DNA Or Third Generation Vaccines

DNA vaccines are also called third generation vaccines. These vaccines 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.

In the DNA vaccine, a piece of bacterial DNA (plasmid) carrying antigen is directly given to us and our body absorbs the DNA into our genetic system. Our body then replicates the production of plasmid carrying antigen. This release of antigen by our own DNA activates our immune system. Like any vaccine, the immune system will then recognize the bacteria or virus in the future—hopefully preventing illness.

What Are the Advantages of DNA Vaccines?

1. Require short time span for development: Quick changes can be easily brought in gene-based vaccine than bacteria- or virus-based. Such changes are important to deal with strains of bacteria or virus that are constantly mutating.

2. DNA vaccines are easy to transport and store: DNA is a very stable molecule and does not need to be stored at low temperatures, making transportation and storage cheaper and easier than conventional vaccines.

3. Less risk to those who are making the vaccine: Conventional vaccines require raising up the infectious bacteria or virus. Thus, there is a risk (even though small) to those who make the vaccines, whereas making of DNA vaccines is less risky .

What Are the Disadvantages of DNA Vaccines?

So far, no DNA vaccine has been licensed for use in humans. Although some DNA vaccines are now in clinical trials, none are licensed for use.

First Generation Vaccines

These vaccines consist of infectious organisms, either in mild or dead form. The first generation vaccines are still widely used today.

Live and mild/attenuated forms produce both humoral (antibody) and cellular immune responses. For example, oral polio virus vaccine uses polio virus in mild form. When we take the vaccine, our body reacts as if it is affected by actual virus. Consequently, our immune system gets activated and T-killer cells attack the polio virus. Thereafter, when there is any actual attack of polio virus, then our immune system is already developed to handle such an attack.

The only problem with these vaccines is that the actual pathogen in these vaccines may assume a dangerous form.

Dead pathogen vaccines do generate an antibody response, but they do not generate cellular responses (no T-killer response). Depending on the disease, antibody production may or may not be enough to ward off an infection. The advantage of using killed pathogen vaccine is that there is no chance of infection from the vaccine.

T-killer cells are T-lymphocytes (a type of white blood cell); these cells kill other cells that are infected (particularly with viruses), or cells that are damaged in other ways.

Second Generation Vaccines

The second generation vaccines were created in order to minimise the risks of having the pathogen revert to a dangerous form.

The way these vaccines work is that they do not contain the whole organism, but rather contain only subunits. Subunits may consist of the toxins that the pathogen uses for infecting the body. A great example for the second generation vaccine is DTP vaccine. The second generation vaccines can generate antibody response but not T-killer response.