Genetic diseases can be directly treated by knowing the genome sequences responsible for the disease. Over the past few decades, bio-chemical and bio-medical research has broken many boundaries in how we treat these types of genomic abnormalities that cause disease. This venture started with adenovirus technology, which efficiently delivers the therapeutics to the cell. Unfortunately, this therapy was causing respiratory illness; primarily in children. So, all genetic therapies using Adenovirus were stopped. However, it’s been used in virology to deliver epitopes, or to trigger an immune response in the cell. Since the adenovirus technology was not able to alter the damaged DNA without causing harm to the patient, a new type of gene editing technology needed to replace it. This is lead to the discovery of CRISPR, and it operates by targeting the damaged genetic material. Then, it allows the proper mechanisms to replace the genetic material that were damaged. CRISPR has created a new type of treatment option for those with genetic diseases. By examining a case study on the treatment of sickle cell that uses CRISPR technology, there is clear evidence that this treatment could make many strides in the world of bio-medical technology.
The capabilities of CRISPR are very expansive, but it was built on the foundation of the discovery and failure of Adenovirus. Adenovirus, or Ad for short, was used as a tool for gene editing because it was able to transport genetic materials to the cell. The NIH describes adenovirus as “ubiquitous, double stranded DNA viruses that are most commonly associated with pediatric illness of the upper respiratory tract, including the common cold.” The article goes on to add, “Adenoviral infections can also manifest with gastrointestinal, ophthalmologic, genitourinary, and neurologic symptoms.” One would think this is very useful for helping the body fight off infection and disease, according to Bativa biosciences, “Ad vectors can deliver genetic cargo to cells very efficiently, so that therapeutic levels can be achieved with fewer viral particles.” This biomechanism was important to cell function because it was supposed to get rid of any irregular or damaged cellular material, but it failed because it had adverse after effects. So, even though the mechanism of Ad was efficiently delivering the therapeutics, it was not actively changing the damaged material to keep it from replicating, and that’s what caused the illness. From that failed endeavor, Botiva describes how Adenovirus became the DNA-based vaccine delivery system, they state “With respect to vaccine development, the main purpose of a DNA-based vector is to deliver epitopes, from viruses to host cells and to ensure production of such epitopes in order to raise an broad and effective immune response against the virus.” Firstly, it’s important to note, that the epitope is where the anti-body attaches to the antigen. So, Ad was changed to be a delivery system to get rid of the damaged material in the cell. The transition from using adenovirus to treat patients, to the much more advanced technology like CRISPR has made many new treatment options possible for fatal genetic diseases, like sickle cell anemia.
Before diving into how CRISPR is used in treatment of sickle cell, there must be an understanding of how CRISPR works in a much wider scope. Firstly, you can’t talk about CRISPR gene editing without talking about Dr. George Church- a professor of genetics at Harvard Medical School. Back in August of 2022, he went on Dr. Rhonda Patrick’s podcast, FoundMyFitness, to discuss CRISPR and gene editing. The most important take away from that interview was when Dr. Patrick asks Dr. Church about “existing capabilities of CRISPR, things that have been done before with transgenic models, and deleting versus addition of a missing genome.” George Church states, “You can think of CRISPR as subset of editing, editing is a subset of genome engineering, and genome engineering- is not a subset of, it’s kind an overlapping set with therapies.” He then adds, “When you have a genetic disease, you’re missing a gene, you don’t want edit that gene you want to add it back in.” In other words, what Dr. Church is saying is that CRISPR is often referred to as a therapy but it’s really the general idea of genome engineering that created the idea that there could be genetically specific therapies, or personalized medicine; medicine created based on the genome of an induvial patient. In the context of Sickle cell disease the best candidates, determined by the FDA, are able to endure the following prosses; “Prior to treatment, a patients’ own stem cells are collected, and then the patient must undergo myeloablative conditioning (high-dose chemotherapy), a process that removes cells from the bone marrow so they can be replaced with the modified cells in Casgevy and Lyfgenia.” So, the patient must be strong and healthy enough to endure both the chemotherapy than the replacement of the modified cells into their body. When they aren’t strong enough, this can cause complications. The actual delivery of the new cells, is described by Sara Redon in Scientific American as “Cas9 deactivates BCL11A in bone marrow stem cells, where red blood cells are made, by cutting its DNA, and the cells begin producing the fetal hemoglobin and creating red blood cells with a normal round shape.” So, the sample of modified cells enter the blood and start to take apart the damaged cells. Then, the replication process is restarted with fresh, undamaged genetic material – or fetal hemoglobin.
By examining a case study on the treatment of sickle cell that uses CRISPR technology, it shows how powerful this gene editing tool really is. There are three different types of Sickle cell disease or SCD; those are HbSS, HbSC, and HbS Beta thalassemia. First, HbSS is a dominate phenotype, meaning it only takes one parent to pass it on for the patient to have it. The CDC classifies it with the following criteria, they state “Hemoglobin S is an abnormal form of hemoglobin that causes the red cells to become rigid, and sickle shaped. This is commonly called sickle cell anemia and is usually the most severe form of the disease.” The shape of a healthy blood cell is most similar to that of a Frisbee, because it needs that surface area to hold the oxygen it’s supposed to carry around the body. Whereas, the sickle shape is named for the way it resembles the curved farming tool. When the patient has HbSC, they have defective genes from both parents and the CDC describes HbSC patients as “People who have this form of SCD inherit a hemoglobin “S” gene from one parent and a gene for a different type of abnormal hemoglobin called “C” from the other parent. This is usually a milder form of SCD.” Even though it’s more mild, if both parents either carry and have a child then there is a strong chance that they will also have sickle cell anemia, either the same type or just HbSS. Lastly, there is HbS Beta thalassemia, which the CDC says the “inheritance of S gene type and another type of hemoglobin abnormality.” The article adds that there are “Two types: zero (HbS beta0) and plus (HbS beta+), and zero is more severe than plus.” Overall, any type of SDC is not what anyone wants, but it’s important to know the difference because it means that one SCD patients experience with the condition isn’t the same as the next. These variants are just the most common forms of SCD, but there are other more rare types.
With the understanding of how sickle cell affects a patient and how CRISPR gene editing has been developed, it’s clear how ground breaking this is. To bring in a specific example, there was a case study that was done by MDPI titled “Precision Editing as a Therapeutic Approach for β-Hemoglobinopathies”. MDPI wrote the review just to highlight how important this research is by stating “This review will summarize β-globin research enabled by continuously evolving viral biotechnologies, highlighting influential findings and setbacks, as well as emerging technological advancements that fostered both γ- and β-globin vector research and, eventually, successful gene therapies for sickle cell disease and β-thalassemia.” So, similarly to this paper, the goal of the review is to show every part of how CRISPR technology works to treat sickle cell anemia, and β-thalassemia; which is genetic condition that causes the body to not make enough Beta globin. The clinical trial was done in 2019 and it was a successful trial. In the follow up, MDPI states “After gene therapy, the patient had approximately 1/3 of the hemoglobin in RBC containing the anti-sickling bT87Q – globin chain, the amino acid substitution acting as a marker.” So, this successful trial made it clear that these treatment options should be rolled out as fast as possible. The MDPI shares “Based on these and additional positive results, bluebird bio’s gene therapy was approved by the European Medicines Agency in June 2019 and by the FDA in October 2022.” So, in terms of the scientific world this article is a little old, and now these treatments are actively available worldwide.
Even though the case study was a success, there are still challenges to navigate in rolling out this new gene therapy, just like any new bio-medical tool. The main goal for the future of CRISPR is highlighted by Roche, and they state “Rather than just treating blood disorders, retinal diseases, neuromuscular and other diseases, we would eliminate them.” So, with the success of bluebird’s therapy, this is clearly going to be a very good option for treating sickle cell. However, with every new medical advancement, there is always many hurdles before it becomes a widespread tool to benefit all people. MDPI highlights some of the current and expected challenges; these span from inaccessibility to the treatment to the various health risks associated with the treatment. In the case study review, they state “Such therapy circumvents the biggest limitation and risks of allogeneic HSCT, which arise from the necessity for an immunologically matched donor and risks from immunological rejection or graft versus host disease.” Even if you are able to get the treatment, you still risk rejection and graft versus host disease. Which means that you have a treatment to manage the symptoms of SCD, but now you still have the symptoms from your body fighting of the donor sample. Other than the risks to the patient, there is also issues with the accessibility of this treatment. The accessibility has to with the financial burden it can cause, and the specialized training required to administer it. The case study address that by saying “The high price of the procedure mostly results from the manufacturing and clinical infrastructure needed, and the extensive medical and scientific training required.” Then they add “Which, overall, makes this ex-vivo autologous gene therapy inaccessible in developed as well as developing countries in which most sickle cell disease and b-thalassemia patients reside.” So, not only is it expensive and hard to find trained professionals, it still is hard for the general public to access the treatment.
By using CRISPR, so many promising treatment options have been discovered, such as those being used to treat sickle cell anemia. Before the discovery of CRISPR, adeno virus was engineered to do the same task, but wasn’t successful because it ended up causing respiratory illness in young children. However, with the proper modifications it has been proven to be effective when used as an mRNA vaccine. On the other hand, CRISPR has not been studied long enough for us to be aware of adverse effects of the bio-medical technology. The successful clinical trial for CRISPR technology that treats sickle cell anemia was expedited due to success and FDA approval. Looking to the future, the next big stride for CRISPR technology will be to irradicate all types of disease known to man. More specifically, once gene therapy has been approved for any and all genetic diseases, it will expand into treating more and more diseases.
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