Introduction
Clustered Regularly Interspaced Palindromic Repeats (CRISPR)/Cas9 is a revolutionary technology used in gene editing providing a promising solution in treating various diseases and genetic disorders. The technology is used in gene therapy, treatment of infectious diseases, HIV, and cancer. CRISPR has been used in gene alteration of mice with genetic disorders making its way to applications in human embryo. In this article we will dive into CRISPR, its role in treating genetic disorders, future prospects, and ethical and regulatory considerations surrounding it.
What is CRISPR?
CRISPR is a gene-editing technology that can be used to make corrections in the genome. It can be used to turn off and on genes in a cell quickly and with ease. CRISPR refers to the sequences in bacterial genome that provides protection against invading viruses with the help of Cas (CRISPR-associated) proteins.
CRISPR requires two major components:
guide RNA: a single guide RNA (sgRNA) that is used to guide the protein (Cas9)
Cas9 protein (CRISPR-associated protein 9): an endonuclease that allows double stranded DNA breakage for genome modifications.
After DNA breakage, the repair occurs through 2 pathways:
Non homologous end joining involves random insertion or deletion of DNA
Homology directed repair; a homologous piece of DNA is used for repair.
The precise genome editing is done with the latter pathway in which a homologous DNA with the required sequence change is delivered with sgRNA and Cas9 nuclease.
Source: Figure - PMC (nih.gov)
CRISPR’s Role in Treating Genetic Disorders
Advancements in gene editing treatments like CRISPR are being explored to correct the diseases due to genetic disorders like Cystic Fibrosis (CF), Duchenne's muscular dystrophy (DMD), and hemoglobinopathies.
Schwank et al demonstrated treatment in 2 patients with CF using CRISPR/Cas9. They extracted stem cells from intestine of the patients, and the mutations were corrected in the intestinal organoids with CF transmembrane conductor receptor (CFTR) being restored.
Tabebordbar et al used CRISPR/Cas9 in a mouse model of DMD. Adeno-associated virus (AAV) was used to transfer the endonucleases to recover dystrophin expression by deleting the exon with gene mutations. Other studies using CRISPR/Cas9 for target duplication of exons in vitro in humans with DMD have demonstrated production of full-length dystrophin.
CRISPR/Cas9 is used in treatment of Haemoglobinopathies like sickle cell diseases or thalassemia. Canver et al demonstrated fetal hemoglobin production in mice and human primary erythroblast cell using BCL11A enhancer disruption by CRISPR/Cas9.
Future Prospects
Recently, groundbreaking clinical trials are being conducted with successful approval for genome editing as medicine in Haemoglobinopathies.
Casgevy is the first-ever FDA approved CRISPR-based treatment for Haemoglobinopathies like sickle cell disease (SCD) and transfusion-dependent beta thalassemia (TDT). It was first approved by UK’s Medicines and Healthcare Products Regulatory Agency on November 16, 2023, in patients aged 12 and later by US FDA on December 8, 2023. Casgevy uses gene edits to increase expression of fetal hemoglobin which in turn boosts healthy adult hemoglobin production.
Another clinical trial by Editas Medicine uses CRISPR system with Cas12a protein for treating patients with severe SCD and TDT. It has similar mechanism as that of Casgevy with no serious adverse events. The FDA has given it the title of orphan drug. Editas is planning to expand the testing in participants from US and Canda this summer 2024.
UTIs are the most common type of bacterial infection, and the alarming rise of antibiotic resistance necessitates the need for alternative therapies. Recent clinical trials are conducted using combinations of bacteriophages and CRISPR-Cas3 that are designed to attack genome of E coli that causes 95% of the UTIs.
Other clinical trials are undergoing for protein folding disorders, inflammatory diseases, cardiovascular diseases, autoimmune disorders, HIV, and even cancers, proving a promising future with CRISPR system of therapy.
Ethical and Regulatory Considerations
CRISPR can be used to edit gene of embryos posing a threat of permanent genetic modifications and unclear long-term complications. Therefore, it is necessary to create ethical boundaries with the use of CRISPR.
Regulatory authorities like US FDA, EMA regulates CRISPR based therapies in humans with continuous monitoring of clinical trials to demonstrate safety and efficacy prior to approval for commercial use.
CRISPR/Cas9 is a breakthrough remedy in treating various genetic disorders. However, ethical use of such technologies must be ensured with adequate legal and regulatory guidelines.
Source
CRISPR Clinical Trials: A 2024 Update - Innovative Genomics Institute (IGI)
Controlling CRISPR Through Law: Legal Regimes as Precautionary Principles (harvard.edu) Assessed and Endorsed by the MedReport Medical Review Board