Gene therapies hold significant promise as a long-lasting, if not permanent, treatment for patients with life-changing disorders such as amyotrophic lateral sclerosis, Parkinson’s disease and certain types of cancers. The concept of gene therapy, which has been around since the 1970s, involves the introduction of normal genes into cells in place of missing or defective ones to correct genetic disorders. After the first clinical success in 1990 in which a patient with severe combined immunodeficiency was delivered a functional copy of the adenosine deaminase gene, the field began to gain momentum and garner significant interest from investors and the pharmaceutical industry. However, the initial enthusiasm was stalled by the death of a healthy volunteer during a clinical trial testing the safety of a treatment for ornithine transcarbamylase (OTC) deficiency in 1999. The patient suffered an immune response triggered by the viral vector used to carry the corrective OTC gene leading to multiple organ failure and brain death. More recently, the field has recovered with the US FDA citing more than 500 active IND applications involving gene therapy products in 2018, reflecting the intensity of interest in this field1. Gene therapies discussed in this White Paper include both in vivo and ex vivo approaches, which refer to the genetic modification of a patient’s cells inside and outside the body (before being returned to the patient), respectively.