Five steps of the first gene therapy for ADA deficiency are listed in a mixed order…

Gene therapy delivers a normal gene to take over the work of a non-functional one. The first clinical gene therapy, in 1990, was for a four-year-old girl with ADA deficiency, which is caused by the deletion of the gene for adenosine deaminase. Lymphocytes are grown outside the body, given a functional ADA cDNA by a retroviral vector, and returned. They are not immortal, so the infusions are repeated. Very low amounts of a germ can be found early by PCR, which copies the nucleic acid, and by ELISA, which uses antigen and antibody interaction.