Characteristics of transcription-regulatory elements for gene expression from plasmid vectors in human trophoblast cell lines

Correction of X-CGD patient HSPCs by targeted CYBB cDNA insertion using CRISPR/Cas9 with 53BP1 inhibition for enhanced homology-directed repair

X-linked chronic granulomatous disease is an immunodeficiency characterized by defective production of microbicidal reactive oxygen species (ROS) by phagocytes. Causative mutations occur throughout the 13 exons and splice sites of the CYBB gene, resulting in loss of gp91phox protein. Here we report gene correction by homology-directed repair in patient hematopoietic stem/progenitor cells (HSPCs) using CRISPR/Cas9 for targeted insertion of CYBB exon 1-13 or 2-13 cDNAs from adeno-associated virus donors at endogenous CYBB exon 1 or exon 2 sites. Targeted insertion of exon 1-13 cDNA did not restore physiologic gp91phox levels, consistent with a requirement for intron 1 in CYBB expression. However, insertion of exon 2-13 cDNA fully restored gp91phox and ROS production upon phagocyte differentiation. Addition of a woodchuck hepatitis virus post-transcriptional regulatory element did not further enhance gp91phox expression in exon 2-13 corrected cells, indicating that retention of intron 1 was sufficient for optimal CYBB expression. Targeted correction was increased ~1.5-fold using i53 mRNA to transiently inhibit nonhomologous end joining. Following engraftment in NSG mice, corrected HSPCs generated phagocytes with restored gp91phox and ROS production. Our findings demonstrate the utility of tailoring donor design and targeting strategies to retain regulatory elements needed for optimal expression of the target gene.

Different roles of G protein subunits beta1 and beta2 in neutrophil function revealed by gene expression silencing in primary mouse neutrophils

Neutrophils play important roles in host innate immunity and various inflammation-related diseases. In addition, neutrophils represent an excellent system for studying directional cell migration. However, neutrophils are terminally differentiated cells that are short lived and refractory to transfection; thus, they are not amenable for existing gene silencing techniques. Here we describe the development of a method to silence gene expression efficiently in primary mouse neutrophils. A mouse stem cell virus-based retroviral vector was modified to express short hairpin RNAs and fluorescent marker protein at high levels in hematopoietic cells and used to infect mouse bone marrow cells prior to reconstitution of the hematopoietic system in lethally irradiated mice. This method was used successfully to silence the expression of Gbeta(1) and/or Gbeta(2) in mouse neutrophils. Knockdown of Gbeta(2) appeared to affect primarily the directionality of neutrophil chemotaxis rather than motility, whereas knockdown of Gbeta(1) had no significant effect. However, knockdown of both Gbeta(1) and Gbeta(2) led to significant reduction in motility and responsiveness. In addition, knockdown of Gbeta(1) but not Gbeta(2) inhibited the ability of neutrophils to kill ingested bacteria, and only double knockdown resulted in significant reduction in bacterial phagocytosis. Therefore, we have developed a short hairpin RNA-based method to effectively silence gene expression in mouse neutrophils for the first time, which allowed us to uncover divergent roles of Gbeta(1) and Gbeta(2) in the regulation of neutrophil functions.