Two is better than one: Advancing gene therapy protocols for enhanced safety and efficacy.

In this issue of Cell Stem Cell, two complementary studies from Zeng et al.1 and Demirci et al.2 improve the efficacy of gene therapy for β-hemoglobinopathies using multiplex CRISPR-Cas9 editing. The authors also optimize editing and conditioning protocols to reduce risks associated with current gene therapy procedures.