Alternative Methods of Vaccine Delivery: An Overview of Edible and Intradermal Vaccines

Criscuolo, E.; Caputo, V.; Diotti, R. A.; Sautto, G. A.; Kirchenbaum, G. A.; Clementi, N.

Many vaccines have been developed and approved against various pathogens, and countless studies have been conducted to improve their efficacy by testing new adjuvants and performing the rational identification of the antigen formulations and pathogen contaminations [134] [135] [136] . Promising results have been also achieved by changing the delivery strategy. In fact, most of the approved vaccines are administrated by injection with intrinsic limitations like those concerning the immunological aspect. Injected vaccines are able to elicit a strong humoral immunity but a weak cellular response. In addition, this type of administration is strongly associated with a systemic immunity but with a lack of mucosal response, which is helpful to block the early stages of infection since most pathogens infect through the mucosal membranes. For these reasons, new vaccination strategies have been proposed. In particular, edible vaccines, triggering the GALT, and intradermal approaches, involving Langerhans cells, are able to elicit both a mucosal and a systemic immune response. The increased knowledge of these approaches has led to the progression of many preclinical studies and several promising clinical trials (Tables 1, 2, and 3). Moreover, these vaccine strategies are considered safe and cost-effective as no extensive antigen processing is needed [137, 138] and they are easy to administrate (Table 4 ). In fact, due to the opportunity of self-administration and ease of distribution compared to an injection-based approach, these two vaccination systems could improve the overall coverage.