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Essay: Will genome editing replace HSCT for blood diseases?

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  • Published: 2 March 2022*
  • Last Modified: 22 July 2024
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  • Words: 1,069 (approx)
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  • Tags: Gene editing essays

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Genome editing involves the modification of the genome at a specific site in a DNA sequence [1]. Today, genetic engineering is used in overcoming many single-gene ailments such as cystic fibrosis, haemophilia, and a plethora of other diseases. However it was not until 2012, that the genome editing technique known as the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) system was adapted from a naturally occurring genome editing system in bacteria with just a single associated protein 9 (Cas9) and a single guide RNA [2]. Its specific genome editing has since “revolutionized the approach in haematology and oncology studies” [3]. The CRISPR-Cas9 system generates infinite opportunities to comprehend the study of drug resistance and establish any probable therapeutic targets [3], with the promise of altering genes to produce desired features and treatment of more complex diseases [4]. This essay therefore aims to discuss the arguments regarding genome editing, with the CRISPR-Cas9 technique in particular, and whether it is feasible to possibly remove and replace donor bone marrow transplants (BMT) in the future.

Although CRISPR-Cas9 has now become synonymous with gene editing, it is not the first technology developed to edit DNA [5]. As seen in table 1 below, the several other discoveries of comparative technologies tend to pale in comparison, as CRISPR-Cas9 has offered a far simpler, and cost-efficient way of gene modification [5].

The CRISPR-Cas9 technology is a multifaceted genome editing technology that is widely used for studying the functionality of genetic elements [4].

It comprises of 2 components: a guide RNA (gRNA) which is specific to the target DNA sequence and a non-specific CRISPR-associated endonuclease protein (Cas9). The Cas9 protein functions as a pair of ‘molecular scissors’ while the sgRNA is the ‘map’ that guides it to the appropriate site [6]. The design specifications of the gRNA can be altered to target the nuclease to cleave any host organisms’ genome at virtually any location

The recognition of the target DNA by the Cas9 enzyme is due to the presence of a short protospacer adjacent motif (PAM) sequence located directly downstream of the untargeted DNA strand. If the match is successful, Cas9 then cleaves both DNA strands 3-4 nucleotides upstream of the PAM site [6]. Typically, this short genetic element only occurs in invading viruses (non-bacterial genome), which ensures that Cas9 does not cleave its own CRISPR-Cas9 locus [6].

Hematologic malignancies encompass a wide array of disease including leukaemia, lymphomas, myelodysplastic syndrome and multiple myeloma [7]. Which are due to bone marrow dysfunction, yielding clinical entities ranging from smouldering pre-leukaemia states to outright acute leukaemia [3]. Table 2 below shows the applications of CRISPR-Cas9 technology in the several non-cancerous hematological disorders

On the other hand, allogeneic blood and bone marrow transplant (BMT) (often called hematopoietic stem cell transplantation (HSCT)) is the treatment of choice for most blood diseases [8]. This is because they contain pluripotent stem cells. The HSCs are capable of infinite self-renewal and differentiation into all mature blood lineages including platelets, red blood cells and white blood cells [9]. HSCT requires the hematopoietic and immune system of the recipient to be obliterated by chemotherapy or radiation, followed by the administration of hematopoietic stem cells harvested from the donor [10]. This has led to a significant increase in life expectancy, whereby 70% to 80% [11] of those who survive the first 2 years following HSCT are expected to become long-term survivors. However, the cure or control of the primary disease is not coupled with full rehabilitation [11].

HSCT survivors are at risk of developing long-term complications, such as endocrinopathies, musculoskeletal disorders, and subsequent malignancies. (summarized in Table 3 below.)

As one would imagine, with such a powerful tool like CRISPR-Cas9, it is possible to precisely engineer genetic changes in cells relatively quickly and efficiently. With the effect of CRISPR- Cas9 on editing the haematological malignant genetic lineage, the designer babies would practically be perfect; free of any possible underlying genetic disorders they would have otherwise been born with. Nevertheless, though the CRISPR-Cas9 system is useful in delineating the molecular mechanisms involving hematological malignancies [3], the effect of off-target in the CRISPR-Cas9 technology can also alter the function of a gene and may result in genomic vulnerability, hindering its potential and use in clinical procedures [4]. The Cas9 complex cuts at an undesirable site, thereby requiring further research to reduce this hindrance [4]. Thus, at this point of its less than a decade old discovery, it is not infallible yet. Considering the fact that genetic engineering utilizes a viral vector that carries functional genes in the human body; the outcomes are still inconclusive [14]. The defective genes are replaced with a functional gene, and is then expected that there will be a reduction in genetic diversity and if humans beings will have identical genomes, the population as a whole will be susceptible to virus or any form of disease [15].

As remarkable as genome editing is, I believe there will always be a need for HSCT in the future. In a perfect world, perhaps yes, if all governments and medical institutions were to permit CRISPR-Cas9, on paper, the children of the future should not be faced with any debilitating health problems. However, with this, the question of ethicality of not using CRISPRI- Cas9 arises; where if one disapproves of the idea of a ‘designer baby’, would that not be condemning the child to preventable suffering and death, denying them of the cure?

As we start exploring deeper into the depths of our new discoveries, it will definitely be difficult to stop our temptation from growing. This is risky, as once we get invested, there is no way of stopping the idea getting into the wrong hands; For example, as gene editing becomes normalized, temptations will grow and who knows what could stop a totalitarian regime like North Korea from engineering an army of modified super-soldiers.

The future for the is of CRISPR-Cas9 technology is unlimited, it cannot be quantified but can only be predicted [15]. While the stem cells were proven to exert some positive effect due to cell replacement mechanisms, immunomodulation, or trophic effects, these effect may still require adjustments and modification to realize their fill therapeutic potential [15]. Further- more, the fact that stem cells are pluripotent is not something we should not take advantage of. Having to be able to make a decision on whether to act on the disease with the aid of HSCT would be a more liable choice, than choosing to eradicate the root of the mutation with CRISPR-Cas9, which may potentially end up having an undesirable irreversible impact on the human race.

2019-2-16-1550318448

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