Autologous Stem-Cell-Based Gene Therapy for Inherited Disorders: State of the Art and Perspectives

Abstract

Gene therapy using patient's own stem cells is rapidly becoming an alternative to allogeneic stem cell transplantation, especially when suitably compatible donors cannot be found. The advent of efficient virus-based methods for delivering therapeutic genes has enabled the development of genetic medicines for inherited disorders of the immune system, hemoglobinopathies, and a number of devastating metabolic diseases. Here, we briefly review the state of the art in the field, including gene editing approaches. A growing number of pediatric diseases can be successfully cured by hematopoietic stem-cell-based gene therapy.

Keywords: SCID; clinical trial; curative treatment; gene editing; gene therapy; lysosomal storage disorder; sickle cell disease; thalassemia.

Figure 1

Current methods for generating lentiviral vectors. Four plasmids (a transfer vector containing the therapeutic gene and viral long terminal repeats, a REV-containing plasmid, a GAG-POL encoding plasmid, and an envelope-encoding plasmid, most often VSV-G) into a packaging line that subsequently secretes replication-deficient lentiviral particles. The latter are purified and then tested in several efficacy and safety assays before clinical use.

Figure 2

The principle of stem-cell-based gene therapy for pediatric diseases. CD34⁺ cells enriched for HSCs are harvested from the patients—either from bone marrow or (increasingly) from mobilized peripheral blood. The CD34⁺ cells are cultured in GMP laboratories with cytokines and viral vectors, harvested, and then subjected to a number of quality control steps prior to reinfusion into the patient. The cell product is often cryopreserved to allow time for quality control tests and the shipment of cells to clinical transplantation centers far from the production site. After reinfusion, HSCs find their niches, differentiate into mature blood cells, and thereby restore the clinical defect.

Figure 3

Genome editing for gene deletion or gene repair. A nuclease (often CAS9 with a guide RNA as part of the CRISPR system) generates double-strand DNA breaks. If a donor template is not provided, NHEJ will generate mutations that typically lead to a loss-of-function mutation. This strategy is used (for example) to remove repressors of fetal hemoglobin. The other approach requires a donor sequence for repair and relies on HDR. The donor template is often provided by an AAV.