New adjuvants for parenteral and mucosal vaccines.

Developing efficient adjuvants for human vaccines, in order to elicit broad and sustained immune responses at systemic or mucosal levels, remains a challenge for the vaccine industry. Conventional approaches in the past have been largely empirical and partially successful. Selection was based on the balance between toxicity and adjuvanticity, first in an animal model, and then in clinical trials. The advent of improved biochemical techniques has allowed for the purification or construction of new and well characterised adjuvants. In addition, recent advances in our understanding of the immune system, most particularly with respect to early proinflammatory signals, have led to the identification of new biological targets for vaccine adjuvants. In particular, one can now choose adjuvants able to selectively induce T helper (Th)-1 and/or Th2 responses, according to the vaccine target and the desired immune response. As our knowledge of the cell types and cytokines interacting in the immune responses increases, so does our understanding of the mode of action of adjuvants, as well as the way in which they produce adverse effects.