Human skin contains numerous antigen-presenting cells that are a potential target for several immune-based therapies, including vaccination and cancer immunotherapy. However, the outermost layer of the skin�the stratum corneum�acts as a major physical barrier against the permeation of antigens that have a molecular weight > 500 Da. In this study, an ionic liquid-assisted delivery system (ILDS) was developed, which enabled the successful transdermal delivery of an antigenic protein, ovalbumin (OVA), with a toll-like receptor agonist, imiquimod, as an adjuvant, to stimulate a specific immune response. Both the ionic liquids and ILDS were completely biocompatible for topical or transdermal application for therapeutic purposes. The skin permeation of the antigenic protein and adjuvant was found to be significantly enhanced because of the incorporation of a surface-active ionic liquid in the ILDS. An in vivo immunization study showed that there was a high level of OVA-specific IgG antibody production because of the enhanced permeation of the antigen and adjuvant across and into the skin. In a preclusive anticancer study, vaccination through ILDS showed stronger tumor-growth inhibition compared to control group. These results indicated that the ILDS could be a promising strategy for transdermal immunization as future therapeutics. © 2021 Elsevier B.V.