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

The genetic defect-adenosine deaminase $(ADA)$ deficiency may be cured permanently by

At present,about $X$ recombinant therapeutics have been approved for human use the world over. Out of these,$Y$ are being marketed in India.

Injecting functional adenosine deaminase into a patient's (lacking $ADA$ gene) blood cells may be considered as

Gene therapy is an attempt to correct a genetic defect by providing a normal gene into the individual. By this,the normal function can be restored. An alternate method would be to provide the gene product (protein/enzyme) known as enzyme replacement therapy,which would also restore the function. Which in your opinion is a better option? Give reason for your answer.

In gene therapy of Adenosine Deaminase $(ADA)$ deficiency,the patient requires periodic infusion of genetically engineered lymphocytes because