Subunit vaccines are composed of pathogen fragments that, on their own, are generally
poorly immunogenic. Therefore, the incorporation of an immunostimulating agent, e.g. adjuvant, into
vaccine formulation is required. However, there are only a limited number of licenced adjuvants and
their immunostimulating ability is often limited, while their toxicity can be substantial. To overcome
these problems, a variety of vaccine delivery systems have been proposed. Most of them are designed to
improve the stability of antigen in vivo and its delivery into immune cells. Cell-penetrating peptides
(CPPs) are especially attractive component of antigen delivery systems as they have been widely used to
enhance drug transport into the cells. Fusing or co-delivery of antigen with CPPs can enhance antigen
uptake, processing and presentation by antigen presenting cells (APCs), which are the fundamental steps
in initiating an immune response. This review describes the different mechanisms of CPP intercellular
uptake and various CPP-based vaccine delivery strategies.