Bright future for multitasking CRISPR as it tackles complex diseases and COVID

We need to understand the mechanism behind the virus’s attacks and how it penetrates cells and blows holes in our immune system if we are to create effective vaccines and concoct useful therapies.

One major weapon which has emerged and is helping to understand and tackle the enigma of COVID-19 is CRISPR. This remarkable gene editing technique, discovered just over decade ago, is by any standard having a “good COVID-19 war”.

In 2020, CRISPR found its place in the pantheon of scientific breakthroughs offering a lifeline in all diverse fields from biotechnology and frontline medicine to commercial interests in pharmaceuticals and agriculture even with the potential to turbo-charge economic output.

The part CRISPR plays in fighting the virus might be compared to the exploits of WW2 Bletchley Park codebreakers on decrypting the Enigma code. It’s a colourful but obvious analogy. However, it is much more than that. The genetic code of the virus was cracked very early on in the pandemic. In the standard timeframe of most biotech research that was like a nanosecond.

It was fitting that Jennifer Doudna and Emmanuelle Charpentier were lauded with the Nobel prize in chemistry because CRISPR has already more than a mere walk-on part in the fight against COVID-19. It is likely to be centre stage as we scramble for long-term solutions. It’s how effectively we use this new tool going forward that we need to observe. There’s no hard evidence yet that the pandemic has diverted R&D money and time away from existing CRISPR projects... but here we look at why it is essential these other research areas continue to be supported.

The joy of six

Here are six research areas to watch out for as CRISPR offers new hope against diseases and conditions which have caused human misery for centuries. 

1 CRISPR hammer falls on sickle cells [1]

It’s estimated 5m people have sickle cell anaemia and there are 43m carriers worldwide who have the sickle trait. About 80 per cent of cases are in sub Saharan Africa.

The disease is caused be a mutation in the HBB gene which provides instructions to make the protein haemoglobin. Haemoglobin is a molecule inside red blood cells that is responsible for carrying oxygen. In sickle cell disease, the mutations result in missing or deficient haemoglobin.

CTX001 has been developed using CRISPR to make a genetic modification to increase the production of foetal haemoglobin in patients’ red blood cells. Foetal haemoglobin is a type of haemoglobin that exists naturally in new borns. The maturing body later replaces it with the adult form of haemoglobin. However, sometimes foetal haemoglobin persists in adults, providing protection for or people with sickle cell disease as well as and beta-thalassemia. Specifically, CRISPR-Cas9 is used to delete the BCL11A in a patient’s own haematopoietic stem cells (HSPCs) on cells extracted from the patient. The modified cells are then transplanted back into the patient where they express HbF to restore healthy red blood cell levels.

Phase 1 and 2 clinical testing are ongoing, and it is anticipated that this will become a one-time curative therapy for both SCD (as well as beta-thalassemia).

The case of Victoria Gray from Mississippi is an inspiration for sufferers and those working on a cure.

(Also revisit LN’s earlier coverage on CTX001 here.)

2 Delicate cuts to MS gene hotspots

Babies born with MS suffer from progressive muscular degeneration. About 3,000 different mutations are believed to cause the disease. There is no treatment beyond palliative care. Last year, a group in the USA used CRISPR to cut twelve strategic gene hotspots covering the vast majority of those mutations – a remarkable achievement in itself.

Previous research has shown that children with DMD have a gene mutation that interrupts the production of a protein known as dystrophin. Research teams have have successfully demonstrated that CRISPR can regenerate muscle suffering from Duchenne muscular dystrophy (DMD) in a mouse model. They believe that going forward, this method may lead to a valid treatment in children with the condition. The study was led by the University of Missouri School of Medicine, US in collaboration with other researchers. 

Dr Dongsheng Duan is lead author of the study. He said: “If we can correct the mutation in muscle stem cells, then cells regenerated from edited stem cells will no longer carry the mutation. A one-time treatment of the muscle stem cells with CRISPR could result in continuous dystrophin expression in regenerated muscle cells.”

3 Homing in on CF’s mutant gene

The scourge of cystic fibrosis affects more than 10,000 people in the UK and the quest for therapies has been a heavy load on a long hard road. 

Researchers have proved it is possible to use CRISPR in human lung cells extracted from patients, altering the most common mutation at the root of the disease. Progress in the next months and years will be closely monitored, and human trials are already underway. Two companies, CRISPR Therapeutics and Editas Medicine, are leading the charge in this sector.

4 Huntington’s ‘cure’ a step nearer

Fine tuning of CRISPR gene-editing techniques holds promise for inactivating the defective gene responsible for the incurable Huntington’s.

In Poland, researchers have recently devised a precise method using CRISPR-Cas9 with the enzyme Nickase. The method shows great promise for successful gene editing.

Any off target effects of using CRISPR-Cas9 on brain cells could have lethal consequences on a patient and off-target effects are the biggest fear in any CRISPR experiments. So far, the Polish study has showed no off target effects, and the Cas9 Nickase pairs were successful in removing the abnormal repetitions from the Huntington gene in patient-derived connective tissue cells, as well as inhibiting toxic protein synthesis. Dr Marta Olejniczak, group leader of the study, has confirmed that no sequence-specific side effects have been observed.

5 Ethics and CRISPR against an old enemy [2]

Certain individuals have natural resistance to HIV; the virus that causes AIDS. They possess a gene which encodes for protein on the surface of immune cells that HIV uses as an entry point to infect the cell. This mutation alters the structure of the protein so that the virus can no longer bind to it.

An attempt to alter the human gene, to incorporate this mutant gene, was associated with the work that caused worldwide outrage and put the scientist He Jiankui behind bars in China. It also reinvigorated the ethical debate around gene editing and CRISPR.

Scientists in China, who are still using CRISPR for its potential to treat various genetic diseases - as well as HIV - by modifying cells other than human embryos, say they fear their colleague’s illegal actions might have a negative effect on their work. Though they too see his actions as reprehensible.

6 Rarest condition now in CRISPR crosshairs

According to The Progeria Research Foundation, there are only about 350 to 400 Progeria patients alive worldwide at any given time. The typical patient only survives to about 14 years and Progeria is never passed from parent to child or shared among siblings. During their brief lifespan, these unfortunate children tend to experience slowed growth, thinning skin and hair loss, skeletal abnormalities like fragile bones and joint problems. Most die of heart disease.

This devasting condition stems from a randomly-occurring mutation, typically a dominant-negative CG-to-TA mutation in the Lamin A (LMNA) gene, which results in a truncated form of the protein progerin. The mutation leads to developmental issues and gives young children the appearance of having rapidly aged.

According to work published recently in Nature [3], a huge team of scientists seems to have arrived at a one-time base editor gene therapy that can repair the point mutation causing HGPS. The efficacy of a CRISPR-Cas9-based approach that reverts several alterations in progeria syndrome cells and in mice by introducing frameshift mutations in the LMNA gene.

In November, the US Food and Drug Administration (FDA) approved the cancer drug lonafarnib as the first medication to directly treat progeria, but there's still no actual cure for the disease. The hope is that CRISPR will unlock a path to one.

Author: Dermot Martin is a freelance science writer with a specialist interest in CRISPR technology

References

1. https://www.wjhl.com/news/national/gene-editing-treatment-shows-promise-for-sickle-cell-disease/ 

2. https://www.livescience.com/crispr-hiv-treatement.html 

3. https://www.nature.com/articles/s41591-018-0338-6