Gene therapy has shown lasting benefits for the immune systems of a small number of children with a rare and fatal immune-deficiency disease.

More than ten years ago, Adrian Thrasher and Bobby Gaspar at University College London and their colleagues began clinical trials treating children with two forms of severe combined immunodeficiency disease (SCID). The researchers took bone marrow stem cells from each patient, used a viral vector to insert a functioning copy of the defective, disease-causing gene and then infused the cells back into the patients. In one trial involving 10 children with the 'X-linked' form of SCID, all saw their T-cell immunity recover and all have survived, with the longest follow-up of more than a decade. One child developed leukaemia but is now in remission.

The form of SCID treated in the second trial is caused by a deficiency of an enzyme called adenosine deaminase. Four of the six children in this trial had their immunity restored and two even cleared a persistent viral infection.

Sci. Transl. Med. 3, 97ra79; (2011), Sci. Transl. Med. 3, 97ra80; (2011)