Intranasal DNA Vaccine for Protection against Respiratory Infectious Diseases: The Delivery Perspectives

Xu, Yingying; Yuen, Pak-Wai; Lam, Jenny Ka-Wing

Cytokines are small proteins that are important in regulating immunological response by recruiting and stimulating T cells, or by directly acting on infected cells. They have potential to be natural adjuvants for DNA vaccines [225] . Cytokines that have been evaluated as possible DNA or intranasal vaccine adjuvants include IL-1, IL-2, IL-6, IL-12, IL-15 and GM-CSF [205, 206, 226, 227] . In particular, IL-12 is found to be an effective mucosal adjuvant [228, 229] . Lynch et al. demonstrated that intranasal administration of pneumococcal polysaccharide conjugate vaccine in the presence of IL-12 was able to enhance systemic and mucosal immune responses to pneumococci in mice [228] . However, cytokines have short half-life in vivo and poor stability. They are also expensive and are associated with dose related toxicity. Therefore, these molecules may not be suitable for use as adjuvants in vaccines designed to protect against infectious diseases [182] . Nevertheless, intranasal administration of IL-12 induced less toxicity than parenteral administration [230] . Alternatively, cytokines can be expressed from plasmid DNA to allow long-lasting expression in vivo and to reduce the cost of production [196, 198] .