Patients suffering from sickle cell disease now have a cutting-edge therapeutic option: the first CRISPR-based intervention in history (in the United States). On December 8, the United States Food and Drug Administration (FDA) gave the green light to this gene editing therapy for patients 12 years old and older. Besides offering a hopeful outlook for those with severe forms of this blood disease, the treatment called Casgevy represents the first in the world of genetic modification of cells using the Nobel Prize-winning molecular scissors CRISPR/Cas9.
CRISPR is an acronym that stands for “Clustered Regularly Interspaced Short Palindromic Repeats.” CRISPR is a gene editing technology that allows precise changes to be made in the DNA of organisms, including humans. The technology is based on a system present in bacteria that allows them to protect themselves against viruses by storing fragments of viral DNA in their own genome.
The most commonly used gene editing tool is CRISPR/Cas9, where “Cas9” refers to a protein that acts like “molecular scissors,” cutting DNA at specific locations. Scientists can design specific sequences of RNA that guide the Cas9 protein to the desired location in the genome, where it can make a precise cut. The cells of the body then naturally repair these cuts, which usually introduce changes in the process, which allows genetic modification.
CRISPR has revolutionized biotechnology and genetic research, allowing scientists to edit genes with greater precision and efficiency than previous techniques. It is used in a variety of applications, from basic genetics research to the development of gene therapies for genetic diseases and the creation of genetically modified organisms. However, the use of CRISPR has also raised ethical questions and concerns about its use in humans and other organisms.
This disease, caused by a genetic defect in hemoglobin, the protein responsible for carrying oxygen in red blood cells, causes sickled blood cells, unlike normal ones, to become rigid and easily obstructed, thereby limiting blood flow and causing debilitating pain. Those severely affected may require several hospitalizations during the year.
Patients with sickle cell disease are often forced to miss days of school, work, or special events due to excruciating pain. The hope that this therapy will relieve symptoms is cause for great excitement.
Although there are some therapies available for sickle cell disease, such as taking drugs such as hydroxyurea or doing bone marrow transplants, these options have limitations. Hydroxyurea is not effective for everyone, and transplants require a genetically compatible donor, usually a sibling, with this match being no less than 20 percent.
Casgevy, like a transplant but with particular use of the patient’s own cells, uses CRISPR technology to change the genetic blueprint of bone marrow stem cells, which produce blood cells. These edited cells produce fetal hemoglobin, a type of hemoglobin commonly found in fetuses and infants, thereby preventing blood cells from becoming sickle-shaped and clogging arteries.
The procedure involves a round of chemotherapy to eliminate the existing cells in the bone marrow, which gives the new cells edited in the lab a chance to grow in the body. Afterwards, the edited cells are re-introduced to the patient through an intravenous line. Both episodes require hospitalization.
In a clinical trial, 29 of 30 patients treated with Casgevy and followed for at least 16 months did not experience pain attacks for a year. However, this treatment is not without risk. Chemotherapy, for example, can increase the risk of blood cancer and cause infertility. In the short term, chemotherapy can destroy the cells of the immune system, which increases the risk of infections and complications.
For some patients, the risks may be considered small compared to the hope of a year without severe pain, while others may choose to wait and evaluate the results.
Another concern is the cost of the therapy, which can reach $2 million per patient. However, the lifetime health care costs for patients with sickle cell disease are also substantial.
Currently, there are clinical studies using CRISPR/Cas9 for inherited genetic disorders such as beta-thalassemia, leukemia, retinal dystrophy, phenylketonuria, and hereditary hemochromatosis, as well as immunotherapy applications to enhance the immune response against cancer.