As a Protein Engineer by training, I was asked to write my take on the huge hype around the gene editing technology called CRISPR. Here is a summary of my deep dive into this thrilling story and its potential to revolutionise Medicine as we know it.
CRISPR – what is it?
The CRISPR-Cas9 (or CRISPR for simplicity) molecular machinery was extracted from bacteria, who employ it for protection against repeated viral infections. It is composed of Cas9 – a nuclease – and a guide RNA made of clustered regularly interspaced short palindromic repeats (CRISPR), which together recognise a specific DNA sequence and cleave it with unprecedented selectively. The CRISPR system is so efficient and precise that it has been nicknamed “the molecular scissors” and “a DNA scalpel”. To add to its convenience, CRISPR works across all kingdoms of life, from bacteria, to plants, humans and other animals.
How does gene editing work?
Once CRISPR has cleaved a DNA sequence, the cell’s repair mechanisms can be utilised to perform diverse modifications. For example, the non-homologous end joining (NHEJ) pathway directly ligates the break ends and often results in a nonsensical DNA sequence that will not be translated into a functional protein. Conversely, homology-directed repair, joins the DNA ends using a template sequence that can be fed to the cell. This pathway offers an opportunity for gene repair, gene removal, and adding new genes.
In summary, CRISPR is a technology that allows accessing the code of life of any type of cell, and editing it to one’s will, albeit with a very low but non-zero rate of off-target effects.
CRISPR in clinical studies
The first clinical trial involving CRISPR-modified cells began in October 2016 (NCT02793856). In this Phase I study led by the Sichuan University, T cells are collected from patients with metastatic non-small cell lung cancer, their programmed cell death protein 1 (PDCD1) gene is knocked-out in the laboratory by CRISPR, before being infused back in each patient. A similar study was due to start early this year in the US, and a total of 6 studies using the same approach are currently listed on clinicaltrials.gov. The careful ex-vivo approach used in these studies, aims at circumventing the potential problems that inaccurate editing could bring in-vivo.
In an even more ambitious study (NCT03057912, due to start in July 2017), a plasmid coding for the molecular machinery of CRISPR directed against HPV will be applied directly on the cervix of women with HPV-related malignant neoplasm. The study’s primary objective is assessing tolerability and therapeutic doses of the treatment.
CRISPR in the future
If initial trials are successful, CRISPR could be used in the future to eradicate infectious illnesses such as HIV, to target various types of cancer, and to fix the genetic errors responsible for cystic fibrosis, Huntington’s disease and other incurable diseases. CRISPR could be the key to most of our current healthcare challenges.
The most controversial aspect of CRISPR is that it could, at least in principle, open the door to genetic engineering of human embryos. A team composed of experts in the field, including the inventors of the CRISPR machinery used nowadays, discussed this issue during a 3-day meeting in December 2015 and issued a statement in which they strongly discourage any use of CRISPR in germline cells at least until the safety of the method has been proven unequivocally, and until there is broad societal consensus.
For the time being, CRISPR is a fantastic research tool that allows probing in-vitro the many mysterious treasures that still hide in the code of life. Investigating carefully its medical potential in clinical research on somatic cells will help discover its true potential as a life-saving technology. In the meantime, it is our duty as scientists, politicians and citizens to ensure that clear regulations are developed to protect our genetic heritage from unethical and dangerous alterations.