In 2019, Wu et al. used CRISPR/Cas9 to cleave the BCL11A enhancer sequence in HSCs and successfully downregulated its expression without inducing significant side effects.296 In December 2020, clinical data were released for a gene therapy called CTX001, a one-time therapy for SCD and TDT developed by CRISPR Therapeutics in association with Vertex Pharmaceuticals.74 This clinical trial used Cas9 to cleave the BCL11A enhancer region in hematopoietic stem and progenitor cells (HSPCs), causing them to lose enhancer activity. The gene discussed is BCL11A; the disease is Schnyder corneal dystrophy.