ELUCIDATING THE MOLECULAR GENETICS BASIS OF GENE THERAPY
DEMONSTRATES HOW THIS TECHNOLOGY HAS IMPACTED THE TREATMENT OF
GENETIC DISEASES SUCH AS SICKLE CELL DISEASE.
Abstract
Gene therapy, in its broadest sense, is the notion of introducing genetic material into a cell, tissue, or
entire organ in order to cure a disease or at the very least improve a patient's clinical condition. The
creation of delivery mechanisms that can effectively transfer genes across a range of tissues without
producing any related harmful consequences is essential to the success of gene therapy. At the moment,
the most effective option for effective gene delivery is provided by vectors based on a wide variety of
viral systems, including as retroviruses, lentiviruses, adenoviruses, and adeno-associated viruses.
Clinical studies to cure genetic problems and acquired illnesses are based on positive outcomes from
evaluations of their performance and pathogenicity in animal models. One of the most prevalent and
potentially fatal monogenic disorders, sickle cell disease (SCD) affects millions of individuals globally.
Although allogenic hematopietic stem cell transplantation is the only known treatment for the illness
with a high success rate, the scientific community is forced to consider other treatments due to the
scarcity of matched sibling donors and the significant risk of transplant-related adverse effects.
Numerous studies have been conducted on ex vivo gene therapy using globin gene addition, and clinical
trials are now testing the technique, with promising results starting to emerge. Recent advances in our
knowledge of the molecular mechanisms governing haemoglobin and mammalian erythropoiesis
provide novel and intriguing treatment possibilities. Significant and quick developments in genome
engineering techniques, especially CRISPR/Cas9, have increased the potential for genetic repair in
patient-derived haematopoietic stem and progenitor cells (HSPCs) and induced pluripotent stem cells
(iPSCs).
Introduction
According to Tebas et al. (2014), gene therapy is the ability to enhance genes by correcting changed
(mutated) genes or site-specific alterations that are the objective of therapeutic treatment. Gene therapy
is mostly used in research labs at the moment, and the majority of studies have been carried out. Its use
is currently experimental (Linden, 2010). The strategy is wide and may be used to treat acquired genetic
diseases like cancer, diseases brought on by recessive gene abnormalities (including haemophilia,
muscular dystrophy, sickle cell anaemia, and cystic fibrosis), and viral infections like AIDS (Misra,
2013). Understanding the clinical difficulties of sickle cell disease (SCD) and creating viable treatments
have not progressed as quickly as the molecular genetics of the disease did in the early 20th century.
The historical limitations of the single-gene illness paradigm, which have unavoidably hampered the
conversion of research findings into therapeutic benefit, should be overcome by the current reevaluation
of SCD as the result of many gene interactions (Pace, Ofori-Acquah & Peterson, 2012).
Gene therapy has long been considered as a possible treatment for sickle cell disease. It may be possible
to produce corrected red blood cells for the patient's lifetime by permanently delivering a correction or
antisickling gene cassette into long-term, repopulating HSCs (Bank, Markowitz & Lerner, 1989).
Sickle cell disease (SCD) is a genetic blood disorders caused by the inheritance of faulty
haemoglobin genes, which causes aberrant haemoglobin to be produced in red blood cells (Akinyanju,
1989). The oxygen that is carried throughout the body in red blood cells is carried by haemoglobin.
Individuals with sickle cell disease (SCD) have red blood cells with aberrant haemoglobin that take on
narrow sickle shapes instead of the typical round disc shape. When Hb S undergoes deoxygenation in
red blood cells, a complicated set of biochemical and biophysical processes culminate in the sickle
shape. Unlike disk-shaped red blood cells, sickle-shaped cells make it difficult for them to pass through
tiny blood channels, which can lead to discomfort and damage to organs.
About 5% of persons worldwide, the majority of whom are from sub-Saharan Africa, inherit the genes
that cause hemoglobinopathies (WHO, 2006). Over 200,000 instances of sickle cell anaemia are
reported in Africa each year, and approximately 300,000 babies are born with serious haemoglobin
abnormalities (WHO, 2006). Approximately 8% of persons of African heritage in the USA and the
Caribbean contain one sickle gene, while up to 10% to 30% of people in some regions of Africa have
sickle cell trait (Ohene-Frempong, 1994; Serjeant, 1992). SCD is managed by a multidisciplinary team.
People with SCD have a higher chance of life thanks to penicillin prophylaxis to avoid pneumococcal
infections, judicious blood transfusion utilisation, and other supportive treatments (Gaston, 1986;
Lezcano, 2006). When hydroxycarbamide (hydroxyurea) was demonstrated to lower morbidity and
mortality, it had a significant effect on sickle cell treatment (Steinberg, 2003). The only viable curative
treatment is still bone marrow transplantation (Mankad, 2001). Despite the development of bone
marrow transplantation and palliative medicines, treatment for these conditions is still suboptimal, and
many people experience severe morbidity and early mortality (Persons, 2003). Thus, for many years,
efforts have been made to establish a gene therapy strategy (Nathan, 2001; Persons, 2003).
Autosomal recessive diseases, such sickle cell disease (SCD), are good candidates for gene therapy
because afflicted cells can regain a normal phenotype with just one normal copy of the mutant gene
(Goncz, 2002). If effective, gene therapy will offer a practical substitute for permanently fixing the
faulty gene in sickle cell disease. It will get around the issue of donor scarcity and steer clear of issues
with graft versus host rejection that arise with bone marrow or other stem cell transplants.
Mice with SCD have been treated using gene therapy (Nathan, 2001). Significant advancements have
been made in the field of globin gene therapy in spite of the technological difficulties encountered. This
development has increased the likelihood that gene therapy for haemoglobin opathies may be available
soon (Persons, 2003; Chang, 2006). Researchers utilised a lentivirus to integrate a normal beta globin
gene into the participants' hematopoetic cells, marking the first successful application of gene therapy
for sickle cell disease in humans (SCD) (Ribeil, 2017). Other researchers are currently conducting a
second clinical trial using the lentivirus (Kohn, 2014).
Genetic approaches that target autologous HSCs are still an option for people without a suitable
allogeneic HSC donor (Figure 1). Theoretically, immunosuppression as part of the conditioning
protocol may be eliminated because genetically engineered therapeutic cells are derived from patients,
hence practically eliminating the possibility of GVHD and transplant rejection. Focus on blood-related
illnesses has been prompted by primary findings from clinical studies using genetically modified
autologous HSCs expressing possible therapeutic genes for immunodeficiency disorders (CavazzanaCalvo et al., 200). Because globin illnesses need controlled, lineage-specific, high-level globin
expression, they have proven to be far more challenging to treat. This study will discuss generic gene
therapy options for sickle cell disease (SCD), such as gene addition and genome editing technologies,
which can reduce symptoms by improving HbF or fixing a mutation in the β-globin sequence.
Figure 1:
A genetic approach to sickle cell disease. The three primary genetic therapies for sickle cell disease
include adding a gene that codes for an anti-sickling protein, foetal globin induction by knocking down
or silencing repressors of the γ-globin gene, and correcting sickle mutations using genome engineering
technologies, especially CRISPR/Cas9. Before beginning clinical trials, however, it is imperative to
solve low-effective gene transfer techniques, editing rates, and safety concerns.
Blood transfusions, preventive treatments like pneumococcal vaccination and penicillin prophylaxis,
and hydroxyurea therapy have all been used in clinics since SCD was first described more than a century
ago (Savitt & Goldberg, 1989). These treatments only lessen the disease's symptoms and complications.
However, without extensive chelation treatment, blood transfusions cause iron overload and do not
correct the phenotype. Treatment with hydroxyurea reduces sickle globin symptoms by inducing foetal
globin (HbF, α2γ2), which competes with sickle globin. However, patient response to hydroxyurea
varies, and long-term use is still a concern despite a wealth of safety evidence (Ware et al., 2017).
References
Akinyanju, O. O. (1989). A profile of sickle cell disease in Nigeria. Annals of the New York Academy
of Sciences, 565, 126-136.
Ohene-Frempong, K., & Nkrumah, F. K. (1994). Sickle cell disease in Africa. Sickle cell disease: basic
principles and clinical practice. New York: Raven Press Ltd, 423-435.
Serjeant, G. R. (1992). Sickle cell disease. 2nd. Oxford: Oxford University Press.
Gaston, M. H., Verter, J. I., Woods, G., Pegelow, C., Kelleher, J., Presbury, G., ... & Prophylactic
Penicillin Study Group. (1986). Prophylaxis with oral penicillin in children with sickle cell anemia. New
England Journal of Medicine, 314(25), 1593-1599.
Lezcano, N. E., Odo, N., Kutlar, A., Brambilla, D., & Adams, R. J. (2006). Regular transfusion lowers
plasma free hemoglobin in children with sickle-cell disease at risk for stroke. Stroke, 37(6), 1424-1426.
Steinberg, M. H., Barton, F., Castro, O., Pegelow, C. H., Ballas, S. K., Kutlar, A., ... & Terrin, M.
(2003). Effect of hydroxyurea on mortality and morbidity in adult sickle cell anemia: risks and benefits
up to 9 years of treatment. Jama, 289(13), 1645-1651.
Mankad, V. N. (2001). Exciting new treatment approaches for pathyphysiologic mechanisms of sickle
cell disease. Pediatric pathology & molecular medicine, 20(1), 1-13.
Persons, D. A., & Nienhuis, A. W. (2003). Gene therapy for the hemoglobin disorders. Current
hematology reports, 2(4), 348-355.
Seppa, N. (2001). Gene therapy for sickle‐cell disease?. Science News, 160(24), 372-372.
Goncz, K. K., Prokopishyn, N. L., Chow, B. L., Davis, B. R., & Gruenert, D. C. (2002). Application of
SFHR to gene therapy of monogenic disorders. Gene therapy, 9(11), 691-694.
Chang, J. C., Ye, L., & Kan, Y. W. (2006). Correction of the sickle cell mutation in embryonic stem
cells. Proceedings of the National Academy of Sciences, 103(4), 1036-1040.
Ribeil, J. A., Hacein-Bey-Abina, S., Payen, E., Magnani, A., Semeraro, M., Magrin, E., ... & Cavazzana,
M. (2017). Gene therapy in a patient with sickle cell disease. New England Journal of Medicine, 376(9),
848-855.
Kohn DB. Clinical Research Study of Autologous Bone Marrow Transplantation for Sickle Cell
Disease (SCD) Using Bone Marrow CD34+ Cells Modified With the Lenti/ßAS3-FB Lentiviral Vector.
https://clinicaltrials.gov/show/NCT02247843.
Cavazzana-Calvo, M., Hacein-Bey, S., Basile, G. D. S., Gross, F., Yvon, E., Nusbaum, P., ... & Fischer,
A.
(2000).
Gene
therapy
of
disease. Science, 288(5466), 669-672.
human
severe
combined
immunodeficiency
(SCID)-X1
Savitt, T. L., & Goldberg, M. F. (1989). Herrick's 1910 case report of sickle cell anemia: the rest of the
story. Jama, 261(2), 266-271.
Ware, R. E., de Montalembert, M., Tshilolo, L., & Abboud, M. R. (2017). Sickle cell disease. The
Lancet, 390(10091), 311-323.
Tebas, P., Stein, D., Tang, W. W., Frank, I., Wang, S. Q., Lee, G., ... & June, C. H. (2014). Gene editing
of CCR5 in autologous CD4 T cells of persons infected with HIV. New England Journal of Medicine,
370(10), 901-910.
Linden, R. (2010). Gene therapy: what it is, what it is not and what it will be. Estud Av, 24(70), 31-69.
Misra, S. (2013). Human gene therapy: a brief overview of the genetic revolution. The Journal of the
Association of Physicians of India, 61(2), 127-133.
Pace, B. S., Ofori-Acquah, S. F., & Peterson, K. R. (2012). Sickle cell disease: genetics, cellular and
molecular mechanisms, and therapies. Anemia, 2012, 143594.
Bank, A., Markowitz, D., & Lerner, N. O. R. M. A. (1989). Gene transfer. A potential approach to gene
therapy for sickle cell disease. Annals of the New York Academy of Sciences, 565, 37-43.
World Health Organization. Sickle-cell anaemia. Report A59/9. Provisional agenda item 11.4. 59th
World Health Assembly. www.who.int/gb/ebwha/pdf_files/WHA59/A59_9-en.pdf 2006 (accessed 06
June 2008).