High Efficiency CRISPR/Cas9-mediated Gene Editing in Primary Human T-cells Using Mutant Adenoviral E4orf6/E1b55k "Helper" Proteins.

Many future therapeutic applications of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 and related RNA-guided nucleases are likely to require their use to promote gene targeting, thus necessitating development of methods that provide for delivery of three components-Cas9, guide RNAs and recombination templates-to primary cells rendered proficient for homology-directed repair. Here, we demonstrate an electroporation/transduction codelivery method that utilizes mRNA to express both Cas9 and mutant adenoviral E4orf6 and E1b55k helper proteins in association with adeno-associated virus (AAV) vectors expressing guide RNAs and recombination templates. By transiently enhancing target cell permissiveness to AAV transduction and gene editing efficiency, this novel approach promotes efficient gene disruption and/or gene targeting at multiple loci in primary human T-cells, illustrating its broad potential for application in translational gene editing.

TALEN-Mediated Gene Editing of HBG in Human Hematopoietic Stem Cells Leads to Therapeutic Fetal Hemoglobin Induction.

Elements within the γ-hemoglobin promoters (HBG1 and HBG2) function to bind transcription complexes that mediate repression of fetal hemoglobin expression. Sickle cell disease (SCD) subjects with a 13-bp deletion in the HBG1 promoter exhibit a clinically favorable hereditary persistence of fetal hemoglobin (HPFH) phenotype. We developed TALENs targeting the homologous HBG promoters to de-repress fetal hemoglobin. Transfection of human CD34+ cells with TALEN mRNA resulted in indel generation in HBG1 (43%) and HBG2 (74%) including the 13-bp HPFH deletion (∼6%). Erythroid differentiation of edited cells revealed a 4.6-fold increase in γ-hemoglobin expression as detected by HPLC. Assessment of TALEN-edited CD34+ cells in vivo in a humanized mouse model demonstrated sustained presence of indels in hematopoietic cells up to 24 weeks. Indel rates remained unchanged following secondary transplantation consistent with editing of long-term repopulating stem cells (LT-HSCs). Human γ-hemoglobin expressing F cells were detected by flow cytometry approximately 50% more frequently in edited animals compared to mock. Together, these findings demonstrate that TALEN-mediated indel generation in the γ-hemoglobin promoter leads to high levels of fetal hemoglobin expression in vitro and in vivo, suggesting that this approach can provide therapeutic benefit in patients with SCD or ß-thalassemia.