Genome and Gene Therapy (2000)

Monday, June 19, 2000, will be remembered by biologists as an historic day. Flanking Bill Clinton, President of the United States of America, were Francis Collins of the NIH, leader of the publicly funded Human Genome Project, and Craig Venter, CEO of Celera Genomics of Rockville, Maryland, to announce the near-completion of the sequencing of the entire human genome. To add to the drama and recognize the international effort of the Genome Consortium were the televised appearances of Tony Blair, Prime Minister of the United Kingdom, John Sulston, Director of the Sanger Centre near Cambridge, and Mike Dexter, Director of the Wellcome Trust, the major financial supporter of the Sanger Centre. Imagine: the entire 3 billion nucleotides of our genome are decoded—an impossible dream just a few short years ago. The estimate of the number of genes ranges from a low of 50,000 to a high of more than 150,000. As we were watching this momentous occasion unfold, our first reaction was “wow … what a bonanza for gene therapy.” The science of gene therapy relies on the introduction of genes to cure a defect or slow the progression of disease and thereby to improve the quality of life. Therefore, we need genes! Suddenly, we have more than 50,000 of them. As the function of these genes is elucidated, our repertoire will increase and we may have to devise vectors that may include more than one, two, or even three genes to tackle complex traits. When we understand more about the functional interaction among proteins, we may not need the whole gene, perhaps only fragments, to allow appropriate protein–protein interactions. Availability of the whole genome sequence will allow us to identify regulatory elements essential for cell- and tissue-specific expression. Comparative genomics, especially between mouse and human, will further delineate important control elements. Some organisms where the genome is more compact, such as the puffer fish (Fugo), may allow easy assembly of regulatory elements, which can sometimes encompass more than 60 to 100 kb of the genome. Why do some sites of integration not permit gene expression? We will learn to identify such sequences and design vectors to avoid insertion in these “genomic graveyards.” Only recently, “insulator sequences” have been identified, which can be crucial to prevent transcriptional shutoff from integrated vectors. Search of the genome will identify many more of these elements, which will be crucial for vector design. Finally, successful gene therapy approaches will continue to depend on animal model systems: Availability of the genome sequence will make generation of “knock-out” mice and other species for a specific gene easier, cheaper, and faster. Sequences do not often reveal function, and here gene transfer approaches developed over the years can make pivotal contributions. cDNA libraries generated in viral vectors can be used to identify functions of unknown genes. All we need is a biological assay. The vectors can also be used to verify the function of a gene in a knock-out animal. They can also be used to generate a disease model by overproducing the wild-type, truncated, or transdominant negative form of a protein. Viral vectors can also be employed to improve efficiency of gene knockout by homologous recombination. The next big step is the annotation of this gigantic database. Most of us would like to have simple software that allows us to convert this “information” into “knowledge” on our desktops. The publicly funded Human Genome Project assures data availability freely to all scientists. It is now up to us to figure how we can effectively and quickly begin to take advantage of this marvelous new resource. For gene therapists, genes are the staple diet and, at least for now, we have a glut of them.