Biotechnology and its Applications - Applications in Medicine (Insulin, Gene Therapy)

Genetically Engineered Insulin: Insulin was traditionally extracted from the pancreas of slaughtered cattle and pigs, which caused allergic reactions. Human insulin consists of two short polypeptide chains: $Chain-A$ and $Chain-B$, linked by disulfide ($-S-S-$) bridges.

Pro-insulin Processing: In mammals, insulin is synthesized as a pro-hormone containing an extra stretch called the $C-peptide$. This $C-peptide$ is removed during maturation to form functional insulin. The main challenge in rDNA production was getting insulin assembled into a mature form.

Eli Lilly's Contribution (1983): An American company prepared two DNA sequences corresponding to $A$ and $B$ chains of human insulin and introduced them into plasmids of $E. coli$ to produce insulin chains. Chains $A$ and $B$ were produced separately, extracted, and combined by creating disulfide bonds to form Humulin.

Gene Therapy: It involves a collection of methods that allows the correction of a gene defect that has been diagnosed in a child or embryo. Normal genes are inserted into the individual or embryo to take over the function of and compensate for the non-functional gene.

Adenosine Deaminase ($ADA$) Deficiency: This disorder is caused due to the deletion of the gene for adenosine deaminase. The enzyme is crucial for the immune system to function. It can be treated by bone marrow transplantation or enzyme replacement therapy (ERT).

Steps in ADA Gene Therapy: Lymphocytes from the patient's blood 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.

Permanent Cure: While lymphocyte injection is not permanent (as cells are not immortal), introducing the gene isolate from marrow cells producing $ADA$ into cells at early embryonic stages could be a permanent cure.