Biotechnology and its Applications
Biotechnological Applications in Medicine
The recombinant DNA technological processes have made immense impact in the area of healthcare by enabling mass production of safe and more effective therapeutic drugs
Further, the recombinant therapeutics do not induce unwanted immunological responses as is common in case of similar products isolated from non-human sources
At present, about 30 recombinant therapeutics have been approved for human-use the world over
In India, 12 of these are presently being marketed
Genetically Engineered Insulin
Management of adult-onset diabetes is possible by taking insulin at regular time intervals
What would a diabetic patient do if enough human-insulin was not available? If you discuss this, you would soon realise that one would have to isolate and use insulin from other animals
Would the insulin isolated from other animals be just as effective as that secreted by the human body itself and would it not elicit an immune response in the human body? Now, imagine if bacterium were available that could make human insulin
Suddenly the whole process becomes so simple
You can easily grow a large quantity of the bacteria and make as much insulin as you need
Think about whether insulin can be orally administered to diabetic people or not
Why? Insulin used for diabetes was earlier extracted from pancreas of slaughtered cattle and pigs
Insulin from an animal source, though caused some patients to develop allergy or other types of reactions to the foreign protein
Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bridges (Figure 10.3)
In mammals, including humans, insulin is synthesised as a pro-hormone (like a pro-enzyme, the pro-hormone also needs to be processed before it becomes a fully mature and functional hormone) which contains an extra stretch called the C peptide
This C peptide is not present in the mature insulin and is removed during maturation into insulin.The main challenge for production of insulin using rDNA techniques was getting insulin assembled into a mature form
In 1983, Eli Lilly an American company prepared two DNA sequences corresponding to A and B, chains of human insulin and introduced them in plasmids of E. coli to produce insulin chains
Chains A and B were produced separately, extracted and combined by creating disulfide bonds to form human insulin
Gene Therapy
If a person is born with a hereditary disease, can a corrective therapy be taken for such a disease? Gene therapy is an attempt to do this
Gene therapy is a collection of methods that allows correction of a gene defect that has been diagnosed in a child/embryo
Here genes are inserted into a person’s cells and tissues to treat a disease
Correction of a genetic defect involves delivery of a normal gene into the individual or embryo to take over the function of and compensate for the non-functional gene
The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency
This enzyme is crucial for the immune system to function
The disorder is caused due to the deletion of the gene for adenosine deaminase
In some children ADA deficiency can be cured by bone marrow transplantation; in others it can be treated by enzyme replacement therapy, in which functional ADA is given to the patient by injection
But the problem with both of these approaches that they are not completely curative
As a first step towards gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body
A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are subsequently returned to the patient
However, as these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes
However, if the gene isolate from marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure
Molecular Diagnosis
You know that for effective treatment of a disease, early diagnosis and understanding its pathophysiology is very important
Using conventional methods of diagnosis (serum and urine analysis, etc.) early detection is not possible
Recombinant DNA technology, Polymerase Chain Reaction (PCR) and Enzyme Linked Immuno-sorbent Assay (ELISA) are some of the techniques that serve the purpose of early diagnosis
Presence of a pathogen (bacteria, viruses, etc.) is normally suspected only when the pathogen has produced a disease symptom
By this time the concentration of pathogen is already very high in the body
However, very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by amplification of their nucleic acid by PCR
Can you explain how PCR can detect very low amounts of DNA? PCR is now routinely used to detect HIV in suspected AIDS patients
It is being used to detect mutations in genes in suspected cancer patients too
It is a powerful techqnique to identify many other genetic disorders
A single stranded DNA or RNA, tagged with a radioactive molecule (probe) is allowed to hybridise to its complementary DNA in a clone of cells followed by detection using autoradiography
The clone having the mutated gene will hence not appear on the photographic film, because the probe will not have complementarity with the mutated gene
ELISA is based on the principle of antigen-antibody interaction