ADA - Adenosine Deaminase Deficiency Gene Therapy - In, 1990 the first trial of actual gene therapy was conducted in USA. A little (4 years old)' girl suffering with adenosine deaminase deficiency (ADA), a lethal disorder, was transfected with lymphocytes bearing the ADA gene carried by retroviral vector.

In 1991 another girl (9 years old) began treatment in USA and received more than a dozen transfusions by 1992, Both these patients are doing well. In Italy also, a five year old boy was given a mixture of ADA gene - corrected T cells and bone marrow cells. In Netherlands also bone marrow gene therapy protocol for ADA deficiency was approved in 1992.