Hematopoietic stem cell gene therapy: towards clinically significant gene transfer efficiency

Area of Science:

• Gene Therapy
• Hematopoietic Stem Cell Transplantation
• Immunology

Background:

• Early gene therapy trials using retroviral vectors showed insufficient transgene expression and low gene transfer efficiency into hematopoietic stem cells (HSC).
• Rodent models and in vitro assays did not accurately predict in vivo transgene levels in human target cells.
• Immune rejection of transduced mature cells was observed, but HSC-mediated gene transfer may induce immunologic tolerance.

Purpose of the Study:

• To improve gene transfer efficiency into HSC.
• To achieve stable and adequate in vivo transgene expression levels in circulating cells.
• To utilize the rhesus monkey model for preclinical evaluation of gene transfer strategies.

Main Methods:

• Utilized the rhesus monkey model for gene transfer studies.
• Employed in vivo priming of target cells, including mobilization of HSC with granulocyte colony-stimulating factor and stem cell factor.
• Optimized in vitro transduction conditions for HSC.

Main Results:

• Achieved stable in vivo gene transfer efficiency of up to 10-15% in both lymphoid and myeloid circulating cells in non-human primates.
• Demonstrated that transgenes introduced via HSC can induce immunologic tolerance.
• The achieved gene transfer levels are considered adequate for many clinical applications.

Conclusions:

• Hematopoietic stem cell-mediated gene transfer is a promising strategy for achieving therapeutic transgene levels.
• In vivo priming and optimized transduction conditions significantly enhance gene transfer efficiency.
• The rhesus monkey model is a valuable preclinical tool for advancing gene therapy for HSC.