Persistent Herpes Simplex Virus Infection In Vitro with Cycles of Cell Destruction and Regrowth

HSV type 1 genome variants from persistently productive infections in Raji and BJAB cell lines

We studied possible genomic changes occurring in herpes simplex virus type 1 (HSV-1) during long-term cell culture which served as a model system for persistence and latency studies as introduced earlier. Sixteen HSV-1 reisolates were isolated from persistently productive HSV-1 (strains F and AK)-infected Burkitt lymphoma cell lines Raji and BJAB at four different times. They were roughly characterized in plaque morphology, plaque size, and infectivity. The viral reisolate DNAs revealed deletions and insertions of up to 1,150 base pairs in fragments BamHI-B, -E, -F, -J, -V, -X, and in the L-terminal and junction fragments S and K. Results were confirmed by additional restriction enzyme analyses and DNA sequencing of selected genomic regions between map units 0.642-0.650, 0.763-0.778 and 0.887-0.934. There was a progressive increase in genomic variability over a three-year period. However, changes in DNA fragment size occurred at different rates, with some reisolates showing stability over several months. The selective pressure for HSV-1 (F and AK) genomic changes was stronger in Raji than in BJAB cells, and stronger for F than for AK strain.

Herpes simplex virus type 1 long-term persistence, latency, and reactivation in infected Burkitt lymphoma cells

The two herpes simplex virus type 1 (HSV-1) strains F and AK which differ in virus-cell interaction and in DNA organization, were used to establish persistently productive infections in Burkitt lymphoma-derived cell lines BJAB and Raji. Four such lines could be maintained over a period of three years. Like the uninfected parental lines, the persistently infected cells display a cyclic pattern of cell proliferation. The expression of HSV-1-specific antigens proved to be variable. As a consequence, virus yields also vary within a subcultivation period. Pooled human HSV antisera, when continuously present, suppress virus production (inducible latency) and support cell proliferation to higher rates. By contrast, removal of the antiserum after a certain period of cultivation leads to virus reactivation with a delay of 8 to 20 days. After cultivation periods of more than 3 to 12 weeks, replacement of HSV antiserum does no longer result in virus reactivation and even inducers fail to reactivate.

Persistent infection with herpes simplex virus type 1 in an Ia antigen-positive murine macrophage cell line

The interaction of herpes simplex virus type 1 (HSV-1) with murine macrophage cell lines was examined. The cell lines appeared to be moderately permissive for HSV-1 replication, though the yield of the virus was limited compared with that in Vero cells. Furthermore, the murine macrophage cell line SL-1, bearing Ia antigen, was persistently infected with HSV-1 for over one year, and was designated SL-1/KOS. Persistent infection could not be established in an Ia antigen-negative macrophage cell line, SL-4. In the SL-1/KOS culture, there was a small number of infected cells as revealed by infectious center assay. Treatment with monoclonal antibody against HSV-1 cured the persistent infection. Therefore maintenance of the persistent infection is considered to be due to a carrier culture consisting of a minority of infected cells and a majority of uninfected cells. In the SL-1/KOS cultures a low level of interferon (IFN) was found. When a large amount of exogenous recombinant murine IFN-beta (10(5)-10(6) international units/ml) was added to the culture, virus production diminished to undetectable levels. These results suggest that IFN plays an important role in the maintenance of persistent infection. In long-term persistently infected cultures, syncytium formation appeared and the virus from such cultures had a different DNA structure from that of the virus originally used for infection as revealed by restriction endonuclease analysis.

Herpes simplex virus persistence in mouse neuroblastoma (C 1300) cell cultures: role of interferon

The Mp strain of herpes simplex virus type 1 (HSV1) induced a persistent infection in the mouse C 1300 neuronal cell line (clone N 115). C 1300 cultures infected at an MOI of 0.01 or 0.001 survived the initial infection and continued to produce infectious virus and viral antigens for 185 days and 31 days, respectively. Viral antigens were not detected in cultures no longer producing infectious virus; these "cured" cultures had comparable susceptibility to reinfection with HSV as previously uninfected C 1300 cells. While significant amounts of interferon were produced by C 1300 cells when challenged with Newcastle Disease Virus (NDV) or when treated with poly I:C, HSV-induced interferon could not be detected in either the acutely or persistently infected cell lines. The persistent state was not significantly altered by the addition of 1,000 units/ml of murine interferon alpha plus beta (MuIFN alpha + beta), nor was it affected by the addition of antibody to MuIFN. It appears that IFN does not play an important role in the establishment and/or maintenance of viral persistence in this neuronal system.

A variant of human cytomegalovirus derived from a persistently infected culture

Infection of cells derived from an osteogenic sarcoma (HOS) with human cytomegalovirus (HCMV) resulted in persistent infection. It appears that persistent infection is due to a balance between release of virus and the growth of uninfected cells. Viruses derived from the persistently infected cultures were not temperature sensitive nor were they defective interfering particles. However, hybridization experiments using the Q-labeled probe from the XbaI Q fragment indicated that one copy of the repeat sequences contained in fragments Q and O of CMV, Towne DNA have been completely deleted from the virus DNA derived from the persistent culture. Thus the mechanism of persistent infection is probably due in part to a variant of CMV present in the cultures.

Herpes simplex virus latency and reactivation in isolated rat sensory neurons

An in vitro herpes simplex virus type 1 (HSV-1) latency model has been established using neurons isolated from dissociated rat fetus sensory ganglia as the host cell. Rat fetal neuron cells were pretreated for 24 hr at 37 degrees with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon, infected with HSV-1 (approximately 2.5 plaque-forming units/cell), and treated for 7 days with the same inhibitor combination. Infectious HSV-1 became undetectable 3 days postinfection and remained undetectable during the remainder of the inhibitor treatment. After removal of inhibitors on day 7, infectious virus remained undetectable for 2-7 days; subsequently, virus replication ensued and neuronal cells were destroyed. Incubation of inhibitor-treated, infected neuron cells at 40.5 degrees after removal of inhibitors resulted in extension of the latent period to at least 15 days. HSV-1 was reactivated from latently infected neurons by reducing the incubation temperature from 40.5 to 37 degrees and virus-specific cytopathology was observed in neurons within 96 hr after reducing temperature. This in vitro model system will provide the first system to analyze, in a primary cell type of neuronal origin, the state of the HSV genome during establishment and maintenance of the latent state and during virus reactivation.

Activation of herpes simplex virus (HSV) type 1 genome by temperature-sensitive mutants of HSV type 2

Previous studies have demonstrated that herpes simplex viruses (HSV) type 1 (HSV-1) and type 2 (HSV-2) can be maintained in a repressed form in human embryo lung cells. Reducing the incubation temperature or superinfecting with a heterologous herpesvirus, human cytomegalovirus (HCMV), results in activation of virus replication. We now report that superinfection with a partially homologous herpesvirus, HSV-2, also resulted in activation of HSV-1. To minimize excessive synthesis of infectious HSV-2 while allowing virus gene expression, repressed HSV-l-infected cultures were superinfected with HSV-2 temperature-sensitive (ts) mutants (tsF3, tsB5, or tsH9). The predominant virus replicated after HSV-2 ts mutant superinfection at a nonpermissive temperature was identified as activated parental-like HSV-1 by (i) plaquing efficiency at permissive (34 degrees) and nonpermissive (40.5 degrees) temperatures, (ii) sensitivity to inhibition by the HSV-l-specific antiviral agent (E)-5-(2-bromovinyl)-2'-deoxyuridine, and (iii) restriction endonuclease cleavage analysis. In addition, the fact that superinfection with HSV-2 tsB5 or tsH9, which are unable to synthesize virus DNA and express only early virus genes at nonpermissive temperature, resulted in synthesis of virus demonstrated that HSV-2 DNA synthesis is not required for activation. This system has provided the basis for further studies concerning the regulation of HSV gene expression in human cells.

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.

Involvement of an early human cytomegalovirus function in reactivation of quiescent herpes simplex virus type 2

We have previously described an in vitro system in which the function lacking for herpes simplex virus type 2 (HSV-2) replication can be induced by human cytomegalovirus (HCMV). The mechanism of this reactivation of quiescent HSV-2 by HCMV has been further defined. The HCMV function(s) responsible for HSV-2 stimulation was examined temporally, and the fraction of cells in quiescent cultures producing HSV-2 after superinfection was determined. Using independent biological, genetic and molecular techniques we have made the following observations. (i) As early as 12 h after HCMV superinfection, HSV-2 RNA was expressed in latently infected cells. (ii) At 24 h after HCMV superinfection, a time when newly synthesized HCMV was not yet apparent, infectious HSV-2 was produced by reactivated cultures. (iii) Four HCMV temperature-sensitive mutants, which are DNA-negative at nonpermissive temperature and represent four different complementation groups, induced reactivation of HSV-2 at 39.5 degrees C. (iv) Early after HCMV superinfection, 1.6% of quiescent cells could be induced to transcribe HSV-2 information. (v) Early after HCMV superinfection, 0.3% of cells in the quiescent cultures could be induced to yield infectious HSV-2. The finding that a significant interaction can occur between HCMV and quiescent HSV-2 in an in vitro model is noteworthy in light of the knowledge that both of these herpesviruses often reside simultaneously in the human host.

Analysis and characterization of herpes simplex virus after its persistence in a lymphoblastoid cell line for 15 months

Infection of a human lymphoblastoid cell line (F-365 line containing Epstein-Barr viral capsid antigen, derived from an individual without overt signs of lymphoma, infectious mononucleosis, or leukemia) with herpes simplex virus (HSV), maintained and observed for 15 months, was characterized by the continuous production of infectious extracellular virus. By the 5th day postinfection 75% of the cells produced HSV antigen as detected by fluorescent antibody, and by the 10th day 90% did so; production continued through the 15th month. Only 11% of single isolated cells produced detectable infectious virus. HSV produced after the 3rd month formed smaller plaque in monolayer cell culture than did the parental virus. No antigenic or polypeptide change in the HSV was detected by crossed immunoelectrophoresis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis over the 15-month cultivation in F-365 cells. Cell susceptibility and HSV virulence did not appear to change. The HSV-lymphoblastoid cell culture provided a useful model in which to study long-term virus-cell interactions.

Persistence of herpes simplex virus genes in cells of neuronal origin

The growth characteristics of the KOS strain of herpes simplex virus type 1 (HSV-1) in cell lines of nervous tissues origin were examined in an attempt to develop a tissue culture system mimicking the in vivo state of HSV-1 latency. We have previously reported that the B103 rat brain neuroma cell line is nonpermissive for growth of the KOS strain. In this report, we show that this nonpermissiveness is a temperature- and multiplicity-dependent phenomenon, with minimum virus yields at an elevated temperature and a low multiplicity of infection. Under these conditions, B103 cells survived infection with active wild-type or mutant HSV-1, whereas similarly treated Vero cells were killed. Six independent cultures of B103 cells surviving HSV-1 infection have been established. The surviving cells ceased production of any HSV-1 virus by 14 days postinfection and resumed growth and division at rates comparable to those of uninfected B103 cells. Survivor cells continued to express HSV-1-specific antigens, however, as detected by indirect immunofluorescence and by surface iodination followed by immunoprecipitation and polyacrylamide gel electrophoresis. The survivor cells did not express all of the surface proteins seen on productively infected B103 cells, and they were not susceptible to complement-mediated immune cytolysis with anti-HSV-1 antiserum. These results demonstrate that at least a portion of the HSV-1 genome is being harbored in these survivor cells.

Viral nucleic acid synthesis in HSV infected neural cells

HSV-1 replication and synthesis of viral DNA and RNA have been examined in gliomas of human (COX) and rat origin (C6) and in mouse neuroblastomas (D2). COX cells fully support HSV-1 replication and show patterns of viral DNA and RNA synthesis similar to those seen in continuous line cells. HSV-1 also grows to high titers in D2 cells but without concomitant high levels of viral DNA and RNA synthesis in the infected cells. Finally, HSV-1 established a persistent infection in C6 cells. Viral mRNA and DNA synthesis could not be detected in these cultures. At cycles of approximately 15--20 days, the persistently infected cultures exhibited massive CPE and relatively high production of infectious HSV.

Regulation of persistent infection with herpes simplex virus in vitro by hydrocortisone

About 1% of Raji cells showed sensitivity to herpes simplex virus type 2 (HSV-2) infection when tested by infectious center assays or immunofluorescence tests, and the percentage did not change during cell passage. The addition of hydrocortisone to Raji cells persistently infected with HSV-2 caused a marked increase in virus production and in the number of HSV-producing cells. In the case of HSV-1, it was shown that the addition of hydrocortisone was required to maintain persistent infection. These observations suggest that control of replication of HSV-1 and HSV-2 in these cells is regulated by different mechanisms.

Persistent infection of human lymphoid and myeloid cell lines with herpes simplex virus

Herpes simplex virus (HSV) type 1 replicated and persisted in human T, B, and myeloid cell lines with different patterns of viral replication and various effects on cell growth. T cell line CEM supported the replication of HSV for over 400 days without detectable differences in cell growth as compared with uninfected cells. HSV persisted in B cell line NC37 and myeloid cell line K562 for up to 222 and 374 days, respectively, but led to a significant decrease in the number of viable cells by 7 weeks of infection. The average number of cells producing infectious virus was very low in these cell lines (range, 0.5 to 2.7+) compared with a larger proportion of cells exhibiting HSV antigens by immunofluorescence (range, 24 to 58%). In contrast, null cell line LAZ 221 failed to replicate HSV even though the viral infection led to a cessation of cell growth.

Persistence of herpes simplex virus type 1 in rat neurotumor cells

Herpes simplex virus type 1 (HSV-1) infection of a rat central nervous system tumor cell line led to almost complete destruction of the cells. Cells that survived the infection could be isolated and shown to produce infectious HSV particles for variable lengths of time in culture ranging from 20 to 57 passages. Even though infectious virus production eventually ceased, the cell lines continued to produce herpes-specified proteins as measured by immunological techniques. These cells also showed herpesvirus-like structures in the electron microscope. The persistently infected cells that produced HSV antigens and bore HSV sequences were resistant to superinfection by HSV-1. The resistance was not due to failure of adsorption of the virus or to the production of interferon by the cells. The nature of the block in HSV replication in these neurotumor cells, which contain and partially express the HSV genome, is unknown, but may offer an interesting parallel to the known latency of HSV in neural tissues.

Detection of latent cytomegalovirus in murine salivary and prostate explant cultures and cells

After infection of adult mice, cytomegalovirus was detectable in salivary gland suspensions by tissue culture inoculation for up to 3 months. After these cultures had become negative, virus apparently latent in these tissues could be detected in explants of salivary and prostate glands and in cell lines derived from these explants. In some cases cycles of virus-induced cell injury and regrowth were observed. Murine cytomegalovirus plaque efficiency and morphology were evaluated in prostate and salivary gland cell cultures derived from previously infected and uninfected mice. No evidence of interference was detected, although plaques size was altered (larger) in prostate cells from previously infected mice. These studies indicate the presence of a range of suppression, latency, or effects of murine cytomegalovirus detectable after the resolution of active infection and provide methods for additional study of the establishment and activation of virus latency.

Persistent infection with bovine herpesvirus-1 (infectious bovine rhinotracheitis virus) in cultured hamster cells

Bovine herpesvirus-1 infection in hamster embryo cells was found to be dependent upon input multiplicity; productive infection was achieved at input multiplicities greater than one, while persistent infection was established when input multiplicities were about 0.5. This persistence was characterized by a noncyclic, minimal degree of cytopathic effect with a low level of released virus. Maintenance of the persistently infected cultures did not require external supportive measures. Subcultivation of the persistently infected cultures led to virus replication followed by CPE and then cell regrowth. With 3 to 4 weeks after subcultivation a persistent infection was re-established. The possible mechanism for the bovine herpesvirus persistence in hamster cells is discussed.

Establishment of a nonproductive herpes simplex virus infection in rabbit kidney cells

A nonproductive infection of rabbit kidney cells was established with a type 2 strain of herpes simplex virus after incubation of the virus-infected cells at 41 C. Although infectious virus could not be recovered from cells disrupted by freeze-thawing or sonication after incubation at 41 C, spontaneous reactivation of virus growth occurred in 84% of the cultures after lag periods of variable length when cultures of viable cells were transferred to 37 C and incubated. Forty-one percent of the cultures had lag periods of 4 or more days, and 24% had lag periods of 7 or more days. The longest lag period was 45 days. A similar infection was established in WI-38 cells, but attempts to establish the infection in human kidney cells was not successful. This nonproductive infection is being used to study the effects of various physical and chemical agents on herpes simplex virus in a latent state.

Herpesvirus type 2 isolated from cervical tumor cells grown in tissue culture

A herpesvirus has been isolated from spontaneously degenerating cultures of cervical tumor cells grown in vitro. The virus was identified as a type 2 herpesvirus on the basis of biologic properties, including plaque morphology and microtubule formation in infected HEp-2 cells, and of immunologic specificity as determined by neutralization. Herpesvirus antigens and virus particles were not seen in duplicate cultures of viable cervical tumor cells.

Persistent cyclic herpes simplex virus infection in vitro. IV. Changes in the severity of the infections in the presence of antibody

Hampar, Berge (National Institute of Dental Research, Bethesda, Md.). Persistent cyclic herpes simplex virus infection in vitro. IV. Changes in the severity of the infections in the presence of antibody. J. Bacteriol. 92:1741-1747. 1966.-The severity of persistent herpes simplex virus (HSV) infections maintained in the presence of viral antibody (AB) changed with time. These changes could be divided into three distinct phases during which the severity of the infections were maintained at low (phase 1), high (phase 2), and intermediate (phase 3) levels. Paralleling these changes was the appearance in the cultures of a new HSV variant which induced the formation of giant cells. The changes in the severity of the infections were attributable to three factors. The first was the presence in the cultures of virus-resistant cells. The second was the suppressive effects due to virus neutralization by the AB. The third was the inherent properties of each HSV variant which determined the amount of virus remaining in an infectious form in the presence of AB. Finally, the period of "exacerbation" in vitro (phase 2) was compared with recurrent episodes in human herpes infection.

Persistent cyclic herpes simplex virus infection in vitro. 3. Asynchrony in the progression of infection and cell regrowth

Hampar, Berge (National Institute of Dental Research, Bethesda, Md.). Persistent cyclic herpes simplex virus infection in vitro. III. Asynchrony in the progression of infection and cell regrowth. J. Bacteriol. 91:1965-1970. 1966.-The progression of virus-induced cytopathic effects (CPE) and virus synthesis was studied in localized areas of Chinese hamster cell cultures persistently infected with herpes simplex virus (HSV). CPE was initially evidenced by the presence of small multinucleated giant cells, followed by expanding plaquelike lesions with an occasional uninfected cell remaining within the infected areas. Cell detachment rapidly followed the appearance of viral antigen in infected cells. The surviving cells which proliferated to re-establish the cell sheet arose from two sources. The first was from viable cells which remained attached after expansion of localized areas of CPE, and the second was from reattachment of viable cells in the medium. CPE in localized areas was initiated at various times during the cycle irrespective of the virus titer in the medium. Cell regrowth in some areas and CPE in other areas occurred simultaneously throughout the cycle in an asynchronous fashion. Consequently, during periods of rising virus titers, most areas showed CPE while few areas displayed cell regrowth. As the virus titers declined, more areas showed cell regrowth and fewer areas displayed new cycles of CPE. CPE in localized areas was not initiated until cell regrowth had occurred. It is proposed that the proliferating cells were temporarily resistant to HSV infection, and that this resistance was ultimately lost in their progeny cells.

Persistent cyclic herpes simplex virus infection in vitro. II. Localization of virus, degree of cell destruction, and mechanisms of virus transmission

Hampar, Berge (National Institute of Dental Research, Bethesda, Md.). Persistent cyclic herpes simplex virus infection in vitro. II. Localization of virus, degree of cell destruction, and mechanisms of virus transmission. J. Bacteriol. 91:1959-1964. 1966. The localization of virus, degree of cell destruction, and mechanisms of virus transmission in persistent herpes simplex virus-infected cultures were studied. The major fraction of infectious virus was associated with the medium and a minor fraction was associated with the attached cells. Virus in the medium was further separable into a sedimentable (cellular) fraction and a nonsedimentable (extracellular) fraction. The sedimentable fraction was comprised of cellular debris, most of which appeared to contain viral antigen, and intact cells of which less than 10% contained infectious virus. Cell destruction during the cycle involved more than 99.9% of the maximal number of cells present. Infection could be transmitted by extracellular virus, cell-to-cell transfer, and reattachment of infectious cellular material. The results indicated that transmission by reattachment was probably mediated through the cellular debris rather than the intact cells.