BIOTECHNOLOGY - Inshyna N.M. - 2009

CHAPTER 4. MEDICAL BIOTECHNOLOGY

DNA Vaccines

Vaccination is an effective method for preventing infectious diseases. In developed countries, mortality from infectious diseases ranges from 4% to 8%, whereas in developing countries it reaches 30% to 50%. Vaccination significantly reduces the incidence of diseases. For instance, in 1995, the incidence of poliomyelitis in the USA and Canada was 200 cases per 1 million population, while in 2000 it dropped to 1 case per 20 million population (a 4,000-fold decrease). However, Vaccines against AIDS, tuberculosis, and malaria have not yet been developed.

There are various types of vaccines containing live, inactivated, or recombinant microorganisms, or individual components of their Cells. For The Human Body to develop Immunity, an antigen must be present, a role most commonly fulfilled by viral envelope Proteins. Recombinant DNA technology allows The production of Antigens using non-pathogenic microorganisms.

In 1990, scientists began developing new vaccines containing DNA molecules. In 1994, the term "nucleic acid

vaccines" emerged. The principle behind DNA vaccination is that a DNA molecule containing genes that encode antigens of a pathogenic microorganism is introduced into the patient's body. DNA vaccines are also referred to as genetic, polynucleotide, or nucleic acid vaccines.

To produce a DNA vaccine, the Gene encoding the immunogenic protein is inserted into bacterial Plasmids, which are then introduced into a bacterial Cell culture to obtain A large number of copies (Gene cloning). The plasmid DNA is isolated from the Bacteria and purified. This purified DNA serves as the vaccine. Administration of the DNA vaccine ensures the synthesis of antigens by the body's cells and The Development of immunity.

Compared to traditional vaccines, DNA vaccines offer the following advantages:

- efficacy and safety of immunization. DNA vaccines induce both humoral and cellular immunity (stimulating the synthesis of cytotoxic T lymphocytes). Traditional vaccines activate only humoral immunity, and there is no risk of infection;

- the possibility of creating combination vaccines and simplifying their manufacturing technology;

- significantly lower storage and transportation costs. DNA vaccines can withstand low and high temperatures as well as various humidity conditions.

However, despite the substantial advantages of DNA vaccines, certain limitations to their use should be noted.

Firstly, DNA vaccines induce immunity only against protein antigens. They cannot replace vaccines whose action relies on other antigenic molecules, such as Polysaccharides (e.g., pneumococcal and meningococcal polysaccharide vaccines).

Secondly, following synthesis, protein molecules may undergo modifications such as glycosylation. These processes occur differently in humans, animals, and microorganisms. Consequently, The Structure of the antigenic protein synthesized in the human body may differ from that produced by microorganisms.

Thirdly, upon administration of DNA vaccines, the immunogenic protein may be synthesized continuously within the body for an extended period.

Most DNA vaccines are currently undergoing clinical trials, meaning they will not be introduced into routine medical practice anytime soon.