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

Combinatorial Herpes Simplex Vaccine Strategies: From Bedside to Bench and Back

The development of vaccines against herpes simplex virus type 1 and type 2 (HSV1 and HSV-2) is an important goal for global health. In this review we reexamined (i) the status of ocular herpes vaccines in clinical trials; and (ii) discusses the recent scientific advances in the understanding of differential immune response between HSV infected asymptomatic and symptomatic individuals that form the basis for the new combinatorial vaccine strategies targeting HSV; and (iii) shed light on our novel "asymptomatic" herpes approach based on protective immune mechanisms in seropositive asymptomatic individuals who are "naturally" protected from recurrent herpetic diseases. We previously reported that phenotypically and functionally distinct HSV-specific memory CD8+ T cell subsets in asymptomatic and symptomatic HSV-infected individuals. Moreover, a better protection induced following a prime/pull vaccine approach that consists of first priming anti-viral effector memory T cells systemically and then pulling them to the sites of virus reactivation (e.g., sensory ganglia) and replication (e.g., eyes and vaginal mucosa), following mucosal administration of vectors expressing T cell-attracting chemokines. In addition, we reported that a combination of prime/pull vaccine approach with approaches to reverse T cell exhaustion led to even better protection against herpes infection and disease. Blocking PD-1, LAG-3, TIGIT and/or TIM-3 immune checkpoint pathways helped in restoring the function of antiviral HSV-specific CD8+ T cells in latently infected ganglia and increased efficacy and longevity of the prime/pull herpes vaccine. We discussed that a prime/pull vaccine strategy that use of asymptomatic epitopes, combined with immune checkpoint blockade would prove to be a successful herpes vaccine approach.

Implication of COVID-19 on Erythrocytes Functionality: Red Blood Cell Biochemical Implications and Morpho-Functional Aspects

Several diseases (such as diabetes, cancer, and neurodegenerative disorders) affect the morpho-functional aspects of red blood cells, sometimes altering their normal metabolism. In this review, the hematological changes are evaluated, with particular focus on the morphology and metabolic aspects of erythrocytes. Changes in the functionality of such cells may, in fact, help provide important information about disease severity and progression. The viral infection causes significant damage to the blood cells that are altered in size, rigidity, and distribution width. Lower levels of hemoglobin and anemia have been reported in several studies, and an alteration in the concentration of antioxidant enzymes has been shown to promote a dangerous state of oxidative stress in red blood cells. Patients with severe COVID-19 showed an increase in hematological changes, indicating a progressive worsening as COVID-19 severity progressed. Therefore, monitored hematological alterations in patients with COVID-19 may play an important role in the management of the disease and prevent the risk of a severe course of the disease. Finally, monitored changes in erythrocytes and blood, in general, may be one of the causes of the condition known as Long COVID.

Alphaherpesvirus Vaccines

Prophylactic and therapeutic vaccines for the alphaherpesviruses including varicella zoster virus (VZV) and herpes simplex virus types 1 and 2 have been the focus of enormous preclinical and clinical research. A live viral vaccine for prevention of chickenpox and a subunit therapeutic vaccine to prevent zoster are highly successful. In contrast, progress towards the development of effective prophylactic or therapeutic vaccines against HSV-1 and HSV-2 has met with limited success. This review provides an overview of the successes and failures, the different types of immune responses elicited by various vaccine modalities, and the need to reconsider the preclinical models and immune correlates of protection against HSV.

Vaccination Route as a Determinant of Protective Antibody Responses against Herpes Simplex Virus

Herpes simplex viruses (HSV) are significant global health problems associated with mucosal and neurologic disease. Prior experimental vaccines primarily elicited neutralizing antibodies targeting glycoprotein D (gD), but those that advanced to clinical efficacy trials have failed. Preclinical studies with an HSV-2 strain deleted in gD (ΔgD-2) administered subcutaneously demonstrated that it elicited a high titer, weakly neutralizing antibodies that activated Fcg receptors to mediate antibody-dependent cellular cytotoxicity (ADCC), and completely protected mice against lethal disease and latency following vaginal or skin challenge with HSV-1 or HSV-2. Vaccine efficacy, however, may be impacted by dose and route of immunization. Thus, the current studies were designed to compare immunogenicity and efficacy following different routes of vaccination with escalating doses of ΔgD-2. We compared ΔgD-2 with two other candidates: recombinant gD protein combined with aluminum hydroxide and monophosphoryl lipid A adjuvants and a replication-defective virus deleted in two proteins involved in viral replication, dl5-29. Compared to the subcutaneous route, intramuscular and/or intradermal immunization resulted in increased total HSV antibody responses for all three vaccines and boosted the ADCC, but not the neutralizing response to ΔgD and dl5-29. The adjuvanted gD protein vaccine provided only partial protection and failed to elicit ADCC independent of route of administration. In contrast, the increased ADCC following intramuscular or intradermal administration of DgD-2 or dl5-29 translated into significantly increased protection. The DgD-2 vaccine provided 100% protection at doses as low as 5 × 104 pfu when administered intramuscularly or intradermally, but not subcutaneously. However, administration of a combination of low dose subcutaneous DgD-2 and adjuvanted gD protein resulted in greater protection than low dose DgD-2 alone indicating that gD neutralizing antibodies may contribute to protection. Taken together, these results demonstrate that ADCC provides a more predictive correlate of protection against HSV challenge in mice and support intramuscular or intradermal routes of vaccination.

Attenuated Phenotype and Immunogenic Characteristics of a Mutated Herpes Simplex Virus 1 Strain in the Rhesus Macaque

Herpes simplex virus type 1(HSV-1) presents a conundrum to public health worldwide because of its specific pathogenicity and clinical features. Some experimental vaccines, such as the recombinant viral glycoproteins, exhibit the viral immunogenicity of a host-specific immune response, but none of these has achieved a valid epidemiological protective efficacy in the human population. In the present study, we constructed an attenuated HSV-1 strain M3 through the partial deletion of UL7, UL41, and the latency-associated transcript (LAT) using the CRISPR/Cas9 system. The mutant strain exhibited lowered infectivity and virulence in macaques. Neutralization testing and ELISpot detection of the specific T-cell responses confirmed the specific immunity induced by M3 immunization and this immunity defended against the challenges of the wild-type strain and restricted the entry of the wild-type strain into the trigeminal ganglion. These results in rhesus macaques demonstrated the potential of the attenuated vaccine for the prevention of HSV-1 in humans.

Worldwide circulation of HSV-2 × HSV-1 recombinant strains

Homo sapiens harbor two distinct, medically significant species of simplexviruses, herpes simplex virus (HSV)-1 and HSV-2, with estimated divergence 6-8 million years ago (MYA). Unexpectedly, we found that circulating HSV-2 strains can contain HSV-1 DNA segments in three distinct genes. Using over 150 genital swabs from North and South America and Africa, we detected recombinants worldwide. Common, widely distributed gene UL39 genotypes are parsimoniously explained by an initial >457 basepair (bp) HSV-1 × HSV-2 crossover followed by back-recombination to HSV-2. Blocks of >244 and >539 bp of HSV-1 DNA within genes UL29 and UL30, respectively, have reached near fixation, with a minority of strains retaining sequences we posit as ancestral HSV-2. Our data add to previous in vitro and animal work, implying that in vivo cellular co-infection with HSV-1 and HSV-2 yields viable interspecies recombinants in the natural human host.

Herpes Simplex Vaccines: Prospects of Live-attenuated HSV Vaccines to Combat Genital and Ocular infections

Herpes simplex virus type-1 (HSV-1) and its closely related type-2 (HSV-2) viruses cause important clinical manifestations in humans including acute ocular disease and genital infections. These viruses establish latency in the trigeminal ganglionic and dorsal root neurons, respectively. Both viruses are widespread among humans and can frequently reactivate from latency causing disease. Currently, there are no vaccines available against herpes simplex viral infections. However, a number of promising vaccine approaches are being explored in pre-clinical investigations with few progressing to early phase clinical trials. Consensus research findings suggest that robust humoral and cellular immune responses may partially control the frequency of reactivation episodes and reduce clinical symptoms. Live-attenuated viral vaccines have long been considered as a viable option for generating robust and protective immune responses against viral pathogens. Varicella zoster virus (VZV) belongs to the same alphaherpesvirus subfamily with herpes simplex viruses. A live-attenuated VZV vaccine has been extensively used in a prophylactic and therapeutic approach to combat primary and recurrent VZV infection indicating that a similar vaccine approach may be feasible for HSVs. In this review, we summarize pre-clinical approaches to HSV vaccine development and current efforts to test certain vaccine approaches in human clinical trials. Also, we discuss the potential advantages of using a safe, live-attenuated HSV-1 vaccine strain to protect against both HSV-1 and HSV-2 infections.

A single intramuscular vaccination of mice with the HSV-1 VC2 virus with mutations in the glycoprotein K and the membrane protein UL20 confers full protection against lethal intravaginal challenge with virulent HSV-1 and HSV-2 strains

Herpes Simplex Virus type-1 (HSV-1) and type-2 (HSV-2) establish life-long infections and cause significant orofacial and genital infections in humans. HSV-1 is the leading cause of infectious blindness in the western world. Currently, there are no available vaccines to protect against herpes simplex infections. Recently, we showed that a single intramuscular immunization with an HSV-1(F) mutant virus lacking expression of the viral glycoprotein K (gK), which prevents the virus from entering into distal axons of ganglionic neurons, conferred significant protection against either virulent HSV-1(McKrae) or HSV-2(G) intravaginal challenge in mice. Specifically, 90% of the mice were protected against HSV-1(McKrae) challenge, while 70% of the mice were protected against HSV-2(G) challenge. We constructed the recombinant virus VC2 that contains specific mutations in gK and the membrane protein UL20 preventing virus entry into axonal compartments of neurons, while allowing efficient replication in cell culture, unlike the gK-null virus, which has a major defect in virus replication and spread. Intramuscular injection of mice with 10⁷ VC2 plaque forming units did not cause any significant clinical disease in mice. A single intramuscular immunization with the VC2 virus protected 100% of mice against lethal intravaginal challenge with either HSV-1(McKrae) or HSV-2(G) viruses. Importantly, vaccination with VC2 produced robust cross protective humoral and cellular immunity that fully protected vaccinated mice against lethal disease. Quantitative PCR did not detect any viral DNA in ganglionic tissues of vaccinated mice, while unvaccinated mice contained high levels of viral DNA. The VC2 virus may serve as an efficient vaccine against both HSV-1 and HSV-2 infections, as well as a safe vector for the production of vaccines against other viral and bacterial pathogens.

The challenges and opportunities for the development of a T-cell epitope-based herpes simplex vaccine

Herpes simplex virus type 1 and type 2 (HSV-1 & HSV-2) infections have been prevalent since the ancient Greek times. To this day, they still affect a staggering number of over a billion individuals worldwide. HSV-1 infections are predominant than HSV-2 infections and cause potentially blinding ocular herpes, oro-facial herpes and encephalitis. HSV-2 infections cause painful genital herpes, encephalitis, and death in newborns. While prophylactic and therapeutic HSV vaccines remain urgently needed for centuries, their development has been difficult. During the most recent National Institute of Health (NIH) workshop titled "Next Generation Herpes Simplex Virus Vaccines: The Challenges and Opportunities", basic researchers, funding agencies, and pharmaceutical representatives gathered: (i) to assess the status of herpes vaccine research; and (ii) to identify the gaps and propose alternative approaches in developing a safe and efficient herpes vaccine. One "common denominator" among previously failed clinical herpes vaccine trials is that they either used a whole virus or a whole viral protein, which contain both "pathogenic symptomatic" and "protective asymptomatic" antigens and epitopes. In this report, we continue to advocate developing "asymptomatic" epitope-based sub-unit vaccine strategies that selectively incorporate "protective asymptomatic" epitopes which: (i) are exclusively recognized by effector memory CD4(+) and CD8(+) T cells (TEM cells) from "naturally" protected seropositive asymptomatic individuals; and (ii) protect human leukocyte antigen (HLA) transgenic animal models of ocular and genital herpes. We review the role of animal models in herpes vaccine development and discuss their current status, challenges, and prospects.

Up to four distinct polypeptides are produced from the γ34.5 open reading frame of herpes simplex virus 2

The herpes simplex virus 1 (HSV-1) ICP34.5 protein strongly influences neurovirulence and regulates several cellular antiviral responses. Despite the clinical importance of HSV-2, relatively little is known about its ICP34.5 ortholog. We found that HSV-2 produces up to four distinct forms of ICP34.5 in infected cells: a full-length protein, one shorter form sharing the N terminus, and two shorter forms sharing the C terminus. These forms appeared with similar kinetics and accumulated in cells over much of the replication cycle. We confirmed that the N-terminal form is translated from the primary unspliced transcript to a stop codon within the intron unique to HSV-2 γ34.5. We found that the N-terminal form was produced in a variety of cell types and by 9 of 10 clinical isolates. ICP27 influenced but was not required for expression of the N-terminal form. Western blotting and reverse transcription-PCR indicated the C-terminal forms did not contain the N terminus and were not products of alternative splicing or internal transcript initiation. Expression plasmids encoding methionine at amino acids 56 and 70 generated products that comigrated in SDS-PAGE with the C1 and C2 forms, respectively, and mutation of these sites abolished C1 and C2. Using a recombinant HSV-2 encoding hemagglutinin (HA)-tagged ICP34.5, we demonstrated that the C-terminal forms were also produced during infection of many human and mouse cell types but were not detectable in mouse primary neurons. The protein diversity generated from the HSV-2 γ34.5 open reading frame implies additional layers of cellular regulation through potential independent activities associated with the various forms of ICP34.5.

IMPORTANCE

The herpes simplex virus 1 (HSV-1) protein ICP34.5, encoded by the γ34.5 gene, interferes with several host defense mechanisms by binding cellular proteins that would otherwise stimulate the cell's autophagic, translational-arrest, and type I interferon responses to virus infection. ICP34.5 also plays a crucial role in determining the severity of nervous system infections with HSV-1 and HSV-2. The HSV-2 γ34.5 gene contains an intron not present in HSV-1 γ34.5. A shorter N-terminal form of HSV-2 ICP34.5 can be translated from the unspliced γ34.5 mRNA. Here, we show that two additional forms consisting of the C-terminal portion of ICP34.5 are generated in infected cells. Production of these N- and C-terminal forms is highly conserved among HSV-2 strains, including many clinical isolates, and they are broadly expressed in several cell types, but not mouse primary neurons. Multiple ICP34.5 polypeptides add additional complexity to potential functional interactions influencing HSV-2 neurovirulence.

Single dose of glycoprotein K (gK)-deleted HSV-1 live-attenuated virus protects mice against lethal vaginal challenge with HSV-1 and HSV-2 and induces lasting T cell memory immune responses

Background

Herpes simplex virus type-1(HSV-1) and HSV-2 are important human pathogens that cause significant ocular and urogenital complications, respectively. We have previously shown that HSV-1 virions lacking glycoprotein K (gK) are unable to enter into neurons via synaptic axonal membranes and be transported in either retrograde or anterograde manner. Here, we tested the ability of HSV-1 (F) gK-null to protect against lethal challenge with either highly virulent ocular HSV-1 (McKrae strain), or genital HSV-2 (G strain). The gK-null virus vaccine efficiently protected mice against lethal vaginal infection with either HSV-1(McKrae) or HSV-2 (G).

Results

Female mice were immunized via a single intramuscular injection with 10⁶ PFU of the gK-null virus. Immunized mice were treated with Depo-Provera fourteen days after vaccination and were challenged via the vaginal route one week later. Ninety percent of mice vaccinated with the gK-null virus survived HSV-1 (McKrae) challenge, while 70% of these mice survived after HSV-2 (G) challenge. Moreover, all vaccinated mice exhibited substantially reduced disease symptoms irrespective of HSV-1 or HSV-2 challenge as compared to the mock vaccinated challenge group. T-cell memory immune responses to specific glycoprotein B (gB) and glycoprotein D (gD) peptide epitopes were detectable at 7 months post vaccination.

Conclusions

These results suggest that the highly attenuated, non-neurotropic gK-null virus may be used as an effective vaccine to protect against both virulent HSV-1 and HSV-2 genital infections and induce lasting immune responses.

Future of an "Asymptomatic" T-cell Epitope-Based Therapeutic Herpes Simplex Vaccine

Considering the limited success of the recent herpes clinical vaccine trial [1], new vaccine strategies are needed. Infections with herpes simplex virus type 1 and type 2 (HSV-1 & HSV-2) in the majority of men and women are usually asymptomatic and results in lifelong viral latency in neurons of sensory ganglia (SG). However, in a minority of men and women HSV spontaneous reactivation can cause recurrent disease (i.e., symptomatic individuals). Our recent findings show that T cells from symptomatic and asymptomatic men and women (i.e. those with and without recurrences, respectively) recognize different herpes epitopes. This finding breaks new ground and opens new doors to assess a new vaccine strategy: mucosal immunization with HSV-1 & HSV-2 epitopes that induce strong in vitro CD4 and CD8 T cell responses from PBMC derived from asymptomatic men and women (designated here as "asymptomatic" protective epitopes") could boost local and systemic "natural" protective immunity, induced by wild-type infection. Here we highlight the rationale and the future of our emerging "asymptomatic" T cell epitope-based mucosal vaccine strategy to decrease recurrent herpetic disease.

Immunization with a vaccine combining herpes simplex virus 2 (HSV-2) glycoprotein C (gC) and gD subunits improves the protection of dorsal root ganglia in mice and reduces the frequency of recurrent vaginal shedding of HSV-2 DNA in guinea pigs compared to immunization with gD alone

Attempts to develop a vaccine to prevent genital herpes simplex virus 2 (HSV-2) disease have been only marginally successful, suggesting that novel strategies are needed. Immunization with HSV-2 glycoprotein C (gC-2) and gD-2 was evaluated in mice and guinea pigs to determine whether adding gC-2 to a gD-2 subunit vaccine would improve protection by producing antibodies that block gC-2 immune evasion from complement. Antibodies produced by gC-2 immunization blocked the interaction between gC-2 and complement C3b, and passive transfer of gC-2 antibody protected complement-intact mice but not C3 knockout mice against HSV-2 challenge, indicating that gC-2 antibody is effective, at least in part, because it prevents HSV-2 evasion from complement. Immunization with gC-2 also produced neutralizing antibodies that were active in the absence of complement; however, the neutralizing titers were higher when complement was present, with the highest titers in animals immunized with both antigens. Animals immunized with the gC-2-plus-gD-2 combination had robust CD4+ T-cell responses to each immunogen. Multiple disease parameters were evaluated in mice and guinea pigs immunized with gC-2 alone, gD-2 alone, or both antigens. In general, gD-2 outperformed gC-2; however, the gC-2-plus-gD-2 combination outperformed gD-2 alone, particularly in protecting dorsal root ganglia in mice and reducing recurrent vaginal shedding of HSV-2 DNA in guinea pigs. Therefore, the gC-2 subunit antigen enhances a gD-2 subunit vaccine by stimulating a CD4+ T-cell response, by producing neutralizing antibodies that are effective in the absence and presence of complement, and by blocking immune evasion domains that inhibit complement activation.

HSV as a vector in vaccine development and gene therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), major human pathogen whose lifestyle is based on a long-term dual interaction with the infected host characterized by the existence of lytic and latent infections, has allowed the development of potential vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous system, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases and targeted infection of specific tissues or organs. Three different classes of vectors can be derived from HSV-1: replication-competent attenuated vectors, replication-incompetent recombinant vectors and defective helper-dependent vectors known as amplicons. This chapter highlights the current knowledge concerning design, construction and recent applications, as well as the potential and current limitations of the three different classes of HSV-1-based vectors.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

Immunization with a dominant-negative recombinant Herpes Simplex Virus (HSV) type 1 protects against HSV-2 genital disease in guinea pigs

Background

CJ9-gD is a novel dominant-negative recombinant herpes simplex virus type 1 (HSV-1) that is completely replication-defective, cannot establish detectable latent infection in vivo, and expresses high levels of the major HSV-1 antigen glycoprotein D immediately following infection. In the present study, CJ9-gD was evaluated as a vaccine against HSV-2 genital infection in guinea pigs.

Results

Animals immunized with CJ9-gD developed at least 700-fold higher titers of HSV-2-specific neutralization antibodies than mock-immunized controls. After challenge with wild-type HSV-2, all 10 control guinea pigs developed multiple genital lesions with an average of 21 lesions per animal. In contrast, only 2 minor lesions were found in 2 of 8 CJ9-gD-immunized animals, representing a 40-fold reduction on the incidence of primary genital lesions in immunized animals (p < 0.0001). Immunization significantly reduced the amount and duration of viral shedding and provided complete protection against neurological symptoms, while 90% of mock-immunized animals succumbed due to the severity of disease. Importantly, immunized animals showed no signs of recurrent disease or viral shedding during a 60-days observation period after recovery from primary infection, and carried 50-fold less latent viral DNA load in their dorsal root ganglia than the surviving mock-vaccinated controls (p < 0.0001).

Conclusions

Collectively, we demonstrate that vaccination with the HSV-1 recombinant CJ9-gD elicits strong and protective immune responses against primary and recurrent HSV-2 genital disease and significantly reduces the extent of latent infection.

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.

Immunization with HSV-1 glycoprotein C prevents immune evasion from complement and enhances the efficacy of an HSV-1 glycoprotein D subunit vaccine

Herpes simplex virus type 1 (HSV-1) glycoprotein C (gC-1) binds complement component C3b and inhibits complement-mediated immunity. HSV-1 glycoprotein D (gD-1) is a potent immunogen and a candidate antigen for a subunit vaccine. We evaluated whether combined immunization with gD-1 and gC-1 provides better protection against challenge than gD-1 alone based on antibodies to gC-1 preventing HSV-1-mediated immune evasion. IgG purified from mice immunized with gC-1 blocked C3b binding to gC-1 and greatly increased neutralization by gD-1 IgG in the presence of complement. Passive transfer of gC-1 IgG protected complement intact mice against HSV-1 challenge but not C3 knockout mice, indicating that gC-1 antibody activity in vivo is complement-dependent. Immunizing mice with gD-1 and gC-1 provided better protection than gD-1 alone in preventing zosteriform disease and infection of dorsal root ganglia. Therefore, gC-1 immunization prevents HSV-1 evasion from complement and enhances the protection provided by gD-1 immunization.

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.

Serological diagnosis of human herpes simplex virus type 1 and 2 infections by luciferase immunoprecipitation system assay

Highly quantitative and high-throughput serological tests for evaluation of humoral responses to herpes simplex virus 1 (HSV-1) and HSV-2 are not available. The efficacy of luciferase immunoprecipitation system (LIPS) assays for antibody profiling and serologic diagnosis of HSV-1 and HSV-2 infection was investigated using a panel of five recombinant HSV antigens. Plasma samples from subjects seropositive for HSV-1 and/or HSV-2 or seronegative for HSV-1 and HSV-2 that had previously been analyzed by Western blotting and the Focus Plexus immunoassay were evaluated. The LIPS test measuring anti-gG1 antibody titers was 96% sensitive and 96% specific for detecting HSV-1 infection, compared with the Focus immunoassay, and was 92% sensitive and 96% specific, compared with Western blotting. The results for the anti-gG2 LIPS test for HSV-2 precisely matched those for Western blotting, with 100% sensitivity and 100% specificity, and showed robust antibody titers in all the HSV-2-infected samples that were over 1,000 times higher than those in HSV-2-negative or HSV-1-positive samples. Antibodies to three additional HSV-2 proteins, gB, gD, and ICP8, were detected in many of the HSV-1- and/or HSV-2-infected plasma samples and showed preferentially higher immunoreactivity in HSV-2-infected plasma. The titers of antibodies to these three HSV-2 antigens also significantly correlated with each other (R=0.75 to 0.81; P<0.0001). These studies indicate that the robust anti-gG1 and anti-gG2 antibody responses detected by LIPS assays are useful for HSV-1 and HSV-2 detection and suggest that profiling of antibody responses to a panel of HSV proteins may be useful for characterizing individual humoral responses to infection and for monitoring responses to vaccines.

Comparison of immunogenicity and protective efficacy of genital herpes vaccine candidates herpes simplex virus 2 dl5-29 and dl5-29-41L in mice and guinea pigs

A replication-defective herpes simplex virus (HSV)-2 vaccine, dl5-29, which is deleted for two essential early genes, UL5 and UL29, is highly immunogenic and protective in mice and guinea pigs. In a prior study, a derivative of HSV-2 dl5-29 termed dl5-29-41L, which has an additional deletion in UL41 (that encodes the virion-host shut-off protein), was more immunogenic and protective against challenge with wild-type HSV-2 in mice when compared with dl5-29. To determine if deletion of UL41 improves the efficacy of dl5-29 in protecting guinea pigs from HSV-2, animals were immunized with dl5-29, dl5-29-41L, or PBS. The geometric mean neutralizing antibody titers from the dl5-29 and dl5-29-41L recipients were comparable (10(1.97) and 10(2.19), respectively, p=0.15). After intravaginal challenge with wild-type HSV-2, the dl5-29-41L and dl5-29 recipients shed similar titers of HSV-2 from the vagina. Mean acute disease severity scores, numbers of recurrences during 3 months after infection, and latent viral loads in sacral ganglia were similar for dl5-29 and dl5-29-41L (all p values >0.05). dl5-29 and dl5-29-41L completely protected mice from lethal challenge with HSV-2 and induced virus-specific CD8(+) T cells in the spleens of the animals. Thus, dl5-29 was as immunogenic and protective as dl5-29-41L under these conditions. dl5-29 was at least 250,000-fold less virulent than parental virus by intracranial inoculation in healthy mice, and caused no disease in SCID mice. Both dl5-29-41L and dl5-29 are equally effective and immunogenic in guinea pigs, and dl5-29 is very safe in immunocompromised animals.

Replication-defective virus vaccine-induced protection of mice from genital herpes simplex virus 2 requires CD4 T cells

Replication-defective herpes simplex virus 2 (HSV-2), used as an immunization strategy, protects against HSV-2 challenge in animal models. The roles of replication-defective virus-induced T cell subsets in control of HSV-2 infection have not been established. Mice lacking B cells (microMT) were immunized, depleted of CD4 or CD8 T cells, and then challenged intravaginally with HSV-2 to elucidate T cell subset contributions in the absence of virus-specific antibody. Immunized, CD4-depleted microMT mice developed severe infection of the genital tract and nervous system. In contrast, depletion of CD8 T cells from microMT mice did not attenuate protection. Immunized wild-type mice depleted of CD4 T cells also developed more severe HSV-2 infection than mice from which CD8 T cells were depleted. Thus, immunization with replication-defective virus induces T cell responses that effectively control HSV-2 infection in the absence of HSV-immune antibody, and CD4 T cells play the predominant role in this protective effect.

An HSV-1 gD mutant virus as an entry-impaired live virus vaccine

HSV-1 glycoprotein D (gD) interacts with HVEM and nectin-1 cell receptors to initiate virus entry. We prepared an HSV-1 strain with mutations in the gD gene at amino acid residues 3 and 38 by changing alanine to cysteine and tyrosine to cysteine, respectively (A3C/Y38C). These mutations were constructed with the intent of evaluating infection in vivo when virus enters by HVEM but not nectin-1 receptors and were based on prior reports demonstrating that purified gDA3C/Y38C protein binds to HVEM but not to nectin-1. While preparing a high-titered purified virus pool, the cysteine mutation at position 38 reverted to tyrosine, which occurred on two separate occasions. The resultant HSV-1 strain, KOS-gDA3C, had a single amino acid mutation at residue 3 and exhibited reduced entry into both HVEM and nectin-1 expressing cells. When tested in the murine flank model, the mutant virus was markedly attenuated for virulence and caused only mild disease, while the parental and rescued viruses produced much more severe disease. Thirty days after KOS-gDA3C infection, mice were challenged with a lethal dose of HSV-1 and were highly resistant to disease. The KOS-gDA3C mutation was stable during 30 passages in vitro and was present in each of 3 isolates obtained from infected mice. Therefore, this gD mutant virus impaired in entry may represent a novel candidate for an attenuated live HSV-1 vaccine.

Intravaginal administration of an inactivated vaccine prevents lesions induced by caprine herpesvirus-1 in goats

To evaluate the efficacy of mucosal vaccination with a beta-propiolactone inactivated caprine herpesvirus-1 (CpHV-1) vaccine, goats received vaginal administrations of two 7-day cycles at 2 weeks intervals. Seven days after the end of the second cycle, goats were challenged intravaginally with 4 ml of virulent BA.1 strain of CpHV-1. Vaccinated goats shed challenge virus for 8 days but, in comparison with control unvaccinated-challenged goats, were significantly protected from the classical clinical signs of genital lesions. Even without adjuvants, prolonged mucosal vaccination induced production of secretory IgA and provided significant clinical protection.

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.

Immunotherapeutic activity of a recombinant combined gB-gD-gE vaccine against recurrent HSV-2 infections in a guinea pig model

The guinea pig model of recurrent genital herpes simplex virus type 2 (HSV-2) infection was used to test the immunotherapeutic activity of a glycoprotein subunit vaccine. Vaccine formulation consisted of three recombinant herpes simplex virus (HSV) glycoproteins, namely gB1s, gD2t and gE1t, plus aluminium hydroxide [Al(OH)3)] adjuvant. One month after viral challenge, infected animals were therapeutically immunised by seven subcutaneous injections of a low dose of antigens with a weekly interval for the first five and a fortnightly interval for the last two administrations. Results showed that the treatment was highly effective in ameliorating the recidivist pathology of animals, suggesting that this kind of vaccine formulation and administration may be helpful for therapeutic intervention in humans affected by recurrent herpes infections.

Comparative efficacy and immunogenicity of replication-defective, recombinant glycoprotein, and DNA vaccines for herpes simplex virus 2 infections in mice and guinea pigs

Many candidate vaccines are effective in animal models of genital herpes simplex virus type 2 (HSV-2) infection. Among them, clinical trials showed moderate protection from genital disease with recombinant HSV-2 glycoprotein D (gD2) in alum-monophosphoryl lipid A adjuvant only in HSV women seronegative for both HSV-1 and HSV-2, encouraging development of additional vaccine options. Therefore, we undertook direct comparative studies of the prophylactic and therapeutic efficacies and immunogenicities of three different classes of candidate vaccines given in four regimens to two species of animals: recombinant gD2, a plasmid expressing gD2, and dl5-29, a replication-defective strain of HSV-2 with the essential genes UL5 and UL29 deleted. Both dl5-29 and gD2 were highly effective in attenuating acute and recurrent disease and reducing latent viral load, and both were superior to the plasmid vaccine alone or the plasmid vaccine followed by one dose of dl5-29. dl5-29 was also effective in treating established infections. Moreover, latent dl5-29 virus could not be detected by PCR in sacral ganglia from guinea pigs vaccinated intravaginally. Finally, dl5-29 was superior to gD2 in inducing higher neutralizing antibody titers and the more rapid accumulation of HSV-2-specific CD8+ T cells in trigeminal ganglia after challenge with wild-type virus. Given its efficacy, its defectiveness for latency, and its ability to induce rapid, virus-specific CD8(+)-T-cell responses, the dl5-29 vaccine may be a good candidate for early-phase human trials.

Pediatrics and herpes simplex virus vaccines

This review explores the development of prophylactic genital herpes vaccines and their potential impact on perinatal and oral-facial disease. Vaccine strategies have included the use of whole killed virus, viral subunits, attenuated live virus, viral vectors, and bare DNA. To date, the recombinant subunit vaccine, truncated HSV-2 gD and alum/MPL, has been the most efficacious. The vaccine is 73 to 74 percent effective in preventing genital disease in herpes simplex virus seronegative women but is not effective in men or seropositive women. Models predict a significant impact on genital herpes if it limits viral shedding. Reductions in perinatal and oral-facial disease are likely to occur as well. Once an efficacious herpes vaccine is available, its effectiveness will depend ultimately on vaccine acceptance by professional organizations, healthcare professionals, and parents. Further research is required to improve on and fully understand the implications of prophylactic herpes simplex vaccines.

Intravaginal administration of herpes simplex virus type 2 to mice leads to infection of several neural and extraneural sites

Female mice have been used extensively to study mucosal immunity against herpes simplex virus type 2 (HSV-2) infection of the vagina, but comparatively little is known about the spread of this virus to other tissues. Here the authors have used immunolabeling to demonstrate that HSV-2 infected the vaginal epithelium; the epithelium covering the vulva, perineum, and anal canal; and perineal hair follicles and sebaceous glands. The kinetics and basal localization of the immunolabeling indicated that the virus spread horizontally within the epithelial layer, starting in the vagina and then proceeding to the distal epithelial sites. HSV-2 also spread from the vagina to multiple neuronal sites including the paracervical ganglia (PCG), which are the major autonomic ganglia of the pelvis. The authors demonstrated both sympathetic and parasympathetic neurons in the PCG by labeling of acetylcholinesterase and tryosine hydroxlyase, and noted that infection was limited mainly or entirely to parasympathetic neurons. Infection of the PCG was correlated with the presence of virus in the autonomic ganglia in the walls of the rectum and urinary bladder, which in turn correlated with distention of these organs and retention of urine and feces. HSV-2 infection was also detected in cell bodies and axons in the lumbosacral sympathetic chain, in lumbosacral dorsal root ganglia, and in the dorsal portions of the lumbar spinal cord. Collectively, the data show that vaginal HSV-2 infection in mice leads to subsequent infection of multiple neural and epithelial sites. This information should be useful for development of a mouse model that can be used to study HSV-2 latency and for development of therapeutic vaccines to prevent recurrent infections.

Characterization of secreted and intracellular forms of a truncated hepatitis C virus E2 protein expressed by a recombinant herpes simplex virus

A replication-defective herpes simplex virus type 1 (HSV-1) recombinant lacking the glycoprotein H (gH)-encoding gene and expressing a truncated form of the hepatitis C (HCV) E2 glycoprotein (E2-661) was constructed and characterized. We show here that cells infected with the HSV/HCV recombinant virus efficiently express the HCV E2-661 protein. Most importantly, cellular and secreted E2-661 protein were both readily detected by the E2-conformational mAb H53 and despite the high expression levels, only limited amounts of misfolded aggregates were detected in either the cellular or secreted fractions. Furthermore, cell-associated and secreted E2-661 protein bound to the major extracellular loop (MEL) of CD81 in a concentration-dependent manner and both were highly reactive with sera from HCV-infected patients. Finally, BALB/c mice immunized intraperitoneally with the recombinant HSV/HCV virus induced high levels of anti-E2 antibodies. Analysis of the induced immunoglobulin G (IgG) isotypes showed high levels of IgG2a while the levels of the IgG1 isotype were significantly lower, suggesting a Th1-type of response. We conclude that the HSV-1 recombinant virus represents a promising tool for production of non-aggregated, immunologically active forms of the E2-661 protein and might have potential applications in vaccine development.

Vaccines against genital herpes: progress and limitations

Herpes simplex viruses (HSV) cause lifelong persistent infections with numerous disease manifestations. Genital herpes infections are widespread in populations throughout the world and a vaccine to protect against or subdue established genital herpes infections has been under development for decades. Vaccine-mediated protection against persistent viral infections can be extremely difficult to achieve. The more rapidly a virus reaches its target tissue for persistence, the more vigorously a vaccine-induced immune response must defend the vaccinated individual. After exposure to HSV through sexual contact, only a few days are required for the virus to establish latent infection of its host. Despite numerous improvements, traditional vaccine approaches of whole virus or protein subunits have met with only marginal success. The many disappointments have heightened interest in determining correlates of immune protection, studies pursued both in animal models and in humans. They have also led to reassessment of the goals of vaccination. Necessity has sparked several creative new vaccine approaches involving nucleic acid or live attenuated viruses and vectors. With improved concepts of protective immune responses has come fervent discussion of the means to stimulate and maintain cell-mediated immunity. The result of this work is likely to be a more thorough understanding of antiviral immunity in the genital mucosa and the nervous system, and of HSV pathogenesis and immune evasion strategies, as additional strides are taken toward the goal of a successful vaccine with which to confront HSV.

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.

Herpes simplex virus gene products required for viral inhibition of expression of G1-phase functions

HSV infection blocks G1 events in the cell cycle and arrests host cell growth in the G1 phase. To further define the mechanism of the effect and determine the viral gene product(s) responsible, we examined various mutant viruses for their effects on cell cycle regulatory proteins (pRb, cyclin D1, and cdk4) and on cell cycle progression into S phase. Unlike the wild-type virus, the ICP27 mutant virus was defective for blocking the phosphorylation of pRb proteins, and the normal pRb pattern was restored in cells infected with a rescued virus. The virion host shutoff (vhs) function, DNA replication, and late gene functions were not required for the virus-induced effects on pRb protein. BrdU incorporation in synchronized HSV-infected cells showed that ICP27 was required for blocking the cell cycle in the G1 phase. Furthermore, ICP27, ICP4, ICP0, and vhs were required for blocking the induction of the G1 cell cycle regulators cyclin D1 and cdk4 in HSV-infected cells. Both ICP27 and the vhs function contributed to the reduction of cyclin D1 mRNA levels in HSV-infected cells: These results provide evidence that HSV-1 ICP27 protein is essential for viral inhibition of G1-phase functions and that certain other HSV proteins are required for some of the viral effects on the cell cycle. Finally, these results show that HSV-1 ICP27 and vhs act jointly to reduce host mRNA levels in infected cells.