It seems like something from a dystopian movie: gene-editing in living cells. CRISPR, or Clustered Regularly Interspaced Short Palindromic Repeat, is a gene-editing technique that uses immune responses to change the DNA in living cells.
CRISPRs are essentially bands of DNA that include repeating genes and sequences of DNA called spacers, which can be used to code specific proteins. When a cell is attacked by a virus, the virus shoves DNA into the cell. These specific proteins coded by CRISPRs can then be coded to attack the viral DNA.
But when viral DNA that the cell does not recognize is inputted into the cell, cas genes, which are part of CRISPR bands, can create a novel spacer that code a protein to attack the viral DNA. The novel spacer then becomes part of the CRISPR gene.
It can be imagined like this:
You carry a set of keys. Each key can open a specific door. Imagine that another lock is added to your door. You’re going to have to create a new key to unlock the door, and then you will add the new key to your set of keys. This is the same way the CRISPR adds new spacers when confronted by novel viral DNA.
Scientists can use the CRISPR mechanism to insert a desired gene into DNA.
One of the pros of the CRISPR mechanism is that it’s cheap to create the tools needed to target a sequence of genes. The mechanism is also efficient because it works much faster than the traditional gene-editing technique of recombination. And because of the way CRISPR works, multiple genes can be introduced at once.
However, because it is a relatively new gene-editing technique, there are significant challenges that need to be faced before it is used on a large scale. For example, it is difficult to deliver the machinery into the cell.
In April, a group of scientists and policymakers met in Paris to discuss the applications of CRISPR and the ethics of putting it into use. According to Caroline Simons, who attended the meeting, it was decided that gene-editing is still in its infancy, and because scientists don’t yet know enough about how it works, CRISPR is not yet ready for clinical investigation.
It was also decided that scientists in the UK can use human embryos up to 14 days old, create human embryos and use CRISPR on early human embryos.
Several startups have plans to use CRISPR to correct DNA disorders. Editas, one of these startups, wants to try to use CRISPR to treat Leber congenital amaurosis, a rare eye disease that affects about 35,000 people worldwide.
Because the exact gene for the Leber disease is known, it is easy to target using CRISPR. The company hopes to get approval for a clinical trial by 2017. Because this condition is rare, it may be easier for the company to get approval; other more widespread conditions will have to wait longer for CRISPR clinical trials.
In China, scientists at Sun Yat-sen University in Guangzhou have used CRISPR to modify a gene for β-thalassaemia, a blood disorder that could be fatal, in human embryos. The gene-altering mechanism only worked on a small fraction of embryos and also resulted in unintended mutations.
Because of the results of the study, the scientists stopped altering human embryos and decided that CRISPR is still too immature to use to alter human embryos.
Other points of discussion around CRISPR have to do more with gene-editing in general, such as how to prevent the unethical editing of genes. Until more research is done on the long-term effects of gene-editing, CRISPR won’t be a widespread medical technique around the world.
By Stephanie Brito