Combination adjuvants: the next generation of adjuvants?

Adjuvants are critical components of many vaccines. The majority of existing vaccines contain a single adjuvant. Owing to their inherent limitations, no single adjuvant is capable of inducing all the protective immune responses required in the many different vaccines. Consequently, investigators are exploring the potential of using formulations with multiple adjuvants in a vaccine. An emerging paradigm is that careful selection of adjuvant combinations can result in complementary and even synergistic enhancement of immune responses to vaccines. This approach is promising and presents tremendous opportunities for vaccinologists to tailor immune responses to specific vaccines. In this article, adjuvant combinations at different stages of development will be reviewed.