DNA vaccination- copy and edited from WIKIPEDIA the best encyclopedia in the world

1.DNA vaccination is a technique for protecting an organism against disease by injecting it with genetically engineered 

DNA to produce an immunological response. DNA vaccines have a number of advantages over conventional vaccines, including the ability to induce a wider range of immune response types.

2.Vaccines are among the greatest achievements of modern medicine – in industrial nations, they have eliminated naturally occurring cases of smallpox, and nearly eliminated polio, while other diseases, such as hepatitis A and B and others are well controlled. 

Conventional vaccines, however, only cover a small number of diseases, and infections that lack effective vaccines kill millions of people every year,for example malaria, hepatitis c and so on.

3.First generation vaccines are whole-organism vaccines – either live and weakened, or killed forms. Live, attenuated vaccines, such as smallpox and polio vaccines, are able to induce killer T cells (T_C or CTL) responses, helper T cells(T_H) responses and antibody immunity. However, there is a small risk that attenuated forms of a pathogen can revert to a dangerous form, and may still be able to cause disease in immuno-compromise people . 

While killed vaccines do not have this risk, they cannot generate specific killer T cell responses, and may not work at all for some diseases.

In order to minimise these risks, so-called second generation vaccines were developed. These are subunit vaccines, consisting of defined protein antigens or recombined protein components (such as the hepatitis B surface antigen). These, too, are able to generate T_Hand antibody responses, but not killer T cell responses.

4.DNA vaccines are third generation vaccines, and are made up of a small, circular piece of bacterial DNA (called a plasmid) that has been genetically engineered to produce one or two specific proteins antigens from a pathogen. 

The vaccine DNA is injected into the cells of the body, where the "inner machinery" of the host cells "reads" the DNA and converts it into pathogenic proteins. Because these proteins are recognised as foreign, when they are processed by the host cells and displayed on their surface, the immune system is alerted, which then triggers a range of immune responses.

4.Table 1. Advantages And Disadvantages Of Nucleic Acid-Based Immunization
Advantages	Disadvantages
Subunit vaccination with no risk for infection Antigen presentation by both MHC class 1 and class 2 molecules Able to polarise T-cell help toward type 1 or type 2 Immune response focused only on antigen of interest Ease of development and production Stability of vaccine for storage and shipping Cost-effectiveness Obviates need for peptide synthesis, expression and purification of recombinant proteins and the use of toxic adjuvants Long-term persistence of immunogen In vivo expression ensures protein more closely resembles normal eukaryotic structure, with accompanying post-translational modifications	Limited to protein immunogens (not useful for non-protein based antigens such as bacterial polysaccharides) Risk of affecting genes controlling cell growth Possibility of inducing antibody production against DNA Possibility of tolerance to the antigen (protein) produced Potential for atypical processing of bacterial and parasite proteins