Genes control all biological life. An organism with “lucky” genes will have better resistance to pathogens and a longer, healthier life. Having “unlucky” genes means greater susceptibility to illness and probably earlier death. Up until recently, scientists’ ability to alter what was encoded in genes was very limited. That is about to change.
It may sound a bit like a snack food, but, in fact, it may be one of the greatest scientific discoveries in a generation. CRISPR (an acronym for Clustered Regularly Interspaced Short Palindromic Repeats) is a revolutionary gene-editing technology that allows scientists to alter sections of DNA. Scientists, however, did not invent this amazing technology. Unknown to them until near the end of the 20th century, nature has been using it for nearly as long as life has existed.
In 1987, dairy scientists working with the bacteria used to ferment cheese and yogurt wondered how some bacteria were especially effective at defending themselves against pathogens known as phage viruses. The scientists eventually discovered that the bacteria employed a strange previously unknown immunization method. The bacteria captured sequential pieces of the attacking virus’ DNA (now named CRISPR arrays). The bacteria stored these arrays and used them as a kind of “mugshot” to identify future similar viral attackers. In this way, the bacteria built up a genetic memory of attackers. If the same virus or a closely related one attacked again, the bacteria could identify it from the CRISPR arrays “mugshots.” It would then neutralize the virus by using a protein to cut up its DNA. Scientists named that protein Cas9, short for CRISPR Associated Protein 9. Unlike animal and human immune systems, which recognize predators through the antibodies on their cells, this immune system operates at the genetic level.
The harnessing of what turned out to be the most advanced and powerful gene-editing system available to scientists to date was the result of work by a team led by Professor Jennifer Downer at the University of California, Berkeley in 2012. They realized that they could program CRISPR-Cas9 to cut targeted sections of any double-stranded DNA. In other words, they had developed a reliable and relatively easy method of cutting out and replacing DNA sections and so, of re-writing genomes. Experts estimate that CRISPR-Cas9 is about four times quicker and significantly less expensive than TALENs (Transcription Activator-Like Effector Nucleases), the previous preferred tool for genome editing.
Because of its speed and cost effectiveness, scientists expect CRISPR technology to become widespread in many areas of genetics and microbiology. For example, though a complete “map” of the human genome has existed since 2003, scientists are unclear about the function of many of the genes in it. By using CRISPR to progressively “turn off” individual genes, they hope to discover their functions one by one.
In fighting disease, CRISPR had almost boundless potential. A team at Imperial College London, funded by the Bill and Melinda Gates Foundation, has already used CRISPR to successfully edit the genes of the mosquito that carries the parasite responsible for malaria. The gene edit prevents the females from producing fertile eggs. So far, these mosquitos exist only in the lab, but the plan is to release them across sub-Saharan Africa. A similar project is planned in India.
Scientists see great potential in using CRISPR to edit human genes. They envisage using it to edit out genetic diseases like hypertrophic cardiomyopathy from the genome, and to genetically alter mutations that cause diseases like cystic fibrosis and breast and ovarian cancer. However, applications involving the editing of human genes are some years away as CRISPR processes have to undergo extensive animal trials followed by lengthy and closely monitored human trials before they are granted regulatory approval.
Though we may not see the results in human medicine in the very near future, CRISPR technology is moving apace. In agriculture, scientists are working on a huge range of projects from developing crops resistant to bugs and bad weather to dairy cattle without horns. Progress is necessarily tempered with caution because of the huge implications of gene editing. Nevertheless, CRISPR gives scientists worldwide the power to make the kind of genetic advances that would have been science fiction only a few decades ago.