Randomized, single-blind, placebo-controlled study of topical application of the immune response modulator resiquimod in healthy adults.

Resiquimod is a Toll-like receptor 7 (TLR7) and TLR8 agonist that is a potent inducer of alpha interferon (IFN-alpha) and other cytokines. The effects of multiple applications of resiquimod gel were assessed in a randomized, single-blind, dose-ranging, placebo-controlled study with 41 healthy subjects. Over a 3-week period, 1-g doses of resiquimod or vehicle gel (3:1 randomization) were applied to a 50-cm2 area of the upper arm according to the following regimens: 0.25% applied for 8 h two times per week, 0.05% applied for 8 h two times per week, 0.05% applied for 8 h three times per week, and 0.01% applied for 24 h three times per week. Skin biopsy specimens were obtained prior to the application of the first dose and after the completion of application of the last dose. Dosing with 0.01 and 0.05% resiquimod was well tolerated, but that with 0.25% was not; a dose-response relationship for local adverse effects was observed. The level of systemic exposure during multiple topical dosings was <1% of the applied dose. A significant increase in responders after completion of application of the last dose was observed for serum IFN and the interleukin-1 (IL-1) receptor antagonist (P<0.01, Fisher's exact test). Increased levels of mRNA for IL-6, IL-8, IFN-alpha, and Mx (an IFN-alpha-inducible protein) were seen in posttreatment biopsy specimens from the group receiving 0.25% resiquimod compared to the levels seen in specimens from the group receiving vehicle only (P<0.01, Wilcoxon rank sum test). A dose-response-related increase in CD3-positive cells consistent with T-lymphocyte infiltration and a decrease in CD1a-positive cells, consistent with emigration of Langerhans' cells, were observed in treated skin. This study suggests that resiquimod is a potent topically active immune response modifier that significantly enhances the cutaneous immune response.