Replication-defective mutants of herpes simplex virus (HSV) induce cellular immunity and protect against lethal HSV infection

The Quest for Immunity: Exploring Human Herpesviruses as Vaccine Vectors

Herpesviruses are large DNA viruses that have long been used as powerful gene therapy tools. In recent years, the ability of herpesviruses to stimulate both innate and adaptive immune responses has led to their transition to various applications as vaccine vectors. This vaccinology branch is growing at an unprecedented and accelerated rate. To date, human herpesvirus-based vectors have been used in vaccines to combat a variety of infectious agents, including the Ebola virus, foot and mouth disease virus, and human immunodeficiency viruses. Additionally, these vectors are being tested as potential vaccines for cancer-associated antigens. Thanks to advances in recombinant DNA technology, immunology, and genomics, numerous steps in vaccine development have been greatly improved. A better understanding of herpesvirus biology and the interactions between these viruses and the host cells will undoubtedly foster the use of herpesvirus-based vaccine vectors in clinical settings. To overcome the existing drawbacks of these vectors, ongoing research is needed to further advance our knowledge of herpesvirus biology and to develop safer and more effective vaccine vectors. Advanced molecular virology and cell biology techniques must be used to better understand the mechanisms by which herpesviruses manipulate host cells and how viral gene expression is regulated during infection. In this review, we cover the underlying molecular structure of herpesviruses and the strategies used to engineer their genomes to optimize capacity and efficacy as vaccine vectors. Also, we assess the available data on the successful application of herpesvirus-based vaccines for combating diseases such as viral infections and the potential drawbacks and alternative approaches to surmount them.

Glycosylated protein 4-deficient PRRSV in complementing cell line shows low virus titer

Porcine Reproductive and Respiratory Syndrome (PRRS) threats the swine industry seriously. The spread of live vaccine virus leads to the emergence of recombinant virus, which brings biosafety problems. The replication-deficient virus as a vaccine candidate would avoid this problem. In the present study, the recombinant lentiviral plasmid pLV-EF1α-EGFP-2A-ORF4 was co-transfected with lentivirus in HEK293FT cells. The transfection mixture was harvested and transduced into Marc-145 to screen a cell line stably expressing the PRRSV ORF4 with puromycin. The cell line Marc-145-GP4 was confirmed with PCR, RT-PCR, IFA, and Western blotting using a monoclonal antibody against Glycoprotein 4 (GP4) of PRRSV. To obtain a replication-deficient PRRSV, Western blotting the recombinant plasmid pNM09-ΔORF4 was constructed by Overlap PCR and DNA recombinant technology with the pNM09 as a backbone plasmid. The pNM09-ΔORF4 was transfected into Marc-145-GP4 with electroporation after transcription in vitro. The replication-deficient virus was rescued on Marc-145-GP4 cells with trans-complementation of ORF4 gene and verified by RT-PCR and IFA. The results indicated that a cell line Marc-145-GP4 stably expressed PRRSV ORF4 was obtained. The recombinant GP4 was successfully expressed and obtained a monoclonal antibody Anti-A-GP4-70, which can specifically react with the virus. Finally, the replication-deficient virus rNM09-ΔORF4 can be rescued with low titer and could only reproduce on the Marc-145-GP4 cells. Unfortunately, the rNM09-ΔORF4 showed too low virus replication titer to determine it. This study lays the foundation for the rapid detection of PRRS and the functional study of GP4 and provides experience for replication-deficient PRRSV.

Prevention of fatal equine herpesvirus type 1 encephalitis in mice by immunization with a limited-replication cycle virus

Equine herpesvirus type 1 (EHV-1) is a devastating pathogen of horses, their natural hosts, and causes fatal encephalitis in non-natural hosts. We previously demonstrated that acylation of the tegument protein UL11 is required for viral replication in cultured cells. We created a mutant virus (EHV-1 UL12 trunc UL11 G2AC7AC9A), in which glycyl and cysteinyl residues at positions 2, 7 and 9 of UL11 that are normally acylated were replaced with alanyl residues. This virus, designated the 2/7/9 mutant, has a limited-replication cycle (LRC), in which replication stops after just a few cycles. Here, we tested whether the 2/7/9 mutant could be used as a vaccine against fatal encephalitis in a mouse model. A virulence test showed that the 2/7/9 mutant was not pathogenic in mice and elicited an antibody response. We also attempted to use the 2/7/9 mutant to immunize mice against a zebra-borne EHV-1, 94-137. Two trials were conducted, each with five immunized mice, five non-immunized and five control mice. In both trials, clinical signs and fatalities were much lower in the immunized mice than in the non-immunized mice. In addition, none of the mice in either trial developed neutralizing antibodies, indicating that the immunity induced by the 2/7/9 mutant was not due to neutralizing activity. The results indicate that the 2/7/9 LRC mutant has promise as a vaccine against EHV-1 infection non-natural hosts.

Replication-Deficient Zika Vector-Based Vaccine Provides Maternal and Fetal Protection in Mouse Model

Zika virus (ZIKV), a mosquito-borne human pathogen, causes dire congenital brain developmental abnormalities in children of infected mothers. The global health crisis precipitated by this virus has led to a concerted effort to develop effective therapies and prophylactic measures although, unfortunately, not very successfully. The error-prone nature of RNA viral genome replication tends to promote evolution of novel viral strains, which could cause epidemics and pandemics. As such, our objective was to develop a safe and effective replication-deficient ZIKV vector-based vaccine candidate. We approached this by generating a ZIKV vector containing only the nonstructural (NS) 5'-untranslated (UTR)-NS-3' UTR sequences, with the structural proteins capsid (C), precursor membrane (prM), and envelope (E) (CprME) used as a packaging system. We efficiently packaged replication-deficient Zika vaccine particles in human producer cells and verified antigen expression in vitro. In vivo studies showed that, after inoculation in neonatal mice, the Zika vaccine candidate (ZVAX) was safe and did not produce any replication-competent revertant viruses. Immunization of adult, nonpregnant mice showed that ZVAX protected mice from lethal challenge by limiting viral replication. We then evaluated the safety and efficacy of ZVAX in pregnant mice, where it was shown to provide efficient maternal and fetal protection against Zika disease. Mass cytometry analysis showed that vaccinated pregnant animals had high levels of splenic CD8+ T cells and effector memory T cell responses with reduced proinflammatory cell responses, suggesting that endogenous expression of NS proteins by ZVAX induced cellular immunity against ZIKV NS proteins. We also investigated humoral immunity against ZIKV, which is potentially induced by viral proteins present in ZVAX virions. We found no significant difference in neutralizing antibody titer in vaccinated or unvaccinated challenged animals; therefore, it is likely that cellular immunity plays a major role in ZVAX-mediated protection against ZIKV infection. In conclusion, we demonstrated ZVAX as an effective inducer of protective immunity against ZIKV, which can be further evaluated for potential prophylactic application in humans. IMPORTANCE This research is important as it strives to address the critical need for effective prophylactic measures against the outbreak of Zika virus (ZIKV) and outlines an important vaccine technology that could potentially be used to induce immune responses against other pandemic-potential viruses.

Nanocarrier vaccines for SARS-CoV-2

The SARS-CoV-2 global pandemic has seen rapid spread, disease morbidities and death associated with substantive social, economic and societal impacts. Treatments rely on re-purposed antivirals and immune modulatory agents focusing on attenuating the acute respiratory distress syndrome. No curative therapies exist. Vaccines remain the best hope for disease control and the principal global effort to end the pandemic. Herein, we summarize those developments with a focus on the role played by nanocarrier delivery.

Rotavirus reverse genetics systems: Development and application

Rotaviruses (RVs) cause acute gastroenteritis in infants and young children. Since 2006, live-attenuated vaccines have reduced the number of RV-associated deaths; however, RV is still responsible for an estimated 228,047 annual deaths worldwide. RV, a member of the family Reoviridae, has an 11-segmented double-stranded RNA genome contained within a non-enveloped, triple layered virus particle. In 2017, a long-awaited helper virus-free reverse genetics system for RV was established. Since then, numerous studies have reported the generation of recombinant RVs; these studies verify the robustness of reverse genetics systems. This review provides technical insight into current reverse genetics systems for RVs, as well as discussing basic and applied studies that have used these systems.

The African Swine Fever Virus (ASFV) Topoisomerase II as a Target for Viral Prevention and Control

African swine fever (ASF) is, once more, spreading throughout the world. After its recent reintroduction in Georgia, it quickly reached many neighboring countries in Eastern Europe. It was also detected in Asia, infecting China, the world's biggest pig producer, and spreading to many of the surrounding countries. Without any vaccine or effective treatment currently available, new strategies for the control of the disease are mandatory. Its etiological agent, the African swine fever virus (ASFV), has been shown to code for a type II DNA topoisomerase. These are enzymes capable of modulating the topology of DNA molecules, known to be essential in unicellular and multicellular organisms, and constitute targets in antibacterial and anti-cancer treatments. In this review, we summarize most of what is known about this viral enzyme, pP1192R, and discuss about its possible role(s) during infection. Given the essential role of type II topoisomerases in cells, the data so far suggest that pP1192R is likely to be equally essential for the virus and thus a promising target for the elaboration of a replication-defective virus, which could provide the basis for an effective vaccine. Furthermore, the use of inhibitors could be considered to control the spread of the infection during outbreaks and therefore limit the spreading of the disease.

Analysis of the Protective Immunity Induced by Herpes Simplex Virus 1 Strain M3 with an Attenuated Phenotype Due to Mutations in the Viral ul7, ul41, and LAT Genes

Herpes simplex virus 1 (HSV1) is an important pathogen with a worldwide epidemic trend that affects populations of various ages. It has a high morbidity, particularly in juveniles, but a successful HSV1 vaccine is not currently available. Thus, our study systematically observed the immune responses induced in mice immunized with the attenuated HSV1 M3 mutant strain, which has mutations in the genes encoding the UL7 and Vhs tegument proteins and the latency-associated transcript. The immunity induced by the M3 mutant strain can control acute viral infection during HSV1 wild-type strain infection. Moreover, this immunity exerts a potent effect on controlling viral entry into the trigeminal neurons. These data encourage further studies investigating the development of M3 as a potential vaccine candidate, and much work is necessary to evaluate the safety and improve the immunogenicity of this strain.

Impact of Type I Interferon on the Safety and Immunogenicity of an Experimental Live-Attenuated Herpes Simplex Virus 1 Vaccine in Mice

Viral fitness dictates virulence and capacity to evade host immune defenses. Understanding the biological underpinnings of such features is essential for rational vaccine development. We have previously shown that the live-attenuated herpes simplex virus 1 (HSV-1) mutant lacking the nuclear localization signal (NLS) on the ICP0 gene (0ΔNLS) is sensitive to inhibition by interferon beta (IFN-β) in vitro and functions as a highly efficacious experimental vaccine. Here, we characterize the host immune response and in vivo pathogenesis of HSV-1 0ΔNLS relative to its fully virulent parental strain in C57BL/6 mice. Additionally, we explore the role of type 1 interferon (IFN-α/β) signaling on virulence and immunogenicity of HSV-1 0ΔNLS and uncover a probable sex bias in the induction of IFN-α/β in the cornea during HSV-1 infection. Our data show that HSV-1 0ΔNLS lacks neurovirulence even in highly immunocompromised mice lacking the IFN-α/β receptor. These studies support the translational viability of the HSV-1 0ΔNLS vaccine strain by demonstrating that, while it is comparable to a virulent parental strain in terms of immunogenicity, HSV-1 0ΔNLS does not induce significant tissue pathology.IMPORTANCE HSV-1 is a common human pathogen associated with a variety of clinical presentations ranging in severity from periodic "cold sores" to lethal encephalitis. Despite the consistent failures of HSV subunit vaccines in clinical trials spanning the past 28 years, opposition to live-attenuated HSV vaccines predicated on unfounded safety concerns currently limits their widespread acceptance. Here, we demonstrate that a live-attenuated HSV-1 vaccine has great translational potential.

Ocular herpes: the pathophysiology, management and treatment of herpetic eye diseases

Herpesviruses are a prominent cause of human viral disease, second only to the cold and influenza viruses. Most herpesvirus infections are mild or asymptomatic. However, when the virus invades the eye, a number of pathologies can develop and its associated sequelae have become a considerable source of ocular morbidity. The most common culprits of herpetic eye disease are the herpes simplex virus (HSV), varicella zoster virus (VZV), and cytomegalovirus (CMV). While primary infection can produce ocular disease, the most destructive manifestations tend to arise from recurrent infection. These recurrent infections can wreck devastating effects and lead to irreversible vision loss accompanied by a decreased quality of life, increased healthcare usage, and significant cost burden. Unfortunately, no method currently exists to eradicate herpesviruses from the body after infection. Treatment and management of herpes-related eye conditions continue to revolve around antiviral drugs, although corticosteroids, interferons, and other newer therapies may also be appropriate depending on the disease presentation. Ultimately, the advent of effective vaccines will be crucial to preventing herpesvirus diseases altogether and cutting the incidence of ocular complications.

Recent advances in vaccine development for herpes simplex virus types I and II

Despite recent advances in vaccine design and strategies, latent infection with herpes simplex virus (HSV) remains a formidable challenge. Approaches involving live-attenuated viruses and inactivated viral preparations were popular throughout the twentieth century. In the past ten years, many vaccine types, both prophylactic or therapeutic, have contained a replication-defective HSV, viral DNA or glycoproteins. New research focused on the mechanism of immune evasion by the virus has involved developing vaccines with various gene deletions and manipulations combined with the use of new and more specific adjuvants. In addition, new "prime-boost" methods of strengthening the vaccine efficacy have proven effective, but there have also been flaws with some recent strategies that appear to have compromised vaccine efficacy in humans. Given the complicated lifecycle of HSV and its unique way of spreading from cell-to-cell, it can be concluded that the development of an ideal vaccine needs new focus on cell-mediated immunity, better understanding of the latent viral genome and serious consideration of gender-based differences in immunity development among humans. This review summarizes recent developments made in the field and sheds light on some potentially new ways to conquer the problem including development of dual-action prophylactic microbicides that prohibit viral entry and, in addition, induce a strong antigen response.

Rationalizing the development of live attenuated virus vaccines

The design of vaccines against viral disease has evolved considerably over the past 50 years. Live attenuated viruses (LAVs)-those created by passaging a virus in cultured cells-have proven to be an effective means for preventing many viral diseases, including smallpox, polio, measles, mumps and yellow fever. Even so, empirical attenuation is unreliable in some cases and LAVs pose several safety issues. Although inactivated viruses and subunit vaccines alleviate many of these concerns, they have in general been less efficacious than their LAV counterparts. Advances in molecular virology--creating deleterious gene mutations, altering replication fidelity, deoptimizing codons and exerting control by microRNAs or zinc finger nucleases--are providing new ways of controlling viral replication and virulence and renewing interest in LAV vaccines. Whereas these rationally attenuated viruses may lead to a new generation of safer, more widely applicable LAV vaccines, each approach requires further testing before progression to human testing.

Rationalizing the development of live attenuated virus vaccines

The design of vaccines against viral disease has evolved considerably over the past 50 years. Live attenuated viruses (LAVs)-those created by passaging a virus in cultured cells-have proven to be an effective means for preventing many viral diseases, including smallpox, polio, measles, mumps and yellow fever. Even so, empirical attenuation is unreliable in some cases and LAVs pose several safety issues. Although inactivated viruses and subunit vaccines alleviate many of these concerns, they have in general been less efficacious than their LAV counterparts. Advances in molecular virology--creating deleterious gene mutations, altering replication fidelity, deoptimizing codons and exerting control by microRNAs or zinc finger nucleases--are providing new ways of controlling viral replication and virulence and renewing interest in LAV vaccines. Whereas these rationally attenuated viruses may lead to a new generation of safer, more widely applicable LAV vaccines, each approach requires further testing before progression to human testing.

A spread-deficient cytomegalovirus for assessment of first-target cells in vaccination

Human cytomegalovirus (HCMV) is a human pathogen that causes severe disease primarily in the immunocompromised or immunologically immature individual. To date, no vaccine is available. We describe use of a spread-deficient murine CMV (MCMV) as a novel approach for betaherpesvirus vaccination. To generate a spread-deficient MCMV, the conserved, essential gene M94 was deleted. Immunization with MCMV-DeltaM94 is apathogenic and protective against wild-type challenge even in highly susceptible IFNalphabetaR(-/-) mice. MCMV-DeltaM94 was able to induce a robust CD4(+) and CD8(+) T-cell response as well as a neutralizing antibody response comparable to that induced by wild-type infection. Endothelial cells were identified as activators of CD8(+) T cells in vivo. Thus, the vaccination with a spread-deficient betaherpesvirus is a safe and protective strategy and allows the linkage between cell tropism and immunogenicity. Furthermore, genomes of MCMV-DeltaM94 were present in lungs 12 months after infection, revealing first-target cells as sites of genome maintenance.

Expanding the repertoire of Modified Vaccinia Ankara-based vaccine vectors via genetic complementation strategies

Background

Modified Vaccinia virus Ankara (MVA) is a safe, highly attenuated orthopoxvirus that is being developed as a recombinant vaccine vector for immunization against a number of infectious diseases and cancers. However, the expression by MVA vectors of large numbers of poxvirus antigens, which display immunodominance over vectored antigens-of-interest for the priming of T cell responses, and the induction of vector-neutralizing antibodies, which curtail the efficacy of subsequent booster immunizations, remain as significant impediments to the overall utility of such vaccines. Thus, genetic approaches that enable the derivation of MVA vectors that are antigenically less complex may allow for rational improvement of MVA-based vaccines.

Principal Findings

We have developed a genetic complementation system that enables the deletion of essential viral genes from the MVA genome, thereby allowing us to generate MVA vaccine vectors that are antigenically less complex. Using this system, we deleted the essential uracil-DNA-glycosylase (udg) gene from MVA and propagated this otherwise replication-defective variant on a complementing cell line that constitutively expresses the poxvirus udg gene and that was derived from a newly identified continuous cell line that is permissive for growth of wild type MVA. The resulting virus, MVAΔudg, does not replicate its DNA genome or express late viral gene products during infection of non-complementing cells in culture. As proof-of-concept for immunological ‘focusing’, we demonstrate that immunization of mice with MVAΔudg elicits CD8+ T cell responses that are directed against a restricted repertoire of vector antigens, as compared to immunization with parental MVA. Immunization of rhesus macaques with MVAΔudg-gag, a udg⁻ recombinant virus that expresses an HIV subtype-B consensus gag transgene, elicited significantly higher frequencies of Gag-specific CD8 and CD4 T cells following both primary (2–4-fold) and booster (2-fold) immunizations as compared to the udg⁺ control virus MVA-gag, as determined by intracellular cytokine assay. In contrast, levels of HIV Gag-specific antibodies were elicited similarly in macaques following immunization with MVAΔudg-gag and MVA-gag. Furthermore, both udg⁻ and udg⁺ MVA vectors induced comparatively similar titers of MVA-specific neutralizing antibody responses following immunization of mice (over a 4-log range: 10⁴–10⁸ PFU) and rhesus macaques. These results suggest that the generation of MVA-specific neutralizing antibody responses are largely driven by input MVA antigens, rather than those that are synthesized de novo during infection, and that the processes governing the generation of antiviral antibody responses are more readily saturated by viral antigen than are those that elicit CD8+ T cell responses.

Significance

Our identification of a spontaneously-immortalized (but not transformed) chicken embryo fibroblast cell line (DF-1) that is fully permissive for MVA growth and that can be engineered to stably express MVA genes provides the basis for a genetic system for MVA. DF-1 cells (and derivatives thereof) constitute viable alternatives, for the manufacture of MVA-based vaccines, to primary CEFs – the conventional cell substrate for MVA vaccines that is not amenable to genetic complementation strategies due to these cells' finite lifespan in culture. The establishment of a genetic system for MVA, as illustrated here to allow udg deletion, enables the generation of novel replication-defective MVA mutants and expands the repertoire of genetic viral variants that can now be explored as improved vaccine vectors.

Prevention of genital herpes simplex virus type 1 and 2 disease in mice immunized with a gD-expressing dominant-negative recombinant HSV-1

CJ9-gD is a novel herpes simplex virus (HSV) type 1 recombinant virus that is completely replication-defective, expresses high-levels of HSV-1 major antigen glycoprotein D (gD), and can function in trans to inhibit replication of wild-type HSV-1 and HSV-2 in co-infected cells. Here, we show that immunization with CJ9-gD elicits strong and long-lasting humoral and Th1-like cellular immune responses against both HSV-1 and HSV-2. Mice immunized with CJ9-gD exhibited significant reductions in the extent and duration of intravaginal replication of challenge HSV-1 and HSV-2 compared with mock-immunized controls, and were completely protected from local or systemic herpetic disease after intravaginal challenge with wild-type HSV-1 or HSV-2.

Genetic engineering of a modified herpes simplex virus 1 vaccine vector

The herpes simplex virus 1 (HSV-1) d106 mutant virus is a multiple immediate-early gene deletion mutant virus that has been effective as an AIDS vaccine vector in rhesus macaques (Kaur A, Sanford HB, Garry D, Lang S, Klumpp SA, Watanabe D, et al. Ability of herpes simplex virus vectors to boost immune responses to DNA vectors and to protect against challenge by simian immunodeficiency virus. Virology 2007;357:199-214). Further analysis of this vector is needed to advance development into clinical trials. In this study we have defined the precise nature of the multiple IE gene mutations in the d106 viral genome and have used this information to construct a new transfer plasmid for gene transfer into d106. We tested the effect of an additional mutation in the U(L)41 gene on d106 immunogenicity and found that it did not improve the efficacy of the d106 vector, in contrast with results from other studies with U(L)41 gene mutants. The safety profile of d106 was improved by generating a new vector strain, d106S, with increased sensitivity to acyclovir. Finally, we have constructed a d106S recombinant vector that expresses the HIV clade C envelope protein. The d106S HIVenvC recombinant has retained the sensitivity to acyclovir, indicating that this phenotype is a stable property of the d106S vector.

Third-generation flavivirus vaccines based on single-cycle, encapsidation-defective viruses

Flaviviruses are arthropod-borne pathogens that cause significant disease on all continents of the world except Antarctica. Flavivirus diseases are particularly important in tropical regions where arthropod vectors are abundant. Live-attenuated virus vaccines (LAVs) and inactivated virus vaccines (INVs) exist for some of these diseases. LAVs are economical to produce and potent, but are not suitable for use in the immunocompromised. INVs are safer, but are more expensive to produce and less potent. Despite the success of both classes of these first-generation flavivirus vaccines, problems associated with their use indicate a need for improved products. Furthermore, there are no suitable vaccines available for important emerging flavivirus diseases, notably dengue and West Nile encephalitis (WNE). To address these needs, new products, including LAVs, INVs, viral-vectored, genetically engineered LAVs, naked DNA, and subunit vaccines are in various stages of development. Here we describe the current state of these first- and second-generation vaccine candidates, and compare these products to our recently described single-cycle, encapsidation defective flavivirus vaccine: RepliVAX. RepliVAX can be propagated in C-expressing cells (or as a unique two-component virus) using methods similar to those used to produce today's economical and potent LAVs. However, due to deletion of most of the gene for the C protein, RepliVAX cannot spread between normal cells, and is unable to cause disease in vaccinated animals. Nevertheless, RepliVAX is potent and efficacious in animal models for WNE and Japanese encephalitis, demonstrating its utility as a third-generation flavivirus vaccine that should be potent, economical to produce, and safe in the immunocompromised.

High-level expression of glycoprotein D by a dominant-negative HSV-1 virus augments its efficacy as a vaccine against HSV-1 infection

Using the T-REx (Invitrogen, Carlsbad, CA) gene switch technology, we previously generated a dominant-negative herpes simplex virus (HSV)-1 recombinant, CJ83193, capable of inhibiting its own replication as well as that of wild-type HSV-1 and HSV-2. It has been further demonstrated that CJ83193 is an effective vaccine against HSV-1 infection in a mouse ocular model. To ensure its safety and augment its efficacy, we generated an improved CJ83193-like HSV-1 recombinant, CJ9-gD, which contains a deletion in an HSV-1 essential gene and encodes an extra copy of gene-encoding glycoprotein D (gD) driven by the tetO-bearing human cytomegalovirus major immediate-early promoter. Unlike CJ83193, which exhibits limited plaque-forming capability in Vero cells and expresses little gD in infected cells, CJ9-gD is completely replication defective, yields high-level expression of gD following infection, and cannot establish detectable infection in mouse trigeminal ganglia following intranasal and ocular inoculation. Mice immunized with CJ9-gD produced 3.5-fold higher HSV-1 neutralizing antibody titer than CJ83193-immunized mice, and were completely protected from herpetic ocular disease following corneal challenge with wild-type HSV-1. Moreover, immunization of mice with CJ9-gD elicited a strong HSV-1-specific T-cell response and led to an 80% reduction in latent infection by challenge wild-type HSV-1 compared with the mock-immunized control.

Immunization with a dominant-negative recombinant HSV type 1 protects against HSV-1 skin disease in guinea pigs

CJ9-gD belongs to a new class of replication-defective recombinant herpes simplex viruses (HSVs) type 1 that can function in trans to prevent the replication of wild-type HSV in co-infected cells. Furthermore, CJ9-gD cannot establish latent infection in vivo and it expresses high levels of the major HSV-1 antigen glycoprotein D immediately following infection. In this study we show that guinea pigs immunized with CJ9-gD developed at least 9,600-fold higher titers of HSV-1-specific neutralization antibodies than mock-immunized controls. After challenge with wild-type HSV-1, all 10 mock-immunized guinea pigs developed multiple skin lesions with an average of 53.3 lesions per animal, whereas only 2 minor lesions were found in 1 of 10 CJ9-gD-immunized animals, representing a 267-fold reduction on the incidence of primary herpetic skin lesions in immunized animals. Quantitative PCR analysis revealed that the amount and frequency of wild-type HSV-1 viral DNA present in dorsal root ganglia of immunized animals was significantly lower than that in mock-immunized controls. Collectively, we demonstrate that vaccination with CJ9-gD elicits strong and protective immune responses against primary HSV-1 skin disease and reduces the extent of latent infection by challenge virus.

Absence or overexpression of the Varicella-Zoster Virus (VZV) ORF29 latency-associated protein impairs late gene expression and reduces VZV latency in a rodent model

Varicella-zoster virus (VZV) ORF29 encodes the viral single-stranded DNA binding protein and is expressed during latency in human ganglia. We constructed an ORF29 deletion mutant virus and showed that the virus could replicate only in cells expressing ORF29. An ORF29-repaired virus, in which ORF29 was driven by a cytomegalovirus promoter, grew to peak titers similar to those seen with the parental virus. The level of ORF29 protein in cells infected with the repaired virus was greater than that seen with parental virus. Infection of cells with either the ORF29 deletion or repaired virus resulted in similar levels of VZV immediate-early proteins but reduced levels of glycoprotein E compared to those observed with parental virus. Cotton rats infected with the ORF29 deletion mutant had a markedly reduced frequency of latent infection in dorsal root ganglia compared with those infected with parental virus (P < 0.00001). In contrast, infection of animals with the ORF29 deletion mutant resulted in a frequency of ganglionic infection at 3 days similar to that seen with the parental virus. Animals infected with the ORF29-repaired virus, which overexpresses ORF29, also had a reduced frequency of latent infection compared with those infected with parental virus (P = 0.0044). These studies indicate that regulation of ORF29 at appropriate levels is critical for VZV latency in a rodent model.

Developments in herpes simplex virus vaccines: old problems and new challenges

Vaccination has remained the best method for preventing virus spread. The herpes simplex virus (HSV) candidate vaccines tested till now were mostly purified subunit vaccines and/or recombinant envelope glycoproteins (such as gB and gD). In many experiments performed in mice, guinea pigs and rabbits, clear-cut protection against acute virus challenge was demonstrated along with the reduction of the extent of latency, when established in the immunized host. The immunotherapeutic effect of herpes vaccines seems less convincing. However, introduction of new adjuvants, which shift the cytokine production of helper T-cells toward stimulation of cytotoxic T-cells (TH1 type cytokine response), reveals a promising development. Mathematical analysis proved that overall prophylactic vaccination of seronegative women, even when eliciting 40-60 % antibody response only, would reduce the frequency of genital herpes within the vaccinated population. Even when partially effective, immunotherapeutic vaccination might represent a suitable alternative of chronic chemotherapy in recurrent labial and genital herpes.

A gamma-herpesvirus deficient in replication establishes chronic infection in vivo and is impervious to restriction by adaptive immune cells

Chronic gamma-herpesvirus infection is a dynamic process involving latent infection, reactivation from latency, and low level persistent replication. The gamma-herpesviruses maintain latent infection in restricted subsets of hematopoietic cells as a result of an intricate balance between host factors that suppress infection and viral factors that facilitate evasion of the immune response. Immune effectors limit reactivation and subsequent replication events, and the adaptive immune response ultimately restricts infection to a level compatible with life-long infection. However, it has not been possible to determine whether the immune system constrains chronic infection by directly targeting latently infected cells in vivo due to the complex nature of chronic infection. To begin to address this issue, we generated a murine gamma-herpesvirus 68 (gammaHV68) deficient in its ability to replicate or undergo reactivation from latency via a mutation in the single-stranded DNA binding protein encoded by ORF6. Even in the absence of lytic replication, this virus established long-term infection in peritoneal cells of wild-type mice at levels identical to that of wild-type gammaHV68, and generated an immune response that was sufficient to protect against secondary challenge with wild-type gammaHV68. Nevertheless, the number of latently infected cells was not significantly altered in mice deficient in T cells or both T cells and B cells, demonstrating that the adaptive immune system is incapable of altering infection with a virus lacking the capacity for lytic replication and reactivation from latency. Thus, these data support the conclusion that latency is immunologically silent.

Replication-defective viruses as vaccines and vaccine vectors

The classical viral vaccine approaches using inactivated virus or live-attenuated virus have not been successful for some viruses, such as human immunodeficiency virus or herpes simplex virus. Therefore, new types of vaccines are needed to combat these infections. Replication-defective mutant viruses are defective for one or more functions that are essential for viral genome replication or synthesis and assembly of viral particles. These viruses are propagated in complementing cell lines expressing the missing gene product; however, in normal cells, they express viral gene products but do not replicate to form progeny virions. As vaccines, these mutant viruses have advantages of both classical types of viral vaccines in being as safe as inactivated virus but expressing viral antigens inside infected cells so that MHC class I and class II presentation can occur efficiently. Replication-defective viruses have served both as vaccines for the virus itself and as a vector for the expression of heterologous antigens. The potential advantages and disadvantages of these vaccines are discussed as well as contrasting them with single-cycle mutant virus vaccines and replicon/amplicon versions of vaccines. Replication-defective viruses have also served as important probes of the host immune response in helping to define the importance of the first round of infected cells in the host immune response, the mechanisms of activation of innate immune response, and the role of the complement pathway in humoral immune responses to viruses.

Development and application of replication-incompetent HSV-1-based vectors

The replication-incompetent HSV-1-based vectors are herpesviruses in which genes that are 'essential' for viral replication have been either mutated or deleted. These deletions have substantially reduced their cytotoxicity by preventing early and late viral gene expression and, together with other deletions involving 'nonessential' genes, have also created space to introduce distinct and independently regulated expression cassettes for different transgenes. Therapeutic effects in gene therapy applications requiring simultaneous and synergic expression of multiple gene products are easily achievable with these vectors. A number of different HSV-1-based nonreplicative vectors for specific gene therapy applications have been developed so far. They have been tested in different gene therapy animal models of neuropathies (Parkinson's disease, chronic pain, spinal cord injury pain) and lysosomal storage disorders. Many replication-incompetent HSV-1-based vectors have also been used either as potential anti-herpes vaccines, as well as vaccine vectors for other pathogens in murine and simian models. Anticancer gene therapy approaches have also been successfully set up; gene therapy to other targets by using these vectors is feasible.

The dominant-negative herpes simplex virus type 1 (HSV-1) recombinant CJ83193 can serve as an effective vaccine against wild-type HSV-1 infection in mice

By selectively regulating the expression of the trans-dominant-negative mutant polypeptide UL9-C535C, of herpes simplex virus type 1 (HSV-1) origin binding protein UL9 with the tetracycline repressor (tetR)-mediated gene switch, we recently generated a novel replication-defective and anti-HSV-specific HSV-1 recombinant, CJ83193. The UL9-C535C peptides expressed by CJ83193 can function as a potent intracellular therapy against its own replication, as well as the replication of wild-type HSV-1 and HSV-2 in coinfected cells. In this report, we demonstrate that CJ83193 cannot initiate acute productive infection in corneas of infected mice nor can it reactivate from trigeminal ganglia of mice latently infected by CJ83193 in a mouse ocular model. Given that CJ83193 is capable of expressing the viral alpha, beta, and gamma1 genes but little or no gamma2 genes, we tested the vaccine potential of CJ83193 against HSV-1 infection in a mouse ocular model. Our studies showed that immunization with CJ83193 significantly reduced the yields of challenge HSV in the eyes and trigeminal ganglia on days 3, 5, and 7 postchallenge. Like in mice immunized with the wild-type HSV-1 strain KOS, immunization of mice with CJ83193 prevents the development of keratitis and encephalitis induced by corneal challenge with wild-type HSV-1 strain mP. Delayed-type hypersensitivity (DTH) assays demonstrate that CJ83193 can elicit durable cell-mediated immunity at the same level as that of wild-type HSV-1 and is more effective than that induced by d27, an HSV-1 ICP27 deletion mutant. Moreover, mice immunized with CJ83193 developed strong, durable HSV-1-neutralizing antibodies at levels at least twofold higher than those induced by d27. The results presented in this report have shed new light on the development of effective HSV viral vaccines that encode a unique safety mechanism capable of inhibiting the mutant's own replication and that of wild-type virus.

Recent progress in herpes simplex virus immunobiology and vaccine research

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) cause prevalent, chronic infections that have serious outcomes in some individuals. Neonatal herpes may occur when the infant traverses the cervix during maternal genital herpes. Genital herpes is a major risk factor for human immunodeficiency virus type 1 transmission. Considerable efforts have been made to design and test vaccines for HSV, focusing on genital infection with HSV-2. Several protein subunit vaccines based on HSV-2 envelope glycoproteins have reached advanced-phase clinical trials. These antigens were chosen because they are the targets of neutralizing-antibody responses and because they elicit cellular immunity. Encouraging results have been reported in studies of treatment of HSV-seronegative women with a vaccine consisting of truncated glycoprotein D of HSV-2 and a novel adjuvant. Because most sexual HSV transmission occurs during asymptomatic shedding, it is important to evaluate the impact of vaccination on HSV-2 infection, clinically apparent genital herpes, and HSV shedding among vaccine recipients who acquire infection. There are several other attractive formats, including subunit vaccines that target cellular immune responses, live attenuated virus strains, and mutant strains that undergo incomplete lytic replication. HSV vaccines have also been evaluated for the immunotherapy of established HSV infection.

Herpes simplex virus vectors elicit durable immune responses in the presence of preexisting host immunity

Herpes simplex virus (HSV) recombinants are being developed as vaccine vectors for the expression of heterologous antigens. There is concern, however, that preexisting HSV immunity may decrease their effectiveness. We have addressed this issue in an animal model. Immunized mice were inoculated with a replication-defective HSV-1 vector that expressed the Escherichia coli beta-galactosidase protein as a model antigen. We assessed vector efficacy by analyzing the immunoglobulin G (IgG) antibody response and cellular proliferative response directed against beta-galactosidase. We report that the ability of the vector to induce antibody or proliferative responses was not diminished by preexisting immunity to HSV. Of further note, the anti-HSV and anti-beta-galactosidase IgG responses following vector administration were extremely durable in both immunized and naive mice. These results indicate that the ability of a replication-defective HSV-derived vaccine vector to elicit long-lived immune responses in mice is not impaired by prior HSV exposure.

Regulation of herpes simplex virus gamma(1)34.5 expression and oncolysis of diffuse liver metastases by Myb34.5

Myb34.5 is a herpes simplex virus 1 (HSV-1) mutant deleted in the gene for ribonucleotide reductase (ICP6). It also carries a version of gamma(1)34.5 (a viral gene product that promotes the dephosphorylation of eIF-2alpha) that is under control of the E2F-responsive cellular B-myb promoter, rather than of its endogenous promoter. Myb34.5 replication in tumor cells results in their destruction (oncolysis). gamma(1)34.5 expression by HSV-1 subverts an important cell defense mechanism against viral replication by preventing shutoff of protein synthesis after viral infection. Infection of colon carcinoma cells with Myb34.5 results in greater eIF-2alpha dephosphorylation and viral replication compared with infection with HSV-1 mutants completely defective in gamma(1)34.5 expression. In contrast, infection of normal hepatocytes with Myb34.5 results in low levels of eIF-2alpha dephosphorylation and viral replication that are similar to those observed with HSV-1 mutants completely defective in gamma(1)34.5 and ICP6. When administered intravascularly into mice with diffuse liver metastases, Myb34.5 has greater antineoplastic activity than HSV-1 mutants with completely defective gamma(1)34.5 expression and more restricted biodistribution compared with HSV-1 mutants with wild-type gamma(1)34.5 expression. Myb34.5 displays reduced virulence and toxicity compared to HSV-1 mutants with wild-type gamma(1)34.5 expression. Portal venous administration of Myb34.5 significantly reduces liver tumor burden in and prolongs the life of mice with diffuse liver metastases. Preexisting Ab's to HSV-1 do not reduce the antitumor efficacy of Myb34.5 in vivo.

Inhibition of herpes simplex virus type 2 (HSV-2) viral replication by the dominant negative mutant polypeptide of HSV-1 origin binding protein

UL9-C535C, the trans-dominant negative mutant polypeptide of herpes simplex virus type 1 (HSV-1) UL9 origin binding protein, is a potent inhibitor of HSV-1 viral DNA replication. This study focused on testing whether HSV-1 UL9-C535C and a genetically engineered UL9-C535C-encoding HSV-1 recombinant virus CJ83193 could inhibit herpes simplex virus type 2 (HSV-2) infection. First, a stable cell line, R-C535C, expressing a high level of UL9-C535C in the presence of tetracycline and little or no UL9-C535C in the absence of tetracycline was established. The single step growth experiment showed that like HSV-1, the de novo synthesis of HSV-2 could be suppressed approximately 1000-fold by UL9-C535C expressed in R-C535C cells in the presence of tetracycline. Secondly, compared with cells singly infected with HSV-2, co-infection of Vero cells with HSV-2 and CJ83193 reduced the replication efficiency of HSV-2 in co-infected cells by 30-40 fold in a single-step growth assay, which coincided with marked reduction in viral late gene expression, but not the expression of viral immediate-early genes. Taken together, in view of our recent demonstration that CJ83193 can serve as an effective vaccine in preventing HSV-1 infection in mice, one can generate a CJ83193-like HSV-2 recombinant virus that could potentially function as a new therapeutic class of recombinant viral vaccine against HSV-2 infection.

A tumor host range selection procedure identifies p150(sal2) as a target of polyoma virus large T antigen

Cancer cells may undergo loss or alterations in functions that certain viruses normally target to promote virus replication. Virus mutants that have lost the targeting function(s) should be able to grow in such cancer cells but not in normal cells. A "tumor host range" (t-hr) selection procedure has been devised and applied to polyoma virus based on this rationale. Studies of one t-hr mutant have led to the identification of the mSal2 gene product (p150(sal2)) as a binding partner of the large T antigen. mSal2 encodes a multizinc finger protein and putative transcription factor homologous to the Drosophila homeotic gene Spalt. The t-hr mutant encodes an altered large T protein that fails to interact with p150(sal2) and is defective in replication and tumor induction in newborn mice.

Comparison of different forms of herpes simplex replication-defective mutant viruses as vaccines in a mouse model of HSV-2 genital infection

Some subunit vaccines composed of herpes simplex virus (HSV) glycoproteins have been shown to protect guinea pigs against primary and recurrent genital infection by HSV-2. However, these vaccines were ineffective or only marginally effective in clinical trials. To attempt to define an animal model that would better discriminate the protective capacity of different vaccine formulations, we have examined the requirements for vaccine-induced protection against HSV-2 infection and disease in a mouse genital model. Unlike the guinea pig model where inactivated viral vaccines can protect nearly as well as live viral vaccines, inactivated viral vaccine afforded little protection in this mouse model. Using replication-defective mutant viruses as a form of live viral vaccine, we found that the extent of protection conferred by live vaccine was proportional to the amount of replication-defective mutant virus inoculated, over doses from 10(4) to 10(6) PFU. Furthermore, the mouse genital model showed quantitative differences in the degree of protection induced by various viral vaccine constructs. An HSV-2 replication-defective mutant virus protected better than an HSV-1 replication-defective mutant that expressed HSV-2 glycoprotein D, which in turn protected better than an HSV-2 replication-defective mutant virus. We conclude that this mouse genital model can rank different vaccine constructs for their capacity to induce protective immunity. Thus, genital infection of the mouse with HSV-2 may provide a stringent animal model that can predict the relative capacity of viral vaccines to stimulate protective immunity against HSV-2.

Combination suicide/cytokine gene therapy as adjuvants to a defective herpes simplex virus-based cancer vaccine

We have used syngeneic, established bilateral subcutaneous tumor models to examine the antitumor activity of herpes simplex virus (HSV) vectors, including the induction of an immune response against non-inoculated distant tumors. In such a model with CT26 murine colon adenocarcinoma, unilateral intratumoral inoculation of replication-deficient HSV-1 tsK inhibited the growth of both the inoculated and noninoculated established tumors. To enhance this limited antitumor immune response, we generated a defective HSV vector, dvIL12-tk encoding both interleukin-12 (IL-12) and HSV thymidine kinase (TK), with tsK as the helper virus. In a 'suicide gene' strategy, ganciclovir (GCV) treatment after intratumoral inoculation of dvlacZ-tk/tsK, encoding E. coli lacZ instead of IL-12, resulted in enhanced antitumor activity. Antitumor activity was also enhanced by local expression of IL-12 from dvIL12-tk/tsK. The combination of IL-12 cytokine therapy with GCV treatment was the most efficacious approach, with significantly greater inhibition of tumor growth than IL-12 or TK + GCV alone. These results illustrate the power of combining different cancer therapy approaches; 'suicide gene' therapy, cytokine therapy, and HSV vector infection. HSV vectors are particularly well suited to this because they can accommodate the insertion of large and multiple gene sequences.

Protective T-cell-based immunity induced in neonatal mice by a single replicative cycle of herpes simplex virus

Newborns are very susceptible to infections because their immune systems are not fully developed and react to antigen exposure preferentially with unresponsiveness. UV-inactivated herpes simplex virus type 1 (HSV-1) represents such an antigen and does not induce an immune response in neonates. In contrast, protective T cells were primed in newborn mice by a single replicative cycle of DISC HSV-1 given once within 24 h of birth. Each of the HSV-1-primed CD4(+) or CD8(+) T cells induced in wild-type or interferon-deficient mice conferred resistance to naive animals exposed to a lethal virus challenge. Inactivated HSV-1, injected at variable doses up to 10(4) times that of DISC HSV-1, was ineffective in inducing any detectable immune responses in neonates. Thus, the capacity of HSV-1 to replicate once, but not the number of virus particles per se, was decisive in inducing protective T-cell-associated immunity in newborn mice.

Effects of preexisting immunity on the response to herpes simplex-based oncolytic viral therapy

Herpes simplex viruses (HSV) type 1 are the basis of a number of anticancer strategies that have proven efficacious in animal models. They are natural human pathogens and the majority of adults have anti-HSV immunity. The current study examined the effect of preexisting immunity on the response to herpes-based oncolytic viral treatment of hepatic metastatic cancer in a murine model designed to simulate a clinical approach likely to be utilized for nonneurological tumors. Specifically, the anticancer effects of NV1020 or G207, two multimutated HSV-1 oncolytic viruses, were tested in immunocompetent mice previously immunized with a wild-type herpes simplex type 1 virus. Mice were documented to have humoral as well as cell-mediated immunity to HSV-1. Tumor response to oncolytic therapy was not measurably abrogated by immunity to HSV at the doses tested. The influence of route of viral administration was also tested in models of regional hepatic arterial and intravenous therapy. Route of viral administration influenced efficacy, as virus delivered intravenously produced some detectable attenuation while hepatic arterial therapy remained unaffected. These results demonstrate that when given at appropriate doses and in reasonable proximity to tumor targets, HSV-based oncolytic therapy can still be expected to be effective treatment for patients with hepatic malignancies.

Biological properties of herpes simplex virus 2 replication-defective mutant strains in a murine nasal infection model

We used a mouse nasal model of herpes simplex virus 2 (HSV-2) infection to examine the biological properties of HSV-2 wild-type (wt), TK-negative, and replication-defective strains in vivo. Nasal septa tissue is the major site of wt viral replication post intranasal (i.n.) inoculation. The HSV-2 strain 186 syn(+)-1 wt virus caused lethal encephalitis at doses of 10(4) PFU and above per nostril, and at lower doses no neurons in the trigeminal ganglia were positive for the latency-associated transcript, indicating a lack of latent infection. The 186DeltaKpn TK-negative mutant virus replicated in nasal septa tissue but showed low-level replication in trigeminal ganglia at only one timepoint. In situ hybridization of trigeminal ganglia showed that the number of LAT-positive neurons was proportional to the inoculum dose from 10(3) to 10(6) PFU per nare. The replication-defective mutant virus 5BlacZ showed no replication in nasal septa tissue and no persistence of viral DNA at the inoculation site or the trigeminal ganglia. Nevertheless, inoculation of 5BlacZ or the double-mutant dl5-29 at distal sites reduced acute replication and latent infection of 186DeltaKpn following intranasal challenge. This infection model provides a biological system to test the properties of HSV-2 strains and shows that replication-defective mutant strains do not persist at sites of inoculation or in sensory ganglia but can induce immune protection that reduces the latent viral load of a challenge virus.

Vaccine protection against simian immunodeficiency virus by recombinant strains of herpes simplex virus

An effective vaccine for AIDS may require development of novel vectors capable of eliciting long-lasting immune responses. Here we report the development and use of replication-competent and replication-defective strains of recombinant herpes simplex virus (HSV) that express envelope and Nef antigens of simian immunodeficiency virus (SIV). The HSV recombinants induced antienvelope antibody responses that persisted at relatively stable levels for months after the last administration. Two of seven rhesus monkeys vaccinated with recombinant HSV were solidly protected, and another showed a sustained reduction in viral load following rectal challenge with pathogenic SIVmac239 at 22 weeks following the last vaccine administration. HSV vectors thus show great promise for being able to elicit persistent immune responses and to provide durable protection against AIDS.

Construction, phenotypic analysis, and immunogenicity of a UL5/UL29 double deletion mutant of herpes simplex virus 2

A number of studies have shown that replication-defective mutant strains of herpes simplex virus (HSV) can induce protective immunity in animal systems against wild-type HSV challenge. However, all of those studies used viruses with single mutations. Because multiple, stable mutations provide optimal levels of safety for live vaccines, we felt that additional mutations needed to be engineered into a candidate vaccine strain for HSV-2 and genital herpes. We therefore isolated an HSV-2 strain with deletion mutations in two viral DNA replication protein genes, UL5 and UL29. The resulting double deletion mutant virus strain, dl5-29, fails to form plaques or to give any detectable single cycle yields in normal monkey or human cells. Nevertheless, dl5-29 expresses nearly the same pattern of gene products as the wild-type virus or the single mutant viruses and induces antibody titers in mice that are equivalent to those induced by single deletion mutant viruses. Therefore, it is feasible to isolate a mutant HSV strain with two mutations in essential genes and with an increased level of safety but which is still highly immunogenic.

Therapeutic vaccination against HSV-2: influence of vaccine formulation on immune responses and protection in mice

Therapeutic immunisation may represent a means of influencing viral infections that persist in the host by modulating the nature or level of host immunity. To assess the influence of the form of the antigenic stimulus on immunity to type-2 herpes simplex virus (HSV-2), mice pre-infected with sublethal doses of HSV-2 were immunised with various HSV-2 vaccine formulations prior to challenge infection with heterologous HSV-1. Measurements of interleukin-2 (IL-2), interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) levels in mouse spleen cell cultures restimulated in vitro with HSV-2 antigens showed that, depending on the form of HSV-2 antigen preparation used in this therapeutic context, changes in the levels of these cytokines could be effected. Measurement of HSV-specific antibody by serological tests support the contention that immunisation of HSV-2-infected mice can either enhance the existing Th1-like immune response elicited following HSV-2 infection, or modulate this response towards a more Th2-like profile, and this is dependent on the form of the antigenic stimulus. The degree of protection against subsequent lethal, heterologous HSV-1 challenge infection varied according to the nature of the infection and the immunisation history of the animals.

Effect of molecular size on the ability of zwitterionic polysaccharides to stimulate cellular immunity

The large-molecular-sized zwitterionic capsular polysaccharide of the anaerobe Bacteroides fragilis NCTC 9343, designated polysaccharide (PS) A, stimulates T cell proliferation in vitro and induces T cell-dependent protection against abscess formation in vivo. In the present study, we utilized a modification of a recently developed ozonolytic method for depolymerizing polysaccharides to examine the influence of the molecular size of PS A on cell-mediated immunity. Ozonolysis successfully depolymerized PS A into structurally intact fragments. PS A with average molecular sizes of 129.0 (native), 77.8, 46.9, and 17.1 kDa stimulated CD4+-cell proliferation in vitro to the same degree, whereas the 5.0-kDa fragment was much less stimulatory than the control 129.0-kDa PS A. Rats treated with 129.0-kDa, 46.9-kDa, and 17.1-kDa PS A molecules, but not those treated with the 5.0-kDa molecule, were protected against intraabdominal abscesses induced by challenge with viable B. fragilis. These results demonstrate that a zwitterionic polysaccharide as small as 22 repeating units (88 monosaccharides) elicits a T cell-dependent immune response. These findings clearly distinguish zwitterionic T cell-dependent polysaccharides from T cell-independent polysaccharides and give evidence of the existence of a novel mechanism for a polysaccharide-induced immune response.

Effect of prior exposure to herpes simplex virus 1 on viral vector-mediated tumor therapy in immunocompetent mice

Replication-competent, attenuated mutants of herpes simplex virus type 1 (HSV-1) have been shown to be efficacious for tumor therapy. However, these studies did not address the consequences of prior exposure to HSV, as will be the case with many patients likely to receive this therapy. Two strains of mice, A/J and BALB/c, were infected with wild-type HSV-1 by intraperitoneal injection and the immune response was determined by plaque reduction assay for neutralizing antibody and ELISA for IgG and IgM. Syngeneic tumors, N18 neuroblastoma and CT26 colon carcinoma, were implanted subcutaneously in HSV-1 seropositive and naive A/J and BALB/c mice, respectively. Established tumors were subsequently treated intratumorally with a multi-mutated HSV-1, G207. G207 inhibited tumor growth to a similar extent whether the mice were seropositive or not. We next examined the effect of multiple intratumoral inoculations of a 10-fold lower dose of G207 on tumor growth. In the multiple treatment group (biweekly for 3 weeks), 75% of tumors were cured, whereas no cures were seen in the single treatment group. We conclude that HSV seropositivity should not deleteriously affect the efficacy of G207 tumor therapy, and multiple inoculations of virus should be considered for clinical evaluation.

A novel anti-herpes simplex virus type 1-specific herpes simplex virus type 1 recombinant

A recombinant herpes simplex virus (HSV) capable of inhibiting its own replication as well as the replication of wild-type virus would have greatly increased safety as a general purpose vector for in vivo gene transfer, antitumor therapy, and viral vaccine against HSV infection. By using a tetracycline repressor (tetR)-mediated HSV-1 viral replication switch [Yao and Eriksson (1999). Hum. Gene Ther. 10, 419-427], we have generated a novel anti-HSV-1-specific HSV-1 recombinant (CJ83193) that expresses a trans-dominant negative HSV-1 UL9 origin-binding protein, UL9-C535C. The de novo synthesis of CJ83193 can be suppressed by UL9-C535C by at least 1 x 10(6)-fold in non-tetR-expressing cells, and is subject to tetracycline regulation over a range of four to five orders of magnitude in a tetR-expressing osteosarcoma line. In particular, the UL9-C535C peptides expressed from the CJ83193 genome can inhibit the replication of wild-type HSV-1 by 100- to 200-fold in single-step growth assays. The construction of CJ83193 creates a new general strategy for developing recombinant viral vectors able to function as an intracellular therapy against wild-type viral infections.

Immunization against genital herpes with a vaccine virus that has defects in productive and latent infection

An effective vaccine for genital herpes has been difficult to achieve because of the limited efficacy of subunit vaccines and the safety concerns about live viruses. As an alternative approach, mutant herpes simplex virus strains that are replication-defective can induce protective immunity. To increase the level of safety and to prove that replication was not needed for immunization, we constructed a mutant herpes simplex virus 2 strain containing two deletion mutations, each of which eliminated viral replication. The double-mutant virus induces protective immunity that can reduce acute viral shedding and latent infection in a mouse genital model, but importantly, the double-mutant virus shows a phenotypic defect in latent infection. This herpes vaccine strain, which is immunogenic but has defects in both productive and latent infection, provides a paradigm for the design of vaccines and vaccine vectors for other sexually transmitted diseases, such as AIDS.

Immunogenicity of herpes simplex virus type 1 mutants containing deletions in one or more alpha-genes: ICP4, ICP27, ICP22, and ICP0

Replication defective mutants of HSV have been proposed both as vaccine candidates and as vehicles for gene therapy because of their inability to produce infectious progeny. The immunogenicity of these HSV replication mutants, at both qualitative and quantitative levels, will directly determine their effectiveness for either of these applications. We have previously reported (Brehm et al., J. Virol., 71, 3534, 1997) that a replication defective mutant of HSV-1, which expresses a substantial level of viral genes without producing virus particles, is as efficient as wild-type HSV-1 in eliciting an HSV-specific cytotoxic T-lymphocyte (CTL) response. In this report, we have further evaluated the immunogenic potential of HSV-1-derived replication defective mutants by examining the generation of HSV-specific CTL following immunization with viruses that are severely restricted in viral gene expression due to mutations in one or more HSV alpha genes (ICP4, ICP27, ICP22, and ICP0). To measure the CTL responses induced by the HSV alpha-mutants, we have targeted two H-2Kb-restricted CTL epitopes: an epitope in a virion protein, gB (498-505), and an epitope in a nonvirion protein, ribonucleotide reductase (RR1 822-829). The HSV mutants used in this study are impaired in their ability to express gB while a majority of them still express RR1. Our findings demonstrate that a single immunization with these mutants is able to generate a strong CTL response not only to RR1 822-829, but also to gB498-505 despite their inability to express wild-type levels of gB. Furthermore, a single immunization with any individual mutant can also provide immune protection against HSV challenge. These results suggest that mutants which are restricted in gene expression may be used as effective immunogens in vivo.

Herpes simplex virus vaccines

Herpes simplex virus (HSV) infections are common and produce not only a primary infection, but also latent and recurrent infections. Therefore, the goals of a HSV vaccine are different from other vaccines. In this review, the goals of both prophylactic and therapeutic HSV vaccines are discussed and related to the immunobiology of acute and recurrent HSV infections. Next, the vaccine strategies that have been and are being evaluated for control of HSV disease are described. Current approaches take advantage of many of the modern methodologies for vaccine development. Thus, as we await final evaluations of subunit HSV glycoprotein vaccines, early phase I trails are evaluating newer vaccine approaches including DNA-based vaccines and replication-impaired viruses. The definitive HSV vaccine may await increased knowledge of the optimal viral antigen(s) and routes to induce genital tract immunity.