Panel Discussion

Gene therapy for gain-of-function genetic disorders requires correction or silencing of the mutant allele(s) in hematopoietic stem cells (HSCs) ex vivo followed by efficient engraftment of the cells following transplantation in the bone marrow. This presentation will describe preclinical development of an efficient protocol for cure of the autosomal dominant gain-of-function disease WHIM syndrome immunodeficiency that couples CRISPR/Cas9-mediated mutant allele silencing in HSCs with efficient and selective engraftment of edited HSCs using CD117-saporin immunotoxin conditioning. The disease gene in WHIM syndrome encodes the chemokine receptor CXCR4 which is critical for homeostatic leukocyte trafficking and positioning, including homing, positioning and retention of HSCs in the bone marrow. The silencing of the mutated CXCR4 allele confers a selective advantage for engraftment of transplanted HSCs without overt safety costs, and the non-genotoxic conditioning by CD117-saporin eliminates upfront toxicity associated with genotoxic conditioning agents, without sacrificing engraftment efficiency.