Delivery systems: a vaccine strategy for overcoming mucosal tolerance?

Antigens administered via the oral and, to a lesser extent, the nasal route are potentially able to invoke tolerance, resulting in a nonreactive immune response. This has been a hurdle for mucosal vaccine development and yet the desire to induce protective local and systemic responses, with pain-free and more convenient products, has been the impetus driving mucosal vaccine R&D. Nevertheless, few mucosal vaccines have reached the marketplace and products are still treated with caution, particularly where live organisms are utilized. In this review, we examine the use of delivery systems with adjuvant properties as key components in a vaccine strategy that does not require the use of live vectors to overcome tolerance and have exemplified their success in mucosal vaccines, concentrating on the nasal and oral routes of administration.