From pg 20:

The potential to deliver “one shot cures” is one of the most attractive aspects of gene therapy, genetically-engineered cell therapy and gene editing. However, such treatments offer a very different outlook with regard to recurring revenue versus chronic therapies, particularly in certain diseases where it is possible to cure a large proportion of the prevalent patient pool (or at least prevent an additional dose from being required for an extended period). While this proposition carries tremendous value for patients and society, it could represent a challenge for genome medicine developers looking for sustained cash flow. GILD is a case in point, where the success of its hepatitis C franchise has gradually exhausted the available pool of treatable patients.