A study by scientists at Sangamo BioSciences, Inc. has demonstrated the use of the Company's zinc finger DNA-binding protein (ZFP) technology to achieve highly efficient, permanent correction of a disease-causing gene in primary human cells.
This research represents a significant advance in the ability to specifically and efficiently modify the human genome and provides the scientific foundation for potential therapeutic approaches for a variety of genetic disorders and infectious diseases.
In this study, the engineered zinc finger nucleases (ZFN) was used to correct errors in the DNA sequence of a disease-causing gene, the IL2Rgamma gene. Correction was achieved in a high percentage of treated cells without the need for selection and that correction was permanent and eliminated the need for integration of any foreign DNA sequence, a cause of problems in certain gene therapy studies.
Michael C. Holmes, Ph.D., Director, Therapeutic Gene Modification at Sangamo says they have used their ZFN technology to advanced the field of targeted homologous recombination to levels of efficiency and specificity that could make potential therapeutic applications feasible, and this will allow them to facilitate modification of a DNA sequence at a very specific point in the genome, in this case, at the site of a mutation in a gene. The cell's own machinery corrects the mutation using a DNA sequence that they provide. This happens without the need for integration of foreign DNA into the genome of cells. Once the gene is repaired, these cells undergo normal division and replication, resulting in daughter cells that carry the modified gene and are permanently corrected.
Nobel Laureate, Professor Sir Aaron Klug, of the MRC Laboratory of Molecular Biology, Cambridge, UK, says scientists have been searching for years for a way to modify or edit the genome of plants and animals in a precise and predictable fashion, and this work is a landmark study that provides the foundation for gene modification-based therapeutics without the safety issues that have plagued many traditional gene therapy applications. It gives him great personal satisfaction to see this remarkable outcome of his original discovery of zinc fingers and their development.
Mutations in the gene encoding the IL2Rgamma protein invariably cause X-linked SCID (X-linked Severe Combined Immunodeficiency Disease) or so-called Bubble-boy disease. Patients with such mutations do not produce a functional IL2Rgamma protein; never develop a functional immune system and die of severe infections within 12-18 months of birth.
In this study, highly specific engineered ZFNs designed to bind to sequences close to an X-linked SCID-causing mutation in the IL2Rgamma gene resulted in a high percentage of the cells undergoing gene correction. In addition, it was observed that approximately one third of the corrected cells acquired the desired modification on both chromosomes. The expected downstream changes in both RNA and protein levels were also observed. Comparably high levels of correction were observed in primary human T-cells. While further work will be required to optimize the system for therapeutic use, the gene correction efficiencies established here may be sufficient to achieve a therapeutic effect.
Edward Lanphier, Sangamo's president and CEO, congratulated all of the Sangamo scientists involved in the generation of these data, and said it was gratifying that their work has been recognized by the prestigious journal Nature. These results highlight the potential for gene correction therapy for human monogenic disorders i.e. those diseases caused by mutation of a single gene. They are now working with their clinical collaborators to move the technology into the clinic. Initial research will focus on monogenic diseases of blood cells such as Sickle Cell Anaemia and beta-Thalassemia. The technology also forms the basis of their program to develop a potential therapeutic for HIV infection by disrupting expression of the CCR5 gene to generate a population of HIV-resistant cells.
This research is published in Nature as an advance online publication.