ADA and severe combined immunodeficiency: Recently, it was reported that a patient treated in 2016 on a compassionate use basis with Strimvelis®, a gammaretroviral engineered haematopoietic stem cell (HSC) product approved by the European Medicines Agency (EMA) for the treatment of ADA-SCID, an adenosine deaminase (ADA) deficiency caused by mutations in the ADA gene leading to severe combined immunodeficiency (SCID), has been diagnosed with lymphoid T-cell leukaemia, possibly caused by an insertional event related to the treatment [25].