The search for novel adjuvants for early life vaccinations: can "danger" motifs show us the way?

Potent but safe adjuvants are required to circumvent the many limitations of the newborn immune system to induce rapidly effective and long lasting immunity to subunit vaccines. By the use of pattern recognition receptors, antigen-presenting cells (APC) can very efficiently be activated by "danger" motifs expressed by various pathogens. APC activated by "danger" motifs, such as immunostimulatory sequences of bacterial DNA, can not only transmit the activation signal from the innate immunity to the adaptive compartment, but also shape the antigen-specific immune responses. Molecules or compounds expressing "danger" motifs could, therefore, be considered for use as adjuvants for subunit vaccines. In this review, the authors discuss the promises and potential drawbacks that such novel adjuvants could hold for their use in experimental and clinical early life vaccinations.