In New Way to Edit DNA, Hope for Treating Disease

An ongoing clinical trial is using a new gene-editing technique to remove a major doorway HIV uses to infect human T cells. The approach uses naturally occurring proteins called zinc fingers, each of which can recognize a set of three letters, or bases, on DNA. Strung together, the zinc fingers can be used to match a particular site on the genome and linked with proteins to clip or insert genes.

For HIV, some of a patient's T cells would be removed and the zinc fingers used to disable the CCR5 gene. This gene encodes the CCR5 receptors on the surface of T cells, and lacking such receptors makes the cells highly resistant to HIV. Treated T cells would be encouraged to multiply and then re-injected into the patient. In mice, the treated cells had a strong advantage over untreated cells, which were under constant assault by HIV.

Sangamo BioSciences, a small California-based biotechnology company, and the University of Pennsylvania's Dr. Carl June and colleagues began a clinical trial in February. Asked whether the technique is practical, Dr. Katherine A. High, a hemophilia expert at the university, responded, "It's a little too early to know since clinical trials are in their early stages."

Even the most carefully designed zinc fingers can slip away from a target site, noted Dr. Matthew H. Porteus, a pediatric geneticist at the University of Texas. The field has struggled to make precise alterations of human DNA. "I think it has the potential to solve a lot of the problems that have plagued the gene therapy field," Porteus said of the technique.

The study, "Engineering Lymphocyte Subsets: Tools, Trials and Tribulations," was published in Nature Reviews Immunology (2009;9:704-716).

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