCMV replication (10(6) to 10(7) PFU/ml) occurred in a well-differentiated, diploid, epithelial cell line, HCMC, which had been derived from normal human colonic mucosa. In contrast, all aneuploid human cell types proved to be nonpermissive, including a fibroblastic cell line designated HT-144. These results indicate that HCMV replication in cultures is not strictly limited to fibroblasts and conversely that not all human fibroblastic cells are permissive for HCMV. Nonpermissive cell types were further investigated by attempts to chemically induce HCMV replication. Treatment of nonpermissive cell types with 25 to 500 micrograms of 5-iodo-2'-deoxyuridine per ml prior to infection did not convert them to the permissive state. The implications of these findings for the possible mechanisms maintaining the nonpermissive state are discussed.

Characterization of a major early gene from the human cytomegalovirus long inverted repeat; predicted amino acid sequence of a 30-kDa protein encoded by the 1.2-kb mRNA

The human cytomegalovirus (CMV) long inverted repeat (TRL:IRL) encodes three major early mRNAs. One of these RNAs is a 1.2-kb transcript that maps between 0.792 and 0.797 map units on the human CMV genome. Primer extension experiments, in addition to nucleotide sequence analyses of cloned cDNA transcripts and human CMV IRL DNA fragments, demonstrated that the 1.2-kb mRNA was not spliced. A single major open reading frame of 254 amino acids was identified, encoding a basic polypeptide of approximately 30 kDa. This polypeptide contains 19% Arg, Lys, and His residues, and would have a net positive charge of 31 at neutral pH. Examination of the deduced amino acid sequence revealed several potential phosphorylation sites and a hydrophobic carboxy terminus which resembles a membrane anchor sequence. In vitro translation of human CMV infected cell RNA, hybrid selected with either cloned cDNA or human CMV IRL DNA fragments specific for the 1.2-kb mRNA, resulted in a unique translation product that migrated on SDS-polyacrylamide gels with an apparent molecular mass of 37 kDa. Potential transcriptional regulatory sequences were also identified upstream of the gene encoding the 30-kDa protein.

Evaluation of mixed cell types and 5-iodo-2'-deoxyuridine treatment upon plaque assay titers of human enteric viruses

Four continuous cell lines, BGM, L-132, HEL-299, and RD, were compared both when cultured separately and as mixtures for use in plaque assay titrations of human adenovirus 1 and six human enterovirus serotypes. The effect of incubating these cell cultures in media containing 5-iodo-2'deoxyuridine (IDU) prior to inoculation with virus was also studied. The use of mixed-cell cultures revealed cell line-dependent synergistic effects as well as inhibitory effects. These effects were strongly virus dependent. In particular, enterovirus 69 did not form plaques on any of the four cell lines when cultured independently. However, it did form plaques on nearly all of the cell lines when cultured as mixtures. Contrary to this effect, when BGM cells were used in combination with the other cell lines, plaque counts for adenovirus 1 were greatly reduced. The effect of IDU pretreatment was also virus and cell line specific and enabled some viruses to form plaques on cell lines when they otherwise would not. Overall, IDU pretreatment resulted in an approximate twofold increase in plaque titers over those obtained without treatment.

Cytomegalovirus infects human lymphocytes and monocytes: virus expression is restricted to immediate-early gene products

In this investigation, we studied the ability of human cytomegalovirus to infect peripheral blood mononuclear cells. With monoclonal antibody technology, we demonstrated that cytomegalovirus could infect human lymphocytes of T- and B-cell lineage, natural killer cells, and monocytes. Furthermore, virus expression was limited to the synthesis of immediate-early cytomegalovirus polypeptides. These peripheral blood mononuclear cells did not produce infectious virus, nor were mature virions visualized by electron microscopy. This abortive infection of mononuclear cells was most convincingly shown with stocks of cytomegalovirus that had been recently isolated from infected patients and passaged minimally in fibroblasts. This argues for an increased lymphotropic effect of some isolates of cytomegalovirus, compared to strains of virus that are extensively adapted to growth in fibroblasts. Furthermore, immunocompetent cells that were shown to be abortively infected with cytomegalovirus lost selected differentiated functions.

Rapid detection of cytomegalovirus in MRC-5 cells inoculated with urine specimens by using low-speed centrifugation and monoclonal antibody to an early antigen

A commercially available monoclonal antibody directed against an early nuclear protein of cytomegalovirus was used with low-speed centrifugation for the rapid detection of this virus from urine specimens inoculated onto MRC-5 cells. A total of 19 of 162 (11.7%) urine specimens inoculated were positive by both immunofluorescence and peroxidase-antiperoxidase procedures (sensitivity, 100%), whereas only 18 of the samples produced cytopathic effects in conventional cell culture (specificity, 94.7%). All specimens were positive by immunofluorescence and peroxidase-antiperoxidase procedures at 36 h postinfection, whereas an average of 9 days was required for cytopathic effects to develop in cell cultures.

Effects of the nucleoside analog 2'-nor-2'-deoxyguanosine on human cytomegalovirus replication

The nucleoside analog 2'-nor-2'-deoxyguanosine (2'NDG) effectively inhibits the replication of several laboratory and clinical isolates of human cytomegalovirus. These isolates included viruses obtained from congenitally infected infants and patients suffering from acquired immune deficiency syndrome. The dose of 2'NDG that inhibited cytomegalovirus plaque formation ranged from 0.1 to 1.6 micrograms/ml. At 10 micrograms/ml, 2'NDG completely blocked the production of virus progeny but not the expression of immediate early and early virus gene functions. Cytomegalovirus DNA was not detectable in 2'NDG-treated virus-infected human embryo lung cells when assayed by CsCl density gradient centrifugation. In contrast, the guanosine analog acyclovir at 100 micrograms/ml did not inhibit the production of virus or the synthesis of cytomegalovirus DNA. In virus-infected cells, 2'NDG and acyclovir at 10 and 100 micrograms/ml, respectively, inhibited the incorporation of [3H]thymidine and 32Pi into cellular DNA by ca. 50%. Uninfected human embryo lung cells grown in these concentrations of acyclovir or 2'NDG exhibited a slightly transient lag phase but, overall, cell growth was not retarded, and there was no decrease in cell viability. The extended lag in cell division was not due to inactivation or breakdown of the antiviral compounds but may be due in part to a temporary decrease in cellular DNA synthesis.

Characterization and location of myc homologous sequences in human cytomegalovirus DNA

Specific DNA fragments from human cytomegalovirus (HCMV) strains Towne and AD169 exhibited homology to myc DNA sequences under hybridization conditions corresponding to a 22-28% base mismatch. In a specific subset of hybridizing HCMV fragments, the homology was restricted to the 5' half of viral v-myc and the 5' half of human c-myc. No hybridization was observed between HCMV fragments and the 3' v-myc and 3' human c-myc probes. In Towne DNA, myc homologous sequences mapped in four regions within the long unique segment (0.070-0.094, 0.134-0.156, 0.454-0.470, and 0.591-0.605 map unit) and one region in each of the short terminal repeats (0.832-0.847 and 0.984-1.0 map unit). In strain AD169, myc homology mapped in three regions within the long unique segment (0.123-0.147, 0.174-0.198, and 0.583-0.606 map unit) and one region in each of the short terminal repeats (0.833-0.863 and 0.976-1.0 map unit). By utilizing probes specific for the 5' and 3' portions of v-myc and human c-myc, we established that the regions of homology in a specific subset of HCMV restriction fragments corresponded to the 5' half of myc and were not due to MC29 viral helper sequences, flanking cellular sequences, or binding of probe to G.C-rich DNA.

The influence of iododeoxyuridine pretreatment of various cell cultures on adenovirus multiplication

Treatment of cell cultures with iododeoxyuridine (IUdR) before virus inoculation may enhance the subsequent virus multiplication. This effect was studied in seven kinds of cell cultures with seven human adenoviruses from six subgenera. IUdR (50 micrograms/ml) was added 24 h after the seeding of cells, left for 2 days, and removed before virus inoculation. IUdR had no effect on cell proliferation. Viral cytopathic effect was enhanced in many instances by IUdR pretreatment. However, virus multiplication was enhanced weakly in only four cases [adenovirus 7 in Vero, African green monkey kidney, cynomolgus monkey kidney; adenovirus 4 (Ad4) in HeLa cells], and strongly only for Ad4 in Vero cells, which are semipermissive for Ad4. IUdR pretreatment of Vero cells shortened the replication cycle for Ad4 and increased sensitivity for minimal virus concentrations about 1000-fold. From immunofluorescence experiments it appears that more than one infectious particle is required to infect an untreated Vero cell.

Induction of cytopathogenicity in mammalian cell lines challenged with culturable enteric viruses and its enhancement by 5-iododeoxyuridine

Cultures of 17 established cell lines were tested against 105 enteric virus types for capacity to support viral replication as indicated by cytopathogenic effect production. Enhancement of susceptibility by treatment of the cells with 5-iododeoxyuridine was evaluated in parallel with untreated cells. Cytopathogenic effect was produced in two or more cell lines by every virus tested except six strains of group A coxsackie virus. No cell line was found to be susceptible to these six virus types. In general, treatment with 5-iododeoxyuridine provided a more rapid onset of cytopathogenic effect in susceptible cells and in some instances resulted in refractory cells becoming permissive to viral replication. The use of 5-iododeoxyuridine allowed two human embryonic lines (HEL-299 and L-132), in combination, to be susceptible to all but the six group A coxsackie virus strains.

Characterization of herpes simplex virus persistence in a human T lymphoblastoid cell line

Persistent, dynamic-state infection with herpes simplex virus (HSV) type 1 has been maintained in human T lymphoblastoid (CEM) cells for many months after initial infection with the wild-type virus (HSV0) (input virus/cell multiplicity of 1.0). Persistently infected cells grew as well as uninfected cells, except during occasional periods of crisis (increased viral replication and cytopathic effect). Cells could survive the crisis when they were maintained for twice the usual time interval (8 to 10 rather than 4 to 5 days) before subculture. Interferon was not detectable in the cultures. HSV0 was compared with HSVp1, a small plaque-forming isolate from persistently infected CEM cells. Primary infection of CEM cells with HSV0 at a low input multiplicity (0.01) led to abortive replication, whereas infection with HSVp1 at the same multiplicity resulted in either rapidly lytic or persistent infection depending upon the time interval of subculture. Approximately 55% of plaque-purified clones of HSVp1, as compared with only 5% of HSV0 clones, displayed temperature-sensitive growth in Vero cells. Defective interfering virus was not detectable in uncloned HSVp1 by interference assay. Persistently infected cultures "cured" by treatment with HSV antiserum or incubation at 39 degrees C were resistant to reinfection with HSV but permissive for vesicular stomatitis virus replication, suggesting that these treatments modulated a shift from the dynamic-state of the static-state, latent infection. These studies provide a model for characterization of HSV persistence and latency in a highly differentiated human cell line.

Conditions for cytomegalovirus stimulation of lymphocytes

Lymphocytes from healthy donors or from patients with chronic lymphocytic leukaemia were subjected to live or inactivated cytomegalovirus (CMV) or the mitogen phytohaemagglutinin. No early or late CMV antigens could be demonstrated in the lymphocytes, indicating that neither abortive nor replicative CMV infection takes place. Only cells from CMV antibody-positive leukaemic and non-leukaemic donors were stimulated by CMV to DNA synthesis, with a maximum on day 5. Cells from all individuals responded to phytohaemagglutinin stimulation, the peak of activity occurring on day 3. The stimulation with CMV occurred in T cells and was independent of early CMV antigen production, viral DNA synthesis, or viral replication. CMV is thus not an in vitro lymphocyte mitogen like Epstein-Barr virus but is a very potent antigen for memory T cells.

PLC/PRF/5 (Alexander) hepatoma cell line: further characterization and studies of infectivity

The Alexander hepatoma cell line, PLC/PRF/5, was studied for evidence of hepatitis B virus markers and alpha-fetoprotein. Only hepatitis B surface antigen and alpha-fetoprotein were detected. Induction experiments with 5-iodo-2'-deoxyuridine and inoculation of chimpanzees with whole cells or tissue culture fluid did not reveal evidence of synthesis of additional hepatitis B virus markers or of production of infectious virus.

Reactivation of herpes simplex virus type 2 from a quiescent state by human cytomegalovirus

The ability of human cytomegalovirus to stimulate replication of herpes simplex virus type 2 (HSV-2) was examined. The system used involved HSV-2-infected human embryonic lung cells under conditions (39.5-40 degrees C) in which HSV-2 remains undetectable. Reactivation of HSV-2 was maximal and persisted for the longest duration when cultures were superinfected with 0.02 plaque-forming unit of human cytomegalovirus per cell. Infectious HSV-2 appeared 2 days after superinfection with human cytomegalovirus and ranged from 10(2) to 10(6) plaque-forming units per culture. Virus reactivated from these cultures was neutralized by rabbit immune serum produced against HSV-2. The specificity of this interaction was demonstrated by various criteria: production of HSV-2 was not observed in cultures treated with mock infecting fluid, and inactivation of human cytomegalovirus by heat, ultraviolet irradiation, or immune serum prior to superinfection eliminated its ability to induce HSV-2 replication. These results sugges that interaction between these two human herpesviruses may be of importance in herpesvirus latency in vivo.

Susceptibility of lymphoblastoid cells to infection with human cytomegalovirus

Human lymphoblastoid cells of B- and T-cell origin were examined for their in vitro susceptibility to infection with human cytomegalovirus (CMV). Results of infectious-center assays, at virus to cell ratios of 10, indicated that in each of the lymphoblastoid cell lines tested less than 1% of the cells produced infectious virus. Under these conditions, CMV specific antigens were undetectable. Infection of lymphoblastoid cells with CMV resulted in atypical virus growth curves similar to those obtained with persistently infected human embryonic kidney cells. Although some variation existed in the relative sensitivity of lymphoblasts, cells of B (Raji, P3J-HR-1, RPMI 8226) and T (CCRF-CEM) origin were susceptible to infection with CMV. Variation in the sensitivity of lymphoblasts to CMV infection did not correlate with differences in virus adsorption or the presence of Epstein-Barr virus deoxyribonucleic acid. These studies suggest that human lymphoblastoid cells could serve as a model to examine persistent CMV infection in lymphoid cells of various origin.

Recognition of virally transformed cells by lymphocytes from patients with prostatic cancer

Data presented describe the first assay using human peripheral blood lymphocytes (PBL) against two unique virally transformed cell lines in vitro. Human cells transformed by a cytomegalovirus (CMV-Mj) isolated from normal human prostate tissue were used as target cells in microcytoxicity assays with lymphocytes from 100 patients. Three target cell types were used: control human embryonic lung cells (HEL), transformed HEL cells (CMV-Mj-HEL-2), and transformed HEL cells retrieved from tumors induced in athymic nude mice (CMV-Mj-HEL-2, T-1) by injection of CMV-Mj-HEL-2 cells. PBL preparations from 84% of all patients tested significantly killed CMV-Mj-HEL-2, T-1 cells. However, only PBL from patients with prostatic carcinoma were cytotoxic for CMV-Mj-HEL-2 cells significantly more often than for control HEL. The implications of this approach are discussed.

Alteration of the growth of cytomegalovirus and herpes simplex virus type 1 by epidermal growth factor, a contaminant of crude human chorionic gonadotropin preparations

Pretreatment (12-48 h) of human fibroblasts with crude, human chorionic gonadotropin (HCG) was found to suppress cytomegalovirus infection and enhance productive herpes simplex type 1 (HSV) infection in vitro. Maximal effect on virus replication occurred at the time of maximal infectivity of control cultures (48 h and 6 days after viral innoculation for HSV and cytomegalovirus, respectively). The alteration in viral growth was not due to the HCG itself, but rather to epidermal growth factor, a contaminant of crude HCG. The effect of epidermal growth factor on viral infectivity was shown to be a cell-mediated event requiring protein synthesis.

The chlamydia: molecular biology of procaryotic obligate parasites of eucaryocytes

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Temperature-sensitive mutants of human cytomegalovirus

Eight temperature-sensitive mutants of human cytomegalovirus have been isolated after mutagenesis with nitrosoguanidine. Three of these mutants have been classified into three separate complementation groups and are capable of synthesizing virus DNA at the nonpermissive temperature (39.5 degrees C). Two others appear unable to synthesize virus DNA at the elevated temperature.

Expression of the human cytomegalovirus genome in mouse cells and in human-mouse heterokaryons

Mouse cells with an established human cytomegalovirus (HCMV) infection were fused with susceptible human embryonic fibroblast cells. CMV-specific early antigens could be demonstrated in the cytoplasm and cell-membrane of the heterokaryons. Treatment with 5-iodo-2'-deoxyuridine (IUdR) of the heterokaryons or of the latently infected mouse cells, prior to their fusion with human cells, could induce the appearance of immunoflourescent elements, characterised as late antigens, and of infectious virus. Our data show that the mouse cells, in the latent stage of infection, contain the whole virus genome and that the replication of the virus is controlled by a genetic mechanism of the host cells both in virus-harbouring mouse cells and in heterokaryons.

Persistence of cytomegalovirus in human lymphoblasts and peripheral leukocyte cultures

The in vitro susceptibility of human peripheral lymhpocytes and lymphoblastoid (F265) cells to infection by human cytomegalovirus was examined. Infection of these cell types with cytomegalovirus resulted in a persistent type of infection rather than the typical growth curve observed with permissive fibroblastic cells. When infection of peripheral lymphocytes was associated with a blastogenic response, the virus persisted for a longer time and at a higher titer than in cells in which a blastogenic response did not occur. Autoradiographic studies and infectious-center assays indicated that only a small number of cells, resembling lymphocytes, were involved in virus persistence. Whether or not the persistence of the virus indicates release of input virus or synthesis or new virus was not determined.

Enhanced SV 40-virus replication in chinese hamster kidney cells pretreated with 5-iodo-2'-deoxyuridine

SV40 virion production was enhanced when semipermissive Chinese hamster kidney cells were treated with 5-iodo-2'-deoxyuridine (IUDR), prior to infection either with virus or viral-DNA. Pretreatment did not increase SV40 replication in fully permissive monkey kidney and nonpermissive Syrian hamster or mouse embryo cells.

Oncogenic transformation of human embryo lung cells by human cytomegalovirus

Persistent infection of human embryo lung fibroblasts with a genital isolate of cytomegalovirus resulted in oncogenic transformation of these cells. Immunofluorescence techniques detected virus-specific antigens, while microcytotoxicity tests established that the transformed cells share a membrane antigen with hamster cells transformed by inactivated cytomegalovirus. The transformed human cells induced progressively growing tumors in weanling athymic nude mice.

5-iododeoxyuridine potentiation of the replication in vitro of several unrelated RNA and DNA viruses

Enhancement of the replication of unrelated viruses (three RNA viruses and one DNA virus), representative of four major virus groups, occurs in human, rodent, or avian cells treated in vitro with 5-iododeoxyuridine (IdU). The results suggest that the potentiation of viral replication by IdU is a widespread phenomenon.

Long-term persistence of cytomegalovirus genome in cultured human cells of prostatic origin

Cells from prostatic tissue obtained from a 3-year-old male donor exhibited scattered foci of cytopathology on primary culture. A virus was isolated and shown by serological analysis to be cytomegalovirus (CMV). After a number of cell culture passages, a cell line (disignated CMV-Mj-P) was obtained in which foci of infection could no longer be demonstrated, nor could virus be rescued. On continued passage the doubling time of the cells decreased markedly, and the fibroblastoid cells ceased to demonstrate contact inhibition. CMV-specific antigen(s) was detected on the surface of the cells by indirect immunofluorescence techniques after exposure of the cultures to iododeoxyuridine. Microcytotoxocity tests established that CMV-Mj-P cells, but not control human prostate cells or human embryonic lung cells, share a membrane antigen with hamster cells transformed by CMV. Nucleic acid hybridization studies revealed that virus genetic information was carried by the human prostate cells and that the cells contained an average of about 10 to 15 genome equivalents of CMV DNA. Karyotypic analysis confirmed that the CMV-Mj-P cells were of human male origin. These results indicate that the cells either have been transformed by CMV or are chronically infected with CMV and releasing virus at levels below detection.

Effects of 5-bromodeoxyuridine and 5-iododeoxyuridine on a latent herpes simplex virus infection

A latent herpes simplex virus infection was established in rabbit kidney cells. Treatment of the cells with 5-bromo-2-deoxyuridine after the latent infection was established had no effect on the rate of virus recovery but did extend the latent period before active virus growth resumed. In contrast to this, treatment of cells with 5-bromo-2-deoxyuridine or 5-iodo-2-deoxyuridine prior to infection with virus increased the subsequent rate of virus recovery.

Stimulation of adenovirus replication in simian cells in the absence of a helper virus by pretreatment of the cells with iododeoxyuridine

Pretreatment of African green monkey kidney cells with 50 mu g of 5'-iododeoxyruidine (IUdR) per ml can modify their susceptibility to the replication of human adenovirus type 7 in the absence of simian virus 40 (SV40) although this enhancement of adenovirus replication is not as efficient as that of the helper SV40 virus. Since the number of infectious centers remains unchanged after IUdR pretreatment whereas the burst size of virus from each infected cell increases, the IUdR appears to allow each infected cell to produce more virus. Cell DNA synthesis appears to be stimulated in IUdR pretreated cells infected with adenovirus 7, but the host cell DNA synthesized is small enough to remain in the Hirt supernatant fluid. The modification of susceptibility to adenovirus replication and the changed pattern of cell DNA synthesis is stable for at least two additional cell passages of the pretreated cells.

Growth of murine cytomegalovirus in a heterologous cell system and its enhancement by 5-iodo-2'-deoxyuridine

Mouse cytomegalovirus replicated in rabbit kidney cultures, a cell system of nonrodent origin. However, the sensitivity of these cultures, and the yields of virus therefrom, were lower than those of mouse cultures. Although a cytopathic effect developed in rabbit kidney cultures inoculated with sufficient amounts of the virus, such cultures were unsatisfactory for plaque assay. This was also true when rabbit fibroblast cultures were used, even though the murine cytomegalovirus replicated much better in mouse fibroblasts than in mouse kidney cultures, the latter of which contained extensive areas of epithelial cells. Viral growth in rabbit kidney cells was considerably enhanced when those cells had been initiated and grown in the presence of 5-iodo-2'-deoxyuridine; not only were the viral titers increased, but also the clarity and distinctness of the inclusion bodies.