Prospects for control of emerging infectious diseases with plasmid DNA vaccines

Moss, Ronald B

In some cases, once various components of the plasmid have been optimized, the encoded protein may be sufficiently immunogenic without the need for additional components (unformulated or "naked" DNA) such as adjuvants. One of the earliest trials in humans of an unformulated or "naked" DNA vaccine was one that targeted the malaria parasite. Wang and colleagues at the Naval Medical Research Institute immunized 20 subjects with a plasmid that encoded naturally occurring forms of malaria proteins [16] . In this trial, more than half of the subjects were shown to have cells that can kill or lyse malaria infected cells (cytotoxic T cell or killer cells). In a more recent clinical trial, a DNA vaccine optimized for human expression and encoding modified forms of West Nile Virus proteins was studied by Martin and colleagues at the National Institute of Health (NIH) and demonstrated that the vaccine stimulated antibodies that inhibited the virus (neutralizing antibodies) in all individuals receiving the vaccination regimen [17] . This unformulated DNA vaccine appears to induce a similar level of immune responses to those observed in vaccinated horses protected from WNV. In addition, a recent clinical trial by these same NIH researchers tested an optimized but unformulated DNA vaccine for SARS coronavirus and demonstrated neutralizing antibodies in all subjects who received three doses of the vaccine [18] .