For the first time Wolf et al (1990) injected naked DNA into the muscles of mice which led to expression of encoded marker protein. Thereafter, there has been a surge to use this approach to generate DNA vaccines against a variety of infectious diseases. Thus DNA vaccines are giving hope of a third vaccine evolution.
The first published report from India indicates modest success in the development of DNA vaccines against rabies and Japanese encephalitis virus (JEV) in experimental animals. The efficacy of DNA vaccine (G protein) against rabies is correlated to levels of neutralizing antibodies, whereas in the case of JEV envelop protein, cell mediated irnmunity appears to be the major mechanism of protection. There is great hope that DNA vaccines can protect against serious infectious diseases. Most likely it is to become a tool to benefit mankind in 21st century as such or in combination with recombinant/cell culture vaccines or as an adjunct to chemotherapy (Padmanaban, 1999).
In case of malaria, DNA vaccines have distinct advantage, where plasmid DNA encoding different antigens and prepared by the same genetic procedure can be mixed and administered A mixture of 4 plasmid DNA (pfCSP, pfSSP2, pfEXP-1 and pfLSA-1) has been injected into Rhesus monkeys and found to elicit multiple antigen specific cytotoxic T-lymphocytes (Padmanaban, 1999).
Lowrie et at. (1999) have reported that a DNA vaccine coding for a mycobacterial heat sock protein of Mr65000 (Hsp 65) when administered in 4 doses to mice, 8 weeks after intravenous injection of virulent M. tuberculosis H37RV, leads to a dramatic decrease in number of live bacteria in spleen and lungs 2 months and 5 months after the first dose of DNA. Certain other mycobacterial antigens and BCG did not have this effect.