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

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.

Development of HSV-specific CD4+ Th1 responses and CD8+ cytotoxic T lymphocytes with antiviral activity by vaccination with the HSV-2 mutant ICP10DeltaPK

A growth compromised herpes simplex virus type 2 (HSV-2) mutant which is deleted in the PK domain of the large subunit of ribonucleotide reductase (ICP10DeltaPK) protects from HSV-2 challenge in the mouse and guinea pig cutaneous and vaginal models and reduces the incidence and frequency of recurrent disease (Vaccine (17) (1999) 1951; Vaccine (19) (2001) 1879). The present studies were designed to identify the immune responses induced by ICP10DeltaPK and define the component responsible for protective activity. We found that ICP10DeltaPK elicits a predominant HSV-specific T helper type 1 (Th1) response, as evidenced by: (1) higher levels of HSV-specific IgG2a (Th1) than IgG1 (Th2) isotypes and (2) higher numbers of CD4+ IFN-gamma than IL-10 secreting T cells in popliteal lymph nodes. This Th1 response pattern was associated with a significant increase in the levels of IL-12 produced by dendritic cells from ICP10DeltaPK than HSV-2 immunized animals. Lymph node cells (LNCs) from ICP10DeltaPK immunized mice had significantly higher levels of HSV-2 specific cytolytic activity than LNCs from mice immunized with HSV-2 and it was mediated by CD8+ T cells. CD8+ CTL were not seen in LNCs from HSV-2 immunized mice. In adoptive transfer experiments, CD8+ T cells and, to a lower extent, CD4+ T cells from ICP10DeltaPK immunized mice inhibited HSV-2 replication, suggesting that they are involved in the protective immunity induced by ICP10DeltaPK vaccination.

New treatments for genital herpes

Genital herpes is a sexually transmitted disease that has been widely investigated from both an epidemiological and a diagnostic viewpoint. Better knowledge of the disease has pointed to the important role of asymptomatic herpes simplex virus type 2 shedding as a major culprit for the spread of the virus in the world, the latest statistics showing that the incidence of genital herpes is constantly increasing. The reference compound for the treatment and prophylaxis of genital herpes is acyclovir. Recently, two drugs with better oral bioavailability, valaciclovir, the oral prodrug of acyclovir, and famciclovir, the oral prodrug of penciclovir, have been made available. Nevertheless, there is a need to develop additional approaches, to extend the therapeutic possibilities and to face the problem of emerging resistant viruses, mostly in immunocompromised patients. Therefore, efforts have been made in different directions including the exploration of new targets for antiviral chemotherapy, the use of immunomodulators and the development of specific vaccines.