Which of the following is used as a vector in gene therapy?

$ELISA$ is based on the principle of

When and on whom was the first clinical gene therapy experiment performed?

How many of the following statements are correct?
$(i)$ Mature insulin is made up of $A, B$ and $C$ peptides.
$(ii)$ Removal of $C$-peptide helps in the maturation of insulin.
$(iii)$ In mature insulin,$C$-peptide is present.
$(iv)$ In insulin,chains $A$ and $B$ are linked by disulphide bonds.

$ELISA$ is used to detect viruses where the key reagent is . . .

How is a mature,functional insulin hormone different from its prohormone form?