Casgevy: Innovative Medicinal Products Require Innovative Approaches to Regulatory Assessment

Abstract

Casgevy (exa-cel) is an autologous cellular therapy modified ex vivo by a CRISPR-Cas9-mediated gene-editing technology. For Casgevy to be granted the indication in transfusion-dependent β-thalassemia, one single-arm trial was submitted which was not amenable to conventional statistical analysis of ‘effect of cause’. Therefore, an analysis was conducted on the basis of ‘cause of effect’ making use of the scheme described by Toulmin coupled to an analysis of causal inference. Based on the current data within the submitted study: subjects with transfusion-dependent β-thalassemia no longer needed a red blood cell transfusion with a 93-percent probability if and only if administered Casgevy; PNS = 93%. It is acknowledged that unknown elements of safety may yet be revealed by long-term follow-up of recipients of Casgevy. Its durability of efficacy is, at present, also an unknown that may also be ascertained by long-term follow-up of recipients. The limitations of a causal analysis are related to assumptions of the proposed causal structure which may not capture the complexity of the real world. Overall, the claim that Casgevy is indicated to treat people with transfusion-dependent β-thalassemia is considered to be supported by the results of the submitted study; the benefit–risk evaluation of Casgevy is found to be positive.