[Show abstract][Hide abstract] ABSTRACT: HBV vaccine needs 3 injections over 6 months to induce immunity. Thus, the use of adjuvants capable of inducing earlier immune protection would be highly desirable. Most adjuvants may act by inducing cytokines, and among them, type I interferons (IFNs), deserve a special attention in view of the potent immunomostimulatory activity observed in mouse models and on dendritic cell functions. The aim of the present trial was to evaluate the effects of IFN-alpha administered as an adjuvant of HBV vaccine in healthy unvaccinated individuals. No significant enhancing effect on the antibody response was observed, in spite of an early and transient upregulation of costimulatory molecule expression on peripheral blood mononuclear cells, which may be suggestive of an IFN-mediated activation of antigen presenting cells. We conclude that, under the conditions used in this trial, natural IFN-alpha does not act as an adjuvant of the HBV vaccine in healthy unvaccinated individuals.