Conventional gene therapy relies on modified viruses to insert the desired bit of DNA into a cell's genome. But viruses can carry only short sequences of DNA. And if the DNA lands in the wrong place, as happened to two boys in a French gene therapy trial, it can trigger cancer. Adding an entirely separate chromosome, however, eliminates this risk. And rather than being limited to one or two small genes, vast chunks of DNA can be added if desired. "For certain diseases it could be very useful to have the ability to deliver multiple therapeutic genes," says Gil Van Bokkelen, chief executive of Athersys in Cleveland, Ohio, one of several teams worldwide trying to develop artificial chromosomes. Most, like Athersys, are trying to create artificial chromosomes from scratch.
Chromos Molecular Systems of Burnaby, British Columbia, has taken a different approach, creating its artificial chromosome by building it up from the key elements of a normal mouse chromosome. This artificial chromosome behaves like a normal one in mice: it is duplicated when cells divide and is passed from generation to generation (New Scientist, 8 July 2000, p 7). Now the company has shown how the chromosome could be used for gene therapy. The researchers started with two cell lines containing the artificial chromosome, and added the gene for the human blood hormone erythropoietin to the chromosome.
Cells with the artificial chromosome carrying the gene were selected and injected into mice. As expected, the animals showed significant increases in their red blood cell counts compared with others injected with cells carrying the artificial chromosome without the added gene. The results will appear in BioProcessing Journal. The hope is that the same approach can be used to treat inherited diseas
Contact: Claire Bowles