Genetic Engineering & Biotechnology News

DEC 2017

Genetic Engineering & Biotechnology News (GEN) is the world's most widely read biotech publication. It provides the R&D community with critical information on the tools, technologies, and trends that drive the biotech industry.

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28 | DECEMBER 2017 | MaryAnn Labant Classical gene therapy took several decades to advance from proof of concept to clinical applications. In contrast, newer forms of gene therapy, such as those exploiting the CRISPR/ Cas9 gene-editing system, may take less than a single decade to do the same. It may seem puzzling that the new gene therapy should mature so much more quickly. After all, the new gene therapy promises more advanced capabilities, such as the targeting of specific genomic loci. Additional capabilities often mean additional complexities—more "bugs" to work out. Yet the new can benefit from the experience of the old, enabling it to progress more quickly. Classical gene therapy went through a difficult developmental period, recalls Theodore Friedmann, M.D., professor of pediatrics, School of Medicine, University of California, San Diego, and director, Center for Genetic Therapies. He points out that during this period, gene therapy strug- gled with gene delivery, the problem of bringing a therapeutic gene to the right tissue at the right time to correct downstream biochemical, physiologi- cal, and metabolic problems. Gene therapy eventually hit upon a workable solution: the viral vector. Engineered for safety, or "disarmed," the viral vector is ready to carry thera- peutic cargo to a diseased tissue or cell. Although viral vectors were first developed for use with classical gene therapy, they are also capable of ad- vancing the new gene therapy. In classical gene therapy, a viral vector can carry a gene that, upon insertion into the genome, restores a missing function and thereby corrects a disease phenotype. Rather than at- tempt to manipulate faulty genes, clas- sical gene therapy inserts a new genes. Despite its limitations, classical gene therapy has shown itself to be a powerful approach, and it has grown into a legitimate clinical field. Respon- sive diseases include severe combined immunodeficiency (SCID), pediatric retinal degeneration and blindness, hemophilia, neurological diseases, and lysosomal storage diseases such as adrenoleukodystrophy, commonly known as Lorenzo's oil disease. An- other application is the use of engi- neered T cells in immuno-oncology. T cells equipped with chimeric antigen receptors have shown remarkable promise against cancer. But in gene therapy, the holy grail is to achieve salutary pheno- typic changes more directly and with greater precision. Instead of merely inserting compensatory patches, gene therapy could resolve genetic diseases at the root level by correcting genetic misspellings. This is genome editing. B E S T O F C R I S P R 2 017 Genome Editing Explores New Depths Classical Gene Therapy Went through a Difficult Period; New Methodologies Are Maturing More Quickly Easi-CRISPR, a genome- editing technology developed at the University of Nebraska, addresses a major challenge of animal genome engineering—the efficiency with which donor DNA may be added. The technology uses exogenous single-strand DNA to shift the balance between two repair pathways, homology directed repair and non- homologous end joining, to efficiently slide a foreign DNA cassette into the cut site.

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