Role of biotechnology in developing vaccines
A vaccine is a safe biological preparation, administered to humans to make them immune against a particular disease. The immune system of the human body identifies the vaccine as a foreign particle and destroys it, but the memory of the foreign matter remains intact with the immune system. Later, when the person factually gets infected withthe virulent form of the disease causing organism, the immune system immediately recognises it and fight against the infection by releasing antibodies.
There are several possible ways to develop a vaccine and it depends upon the procedure of infection by disease-causing microbes, the response of the immune system, the target site of the vaccine and the different physical characteristics of the microbe. Monovalent vaccines can immunize against one disease and multivalent vaccines immunize against two or more strains of the same disease-causing microbe or more than one disease.
These types of vaccines comprise attenuated form of a disease-causing microbe, so that it can no longer cause disease but only stimulate the immune system to memorize it. These vaccines produce a strong immune reaction and only one or two doses of the vaccines are enough to give immunity for whole life. It is predominantly used against viral diseases viz. chickenpox, mumps and measles. It should not be administered upon a person having a weak immune system such as HIV patients and patients undergoing chemotherapy. Some of the drawbacks are that they need to be refrigerated to remain effective which limits their utilization in some poor countries. Rarely, the weakened microbe can revert back to its virulent form.
In these types of vaccines, microbes are not weakened but inactivated by killing them using radiation, heat or chemicals. Therefore, the microbe is unable to mutate back to its potent form. Booster doses are required as this kind of vaccine does not generate a strong immune response. These can be used in developing countries since they arefreeze-dried, thus, are stored easily. For example, inactivated vaccines are manufactured against cholera, hepatitis A and bubonic plague.
To combat diseases like tetanus and diphtheria caused by toxin secreting bacteria, these vaccines are used. It is made by exposing the toxin to formalin and making the toxin harmless. The immune system releases antibodies against the toxin which bind and block the action of toxins.
These vaccines contain only the antigens of disease-causing microbe and not the entire microbe. Evidently, antigens induce the immune system the most. Antigens are recognised and bound by the T-cells of the immune system. Using recombinant DNA technology antigens can be made from the microbes in the laboratory. Such vaccines are referred as combining subunit vaccine. The vaccine against the hepatitis B virus is one of the examples.
Although vaccines against influenza and herpes are currently being administered, these types of vaccines are still in the trial phase. In DNA vaccines, when the genes that code for the antigens of that microbe are introduced into the body cells they initiate the body cells to generate antigens. As a result, the antigens stimulate the immune response of the body. These vaccines are easily producible and storable.
In bacteria with polysaccharides outer coating cannot be recognised by the immature immune system of a baby as polysaccharides mask the antigens present on the surface of bacteria. These antigens from the microbe are linked to the polysaccharides, so that the immature immune system can recognise them. These are known as conjugate vaccines. Haemophilus influenzae type B (Hib) is one of the examples for conjugate vaccine.
Functionally similar to DNA vaccines, recombinant vector vaccines use a different method to introduce itself. The vector, either an attenuated bacterium or virus, is used to carry the DNA of the microbe into the body of the patient and infects it followed by delivering the DNA to the body cells. Research is in progress to develop bacterium-based and viral-based recombinant vector vaccines against rabies, HIV and measles.