What are DNA Vaccines?

DNA vaccines are made up of small genetically engineered plasmids, each containing a DNA sequence which codes for antigenic protein of a pathogen. This form of immunization, also known as third generation vaccination, is a novel technique used to efficiently stimulate innate and humoral (antibody) immune responses to protein antigens.

PICTURE

How are DNA vaccines different from other vaccines?

First generation vaccines are whole-organism vaccines – either live and attenuated, or killed forms. Live, attenuated vaccines, such as smallpox and polio vaccines, are able to induce both innate and humoral immune responses (killer T-cell response, helper T-cell response and antibody immunity)[2]. However, there is a small risk that attenuated forms of a pathogen can revert to the wild-type virulent form, and may still be able to cause disease in immunocompromised people (such as those with AIDS)[3]. While killed vaccines have the advantage of non-infectivity and therefore relative safety, they cannot generate specific killer T-cell responses (lower immunogenicity and consequently need for several doses) and may not work at all for some diseases[4].

In order to minimise these risks, so-called second generation vaccines were developed. These are subunit vaccines, consisting of defined protein antigens such as tetanus or diphtheria toxoid (inactivated bacterial toxins that can induce protective antibody)[5] or recombinant protein compounds such as the hepatitis B surface antigen. These, too, are able to generate T-helper cell and antibody responses, but not killer T-cell responses.

Firstly, the vaccine DNA is delivered into the cells of the body where the “inner machinery” of the host cells transcribes the DNA to mRNA. Then the DNA is translated to form pathogenic proteins[1]. 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 of the host against the gene delivered antigen. In this way, DNA vaccine provides immunity.