Gene correction for SCID-X1 in long-term hematopoietic stem cells

Area of Science:

• Hematology
• Immunology
• Gene Therapy

Background:

• Monogenic blood and immune disorders can be treated by correcting gene defects in long-term hematopoietic stem cells (LT-HSCs).
• X-linked Severe Combined Immunodeficiency (SCID-X1) is a debilitating primary immunodeficiency caused by mutations in the IL2RG gene.

Purpose of the Study:

• To develop and evaluate a CRISPR-Cas9/AAV6 gene editing strategy for functional correction of SCID-X1 by targeting the endogenous start codon in LT-HSCs.
• To assess the safety, specificity, and efficacy of this gene editing approach in patient-derived cells and in vivo models.

Main Methods:

• Utilized a CRISPR-Cas9 and Adeno-Associated Virus 6 (AAV6) delivery system for targeted integration of a cDNA into the start codon of the IL2RG gene.
• Employed high-fidelity Cas9 as a ribonucleoprotein complex to minimize off-target mutations.
• Transplanted edited LT-HSCs and evaluated hematopoiesis and lymphopoietic function in vitro and in vivo.

Main Results:

• Achieved up to 20% targeted integration frequencies in LT-HSCs and a median of 45% in patient-derived CD34+ HSPCs.
• Observed no evidence of abnormal hematopoiesis post-transplantation, indicating a lack of toxicity.
• Demonstrated rescue of the lymphopoietic defect in patient-derived HSPCs in vitro and in vivo, confirming functional correction.
• Confirmed no off-target mutations using sensitive detection methods.

Conclusions:

• The developed CRISPR-Cas9/AAV6 strategy shows high targeting efficiency and specificity for correcting SCID-X1 mutations.
• The approach is safe, with no observed toxicity or off-target effects, supporting its clinical potential.
• This gene editing method offers a viable therapeutic strategy for SCID-X1 and potentially other monogenic blood disorders.