Mark A. Tomai

TLR Agonists as Vaccine Adjuvants

Small molecule TLR7/8 agonists have demonstrated great potential as vaccine adjuvants, since they quantitatively and qualitatively enhance both humoral and cellular immune responses. However, most small molecule TLR agonists evaluated thus far as vaccine adjuvants are highly soluble and have a propensity to rapidly disperse away from the vaccination site, resulting in decreased efficacy and increased systemic adverse effects. Intense effort and progress has been made to increase their ability to maintain close proximity to antigen at the administration site. Here, we will discuss three vaccine approaches utilizing small molecule TLR7/8 agonists as vaccine adjuvants. These approaches are designed to improve the adjuvanticity and to reduce the potential for systemic adverse events associated with these small molecule TLR7/8 agonists when used as vaccine adjuvants. One approach utilizes the TLR7/8 agonist resiquimod gel as a topically applied adjuvant at the vaccination site. The other two approaches utilize novel TLR7/8 agonists in a conventional vaccine format where the adjuvant and antigen are administered together. These novel TLR7/8 agonists are lipid modified or chemically modified for conjugation to antigen—all three approaches are designed to promote retention of the TLR7/8 agonists at the administration site in order to maintain their spatial and temporal proximity to the antigen, resulting in enhanced immune responses and reduced systemic adverse effects.

Mechanism of action of imiquimod 5% cream in the treatment of anogenital warts

Objective: The objective of this randomized, double-blind, placebo-controlled trial was to evaluate the mechanism of action of imiquimod cream in the treatment of anogenital warts, and to apply the findings to the results of previously conducted safety and efficacy trials.Methods: Imiquimod (16 patients) or placebo (3 patients) cream was applied 3 times a week for up to 16 weeks; cream remained on the skin overnight for 8 +/- 2 hours. Wart biopsies were taken at prestudy, week 6, and the end of treatment (just prior to clearance or at week 16) and analyzed using PCR for HPV/DNA and RT-PCR for mRNA to identify cytokines, cellular markers, markers of proliferation and differentiation, and viral gene products. Efficacy was assessed based on wart area regression as documented by wart area measurements and photographs.Results: All patients enrolled in the trial had HPV type 6/11. All imiquimod-treated patients experienced a >/=75% clearance in baseline/target wart area. Imiquimod treatment stimulated significant increases in mRNA for IFN-alpha, 25 AS and IFN-gamma. Increases in mRNA for CD4, CD8, and TNF-alpha were also observed, suggesting activation of a T-helper type-1 cell mediated response. During the trial one of the vehicle treated patients also experienced spontaneous wart clearance; comparisons of the cytokine levels for this patient were similar to those observed for the imiquimod treated patients.Conclusions: The results of this mechanism of action trial indicate that the stimulation of local cytokines and cellular infiltrates by imiquimod leads to a reduction of HPV types 6 and 11 viral load with subsequent wart regression and normalization of keratinocyte proliferation without evidence of scarring. In two previous randomized vehicle-controlled trials evaluating patients with anogenital warts, the majority of patients had HPV-DNA types 6 or 11 as assessed by in situ hybridization. These results provide additional insight into the mechanism of total clearance for these otherwise healthy patients. The Th1 response demonstrated in this trial also explains the lower total clearance rates demonstrated in HIV-positive and AIDS patients.