Posttherapy suppression of genital herpes simplex virus (HSV) recurrences and enhancement of HSV-specific T-cell memory by imiquimod in guinea pigs

Abstract

Imiquimod, an immunomodulator with no direct in vitro antiviral activity, has in vivo anti-herpesvirus activity by inducing interferon and enhancing other only partially defined immune responses. Imiquimod treatment of primary genital herpes simplex virus (HSV) infection in guinea pigs reduces the level of genital disease by 90%. We further investigated its utility as suppressive therapy of recurrent disease in animals that had recently recovered from primary genital HSV-2 disease. Imiquimod administered intravaginally once per day for 5 days reduced the number of recurrences only during treatment, while a 21-day regimen reduced the number of recurrences for 8 weeks. For the entire 10 weeks of observation, overall numbers of recurrences were reduced 67% by the 21-day imiquimod treatment (P < 0.0001). Latent HSV in ganglia was not affected by either regimen. Increased circulating alpha interferon activity was observed during therapy with both regimens. Interferon levels rapidly returned to baseline with cessation of treatment. Posttreatment, 5-day imiquimod treatment did not provide clinical benefit or enhancement of cell-mediated or cytokine responses. Twenty-one-day imiquimod treatment reduced both the number of clinical recurrences and levels of HSV antibody for 5 to 6 weeks posttreatment compared with the placebo. Additionally, 21-day imiquimod treatment enhanced HSV antigen-specific interleukin 2 production and proliferative responses by mononuclear cells (P < 0.001) for 4 weeks after treatment. Twenty-one-day imiquimod therapy suppressed recurrent HSV genital disease during and for weeks after therapy, enhanced memory-dependent cytokine and T-cell responses, and reduced the level of antibody responses.