Efficacy of oral administration of live herpes simplex virus type 1 as a vaccine

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

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

Pathogenesis of herpes simplex hepatitis in macrophage-depleted mice: possible involvement of tumor necrosis factor-alpha and inducible nitric oxide synthase in massive apoptosis

Massive liver cell death provoked in silica-treated mice subsequently infected with herpes simplex virus (HSV)-1 is very similar pathohistologically to the cell death observed in human fulminant hepatitis. Previously, we have shown this liver cell death to be extensive apoptosis. In the present study, we examined various factors related to liver damage patho- and immunologically, as well as by reverse transcription-polymerase chain reaction. Tumor necrosis factor (TNF)-alpha, inducible nitric oxide synthase (iNOS), interferon (IFN)-alpha, and interleukin-6 mRNAs were detected to a much greater extent in silica-treated mice compared with control mice after HSV-1 infection, and excessive expression of iNOS mRNA and cytokine mRNAs in the liver may be closely related to massive liver cell apoptosis. The apoptosis was less related to the fas ligand than to TNF-alpha. Silica blockage of macrophages makes the liver cell extremely vulnerable to HSV-1 infection, and it induced expression of E-selectin and neutrophil margination in the liver. Subsequent HSV-1 infection induced excessive production of iNOS and cytokines, particularly TNF-alpha, but administration of anti-TNF-alpha antibody or NG-monomethyl-L-arginine was not completely efficacious for the survival of the mice. Overproduction of free radicals in combination with cytokines, such as TNF-alpha, IL-6 and IFN-alpha, may result in hepatic cell apoptosis.

Temporal progression of viral replication and gross and histological lesions in Balb/c mice inoculated epidermally with Saimiriine herpesvirus 1 (SaHV-1)

Saimiriine herpesvirus 1 (SaHV-1), an alphaherpesvirus enzootic in squirrel monkeys, is genetically related to monkey B virus and human herpes simplex virus (HSV). To study the temporal progression of viral spread and associated lesions, Balb/c mice were inoculated epidermally by scarification with a green fluorescent protein (GFP)-expressing recombinant strain of SaHV-1 and killed sequentially. Pinpoint ulcerative lesions in the inoculated epidermis progressed over a few days to unilateral or bilateral hindlimb paresis or paralysis, urinary and faecal incontinence, abdominal distension, hunched posture and eventual depression warranting euthanasia. Viral replication was present within epidermal keratinocytes, neurons of the dorsal root ganglia and thoracolumbar spinal cord, regional autonomic ganglia, lower urinary tract epithelium and colonic myenteric plexuses, as indicated by histological lesions and GFP expression. Almost all mice inoculated with 10(5) or 10(6) plaque-forming units (PFU) of SaHV-1 developed rapidly progressive disease. Two of eight mice given 10(4)PFU developed disease, but no mice receiving less than 10(4)PFU gave evidence of infection. Mice that showed no clinical signs also failed to develop an antiviral IgG response, indicating absence of active viral infection. For SaHV-1 inoculated epidermally, the ID(50), CNSD(50) and LD(50) values were identical (10(4.38)), indicating that successful infection by this route invariably resulted in lethal CNS (central nervous system) disease. Consistently severe disease in all infected animals, with regionally extensive distribution of viral replication, constituted a marked difference from the disease produced by intramuscular inoculation.

Development of prophylactic vaccines for genital and neonatal herpes

Over five decades numerous conventional candidate live attenuated and killed vaccines have failed to prevent genital herpes in clinical trials. However, a vaccine consisting of recombinant glycoprotein D from herpes simplex virus (HSV)-2 and deacylated monophosphoryl lipid A adjuvant has recently shown partial efficacy against clinical disease transmitted from HSV-1 and -2 seronegative women (73-74%). Comparisons between the efficacy of this vaccine and previous failed candidates and their effects on the immune system should help guide development of better vaccines through selection of appropriate HSV proteins, adjuvants or cytokines and newer vaccine vectors, such as DNA vaccines, recombinant viral vaccines and specific HSV mutants.

Comparison of adjuvant efficacy of herpes simplex virus type 1 recombinant viruses expressing TH1 and TH2 cytokine genes

The adjuvant effects of cytokines in humoral and cell-mediated immunity to herpes simplex virus type 1 (HSV-1) have been examined in mice using HSV-1 recombinant viruses expressing murine interleukin-2 (IL-2), IL-4, or gamma interferon (IFN-gamma) gene. Groups of naive BALB/c mice were immunized intraperitoneally with one or three doses of the HSV-1 recombinant viruses expressing IL-2, IL-4, or IFN-gamma or with parental control virus. Despite similar replication kinetics, these three recombinant viruses elicited different immune responses to HSV-1 on immunization. Immunization with the recombinant virus expressing IL-4 elicited a humoral response of greater magnitude than immunization with the recombinant viruses expressing IL-2 or IFN-gamma or with parental virus. In contrast, immunization with recombinant virus expressing IL-2 elicited a higher cytotoxic T-cell response than immunization with viruses expressing IL-4 or IFN-gamma. Stimulation in vitro of splenocytes obtained from the mice immunized with UV-inactivated HSV-1 McKrae resulted in a T(H)1 pattern of cytokine expression irrespective of the recombinant virus used in the immunization. As observed for the parental virus, both CD4(+) and CD8(+) T cells contributed equally to the production of IL-2 by the splenocytes of mice immunized with any of the three recombinant viruses. However, the pattern of IFN-gamma production by CD4(+) and CD8(+) T cells differed according to the recombinant virus used. After lethal ocular challenge, all immunized mice were protected completely against death and manifestations of eye disease caused by HSV-1, which are typical responses in unimmunized mice. Mice immunized with IL-4-expressing virus cleared the virus from their eyes more rapidly than mice immunized with IL-2- or IFN-gamma-expressing virus. Taken together, our results suggest that, in contrast to IFN-gamma which did not exhibit an adjuvant effect, both IL-4 and IL-2 act as adjuvants in immunization with HSV, with IL-4 showing greater efficacy.

Antibody responses, cytokine levels and protection of mice immunised with HSV-2 antigens formulated into NISV or ISCOM delivery systems

The immunogenicity of a type 2 herpes simplex virus (HSV-2) antigen preparation following its formulation into immunostimulating complexes (ISCOMs) or non-ionic surfactant vesicles (NISV) was investigated in a murine model. The immune responses induced by each formulation were characterised by antigen specific total and subclass serum responses, and by lymphocyte proliferation and cytokine (interleukin-2 (IL-2), interleukin-4 (IL-4) and interferon-gamma (IFN-gamma)) production by in vitro restimulated spleen cells. The degree of protection afforded to mice by these various HSV-2 vaccine preparations against homologous (HSV-2) and heterologous (HSV-1) challenge infection was also determined. The findings suggest that formulation of the HSV-2 glycoprotein antigens with ISCOM or NISV delivery vehicles, and the methods used to prepare these formulations, influenced the immunogenicity of the final preparation. Higher IgG2a and neutralising antibody levels, IL-2 and IFN-gamma levels and lymphoproliferative responses were noted in mice immunised with the HSV-2 ISCOM formulated vaccine preparation. Furthermore, although HSV-2 antigens formulated in dehydration-rehydration NISV, or entrapped in NISV by freeze-thawing at 30 degrees C (HSV-2 NISV 30), also elicited relatively high antibody, IL-2 and IFN-gamma levels and relatively high lymphoproliferative responses, formulation of HSV-2 antigens by freeze-thawing with NISV at 60 degrees C (HSV-2 NISV 60) did not. There were no differences between any of the HSV-2 vaccine formulations in terms of IL-4 induction in in vitro stimulated spleen cell cultures. Almost complete protection against HSV-2 challenge was afforded by the HSV-2 ISCOM preparation, while partial protection against challenge infection was afforded by the HSV-2 NISV 30 vaccine formulation. The findings are discussed in relation to the nature of the immune mechanisms, particularly Th1- or Th2-like responses, that may be elicited by HSV-2 antigen preparations formulated into various delivery systems and the relevance of these immune responses to protection against HSV infection in the murine model.

Modulation of mucosal and systemic immunity by enteric administration of nonreplicating herpes simplex virus expressing cytokines

In this report the ability of enteric immunization with recombinant replication deficient (ICP4-/-) HSV expressing IFN gamma to generate protection and modulate mucosal and systemic immunity was evaluated. ICP4-/-HSV, ICP4-/-HSV expressing IL4, live replicating, and uv HSV were used as controls. Following enteric administration of live HSV, a Th1 cytokine response was induced in the spleen, while both Th1 and notable Th2 cytokine production were detected at mucosal sites. Modulation of mucosal and systemic immune response was achieved when nonreplicating recombinant HSV viruses expressing cytokines were used. Compared to the control replication defective viruses, decreased frequency of Th2 cytokine producing cells in Peyer's patches was observed following enteric administration of nonreplicating HSV expressing IFN gamma. When IFN gamma expressing virus was given enterically, modulation was observed at the systemic level, measured by ELISPOT for cytokine producing cells, ELISA from the in vitro restimulated splenic cell cultures, and by the increase of the IgG2a/IgG1 ratio in the serum. This report provides evidence that replication defective viruses expressing cytokine genes in contrast to uv HSV, are immunogenic when administered enterically and can generate significant immunomodulatory effects at the mucosal and systemic levels.

Enhancement of the immune response to non-replicating herpes simplex virus type-1 preparations by mucosal administration in the presence of cholera toxin

Different immunization regimes were compared in order to enhance the immune response following mucosal administration of non-replicating HSV-1 preparations to mice. The serum anti-HSV Ig response following intragastric administration of heat or UV inactivated HSV-1 strain SC16 was compared with that elicited by an attenuated derivative of SC16 (TKDM21). The highest response followed immunization with TKDM21 and this was markedly enhanced by repeated intragastric administration, reaching ca 35% of that elicited following a cutaneous infection with live virus. Repeated doses of killed virus produced only a minimal increase in the response even when given intranasally (i.n.). However, cholera toxin and its B-subunit with UV-inactivated virus or a mixture of purified viral glycoproteins enhanced the anti-HSV response after i.n. immunization and produced antibody levels equivalent to those following intragastric delivery of live TKDM21.

Induction of a protective immune response by mucosal vaccination with a DISC HSV-1 vaccine

The vaccine potential of a genetically disabled Herpes Simplex Virus Type 1 virus (DISC HSV-1) was investigated in the guinea pig model of intravaginal (i.vag.) HSV-2 infection. Three mucosal vaccination routes, i.vag., intranasal (i.n.) and oral, were compared for their ability to protect guinea pigs from challenge with wild-type HSV-2. Each was effective, particularly the i.n. route, which almost completely abolished primary disease. This was accompanied by significantly lower challenge virus titres in vaginal swabs collected from the vaccinated animals. In all cases, vaccination with the inactivated virus preparation provided substantially less protection from disease than the live DISC HSV-1 by the equivalent route. Antibody levels in serum and vaginal washes were measured both after vaccination and challenge by ELISA and neutralization tests. The highest titres were observed following administration of the DISC HSV-1 vaccine by the i.n. route. Significant increases in IgA and IgG in vaginal wash fluids were also found in these vaccinated animals.

Mucosal immunity to infection with implications for vaccine development

The induction of effective mucosal immunity that also provides systemic immunity is a considerable challenge. Over the past two years, efforts to develop novel mucosal vaccine delivery systems to induce mucosal immunity against bacterial and viral diseases, including HIV, have dramatically increased. Here we cite novel vaccines and delivery systems being used to establish effective mucosal immunity.

Immunization with replication-defective mutants of herpes simplex virus type 1: sites of immune intervention in pathogenesis of challenge virus infection

Replication-defective mutants of herpes simplex virus type 1 (HSV-1) were used as a new means to immunize mice against HSV-1-mediated ocular infection and disease. The effects of the induced immune responses on pathogenesis of acute and latent infection by challenge virus were investigated after corneal inoculation of immunized mice with virulent HSV-1. A single subcutaneous injection of replication-defective mutant virus protected mice against development of encephalitis and keratitis. Replication of the challenge virus at the initial site of infection was lower in mice immunized with attenuated, wild-type parental virus (KOS1.1) or replication-defective mutant virus than in mice immunized with uninfected cell extract or UV-inactivated wild-type virus. Significantly, latent infection in the trigeminal ganglia was reduced in mice given one immunization with replication-defective mutant virus and was completely prevented by two immunizations. Acute replication in the trigeminal ganglia was also prevented in mice immunized twice with wild-type or mutant virus. The level of protection against infection and disease generated by immunization with replication-defective mutant viruses was comparable to that of infectious wild-type virus in all cases. In addition, T-cell proliferative and neutralizing antibody responses following immunization and corneal challenge were of similar strength in mice immunized with replication-defective mutant viruses or with wild-type virus. Thus, protein expression by forms of HSV-1 capable of only partially completing the replication cycle can induce an immune response in mice that efficiently decreases primary replication of virulent challenge virus, interferes with acute and latent infection of the nervous system, and inhibits the development of both keratitis and systemic neurologic disease.