Evaluation of immunomodulatory compounds for identification of an anti-herpetic innate immune response profile

Abstract

Herpes simplex virus type 2 (HSV-2) is a prevalent world-wide sexually transmitted infection (STI) that commonly infects the genital mucosa and establishes a life-long latent infection. The virus periodically reactivates producing recurrent shedding episodes that increase the risk of acquiring other STI. There are no FDA-approved HSV-2 vaccines and treatment involves chronic therapy that does not prevent all recurrences; therefore novel anti-herpetic intervention strategies are needed that provide resistance to HSV-2 infection. Because genital HSV-2 infections are more prevalent in women than men, most anti-herpetic strategies focus on vaginal application. One promising intervention involves the use of immunomodulatory compounds to engender an HSV-2 resistant environment by stimulating the natural innate immune defenses of the vaginal mucosa. The compounds consist of evolutionarily conserved pathogen-associated molecular patterns termed toll-like receptor (TLR) agonists that are recognized by vaginally expressed TLR and elicit specific cytokine response profiles. As an initial step in identifying cytokines that are associated with resistance to HSV-2 infection, selected TLR agonists were evaluated in human cell culture or small animal models. An assay scheme was developed to identify anti-herpetic and non-anti-herpetic compounds and identified, for the first time, fibroblast stimulating ligand-1 as a novel anti-herpetic TLR agonist. Immunological evaluations of the compounds in human vaginal epithelial cells (EC) identified IL-2, IL-12(p70), IFN, MIP-1, MIP-1 and RANTES as important for establishing an HSV-2 resistant environment. The profile was confirmed and expanded to include IL-12(p40) and IFN following evaluations in a mouse model of genital HSV-2 infection. Additionally, the profile was observed in a novel in vitro air-interface vaginal EC model of the human vaginal mucosa. Colonization of the in vitro model with common vaginal commensal bacteria showed a temporally-dependent tempering of the TLR agonist elicited cytokine response and enhancement of agonist induced anti-herpetic activity. The identified anti-herpetic cytokine response profile provides an invaluable resource for the future design of novel immunomodulatory compounds that will aid in reducing HSV-2 transmission world-wide. Additionally, the studies in the novel in vitro model of the human vaginal mucosa showed that commensal bacterial play an important role in the vaginal defenses against pathogenic infection.