Removal of which chain results in maturation of proinsulin to insulin?

In the treatment of $ADA$ deficiency during gene therapy,which cells are collected from the patient's blood?

In $1983$,Eli Lilly,an American company,first prepared two $DNA$ sequences corresponding to $A$ and $B$-chains of human insulin and introduced them into the plasmids of $Escherichia$ $coli$ to produce insulin chains. Chains $A$ and $B$ were prepared separately,extracted,and combined by creating:

Which of the following is used for gene transfer in animals?

$\text{ELISA}$ is :-

Which kind of therapy was given in $1990$ to a four-year-old girl with adenosine deaminase $(ADA)$ deficiency?