Effect of Skin Barrier Disruption on Immune Responses to Topically Applied Cross-Reacting Material, CRM₁₉₇, of Diphtheria Toxin

The high accessibility of the skin and the presence of immunocompetent cells in the epidermis makes this surface an attractive route for needle-free administration of vaccines. However, the lining of the skin by the stratum corneum is a major obstacle to vaccine delivery. In this study we examined the effect of skin barrier disruption on the immune responses to the cross-reacting material CRM₁₉₇, a nontoxic mutant of diphtheria toxin (DTx) that is considered as a vaccine candidate. Application of CRM₁₉₇, together with cholera toxin (CT), onto the tape-stripped skin of mice elicited antibody responses that had anti-DTx neutralizing activity. Vaccine delivery onto mildly ablated skin or intact skin did not elicit any detectable anti-CRM₁₉₇ antibodies. Mice immunized with CRM₁₉₇ alone onto the tape-stripped skin mounted a vigorous antigen-specific proliferative response. In contrast, the induction of cellular immunity after CRM₁₉₇ deposition onto mildly ablated or intact skin was adjuvant dependent. Furthermore, epidermal cells were activated and underwent apoptosis that was more pronounced when the stratum corneum was removed by tape stripping. Overall, these findings highlight the potential for transcutaneous delivery of CRM₁₉₇ and establish a correlation between the degree of barrier disruption and levels of antigen-specific immune responses. Moreover, these results provide the first evidence that the development of a transcutaneous immunization strategy for diphtheria, based on simple and practical methods to disrupt the skin barrier, is feasible.