Follow-up report on 50 subjects vaccinated against herpes genitalis with Skinner vaccine

The potential of currently unavailable herpes virus vaccines

INTRODUCTION

Despite overwhelming experimental work, there are no licensed vaccines against the most frequent Alphaherpesviruses, namely herpes simplex virus 1 and 2 (HSV1 and 2) nor against the Epstein-Barr virus (EBV), a member of the subfamily Gammaherpesvirus.

AREAS COVERED

Since the DNAs of both HSVs reside in the regional sensory ganglia in a latent state (i.e. as circularized episomal molecules), a corresponding vaccine might be useful for immunotherapy rather than for prevention of primary infection. Here we describe the design of a purified subunit vaccine as well as the preparation and efficacy of a recombinant fusion protein consisting of the gD ectodomain from our domestic attenuated HSV1 strain HSZP. The EBV vaccines considered so far, were destined for prevention of infectious mononucleosis (IM) or to prevent formation of EBV related tumors. To design the EBV peptide vaccine, at least 15 carefully selected immunogenic epitopes coming from 12 virus coded proteins were bound to synthetic micro-particle carriers along with a non-specific pathogen recognizing receptor (PRR) stimulating both the T as well as B lymphocytes.

EXPERT COMMENTARY

The efficacy of a novel EBV peptide in the rabbit model was based on criteria such as antibody formation (EA-D detected by ELISA, early and capsid proteins tested by immunoblot), presence of LMP1 antigen and of viral DNA in peripheral white blood cells. Out of 19 peptide combinations used for vaccination, at least 6 showed a satisfactory protective effect.

Antigenic breadth: a missing ingredient in HSV-2 subunit vaccines?

The successful human papillomavirus and hepatitis B virus subunit vaccines contain single viral proteins that represent 22 and 12%, respectively, of the antigens encoded by these tiny viruses. The herpes simplex virus 2 (HSV-2) genome is >20 times larger. Thus, a single protein subunit represents 1% of HSV-2's total antigenic breadth. Antigenic breadth may explain why HSV-2 glycoprotein subunit vaccines have failed in clinical trials, and why live HSV-2 vaccines that express 99% of HSV-2's proteome may be more effective. I review the mounting evidence that live HSV-2 vaccines offer a greater opportunity to stop the spread of genital herpes, and I consider the unfounded 'safety concerns' that have kept live HSV-2 vaccines out of U.S. clinical trials for 25 years.

The ongoing pursuit of a prophylactic HSV vaccine

HSV is among the most common human pathogens in the world. It is known to cause painful, persistent skin lesions, while also being the most common cause of fatal non-epidemic encephalitis as well as the leading cause of corneal blindness. The development of prophylactic vaccines could substantially reduce global health problems associated with HSV. So far, HSV vaccine strategies have shown noticeable efficacy in early development during preclinical phases but remained unsuccessful or unproven in human trials. New understanding of how the immune system mounts a defence against HSV offers practical strategies for vaccine development. A number of promising vaccine candidates are currently awaiting clinical development or already undergoing clinical testing. Therefore, this is a suitable time to assess the progress of HSV vaccine development and consider existing challenges and future improvements needed to achieve an effective prophylactic HSV vaccine.

Prevalence of specific antibodies to herpes simplex virus type 2 as revealed by an enzyme-linked immunoassay and western blot analysis

A solid-phase ELISA for the detection of antibodies to gG-2 was developed. The assay utilizes a recombinant DNA-derived gG-2 as a solid-phase "capture" reagent and goat anti-human IgG (gamma) conjugate to horseradish peroxidase as a probe (detector) reagent. A total of 229 serum samples collected from various populations were tested by ELISA and western blot analysis. On comparison with confirmed HSV-2 infection, the sensitivity and specificity of the ELISA were 92.9% and 98.7%, respectively. Western blot had a sensitivity of 83.9% and a specificity similar to the ELISA. The ELISA is fast and easy to perform and may be used to diagnose previous exposure to genital herpes and to monitor human response to future HSV-2 vaccines.

Systemic and mucosal cell mediated immune responses against herpes simplex virus in vaccinated guinea-pigs detected by lymphocyte proliferation and monoclonal antibodies against macrophages and T cells

Peripheral blood lymphocytes from guinea-pigs immunized with a herpes simplex virus (HSV) sub-unit vaccine (Skinner vaccine) were shown to produce an HSV antigen-specific lymphocyte proliferative response post vaccination. This response was associated with a reduction, compared with mock vaccinated and unvaccinated animals, in the clinical disease scores post intravaginal challenge. This reduction was not associated with the presence of macrophage or T cell infiltration in the vaginal mucosa postchallenge. In contrast mock vaccinated and unvaccinated guinea-pigs did not produce an HSV antigen-specific response post-vaccination but did demonstrate HSV antigen-specific lymphocyte proliferative responses post intra-vaginal challenge. The mock and unvaccinated animals had higher clinical disease scores postchallenge compared with sub-unit vaccinated animals and this was associated with the presence of cellular infiltrates in the vaginal mucosa. These results are discussed in relation to the immunopathology of the disease.

Mucosal antibody response to vaginal infection with herpes simplex virus in pre-vaccinated guinea-pigs

The mucosal antibody response, in female guinea-pigs vaccinated with the Skinner herpes simplex virus vaccine, has been investigated. The HSV-specific secretory IgA response was assessed using the cross-reactivity of an antiserum raised against human secretory component. Animals vaccinated subcutaneously at a distant site were shown to respond to subsequent infection with HSV by the production of HSV-specific vaginal IgG and secretory IgA. No vaginal HSV-specific antibodies were found in infected, non-vaccinated animals.