Revolutionising Synthetic Biology
The development of CRISPR-Cas 9 – a simple and effective gene editing tool that can find, cut and replace DNA at a specific location – is revolutionising the synthetic biology industry.
The beauty of the system is that it consists of just two elements: a guide RNA, which binds the targeted DNA, and the DNA cutting nuclease Cas9, which complexes with the guide RNA. Both elements can be delivered into cells using a single vector. The highly efficient and cost-effective technique is so versatile it is set to transform a host of disciplines, from medicine to agriculture and industrial biotechnology.
The use of CRISPR-Cas9 carries enormous possibilities to further advance human health and well-being. While the ultimate aim is to eradicate diseases, the majority of work using the technique is still at the research stage. For example, CRISPR is having a huge impact on how potential drug targets for cancer and other conditions are discovered, as it enables researchers to hone in on and edit specific genes much more efficiently and less expensively than with previous genome editing methods.
In February 2016, research scientists in London were granted permission to use CRISPR-Cas9 to edit healthy human embryos in a quest to develop treatments for infertility. This was the world’s first endorsement of such research and sets a strong precedent for allowing similar applications to go forward.
So who will win the race to develop the first CRISPR therapeutic? In 2015, Editas Medicine announced its plans to use CRISPR to try to treat a rare form of blindness known as Leber congenital amaurosis.
More recently, in June 2016, approval was given by a federal panel in the USA for the first ever clinical trial of CRISPR to create genetically altered immune cells for the treatment of cancer. Scientists at the University of Pennsylvania plan to use CRISPR in the pioneering technology of Chimeric Antigen Receptor (CAR)-T cell therapy to engineer T-cells to make them more effective at identifying and destroying three types of cancerous tumour cells. CAR-T cell therapy has received striking early success against certain blood cancers in patients who have failed to respond to other treatments. The use of CRISPR-Cas9 in combination with CAR T-cells could prove to be a game changer in saving the lives of those with previously untreatable cancers.
Elsewhere, researchers are exploring the possibility of using CRISPR to cure HIV, with some success already being reported both in isolated human cells and in mice and rat models, while another team at Berkeley is attempting to use the technique to correct the mutation that causes sickle cell anaemia.
While the spotlight is undoubtedly on CRISPR’s potential role in therapy, it is also being used as a genome editing tool in a diverse range of crops, including wheat, rice, soybeans, potatoes, sorghum, oranges and tomatoes. In a recent study, John Innes Centre scientists used the technology to make targeted edits to two UK crops – a broccoli-like brassica and barley – and these edits are shown to be preserved in subsequent generations. CRISPR has also been used to create grapevines that are resistant to downy mildew disease and wheat that is resistant to powdery mildew.
There is huge potential for the use of CRISPR in industrial biotechnology. A major player in the field is Caribou Biosciences who are working to improve microbial production strains to generate better cell factories for fermentation. They are also using the technique to unlock the potential of microbes to bioproduce chemicals and enzymes never previously produced by fermentation.
The Swiss synthetic biology company Evolva is also adding CRISPR to its toolkit, which promises a major boost to its search for new ingredients and specialty chemicals with brewing and engineered microorganisms. Evolva’s products range from nootkatone, a flavour ingredient of grapefruit that could help stop the spread of Zika, to agricultural bioactives and components of next-generation materials.
Despite the extraordinary power and potential applications of the technique, there is concern in the scientific community that CRISPR might inadvertently alter regions of the genome other than the intended ones, thereby affecting the treated cell in possibly unpredictable ways. While the potential for off-target mutations has less significance in techniques such as CAR-T cell therapy, which involve somatic rather than genome edits, it is a problem that must be addressed. Many researchers, including those planning clinical trials, are using web-based algorithms to predict the off-target effects of CRISPR. However, it is now known that they are not one hundred per cent accurate, which means that off-target identifying methods will need to be greatly improved if genome editing is to be used safely to treat patients.
CRISPR has other limitations that have driven the search for alternative gene editing techniques. For example, the components of CRISPR are too large to insert into the genome of the virus normally used for gene therapy. A potential solution to this comes in the form of a mini-Cas9 that has been used successfully in mice to correct the gene responsible for muscular dystrophy. Other issues are that Cas9 will not cut everywhere it is directed to, and the pathway it uses to insert a new sequence of DNA is error-prone. Researchers are actively seeking alternative enzymes to Cas9 to expand the technique’s repertoire, in addition to strategies that involve disabling Cas9 and tethering it to other enzymes to enable different sequence changes.
In May, an entirely new gene-editing system – a bacterium-derived protein called NgAgo, which is programmed using a short DNA sequence that corresponds to the target area – caused an initial flurry of excitement. Although laboratories have so far failed to reproduce the results, the technique promises to forge a new way forward in the field.
Public concern about the use of CRISPR for genome manipulation cannot be ignored, with many people believing it paves the way to a future in which parents can choose the traits of their children. Another fear is that such germline editing enables the modified gene to be passed onto future generations with unpredictable results. Others offer more subjective arguments. Who gets to decide what constitutes an improvement to a genome? Should we be altering living organisms at all?
The scientific community fully recognises the need to tread carefully in this controversial area and to lay down specific guidelines for responsible practice. A conference in Washington DC in December 2015, to discuss the ethics of using CRISPR technology in humans, called for a “moratorium on any attempts at germline genome modification for clinical application in humans” and for a “framework for open discourse on the use of CRISPR-Cas9 technology to manipulate the human genome”.
It is right that scientists should continue to address public concerns and to openly discuss the benefits and risks of CRISPR. With time, it is likely that the technique will become more accepted as its extraordinary powers are realised and fears of its potential misuse are allayed. In the meantime, the fact cannot be ignored that CRISPR is already reaching into all sectors of the life sciences and it is only a matter of time before we are facing a serious technological revolution.