Experimental ulcerative herpetic keratitis. IV. Preliminary observations on the efficacy of a herpes simplex subunit vaccine

Twenty-five-year panorama of corneal immunology: emerging concepts in the immunopathogenesis of microbial keratitis, peripheral ulcerative keratitis, and corneal transplant rejection

PURPOSE

To describe the most recent advances in our understanding of the cellular and molecular mechanisms involved in the immunopathogenesis of corneal immunoinflammatory disorders including microbial keratitis, peripheral ulcerative keratitis. and allograft rejection.

METHODS

Review of the published peer-reviewed literature that has contributed significantly to our modern understanding of corneal immunology. In addition, the authors have summarized the information in conceptual diagrams that highlight the critical cellular and molecular pathways that lead to corneal immune responses in the two most thoroughly studied corneal immune disorders, herpes simplex keratitis (HSK) and transplant rejection.

RESULTS

In spite of the wide array of molecular and cellular factors that mediate corneal immunity, critical mechanistic facets are shared by the various corneal immunoinflammatory disorders. These include activation and migration of local antigen-presenting cells (APCs), including Langerhans cells (LCs), upregulation in pleiotropic proinflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor-alfa (TNF-alpha) that can mediate a wide array of immune functions in addition to up-regulating protease expression. and chemokines that play a critical role on the one hand in attracting nonantigen-specific inflammatory cells such as neutrophils and on the other in attracting CD4+ T helper type 1 (Th1) cells that mediate most of the destruction in the cornea.

CONCLUSIONS

In the last 25 years, we have seen our field develop from a descriptive stage into a new phase where the fundamental processes that mediate and effect corneal immunity are being accurately deciphered. It is anticipated that this new knowledge will allow development of specific molecular and genetic therapeutic strategies that could target critical steps in the immunopathogenesis of disease without the untoward side-effects of nonspecific generalized immune suppression that still remains the standard of care today.

Immunisation against HSV-1 keratitis with a synthetic gD peptide

The authors tested the protective efficacy of, and the immune response to, immunisation with a synthetic peptide of glycoprotein D (gD) of HSV-1 in a murine model of herpes stromal keratitis (HSK). HSV-1 susceptible A/J mice were immunised subcutaneously with a peptide corresponding to the N-terminal epitope gD(5-23) prior to corneal HSV-1 challenge. Divergent immunisation protocols were compared for their protective potency, their ability to prevent the establishment of latency in the trigeminal ganglion, and their effect on the immune system. Low dosages (31 micrograms) of gD(5-23) protected against encephalitis and HSK. Protective efficacy was higher when gD(5-23) was coupled to the carrier protein keyhole limpet haemocyanin (KLH) and was emulsified with adjuvant. Latent infection was found in all control mice but in only 50-75% of immunised mice. The most potent protection was correlated with anti-HSV-1 neutralising antibodies of IgG1 and IgG2a isotypes, but free gD(5-23) protected in the absence of anti-HSV-1 antibodies. Our results suggest that immunisation with gD(5-23) stimulates both humoral and cellular immune mechanisms which protect against HSV-1 keratitis.

Report of twelve years experience in open study of Skinner herpes simplex vaccine towards prevention of herpes genitalis

Three hundred and forty-seven subjects at risk for herpes genitalis were vaccinated with Skinner vaccine, NFUAc.HSV1.(S-MRC5), and were followed for an average duration of 2 years representing a total consortship of 664.4 years. Based on survey information obtained during this consortship, there were estimated to be 3076 recurrences which summated to 3.5 years total duration of disease and comprised at least 6794 lesions; there were an estimated 51997 episodes of intercourse including at least 241 episodes of unprotected intercourse in the presence of herpetic lesions. The rate of contraction of herpes genitalis was 6 of 54 consorts (11.1%) who received one vaccination and 7 of 293 (2.4%) who received two, three of four vaccinations. There was no evidence of physical or psychological side effects from vaccination.

A virus-particle vaccine prepared from bovine mammillitis virus against herpes genitalis

A vaccine against herpes genitalis was prepared from the extracellular virus particles from baby hamster kidney cells infected with bovine mammillitis virus (BMV) strain "Allerton". The virus was inactivated by formaldehyde followed by ultracentrifugation to concentrate the virus particles and eliminate formaldehyde to an acceptable concentration for immunisation of human subjects. The vaccine was cross antigenic and cross immunogenic with herpes simplex virus type 1. Thirty-four consorts at high risk of herpes genitalis were immunised with two or three doses each containing 10(9) virus particles equialent to approx. 150 micrograms protein. There has been no evidence of local or general side effect in a follow-up period of over 100 patient years. The immunogenicity and protective efficacy of this vaccine in human subjects will be investigated in a double-blind placebo-controlled trial.

Management and prevention of ocular viral and chlamydial infections

A majority of cases of preventable and/or curable ocular morbidity and blindness are caused by ocular infections. They may account for 70 to 90% of all ocular morbidity seen by family doctors, general practitioners, health centers, and local ophthalmologists in both developed and developing countries. Unfortunately, most health authorities and doctors, including ophthalmologists, consider these diseases to be of little or no importance because they are not fully aware of the high prevalence of these infections and the blinding sequelae which may occur following incorrect diagnosis and treatment. Also, they are not aware of the social and economic impact of these infections in the absence of proper management and implementation of preventive measures. In this review, we examine present knowledge of chlamydial and common viral ocular infections. We discuss the problems of diagnosis, management, and prevention and propose solutions relevant to developed and developing countries.

Immunomodulation of experimental murine herpes simplex keratitis: II. Glycoprotein D protection

Subcutaneous immunization with purified HSV-1 glycoprotein D (gD) protects susceptible A/J mice against keratitis and encephalitis following corneal HSV-1 challenge. Mice were immunized with gD, in complete Freund's adjuvant, 3.0 micrograms/mouse followed by two booster doses of 1.5 micrograms/mouse at weeks 2 and 4. Control groups of A/J mice were injected with either complete Freund's adjuvant (unimmunized controls) or live HSV-1 MP strain (immunized controls). All mice were challenged ocularly at week 5 with HSV-1, F strain (6.5 x 10(3) PFU) after corneal scarification. None of the 16 animals immunized with gD developed stromal keratitis; only 3 out of 12 animals immunized with live HSV-1 developed a stromal keratitis; 13 out of 16 CFA primed unimmunized mice developed severe stromal keratitis within 14 days post corneal challenge, and 3 out of 16 control CFA primed animals died within 16 days post corneal challenge. At the time of sacrifice (3 weeks post corneal challenge), the ipsilateral trigeminal ganglia were removed and assayed for latent HSV-1 using cocultivation on Vero cell monolayers. The results of these experiments indicate that immunization with gD produces protection against latent ganglionic infection in 56% of the immunized animals, and provides protection against keratitis and death following HSV corneal challenge.

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

Fifty subjects at risk of herpes genitalis received 109 immunizations with Skinner herpes vaccine and were assessed after a follow-up period of 4-48 months, representing a total follow-up period of 694 patient months. There was no evidence of contraction of herpes genitalis in 49 subjects. The risk of virus transmission and rate of contraction of disease was quantified by construction of two functions, namely a unit of exposure risk calculated per year (UYE) and standard contraction rate (SCR); in this study the SCR was 0.02. There was no evidence of significant side-effects from vaccination. Administration of Alhydrogel adjuvant with vaccine induced temporary granuloma formation in most subjects but was only detectable beyond 1 year of follow-up in one subject, in whom a painless swelling of 0.2 cm was detected 3 years after vaccination. There was no evidence of immunological reactivity to host cell or calf serum antigens in any of the subjects vaccinated.

Preparation and immunogenicity of vaccine Ac NFU1 (S-) MRC towards the prevention of herpes genitalis

A subunit antigenoid vaccine, Ac NFU1 (S-) MRC, was used to prevent primary herpes genitalis in 60 subjects considered to be at risk of this infection. There was no evidence of serious local or general side effects. Neutralising antibody responses were detected in 59% and 90% of subjects receiving the low and high doses of vaccine respectively; immunoprecipitating antibody was detected at a lower frequency, namely in 23% and 43% of subjects receiving the low and high doses respectively. After a mean follow-up period of 18 months none of the vaccinated subjects contracted herpes genitalis after completing the vaccination course.

Immunogenicity and protective efficacy in a rhesus monkey model of vaccine Ac NFUi(S-) MRC against primary type 2 herpes simplex virus infection

Adult and juvenile Rhesus monkeys were vaccinated with sub-unit formaldehyde-inactivated vaccine Ac NFU₁(S-) MRC; no local or systemic side-effects followed vaccination.

Vaccinated monkeys developed neutralizing and immunoprecipitating antibody to both type 1 and 2 herpes simplex virus. Antibody levels declined with time but were re-stimulated after virus challenge and to a lesser extent after attempted virus reactivation. There was evidence of protection against s.c. challenge with live type 2 herpes simplex virus.