Detection of antibodies to herpes simplex virus with a continuous cell line expressing cloned glycoprotein D

Glycoform and net charge heterogeneity in gp120 immunogens used in HIV vaccine trials

BACKGROUND

The RV144 clinical trial showed for the first time that vaccination could provide modest but significant protection from HIV-1 infection. To understand the protective response, and to improve upon the vaccine's efficacy, it is important to define the structure of the immunogens used in the prime/boost regimen. Here we examined the heterogeneity in net charge, attributable to glycoform variation, of the gp120 immunogens contained in the AIDSVAX B/E vaccine.

METHODOLOGY/PRINCIPAL FINDINGS

Isoelectric focusing and glycosidase digestion were used to assess variation in net charge of the gp120s contained in the AIDSVAX B/E vaccine used in the RV144 trial. We observed 16 variants of MN-rgp120 and 24 variants of A244-rgp120. Glycoform variation in gp120 produced in Chinese hamster ovary cells was compared to glycoform variation in gp120 produced in the 293F human embryonic kidney cell line, often used for neutralization assays. We found that gp120 variants produced in CHO cells were distinctly more acidic than gp120 variants produced in 293 cells. The effect of glycoform heterogeneity on antigenicity was assessed using monoclonal antibodies. The broadly neutralizing PG9 MAb bound to A244-rgp120, but not to MN-rgp120, whether produced in CHO or in 293. However, PG9 was able to bind with high affinity to MN-rgp120 and A244-rgp120 produced in 293 cells deficient in N-acetylglucosaminyltransferase I.

CONCLUSIONS/SIGNIFICANCE

MN- and A244-rgp120 used in the RV144 trial exhibited extensive heterogeneity in net charge due to variation in sialic acid-containing glycoforms. These differences were cell line-dependent, affected the antigenicity of recombinant envelope proteins, and may affect assays used to measure neutralization. These studies, together with recent reports documenting broadly neutralizing antibodies directed against carbohydrate epitopes of gp120, suggest that glycoform variation is a key variable to be considered in the production and evaluation of subunit vaccines designed to prevent HIV infection.

Prospects for Developing an Effective Vaccine Against Ocular Herpes Simplex Virus Infection

One of the hallmarks of herpes simplex virus (HSV) infection is the establishment of a lifelong latent infection accompanied by periods of recurrent disease. Primary HSV infections or repeated clinical recurrences do not elicit immune responses capable of completely preventing recurrences of endogenous virus. It is therefore questionable if vaccination approaches that seek to mimic the immune response to natural infection will reduce infection or disease due to an exogenous viral challenge. Approaches to the induction of protective responses by altering or enhancing both innate and adaptive immunity, using novel vaccines specifically tested in models of HSV infections of the eye, such as recombinant viral vaccine vectors and DNA vaccines, are detailed in this review.

Efficacy of replication-defective adenovirus-vectored vaccines: protection following intramuscular injection is linked to promoter efficiency in muscle representative cells

To investigate the respective role of transduced cells in the induction of immune response following intramuscular inoculation of adenovirus-based vaccines, we generated several replication-defective adenoviruses expressing the glycoprotein D gene of pseudorabies virus under the control of four different promoters: major late promoter of adenovirus type 2, human cytomegalovirus immediate-early promoter/enhancer (CMV), Rous sarcoma virus-long terminal repeat promoter, and human desmin gene 5' regulatory region (DES). All the adenovirus constructs were able to fully protect mice, in the contrary of direct DNA inoculation of plasmids harboring the same transcription units. The far most effective adenovirus constructs, on the criterion of protective doses and specific antibody response induction, were those in which the foreign gene was driven by the DES or CMV promoter. Wide variations in promoter strength in vitro were evidenced in several cell culture types representative of putative target cells following muscular inoculation (myoblasts, myotubes, fibroblasts, macrophages, and endothelial cells). The level of efficacy in vivo, was not correlated with the level of expression in vitro in myotubes, but paralleled the level of expression in endothelial cells and in myoblasts. Together with previously published data, these results suggest that, following adenovirus injection, locally produced cytokines may induce myoblasts to act as local antigen presenting cells.

Replication of simian virus 40 origin-containing DNA during infection with a recombinant Autographa californica multiple nuclear polyhedrosis virus expressing large T antigen

Autographica californica multiple nuclear polyhedrosis virus (AcMNPV) has been shown to encode many of the enzymes involved in the replication of its own DNA. Although the AcMNPV genome contains multiple sets of reiterated sequences that are thought to function as origins of DNA replication, no initiator protein has yet been identified in the set of viral replication enzymes. In this study, the ability of a heterologous origin initiator system to promote DNA replication in AcMNPV-infected cells was examined. A recombinant AcMNPV that expressed the simian virus 40 (SV40) large T antigen was surprisingly found to induce the efficient replication of a transfected plasmid containing an SV40 origin. This replication was subsequently found to involve three essential components: (i) T antigen, since replication of SV40 origin-containing plasmids was not induced by wild-type AcMNPV which did not express this protein; (ii) an intact SV40 core origin, since deletion of specific functional motifs within the origin resulted in a loss of replicative abilities; and (iii) one or more AcMNPV-encoded proteins, since viral superinfection was required for plasmid amplification. Characterization of the replicated DNA revealed that it existed as a high-molecular-weight concatemer and underwent significant levels of homologous recombination between inverted repeat sequences. These properties were consistent with an AcMNPV-directed mode of DNA synthesis rather than that of SV40 and suggested that T antigen-SV40 origin complexes may be capable of initiating DNA replication reactions that can be completed by AcMNPV-encoded enzymes.

Pathogenesis of HSV and CMV Infections in Pregnancy

Human herpesvirus (HHSV) and human cytomegalovirus (HCMV) infections during pregnancy are a major concern of public health because of the risk for severe sequelae for the fetuses and the neonates and because primary infections, reinfections and reactivations can be asymptomatic. The risk for neonatal herpes is mostly congenital, while the risk for HCMV infection is either prenatal or congenital. Screening exposed women has not brought definite solutions but is currently being evaluated. Among pregnant women with active infection, evaluation of the fetus for contamination and thus for the risk for severe immediate or long-term sequelae for neonates is the major goal. Diagnostic tools are available, cell culture still being the gold standard, and polymerase chain reaction (PCR) being currently evaluated for its contribution to diagnosis of active infection. Consensus for screening pregnant women as well as achievement of antiviral vaccines are the most urgent intervention strategies to develop in the near future.

Role of mannose-6-phosphate receptors in herpes simplex virus entry into cells and cell-to-cell transmission

Herpes simplex virus (HSV) glycoprotein D (gD) is essential for virus entry into cells, is modified with mannose-6-phosphate (M-6-P), and binds to both the 275-kDa M-6-P receptor (MPR) and the 46-kDa MPR (C. R. Brunetti, R. L. Burke, S. Kornfeld, W. Gregory, K. S. Dingwell, F. Masiarz, and D. C. Johnson, J. Biol. Chem. 269:17067-17074, 1994). Since MPRs are found on the surfaces of mammalian cells, we tested the hypothesis that MPRs could serve as receptors for HSV during virus entry into cells. A soluble form of the 275-kDa MPR, derived from fetal bovine serum, inhibited HSV plaques on monkey Vero cells, as did polyclonal rabbit anti-MPR antibodies. In addition, the number and size of HSV plaques were reduced when cells were treated with bovine serum albumin conjugated with pentamannose-phosphate (PM-PO4-BSA), a bulky ligand which can serve as a high-affinity ligand for MPRs. These data imply that HSV can use MPRs to enter cells; however, other molecules must also serve as receptors for HSV because a reasonable fraction of virus could enter cells treated with even the highest concentrations of these inhibitors. Consistent with the possibility that there are other receptors, HSV produced the same number of plaques on MPR-deficient mouse fibroblasts as were produced on normal mouse fibroblasts, but there was no inhibition with PM-PO4-BSA with either of these embryonic mouse cells. Together, these results demonstrate that HSV does not rely solely on MPRs to enter cells, although MPRs apparently play some role in virus entry into some cell types and, perhaps, act as one of a number of cell surface molecules that can facilitate entry. We also found that HSV produced small plaques on human fibroblasts derived from patients with pseudo-Hurler's polydystrophy, cells in which glycoproteins are not modified with M-6-P residues and yet production of infectious HSV particles was not altered in the pseudo-Hurler cells. In addition, HSV plaque size was reduced by PM-PO4-BSA; therefore, it appears that M-6-P residues and MPRs are required for efficient transmission of HSV between cells, a process which differs in some respects from entry of exogenous virus particles.

Transformed cells producing the glycoprotein D of HSV-1 are resistant to infection with clinical strains of HSV

The generality of the resistance exhibited by gD producing cells to HSV-1 infection was tested. We tested three different cell lines producing various amounts of gD for resistance against three HSV-1 strains. The strains used were the prototype laboratory F strain and two recently isolated low passage local clinical strains, VG and VD. The results indicate that: (i) the resistance of the cell lines is directly related to the amount of gD they produce, (ii) the cell lines showed greater resistance against the two local clinical HSV-1 strains than against the laboratory strain, and (iii) the resistance is not mediated at the level of virus adsorption to the cell membranes.

HIV-1 envelope-elicited neutralizing antibody titres correlate with protection and virus load in chimpanzees

In an attempt to compare the protective effect of vaccination with two forms of envelope antigens, and to define immunological correlates of protection against HIV infection, chimpanzees were vaccinated with either recombinant gp160 or gp120. Homologous HIV challenge was performed 3 weeks after the fourth immunization. The animal with the highest level of serum neutralizing antibodies (gp160 immunogen) was protected against HIV infection. All other chimpanzees became infected, but displayed various levels of infected PBMCs. The postchallenge data gave rise to the following conclusions: (1) protection correlated with the level of the serological immune response, but not with the nature of immunogen (gp120 versus gp160); (2) the virus-neutralizing titre at day of challenge correlated with protection from infection; (3) the relative magnitude of the lymphoproliferative T-cell response at day of challenge did not correlate with any protective effect; (4) the peak numbers of virus-infected PBMCs in vaccinated animals were lower than those observed in control animals, and this effect was correlated with the intensity of the antibody response at day of challenge. This raises the possibility that a beneficial effect of HIV vaccination may be achieved in a situation where sterile immunity is not consistently obtained.

Identification of functional regions of herpes simplex virus glycoprotein gD by using linker-insertion mutagenesis

Glycoprotein gD is a component of the herpes simplex virus (HSV) envelope essential for virus entry into susceptible cells. Previous studies using deletion and point mutations identified a functional domain of HSV-1 gD (gD-1) from residues 231 to 244. However, many of the deletion mutations had global effects on gD-1 structure, thus precluding assessment of the functional role of large portions of the protein. In this study, we constructed a large panel of linker-insertion mutants in the genes for gD-1 and HSV-2 gD (gD-2). The object was to create mutations which would have only localized effects on protein structure but might have profound effects on gD function. The mutant proteins were expressed in transiently transfected L cells. Monoclonal antibodies (MAbs) were used as probes of gD structure. We also examined protein aggregation and appearance of the mutant glycoproteins on the transfected cell surface. A complementation assay measured the ability of the mutant proteins to rescue the infectivity of the gD-null virus, FgD beta, in trans. Most of the mutants were recognized by one or more MAbs to discontinuous epitopes, were transported to the transfected cell surface, and rescued FgD beta virus infectivity. However, some mutants which retained structure were unable to complement FgD beta. These mutants were clustered in four regions of gD. Region III (amino acids 222 to 246) overlaps the region previously defined by gD-1 deletion mutants. The others, from 27 through 43 (region I), from 125 through 161 (region II), and from 277 to 310 (region IV), are newly described. Region IV, immediately upstream of the transmembrane anchor sequence, was previously postulated to be part of a putative stalk structure. However, residues 277 to 300 are directly involved in gD function. The linker-insertion mutants were useful for mapping MAb AP7, a previously ungrouped neutralizing MAb, and provided further information concerning other discontinuous epitopes. The mapping data suggest that regions I through IV are physically near each other in the folded structure of gD and may form a single functional domain.

Expression of seven herpes simplex virus type 1 glycoproteins (gB, gC, gD, gE, gG, gH, and gI): comparative protection against lethal challenge in mice

We have constructed recombinant baculoviruses individually expressing seven of the herpes simplex virus type 1 (HSV-1) glycoproteins (gB, gC, gD, gE, gG, gH, and gI). Vaccination of mice with gB, gC, gD, gE, or gI resulted in production of high neutralizing antibody titers to HSV-1 and protection against intraperitoneal and ocular challenge with lethal doses of HSV-1. This protection was statistically significant and similar to the protection provided by vaccination with live nonvirulent HSV-1 (90 to 100% survival). In contrast, vaccination with gH produced low neutralizing antibody titers and no protection against lethal HSV-1 challenge. Vaccination with gG produced no significant neutralizing antibody titer and no protection against ocular challenge. However, gG did provide modest, but statistically significant, protection against lethal intraperitoneal challenge (75% protection). Compared with the other glycoproteins, gG and gH were also inefficient in preventing the establishment of latency. Delayed-type hypersensitivity responses to HSV-1 at day 3 were highest in gG-, gH-, and gE-vaccinated mice, while on day 6 mice vaccinated with gC, gE, and gI had the highest delayed-type hypersensitivity responses. All seven glycoproteins produced lymphocyte proliferation responses, with the highest response being seen with gG. The same five glycoproteins (gB, gC, gD, gE, and gI) that induced the highest neutralization titers and protection against lethal challenge also induced some killer cell activity. The results reported here therefore suggest that in the mouse protection against lethal HSV-1 challenge and the establishment of latency correlate best with high preexisting neutralizing antibody titers, although there may also be a correlation with killer cell activity.

High-level expression and purification of secreted forms of herpes simplex virus type 1 glycoprotein gD synthesized by baculovirus-infected insect cells

Two forms of herpes simplex virus glycoprotein gD were recombined into Autographa californica nuclear polyhedrosis virus (baculovirus) and expressed in infected Spodoptera frugiperda (Sf9) cells. Each protein was truncated at residue 306 of mature gD. One form, gD-1(306t), contains the coding sequence of Patton strain herpes simplex virus type 1 gD; the other, gD-1(QAAt), contains three mutations which eliminate all signals for addition of N-linked oligosaccharides. Prior to recombination, each gene was cloned into the baculovirus transfer vector pVT-Bac, which permits insertion of the gene minus its natural signal peptide in frame with the signal peptide of honeybee melittin. As in the case with many other baculovirus transfer vectors, pVT-Bac also contains the promoter for the baculovirus polyhedrin gene and flanking sequences to permit recombination into the polyhedrin site of baculovirus. Each gD gene was engineered to contain codons for five additional histidine residues following histidine at residue 306, to facilitate purification of the secreted protein on nickel-containing resins. Both forms of gD-1 were abundantly expressed and secreted from infected Sf9 cells, reaching a maximum at 96 h postinfection for gD-1(306t) and 72 h postinfection for gD-1(QAAt). Secretion of the latter protein was less efficient than gD-1(306t), possibly because of the absence of N-linked oligosaccharides from gD-1(QAAt). Purification of the two proteins by a combination of immunoaffinity chromatography, nickel-agarose chromatography, and gel filtration yielded products that were > 99% pure, with excellent recovery. We are able to obtain 20 mg of purified gD-1(306t) and 1 to 5 mg of purified gD-1(QAAt) per liter of infected insect cells grown in suspension. Both proteins reacted with monoclonal antibodies to discontinuous epitopes, indicating that they retain native structure. Use of this system for gD expression makes crystallization trials feasible.

Cytochrome P450IID6 recognized by LKM1 antibody is not exposed on the surface of hepatocytes

LKM1 autoantibody, directed against P450IID6, is accepted as a marker of a particular type of autoimmune hepatitis, but its role in the pathogenesis of the disease is controversial. Localization of P450IID6 on the cell surface of rat hepatocytes was previously reported, suggesting that membrane-bound P450IID6 could be the target of LKM1 antibodies, thus allowing immune lysis of hepatocytes. The objective of the present study was to determine, using various methods, the cell localization of P450IID6 in human and rat hepatocytes. Incubation of rat and human hepatocytes with LKM1-positive serum showed slight, if any, cell membrane staining using immunofluorescence, immunoperoxidase and immunoelectron microscopic studies. No staining of the plasma membrane of human hepatocytes was observed when incubations were carried out with immunoaffinity-purified antibody directed against peptide 254-271, the main epitope of P450IID6 recognized by all LKM1 sera tested. Chinese hamster ovary cells, transfected with the complete P450IID6 cDNA and incubated with the supernatant from a B cell lymphoblastoid cell line prepared with the lymphocytes of a LKM1-positive patient, did not show any staining of the cell surface by immunofluorescence. Incubation of rat microsomal fraction vesicles with LKM1-positive serum, followed by protein A-gold immunoelectron microscopy, displayed a staining of almost all vesicles, confirming that P450IID6 is present on the cytoplasmic side of the microsomal membrane, which makes it unable to be expressed on the cell surface even if it were transported from the endoplasmic reticulum (ER). Sulpho NHS Biotin labelling of rat hepatocyte cell membranes did not show the presence of a 50-kD molecule that could have reacted with LKM1 antibody. DNA sequencing of exon 1 of the CYP2D6 gene of a patient positive for LKM1 antibody did not show any difference from that of the normal published sequence of the gene. This does not favour an alteration of the NH2 terminal sequence of the P450IID6 molecule that could explain a translocation of the molecule to the luminal side of the ER, allowing its expression on the cell surface. These results indicate that, in all likelihood, P450IID6 molecule is not present on the cell surface of normal rat and human hepatocytes. Other mechanisms than antibody-mediated cell lysis directed against membrane P450IID6 antigenic determinants must be found to account for the destruction of hepatocytes observed in this disease.

Protection against Marek's disease by a fowlpox virus recombinant expressing the glycoprotein B of Marek's disease virus

Fowlpox virus (FPV) recombinants expressing the glycoprotein B and the phosphorylated protein (pp38) of the GA strain of Marek's disease virus (MDV) were assayed for their ability to protect chickens against challenge with virulent MDV. The recombinant FPV expressing the glycoprotein B gene elicited neutralizing antibodies against MDV, significantly reduced the level of cell-associated viremia, and, similar to the conventional herpesvirus of turkeys, protected chickens against challenge with the GA strain and the highly virulent RB1B and Md5 strains of MDV. The recombinant FPV expressing the pp38 gene failed to either elicit neutralizing antibodies against MDV or protect the vaccinated chickens against challenge with MDV.

Immunoselection of recombinant baculoviruses expressing high levels of biologically active herpes simplex virus type 1 glycoprotein D

The DNA sequence encoding the complete herpes simplex virus type 1 (HSV-1) glycoprotein D (gD) was inserted into a baculovirus transfer vector under control of the polyhedrin gene promoter of the baculovirus Autographa california nuclear polyhedrosis virus (AcNPV). After co-transfection of Spodoptera frugiperda (Sf9) insect cells with wild-type AcNPV DNA and the recombinant transfer vector DNA, polyhedrin-negative recombinants that expressed high levels of HSV-1 gD were isolated using immunoaffinity selection with antibody coated magnetic particles followed by plaque purification. These recombinant baculoviruses expressed a protein that was slightly smaller than virion HSV-1 gD made in Vero cells. This recombinant protein was expressed at high levels. The expressed protein was glycosylated, was found on the membrane of Sf9 cells, and reacted with gD specific antibodies. Antibodies raised in mice to the recombinant gD neutralized HSV-1 as measured by plaque reduction assays. Mice inoculated with the recombinant baculovirus were completely protected from lethal challenge with HSV-1.

Soluble forms of herpes simplex virus glycoprotein D bind to a limited number of cell surface receptors and inhibit virus entry into cells

Herpes simplex virus type 1 (HSV-1) and HSV-2 plaque production was inhibited by treating cells with soluble forms of HSV-1 glycoprotein D (gD-1t) and HSV-2 glycoprotein D (gD-2t). Both glycoproteins inhibited entry of HSV-1 and HSV-2 without affecting virus adsorption. In contrast, a soluble form of HSV-2 glycoprotein B had no effect on virus entry into cells. Specific binding of gD-1t and gD-2t to cells was saturable, and approximately 4 x 10(5) to 5 x 10(5) molecules bound per cell. Binding of gD-1t was markedly reduced by treating cells with certain proteases but was unaffected when cell surface heparan sulfate glycosaminoglycans were enzymatically removed or when the binding was carried out in the presence of heparin. Together, these results suggest that gD binds to a limited set of cell surface receptors which may be proteins and that these interactions are essential for subsequent virus entry into cells. However, binding of gD to its receptors is not required for the initial adsorption of virus to the cell surface, which involves more numerous sites (probably including heparan sulfate) than those which mediate gD binding.

From virus to vaccine: recombinant mammalian cell lines as substrates for the production of herpes simplex virus vaccines

The use of mammalian cells as substrates for the production of various vaccines is a time-honored procedure. With the advent of recombinant DNA technology, various investigators soon realized that these techniques could be applied to mammalian cells to convert them to reliable, safe producers of a variety of vaccines. While none of these types of recombinant vaccines have, as yet, been widely utilized, many individuals believe that these technologies are the wave of the future in vaccine production. In this paper our work on the use of mammalian cells for the development of subunit vaccines for the prevention of infection by herpes simplex virus (HSV) types 1 and 2 is reviewed. A surface glycoprotein of these viruses, gD, was chosen as a likely candidate for a subunit vaccine based upon its primary sequence conservation between the two viral types as well as upon data suggesting that antibodies against this glycoprotein were highly efficient at neutralizing virus infectivity. Stable mammalian cell lines were constructed that expressed secreted forms of this protein, and the protein could be purified from cell-conditioned supernatants to near-homogeneity. Vaccination of mice with this glycoprotein was found to protect them from a lethal intraperitoneal infection by either the type 1 or type 2 forms of this virus. In a more realistic study, guinea pigs vaccinated with either the type 1 or type 2 form of gD were found to be protected from a genital form of HSV 2 infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Coexpression by vaccinia virus recombinants of equine herpesvirus 1 glycoproteins gp13 and gp14 results in potentiated immunity

The equine herpesvirus 1 glycoprotein 14 (EHV-1 gp14) gene was cloned, sequenced, and expressed by vaccinia virus recombinants. Recombinant virus vP613 elicited the production of EHV-1-neutralizing antibodies in guinea pigs and was effective in protecting hamsters from subsequent lethal EHV-1 challenge. Coexpression of EHV-1 gp14 in vaccinia virus recombinant vP634 along with EHV-1 gp13 (P. Guo, S. Goebel, S. Davis, M. E. Perkus, B. Languet, P. Desmettre, G. Allen, and E. Paoletti, J. Virol. 63:4189-4198, 1989) greatly enhanced the protective efficacy in the hamster challenge model over that obtained with single recombinants. The inoculum doses (log10) required for protection of 50% of hamsters were 6.1 (EHV-1 gp13), 5.2 (EHV-1 gp14), and less than 3.6 (vaccinia virus recombinant expressing both EHV-1 glycoproteins [gp13 and gp14]).

Deletions in herpes simplex virus glycoprotein D define nonessential and essential domains

Herpes simplex virus glycoprotein D (gD) is a major component of the virion envelope and infected cell membranes and is essential for virus entry into cells. We have recently shown that gD interacts with a limited number of cell surface receptors which are required for virus penetration into cells. To define domains of gD which are required for aspects of virus replication including receptor binding, deletion mutations of 5 to 14 amino acids were constructed by using oligonucleotide-directed mutagenesis. Plasmids containing mutant genes for gD were assayed for the ability to rescue a recombinant virus, F-gD beta, in which beta-galactosidase sequences replace gD-coding sequences. Effects on global folding and posttranslational processing of the molecules were assessed by using a panel of monoclonal antibodies which recognize both continuous and discontinuous epitopes. A region near the amino terminus (residues 7 to 21) of gD which is recognized by monoclonal antibodies able to neutralize herpes simplex virus in the absence of complement was not essential for function. In addition, virtually all of the cytoplasmic domain of gD and an extracellular domain close to the membrane were dispensable. In contrast, deletion mutations in the central region of the molecule, save for one exception, led to alterations in global folding of the molecule and maturation of the protein was inhibited.

Development of new cell lines for animal cell biotechnology

Mammalian cell culture has been an important technique in laboratory-scale experimentation for many decades. Developments in large-scale culture have been due to the need to grow large numbers of cells to support the growth of viruses for vaccine production, and more recently, for growing hybridoma cells as a source of monoclonal antibody. Increasingly, however, pharmaceutical products such as hormones, enzymes, growth factors, and clotting factors are being produced from cell lines which have been manipulated by recombinant DNA techniques. It is clear, therefore, that the high cost of growing mammalian cells on a large scale does not necessarily prohibit their use for biotechnology, and indeed there is considerable evidence to suggest that animal cell biotechnology will continue to be a major growth area in the future.

Expression of a viral gene in insulin-producing cell lines renders them susceptible to immunological destruction

The gene coding for the glycoprotein D of herpes simplex virus type 1 was cloned into plasmids under the transcriptional control of the SV40 promoter-enhancer or the rat insulin 1 promoter-enhancer sequences. These plasmids were transfected into rat insulinoma cells (RINm5F) and mouse NIH/3T3 cells and the expression of glycoprotein D was examined using cell surface immunofluoresence. The rat insulin 1 promoter-enhancer sequences directed efficient expression in RINm5F cells, but not in NIH/3T3 cells. In contrast, the SV40 promoter-enhancer sequences worked well in NIH/3T3 cells, but not in RINm5F cells. Expression of glycoprotein D did not interfere with insulin production by RINm5F cells. When stable cel lines expressing glycoprotein D were exposed to anti-herpes simplex virus type 1 antibodies and complement, they were destroyed. These studies provide additional evidence that specific promoter-enhancer elements are required for efficient gene expression in certain cell types and demonstrate that the expression of foreign antigens on the surface of insulin-producing cells can lead to their immunological destruction.

Expression in recombinant vaccinia virus of the equine herpesvirus 1 gene encoding glycoprotein gp13 and protection of immunized animals

The equine herpesvirus 1 (EHV-1) gene encoding glycoprotein 13 (gp13) was cloned into the hemagglutinin (HA) locus of vaccinia virus (Copenhagen strain). Expression of the gp13 gene was driven by the early/late vaccinia virus H6 promoter. Metabolically radiolabeled polypeptides of approximately 47 and 44 kilodaltons and 90 kilodaltons (glycosylated form) were precipitated with both polyclonal and gp13-specific monoclonal antibodies. Presentation of gp13 on the cytoplasmic membrane of cells infected with the recombinant gp13 vaccinia virus was demonstrated by immunofluorescence of unfixed cells. Inoculation of the recombinant gp13 vaccinia virus into guinea pigs induced neutralizing antibodies to both EHV-1 and vaccinia virus. Hamsters vaccinated with the recombinant gp13 vaccinia virus survived a lethal challenge with the hamster-adapted Kentucky strain of EHV-1. These results indicate that expression in vaccinia virus vectors of EHV-1 gp13, the glycoprotein homolog of herpes simplex virus gC-1 and gC-2, pseudorabies virus gIII, and the varicella-zoster virus gpV may provide useful vaccine candidates for equine herpesvirus infections.

Use of a glucocorticoid-inducible promoter for expression of herpes simplex virus type 1 glycoprotein gC1, a cytotoxic protein in mammalian cells

Abundant expression of herpes simplex virus type 1 glycoprotein gC (gC1) in transfected mammalian cells has not previously been achieved, possibly because gC1 protein is toxic to cells. To approach this problem, the gC1 coding sequence was placed under the control of the weak but inducible glucocorticoid-responsive promoter from the mouse mammary tumor virus (MMTV) long terminal repeat (LTR). As controls to evaluate for gC1 cytotoxicity, the MMTV LTR promoter was used to express glycoprotein gD1, and a strong, constitutive promoter from the Moloney murine sarcoma virus LTR was used to express gC1. L cells were transfected with these constructs, and a clone expressing gC1 from the inducible MMTV LTR promoter was analyzed. In the absence of glucocorticoid (dexamethasone) stimulation, only a low level of gC1 mRNA expression was detected; after overnight stimulation with dexamethasone, transcription increased approximately 200-fold. Abundant gC1 protein that was functionally active in that it bound complement component C3b, was produced. From passages 5 through 26 (70 cell population doublings), the gC1-producing clone became less responsive to overnight dexamethasone stimulation. The block to gC1 expression occurred at the level of transcription and was associated with hypermethylation of the MMTV LTR DNA. Treatment of the clone with 5-aza-2'-deoxycytidine partially reversed the block in gC1 protein production. Late-passage cells assumed a gC1-negative phenotype that appeared to offer a selective growth advantage, which suggested that gC1 was cytotoxic. Several findings support this view: (i) some cells expressing gC1 after overnight stimulation with dexamethasone assumed bizarre, syncytial shapes; (ii) continuous stimulation with dexamethasone for 5 weeks resulted in death of most cells; (iii) cells transfected with gC1 under the control of the strong Moloney murine sarcoma virus promoter assumed bizarre shapes, and stable gC1-expressing clones could not be established; and (iv) cells induced to express gD1 retained a normal appearance after overnight stimulation or 15 weeks of continuous stimulation with dexamethasone. The inducible MMTV LTR promoter is useful for expressing gC1 and may have applications for expressing other cytotoxic proteins.

Isolation of glycoprotein D from herpes simplex virus type 1 by gel filtration high performance liquid chromatography

Rabbit kidney (RK-13) and human jejunum and ileum (I-407) cells infected with herpes simplex virus type 1, strain F, were radiolabelled with [14C]glucosamine or [35S]methionine for 24 h. The cells were extracted with 1% Triton X-100 and the extracts were separated by gel filtration high performance liquid chromatography. Monoclonal antibody immunoprecipitation of the fractions collected from the column revealed a monomeric glycoprotein D (gD) of 52 - 56,000 molecular weight from RK-13 cells and two monomeric forms of gD, 54,000 and 58,000 molecular weight, from I-407 cells. Densitometry scanning of the autoradiograms from SDS-PAGE showed gD from the RK-13 host cells to be 98.7% pure with the [35S]methionine label and 97.0% pure with the [14C]glucosamine. On the other hand, gD from the I-407 host cells was only 78.6% with the [35S]methionine label and 96% pure with the [14C]glucosamine. This method could provide a means for the isolation of native gD for structural and immunological studies.

Use of a glucocorticoid-inducible promoter for expression of herpes simplex virus type 1 glycoprotein gC1, a cytotoxic protein in mammalian cells

Abundant expression of herpes simplex virus type 1 glycoprotein gC (gC1) in transfected mammalian cells has not previously been achieved, possibly because gC1 protein is toxic to cells. To approach this problem, the gC1 coding sequence was placed under the control of the weak but inducible glucocorticoid-responsive promoter from the mouse mammary tumor virus (MMTV) long terminal repeat (LTR). As controls to evaluate for gC1 cytotoxicity, the MMTV LTR promoter was used to express glycoprotein gD1, and a strong, constitutive promoter from the Moloney murine sarcoma virus LTR was used to express gC1. L cells were transfected with these constructs, and a clone expressing gC1 from the inducible MMTV LTR promoter was analyzed. In the absence of glucocorticoid (dexamethasone) stimulation, only a low level of gC1 mRNA expression was detected; after overnight stimulation with dexamethasone, transcription increased approximately 200-fold. Abundant gC1 protein that was functionally active in that it bound complement component C3b, was produced. From passages 5 through 26 (70 cell population doublings), the gC1-producing clone became less responsive to overnight dexamethasone stimulation. The block to gC1 expression occurred at the level of transcription and was associated with hypermethylation of the MMTV LTR DNA. Treatment of the clone with 5-aza-2'-deoxycytidine partially reversed the block in gC1 protein production. Late-passage cells assumed a gC1-negative phenotype that appeared to offer a selective growth advantage, which suggested that gC1 was cytotoxic. Several findings support this view: (i) some cells expressing gC1 after overnight stimulation with dexamethasone assumed bizarre, syncytial shapes; (ii) continuous stimulation with dexamethasone for 5 weeks resulted in death of most cells; (iii) cells transfected with gC1 under the control of the strong Moloney murine sarcoma virus promoter assumed bizarre shapes, and stable gC1-expressing clones could not be established; and (iv) cells induced to express gD1 retained a normal appearance after overnight stimulation or 15 weeks of continuous stimulation with dexamethasone. The inducible MMTV LTR promoter is useful for expressing gC1 and may have applications for expressing other cytotoxic proteins.

Expression of membrane-associated and secreted variants of gp160 of human immunodeficiency virus type 1 in vitro and in continuous cell lines

The gene encoding the 856-amino-acid envelope glycoprotein, gp160, of human immunodeficiency virus type 1 was mutagenized and transfected into Chinese hamster ovary cells. Continuous cell lines that constitutively produced gp160 variants were isolated and used to study the biosynthesis and orientation of gp160 in cellular membranes. In vivo studies of gp160 variants failed to reveal domains upstream of amino acid residue 665 that could serve as stop transfer sequences. Analyses of gp160 variants expressed in vitro in a translation-coupled translocation system were consistent with the in vivo studies and provided evidence that gp160 is a simple bitopic membrane protein. A model for the orientation and function of gp160 in cellular membranes is presented. The cell lines described provide a convenient source of the gp120-gp41 complex.

Inversion events in the HSV-1 genome are directly mediated by the viral DNA replication machinery and lack sequence specificity

The bacterial transposable element Tn5 was observed to undergo high-frequency sequence inversion when integrated into the herpes simplex virus type 1 (HSV-1) genome. Deletion analysis of the IS50 elements through which this recombination event occurred demonstrated the absence of cis-acting signals involved in the inversion process. Several observations suggested an intimate association of the recombination mechanism with HSV-1 DNA replication, including the ability of the seven viral genes that are essential for HSV-1 DNA synthesis to mediate Tn5 inversion in the absence of any other viral functions. Comparable results were obtained by using duplicate copies of the L-S junction of the HSV-1 genome. Thus inversion of the L and S components of the HSV-1 genome during productive infection does not appear to be a site-specific process, but rather is the result of generalized recombination mediated by the complex of gene products that replicate the viral DNA.

Entry of herpes simplex virus 1 in BJ cells that constitutively express viral glycoprotein D is by endocytosis and results in degradation of the virus

The BJ cell line which constitutively expresses herpes simplex virus 1 glycoprotein D is resistant to infection with herpes simplex viruses. Analysis of clonal lines indicated that resistance to superinfecting virus correlates with the expression of glycoprotein D. Resistance was not due to a failure of attachment to cells, since the superinfecting virus absorbed to the BJ cells. Electron microscopic studies showed that the virions are juxtaposed to coated pits and are then taken up into endocytic vesicles. The virus particles contained in the vesicles were in various stages of degradation. Viral DNA that reached the nucleus was present in fewer copies per BJ cell than that in the parental BHKtk- cells infected at the same multiplicity. Moreover, unlike the viral DNA in BHKtk- cells which was amplified, that in BJ cells decreased in copy number. The results suggest that the glycoprotein D expressed in the BJ cell line interfered with fusion of the virion envelope with the plasma membrane but not with the adsorption of the virus to cells and that the viral proteins that mediate adsorption to and fusion of membranes appear to be distinct.

Prospects for vaccines for herpes simplex viruses

A subunit vaccine consisting of glycoprotein D from the surface of herpes simplex virus was prepared using recombinant deoxyribonucleic acid techniques to transfer the viral gene for glycoprotein D into Chinese hamster ovary cells. The glycoprotein D produced by these Chinese hamster cells combined with appropriate adjuvants effectively immunized mice and guinea pigs against herpes simplex infections. In addition to protecting guinea pigs from serious or fatal disease, the vaccine prevented a small group of guinea pigs from developing latent ganglionic infections. The vaccine has not yet been used in humans.

Signal for attachment of a phospholipid membrane anchor in decay accelerating factor

Decay accelerating factor (DAF) belongs to a novel group of membrane proteins anchored to the cell surface by a glycophospholipid membrane anchor that is covalently attached to the carboxyl terminus of the protein. The last 37 amino acids of membrane DAF, when fused to the carboxyl terminus of a secreted protein, are sufficient to target the fusion protein to the plasma membrane by means of a glycophospholipid anchor. This approach provides a novel means of targeting proteins to the cell-surface membrane.

Sequence analysis, cellular localization, and expression of a neuroretina adhesion and cell survival molecule

A cDNA for purpurin, a secreted 20,000 dalton neural retina cell adhesion and survival protein, has been sequenced and expressed in mammalian cells. Purpurin mRNA is found in both embryonic and adult retina, but not the brain, heart, or liver. The protein is highly concentrated in the neural retina between the pigmented epithelium and the outer segments of the photoreceptor cells; it is synthesized by photoreceptor cells. The predicted purpurin sequence contains 196 residues, has approximately 50% sequence homology with serum retinol binding protein, and is a member of the alpha-2 mu-globulin superfamily. Purpurin binds retinol and may play a major role in retinol transport across the interphotoreceptor cell matrix.

Delineation of a region of the human immunodeficiency virus type 1 gp120 glycoprotein critical for interaction with the CD4 receptor

The primary event in the infection of cells by HIV is the interaction between the viral envelope glycoprotein, gp120, and its cellular receptor, CD4. A recombinant form of gp120 was found to bind to a recombinant CD4 antigen with high affinity. Two gp120-specific murine monoclonal antibodies were able to block the interaction between gp120 and CD4. The gp120 epitope of one of these antibodies was isolated by immunoaffinity chromatography of acid-cleaved gp120 and shown to be contained within amino acids 397-439. Using in vitro mutagenesis, we have found that deletion of 12 amino acids from this region of gp120 leads to a complete loss of binding. In addition, a single amino acid substitution in this region results in significantly decreased binding, suggesting that sequences within this region are directly involved in the binding of gp120 to the CD4 receptor.

Prospects for the clinical management of human cytomegalovirus infections

Infection of susceptible populations by human cytomegalovirus (HCMV) is a significant public health problem in Western societies. Vaccination with live attenuated strains of HCMV has demonstrated some degree of clinical benefit but objections based on the possibility of these viruses becoming latent and their potential oncogenicity must be considered. Our knowledge of the biology and immunology of HCMV, although advancing rapidly, is still a long way short of being able to predict candidate subunit vaccines based on virus encoded proteins or glycoproteins. Treatment of the disease by injection of antibodies awaits a breakthrough and chemicals effective in the control of other human herpes viruses are disappointingly ineffective against HCMV. Clearly, prophylaxis is preferable to therapy and it is in the design of new effective vaccines that endeavours must be channelled so that we can control complications associated with severe clinical infection with this virus.

The quest for a herpes simplex virus vaccine: background and recent developments

Herpes simplex virus infections in humans range from localized skin infections of the oral, ocular and genital regions, to severe and often fatal disseminated infections of immunocompromised hosts. Following primary infection, the virus often becomes established in a latent form in the neurons of sensory ganglia and can reactivate to excrete virus asymptomatically or produce recrudescent lesions. This review describes some of the mechanisms involved in the immune response against HSV infections and examines the different strategies adopted to develop a vaccine against this seemingly intractable disease.

Expression and regulation of glycoprotein C gene of herpes simplex virus 1 resident in a clonal L-cell line

Ltk- cells were transfected with a plasmid containing the entire domain of glycoprotein C (gC), a true gamma or gamma 2 gene of herpes simplex virus 1 (HSV-1) and the methotrexate-resistant mouse dihydrofolate reductase mutant gene. The resulting methotrexate-resistant cell line was cloned; of the 39 clonal lines tested only 1, L3153(28), expressed gC after infection with HSV-1(MP), a gC- mutant, and none expressed gC constitutively. The induction of gC was optimal at multiplicities ranging between 0.5 and 2 PFU per cell, and the quantities produced were equivalent to or higher than those made by methotrexate-resistant gC- L cells infected with wild-type (gC+) virus. The gC gene resident in the L3153(28) cells was regulated as a beta gene inasmuch as the amounts of gC made in infected L3153(28) cells exposed to concentrations of phosphonoacetate that inhibited viral DNA synthesis were higher than those made in the absence of the drug, gC was induced at both permissive and nonpermissive temperatures by the DNA- mutant tsHA1 carrying a lesion in the gene specifying the major DNA-binding protein and which does not express gamma 2 genes at the nonpermissive temperature, and gC was induced only at the permissive temperature in cells infected with ts502 containing a mutation in the alpha 4 gene. The gC induced in L3153(28) cells was made earlier and processed faster to the mature form than that induced in a gC- clone of methotrexate-resistant cells infected with wild-type virus. Unlike virus stocks made in gC- cells, HSV-1(MP) made in L3153(28) cells was susceptible to neutralization by anti-gC monoclonal antibody.

Protection from genital herpes simplex virus type 2 infection by vaccination with cloned type 1 glycoprotein D

Guinea pigs were vaccinated with truncated herpes simplex virus type-1 (HSV-1) glycoprotein D produced in the genetically engineered mammalian cell line gD10.2. Vaccinated animals formed antibodies that neutralized both HSV-1 and herpes simplex virus type 2 (HSV-2) in an in vitro neutralization assay. Vaccinated animals were challenged with HSV-2 by intravaginal infection. Animals that received the immunogen in Freund's complete adjuvant were completely protected from the clinical manifestations of genital HSV-2 infection. Animals that received the immunogen incorporated in alum adjuvants were partly protected from clinical disease; the infections that did develop were significantly less severe than those that occurred in control animals injected with adjuvant alone. The results demonstrate that immunization with a purified viral protein can provide significant protection against primary genital infection by HSV-2 in guinea pigs.

Expression of an immediate early polypeptide and activation of a viral origin of DNA replication in cells containing a fragment of herpes simplex virus DNA

A thymidine kinase cotransformation procedure has been used to introduce the sequences encoding the herpes simplex virus type 1 (HSV-1) immediate early protein, Vmw175, into permissive cells either in the presence or the absence of the adjacent origin of viral DNA replication. Cells transformed by either origin-plus or origin-minus DNA were capable of expressing functional Vmw175 as indicated by their ability to complement the growth at the nonpermissive temperature of an HSV-1 mutant, ts K, containing a temperature-sensitive lesion in the Vmw175 gene. A proportion of the virus yield from cells transformed with the origin-plus, but not the origin-minus, plasmid exhibited a ts+ phenotype. The generation of ts+ virus correlated with an amplification of input plasmid DNA sequences which occurred following superinfection, suggesting that recombination between the ts mutant and the amplified viral DNA sequences had taken place. Encapsidation of the amplified DNA sequences was also detected, suggesting that in addition to a functional origin of replication and Vmw175 gene the transformed cells also retain the viral DNA packaging signals.

Expression in bacteria of gB-glycoprotein-coding sequences of Herpes simplex virus type 2

A plasmid with an insert that encodes the glycoprotein B(gB) gene of Herpes simplex virus type 2 (HSV-2) has been isolated. DNA sequences coding for a portion of the HSV-2 gB peptide were cloned into a bacterial lacZ alpha expression vector and used to transform Escherichia coli. Upon induction of lacZpo-promoted transcription, some of the bacteria became filamentous and produced inclusion bodies containing a large amount of a 65-kDal peptide that was shown to be precipitated by broad-spectrum antibodies to HSV-2 and HSV-1. The HSV-2 insert of one of these clones specifies amino acid residues corresponding to 135 through 629 of the gB of HSV-1 [Bzik et al., Virology 133 (1984) 301-314].