Dna Vaccines

The Making of a DNA Vaccine Against West Nile Virus. View the illustration. Credit: NIAID

Once the genes from a microbe have been analyzed, scientists could attempt to create a DNA vaccine against it.

Still in the experimental stages, these vaccines show great promise, and several types are being tested in humans. DNA vaccines take immunization to a new technological level. These vaccines dispense with both the whole organism and its parts and get right down to the essentials: the microbe’s genetic material. In particular, DNA vaccines use the genes that code for those all-important antigens.

Researchers have found that when the genes for a microbe’s antigens are introduced into the body, some cells will take up that DNA. The DNA then instructs those cells to make the antigen molecules. The cells secrete the antigens and display them on their surfaces. In other words, the body’s own cells become vaccine-making factories, creating the antigens necessary to stimulate the immune system.

A DNA vaccine against a microbe would evoke a strong antibody response to the free-floating antigen secreted by cells, and the vaccine also would stimulate a strong cellular response against the microbial antigens displayed on cell surfaces. The DNA vaccine couldn’t cause the disease because it wouldn’t contain the microbe, just copies of a few of its genes. In addition, DNA vaccines are relatively easy and inexpensive to design and produce.

So-called naked DNA vaccines consist of DNA that is administered directly into the body. These vaccines can be administered with a needle and syringe or with a needle-less device that uses high-pressure gas to shoot microscopic gold particles coated with DNA directly into cells. Sometimes, the DNA is mixed with molecules that facilitate its uptake by the body’s cells. Naked DNA vaccines being tested in humans include those against the viruses that cause influenza and herpes.

Recombinant Vector Vaccines

Recombinant vector vaccines are experimental vaccines similar to DNA vaccines, but they use an attenuated virus or bacterium to introduce microbial DNA to cells of the body. “Vector” refers to the virus or bacterium used as the carrier.

In nature, viruses latch on to cells and inject their genetic material into them. In the lab, scientists have taken advantage of this process. They have figured out how to take the roomy genomes of certain harmless or attenuated viruses and insert portions of the genetic material from other microbes into them. The carrier viruses then ferry that microbial DNA to cells. Recombinant vector vaccines closely mimic a natural infection and therefore do a good job of stimulating the immune system.

Attenuated bacteria also can be used as vectors. In this case, the inserted genetic material causes the bacteria to display the antigens of other microbes on its surface. In effect, the harmless bacterium mimics a harmful microbe, provoking an immune response.

Researchers are working on both bacterial and viral-based recombinant vector vaccines for HIV, rabies, and measles.

There are many problems inherent in developing a good protective anti-viral vaccine. Among these are:

• Different types of virus may cause similar diseases -- e.g. the common cold. As a result, a single vaccine will not be possible against such a disease

• Antigenic drift and shift -- This is especially true of RNA viruses and those with segmented genomes

• Large animal reservoirs. If these occur, re-infection after elimination from the human population may occur

• Integration of viral DNA. Vaccines will not work on latent virions unless they express antigens on the cell surface. In addition, if the vaccine virus integrates into host cell chromosomes, it may cause problems (This is, for example, a problem with the possible use of anti-HIV vaccines based on attenuated virus strains)

• Transmission from cell to cell via syncytia - This is a problem for potential AIDS vaccines since the virus may spread from cell to cell without the virus entering the circulation.

• Recombination and mutation of the vaccine virus in an attenuated vaccine.

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Any organic compound containing both an amino and a carboxylic acid functional group.

Source: Boundless. “Vitamins and Amino Acids.” Boundless Microbiology Boundless, 08 Aug. 2016. Retrieved 20 Jan. 2017 from https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/industrial-microbiology-17/microbial-products-in-the-health-industry-199/vitamins-and-amino-acids-1002-4866/

The fermentation is performed in two stages, in the first stage the organism is allowed to grow and increase its biomass and in second stage riboflavin production is stimulated by restricting the growth or by feeding glucose and inositol along with micronutrients such as iron to obtain high yield of riboflavin. After completion of fermentation, the pH of the fermentation broth is adjusted to 4.5. For feed grade product, the broth is concentrated to about 30% solids and dried on double-drum driers and to obtain crystalline product, the broth is heated for 1 h at 121 ºC to solublize the riboflavin and also release the bound vitamin from the cells. Insoluble matter is removed by centrifugation and the riboflavin so recovered is converted to less soluble form either chemical or by microbiological methods (Riegel and Bissinger, 2003).