Gene Therapy A Solution to Genetic Diseases - IJGHC

IJGHC, June 2013 – August 2013; Vol.2, No.3; 596-609. 

International Journal of Green and 

Herbal Chemistry 

An International Peer Review E-3 Journal of Sciences 

Available online at www.ijghc.com 

Green Chemistry 

E-ISSN: 2278-3229 

Review Article 

CODEN (USA): IJGHAY 

Gene Therapy A Solution to Genetic Diseases 

Ighere D.A,* and Okere A.U 

National Centre for Genetic Resources and Biotechnology (NACGRAB), 

P.M.B 5382, Moor Plantation, Apata, Ibadan, Nigeria. 

Received: 20 May 2013; Revised: 10 July 2013; Accepted: 24 July 2013 

Abstract: Over the years, some diseases have come to plague the human race 

that there appears to be no solution in sight. The emergence of gene therapy 

techniques has gradually unveiled the mystery behind these diseases and at the 

same time provides promising therapeutic measures to these disease conditions. 

Gene Therapy has exposed researchers to the effective and promising ways to 

tackle diseases that are genetic in nature. This review article articulates the major 

landmark achievements of Gene Therapy over the years while also enunciating the 

different approaches that used in delivering therapeutic genes to target host cells. 

In gene therapy, a therapeutic gene could be delivered to the host target cell 

through a viral vector or non-viral vector. In viral vector delivery of therapeutic 

gene, a modified virus that lacks a pathogenic gene used to deliver the therapeutic 

gene to the host. The technique of gene therapy involves the correction of 

defective genes responsible for disease development. Researchers use one of 

several approaches for correcting faulty genes: A normal gene may be inserted 

into a nonspecific location within the genome to replace a nonfunctional gene. 

This approach is most common. An abnormal gene could be swapped for a normal 

gene through homologous recombination. The abnormal gene could be repaired 

through selective reverse mutation, which returns the gene to its normal function. 

The regulation (the degree to which a gene is turned on or off) of a particular gene 

could be altered. Cancer is one of the major diseases that researchers are trying to 

596 IJGHC; June – August 2013, Vol.2, No.3, 596-609.

Gene... 

Ighere D.A. et al. 

use gene therapy to cure. Cancer is a disease that occurs because of multiple 

mutations in a cell that cause the cell to proliferate out of control. 

Keywords: Gene Therapy, Vector, Gene, Virus and Mutation 

. 

INTRODUCTION 

A gene is the basic unit of heredity found in the cells of living organisms, from bacteria to humans. It 

is the gene in combination with the environment that determines the phenotypic characteristics of an 

individual. The genes are specific base sequences that encode instruction on how to make proteins. A 

disorder may result in a gene such that the gene is altered and the encoded proteins are unable to carry 

out their normal functions. Basic gene therapy approaches usually involve adding a therapeutic gene 

to a cell through a variety of vectors. Most research and testing has been done with the vector 

introduction of a sequence that codes for a needed protein, either to counter a deficiency, induce a 

strong immune response, or destroy tumour cells 1 . 

The concepts of gene therapy arose initially during the 1960s and early 1970s whilst the development 

of genetically marked cell lines and the clarification of mechanisms of cell transformation by the 

papovaviruses polyoma and SV40 was in progress 2 . With the arrival of recombinant DNA techniques, 

cloned genes became available and were used to demonstrate that foreign genes could indeed correct 

genetic defects and disease phenotypes in mammalian cells in vitro 2 . Efficient retroviral vectors and 

other gene transfer methods have permitted convincing demonstrations of efficient phenotype 

correction in vitro and in vivo, now making gene therapy a broadly accepted approach to therapy and 

justifying clinically applied studies with human patients. Gene therapy is the introduction of gene into 

existing cells to prevent or treat a wide range of diseases 3 . Gene therapy is thus the medical treatment 

that manipulates a gene or genes within cells in order to produce proteins that change the function of 

those cells. Gene therapy originated in efforts to treat and cure some of the more than 9,000 known 

genetic disorders, most of which lack an effective therapy. Scientists first took the logical step of 

trying to introduce genes directly into human cells, focusing on diseases caused by single-gene 

defects, such as cystic fibrosis, haemophilia, muscular dystrophy and sickle cell anaemia. However, 

this has proven more difficult than modifying bacteria, primarily because of the problems involved in 

carrying large sections of DNA and delivering them to the correct site on the comparatively large 

genome. Today, most gene therapy studies are aimed at cancer and hereditary diseases linked to a 

genetic defect 4 . 

Although gene therapy offers seemingly limitless possibilities, researchers have been thwarted by 

many technical problems. Successful clinical trial using gene therapy started in April 2000, when 

French researchers reported the successful use of gene therapy to treat two female infants with severe 

combined immunodeficiency disease (SCID), a deadly inherited disease that impairs the immune 

system. However, even this success was marred when each child later developed a rare leukaemia-like 

illness, thought to be a result of gene therapy. Most clinical trials of gene therapy have not resulted in 

enough improvement in the patient’s underlying condition to consider it an unqualified success and to 

justify treating large numbers of people. The extraordinary potential of gene therapy has also raised 

alarms among critics who warn that the technology could go too far. They note, for example, that 

gene therapy could offer wealthy families opportunities for genetic enhancement unavailable to the 

poor. More troubling still for some critics is that gene therapy is potential to narrow the human gene 

pool, producing unknown, and possibly harmful, consequences. 

The majority of clinical gene therapy trials are being conducted in the United States and Europe, with 

only a modest number initiated in other countries, including Australia. The majority of these trials 




focus on treating acquired conditions such as cancer. The only gene therapy that has been approved 

for routine treatment so far is for a form of cancer which was approved 5 in China in early 2004. 

Gene Therapy has made important medical advances in less than two decades. Within this short time 

span, it has moved from the conceptual stage to technology development and laboratory research to 

clinical translational trials for a variety of deadly diseases. This article wish to bring to the general 

public recent development that has happen in gene therapy technology and at the same time state 

some potentials that gene therapy technology posses. In time past, some diseases have posed serious 

challenges to the field of medicine especially genetic diseases, and gradually with the emergence of 

gene therapy, those disease will be adequately treated with the technique. 

GENE THERAPY AND HOW IT WORKS 

Gene therapy involves the insertion of a therapeutic gene into a cell to replace a nonfunctional gene. 

This is done by using a carrier molecule called a vector in delivering the therapeutic gene to the target 

cell. The vector is usually a virus that has been genetically altered to carry normal human DNA to the 

target cell. All viruses attack their hosts and introduce their genetic material into the host cell as part 

of their replication cycle, it is this act that researcher took advantage of by removing the pathogenic 

gene of the virus. The pathogenic gene present in the virus is removed and replaced with a therapeutic 

gene, this act render the virus harmless before it is inserted into the host target cell. Stem cell can be 

manipulated to accept therapeutic genes. In gene therapy, only somatic cells are targeted for 

treatment. Therefore, any changes to the genes of an individual by gene therapy will only influence 

the cells of their body and cannot be passed on to their children. Changes to the somatic cells cannot 

be passed on to future generations (cannot be inherited). Somatic gene therapy treats the individual 

and has no impact on future generations. 

The technique of Gene therapy corrects defective genes responsible for disease development. 

Researchers may use one of several approaches for correcting faulty genes. 

• A normal gene may be inserted into a nonspecific location within the genome to replace a 

non-functional gene. This approach is most common. 

• An abnormal gene could be swapped for a normal gene through homologous recombination. 

• The abnormal gene could be repaired through selective reverse mutation, which returns the 

gene to its normal function. 

• The regulation (the degree to which a gene is turned on or off) of a particular gene could be 

altered. 

SUCCESS STORIES AND SOME DISEASES THAT HAVE BEEN TREATED WITH 

GENE THERAPY 

• Fisher Jennifer in an article published in the Scientist, Magazine of Life Sciences reported 

that Sickle Cell disease has been successfully treated in mice through gene therapy; these will 

open doors for the disease to be treated in man through gene therapy. 

• Severe Combined Immune Deficiency (ADA-SCID) is also known as the bubble boy disease. 

Affected children are born without an effective immune system and will succumb to 

infections outside of the bubble without bone marrow transplantation from matched donors. 

Investigators in Italy conducted a landmark study representing a first case of gene therapy 

“cure,” or at least a long-term correction, for patients with deadly genetic disorder. The 




therapeutic gene called ADA was introduced into the bone marrow cells of such patients in 

the laboratory, followed by transplantation of the genetically corrected cells back to the same 

patients 6 . The immune system was reconstituted in all six treated patients without noticeable 

side effects, who now live normal lives with their families without the need for further 

treatment. 

• Two scientists at the National Institutes of Health (Bethesda, Maryland) used killer T cells to 

successfully treat metastatic melanoma with gene therapy. 

• In a study published in the nature medicine, Ott M.G reported that two adult patient were 

successfully treated for disease that affect myeloid cells through gene therapy. 

• In March 2006, an international group of scientists announced the successful use of gene 

therapy to treat two adult patients for a disease affecting myeloid cells 7 . The study, published 

in Nature Medicine, is believed to be the first to show that gene therapy can cure diseases of 

the myeloid system. 

• Chronic Granulomatus Disorder (CGD) is a genetic disease in the immune system that leads 

to the patients' inability to fight off bacterial and fungal infections that can be fatal. Using 

similar technologies as in the ADA-SCID trial, investigators in Germany treated two patients 

with this disease, whose reconstituted immune systems have since been able to provide them 

with full protection against microbial infections for at least two years. 

• Leber’s congenital amaurosis is an inherited blinding disease caused by mutation in the 

RPE65 gene, this disease was treated with gene therapy by inserting a recombinant adeno 

associated virus (AAV) that carries the RPE65 gene 8 . UK researchers from the UCL Institute 

of Ophthalmology and Moor fields Eye Hospital NIHR Biomedical Research Centre have 

announced results from the world’s first clinical trial to test a revolutionary gene therapy 

treatment for a type of inherited blindness. The results, published in the New England Journal 

of Medicine, show that the experimental treatment is safe and can improve sight. The findings 

are a landmark for gene therapy technology and could have a significant impact on future 

treatments for eye disease. The trial, conducted in the NIHR Biomedical Research Centre that 

received additional funding from the Department of Health, represented a world first when it 

began in February 2007. It involves young patients with a condition called Leber’s congenital 

amaurosis (LCA), a rare inherited eye disease caused by an abnormality in a gene called 

RPE65. The condition appears at birth or in the first few months of life and causes 

progressive deterioration and loss of vision. There are currently no effective treatments 

available. The trial’s purpose was firstly to find out whether gene therapy for retinal disease is 

safe, and secondly to find out if it can benefit vision in young adults who already have 

advanced retinal disease. 

• Squirrel monkey was given trichromatic vision through gene therapy. 

• The journal Nature reported that researchers at the University of Washington and University 

of Florida were able to give trichromatic vision to squirrel monkeys using gene therapy, a 

hopeful precursor to a treatment for color blindness in humans. 

• Patients born with Haemophilia are not able to induce blood clots and suffer from external 

and internal bleeding that can be life threatening 6 . In a clinical trial conducted in the United 

States, the therapeutic gene was introduced into the liver of patients, who then acquired the 

ability to have normal blood clotting time. The therapeutic effect however, was transient 

because the genetically corrected liver cells were recognized as foreign and rejected by the 




healthy immune system in the patients. This is the same problem faced by patients after organ 

transplantation, and curative outcome by gene therapy might be achievable with immunesuppression 

or alternative gene delivery strategies currently being tested in preclinical animal 

models of this disease. 

• Researchers have halted a fatal brain disease (Adrenoleukodystropy) by delivering a 

therapeutic gene to the stem cells that mature into blood cells 9. The gene was transferred using 

a virus derived from HIV, a technique that researchers have pursued for more than a decade 

but has not been successful in humans until now. 

• Recent progress in gene therapy has allowed for novel treatments of neurodegenerative 

diseases such as Parkinson's disease and Huntington's disease, for which exciting treatment 

results have been obtained in appropriate animal models of the corresponding human 

diseases 6 . 

• In 2007 and 2008, a man being treated by Gero Hutter was cured of HIV by repeated 

Hematopoietic stem cell transplantation with double-delta-32 mutation that disables the 

CCR5 receptor; this cure was not completely accepted by the medical community until 2011. 

This cure required complete ablation of existing bone marrow, which is very debilitating. 

• In two land-mark papers, Zhu 10 and Beetham 11 reported the first uses of chimaeric 

oligonucleotides to cause site-specific base changes in plants and plant cells. Delivery of 

oligonucleotides was accomplished through microparticle bombardment, but has also been 

accomplished via electroporation into protoplasts 12 . This specific conversion of point 

mutations leading to amino acid substitutions in the genes for either acetohydroxyacid 

synthase or acetolactate synthase conferred a herbicide-resistance phenotype. Functionality 

was also restored to a mutant green fluorescent protein gene. Subsequent DNA sequence 

analysis of the targeted regions confirmed that the targeted codon had been modified. 

Surprisingly, however, non-specific conversions were detected at the targeted base and at the 

immediately 5´ position. Diminished precision, or slippage, has now also been observed in 

vitro using tobacco cell-free extracts in an assay developed by our groups. These were the 

first examples of lack of precision in targeting specificity by chimaeric oligonucleotides. 

Gene therapy was first tried on a human being late in 1990, when W. French Anderson, R. Michael 

Blaese, and Kenneth W. Culver of the National Institutes of Health infused genetically altered cells 

into a four-year-old girl. Those cells produced adenosine deaminase (ADA), an essential enzyme 

missing from the girl's body. Those cells produced adenosine deaminase (ADA), an essential enzyme 

missing from the girl's body. According to progress reports issued by Blaese throughout the year, she 

was responding well to the treatments, although it was premature to say whether she had actually been 

cured. A second child was also enrolled in the ADA gene therapy trials, and she, too, seemed to be 

doing well. 

PLANT GENE THERAPY 

Genetics allows the elucidation of gene function through the analysis of gene malfunction. Modern 

genetics and genomics require ways for in situ modification of genes, by means of point mutations, 

deletions, and additions. The availability of sequence information of many organisms dictates rapid 

development of reverse genetics procedures. Until recently, targeting of genes with the help of 

introduced homologous sequences, here referred to as homologous recombination-dependent gene 

targeting (hrdGT), was the method of choice, at least for mammalian systems. However, in higher 

eukaryotic organisms such as mammals and plants, exogenously introduced DNA preferably 




integrates in random positions in the genome, by the process of illegitimate recombination, and only 

infrequently can targeted integration events be detected. Recently an alternative strategy became 

available for precise reverse genetics. Specific chimeric oligonucleotides, COs, consisting of DNA 

and RNA stretches, were found to induce point mutations in several mammalian genes tested. 

Researchers are developing new techniques that use nanoparticles for smuggling foreign DNA into 

cells. For example, at Oak Ridge National Laboratory, the US Department of Energy lab that played a 

major role in the production of enriched uranium for the Manhattan Project, researchers have hit upon 

a nano-technique for injecting DNA into millions of cells at once. Millions of carbon nanofibres are 

grown sticking out of a silicon chip with strands of synthetic DNA attached to the nanofibres. Living 

cells are then thrown against and pierced by the fibres, injecting the DNA into the cells in the process. 

METHODS OF TRANSFERRING THERAPEUTIC GENES 

Therapeutic genes can be transfer to host target cell via the use of viral vectors and the use of nonviral 

vectors. 

Viral vectors: The use of viruses as vector in gene therapy was first reported in 1968 when tobacco 

mosaic virus was used to transfer specific genetic materials into a cell, since then researcher has been 

improving on the discovery. There are two main types of virus infection: lytic and lysogenic. Shortly 

after inserting its DNA, viruses of the lytic cycle quickly produce more viruses, burst from the cell 

and infect more cells. Lysogenic viruses integrate their DNA into the DNA of the host cell and may 

live in the body for many years before responding to a trigger. The virus reproduces as the cell does 

and does not inflict bodily harm until it is triggered. The trigger releases the DNA from that of the 

host and employs it to create new viruses. Further research showed that Retrovirus, Adenovirus, 

Adeno-associated virus and Herpes simplex virus (HSV) are use as viral vectors in gene therapy. 

Retroviral remain the most popular vector system for gene therapy protocols 13 . This may in part be 

due to their historical significance as the first vectors developed for efficient gene therapy and the 

infancy of the field of gene therapy. Retroviruses are a class of enveloped viruses containing a single 

stranded RNA molecule as the genome. Following infection, the viral genome is reverse transcribed 

into double stranded DNA, which integrates into the host genome and is expressed as proteins. The 

viral genome is approximately 10kb, containing at least three genes: gag (coding for core proteins), 

pol (coding for reverse transcriptase) and env (coding for the viral envelope protein). At each end of 

the genome are long terminal repeats (LTRs) which include promoter/enhancer regions and sequences 

involved with integration. In addition there are sequences required for packaging the viral DNA (psi) 

and RNA splice sites in the env gene. 

Some retroviruses contain protooncogenes, which when mutated can cause cancer; however, in the 

production of vectors these are removed. Retroviruses can also transform cells by integrating near to a 

cellular protooncogene and driving inappropriate expression from the LTR, or by disrupting a tumour 

suppresser gene. This event, termed insertional mutagenesis, though extremely rare could still occur 

when retroviruses are used as vectors. In gene therapy, the virus pathogenic gene is removed and the 

desire gene is inserted into the retroviral genome. The modified retroviral is then inserted into the host 

target cell. When the retroviral get to the host target cell, the reverse transcriptase with the aid of the 

virus RNA as template will synthesis DNA for the virus. The cellular machinery then synthesizes the 

complementary DNA, which is then circularized, and then inserted into the host genome. When the 

viral DNA has been inserted into the genome, the viral genome is transcribed these complete the viral 

replication cycle. 




It was during the search of a cure for common cold that adenovirus discovered 13 in 1953. There are as 

many as 93 different known varieties of the virus and all of them are infectious. 

To avoid the problem of inserting genes at the wrong sites, some researchers have turned to the types 

of viruses, such as the adenoviruses, which cause the common cold. Stripped of their disease-causing 

genes, adenoviruses take healthy genes into the nucleus of cells, where the DNA is located, but do not 

usually integrate them into a cell's DNA. The E1A and E3 region are deleted from must adenovirus 

used as viral vector. The ability to replicate lies in the E1A region of the adenovirus, hence the 

adenoviral vector do not replicate. In adenovirus DNA replication and transcription is complex, and 

viral replication and assembly occur only in the nucleus of infected cells 13 . Mature virions released by 

cellular disintegration. 

14, 15, 

The wild type adenovirus genome is approximately 35 kb of which up to 30 kb can be replaced 

with foreign DNA. There are four early transcriptional units (E1, E2, E3 and E4), which have 

regulatory functions, and a late transcript, which codes for structural proteins. Progenitor vectors have 

either the E1 or E3 gene inactivated, with the missing gene being supplied in trans either by a helper 

virus, plasmid or integrated into a helper cell genome 16 (human fetal kidney cells, line 293. Second 

generation vectors additionally use an E2a temperature sensitive mutant 17 or an E4 deletion 18 recent 

"gutless" vectors contain only the inverted terminal repeats (ITRs) and a packaging sequence around 

the transgene, all the necessary viral genes being provided in trans by a helper virus 19 . 

Adenoviral vestors are very efficient at transducing target cells in vitro and vivo, & can be produced 

at high titres (>10 11 /ml). With the exception of Geddes et al. 20 , who showed prolonged transgene 

expression in rat brains using an E1 deletion vector, transgene expression in vivo from progenitor 

vectors tends to be transient 15 . Following intravenous injection, 90% of the administered vector is 

degraded in the liver by a non-immune mediated mechanism 21 . Thereafter, an MHC class I restricted 

immune response occurs, using CD8+ CTLs to eliminate virus infected cells and CD4+ cells to 

secrete IFN-alpha which results in anti-adenoviral antibody 22 . Alteration of the adenoviral vector can 

remove some CTL epitopes, however the epitopes recognised differ with the host MHC 

haplotype 23, 24 . The remaining vectors, in those cells that are not destroyed, have their promoter 

inactivated 18 and persisting antibody prevents subsequent administration of the vector. 

Approaches to avoid the immune response involving transient immunosupressive therapies have been 

successful in prolonging transgene expression and achieving secondary gene transfer 18,25 . A less 

interventionist method has been to induce oral tolerance by feeding the host UV inactivated vector 26 . 

However, it is desirable to manipulate the vector rather than the host. Although only replication 

deficient vectors are used, viral proteins are expressed at a very low level which is presented to the 

immune system. The development of vectors containing fewer genes, culminating in the "gutless" 

vectors which contain no viral coding sequences, has resulted in prolonged in vivo transgene 

expression in liver tissue 27 . The initial delivery of large amounts of DNA packaged within adenovirus 

proteins, the majority of which will be degraded & presented to the immune system may still cause 

problems for clinical trials. Moreover, the human population is heterogeneous with respect to MHC 

haplotype and a proportion of the population will have been already exposed to the adenoviral strain 28 

One of the most promising potential gene-delivery systems, or vectors, is a recently discovered virus 

called the adeno-associated virus, which infects a broad range of cells, including both dividing and 

non-dividing cells. Researchers believe that most humans carry adeno-associated viruses, which do 

not cause disease and do not provoke an immune response 29 . Adeno associated viruses (AAV) are 

satellite viruses of human viruses and require co-infection with other virus for their replication. The 

virus contains either the sense or antisense strand of the DNA molecule and appears to show no 

preference for which strand is incorporated into the virion. A unique feature of the DNA molecule 




contains within is the palindromic sequence at each end (inverted terminal repeat ITR). These ITRs 

are important in site-specific integration of AAV DNA into specific site in chromosome 19. The 

ability of the wild-type AAV to selectively integrate into chromosome 19 makes them an attractive 

candidate for the production of a gene therapy vector that could do the same 13 . 

The wild type genome is a single stranded DNA molecule, consisting of two genes; rep, coding for 

proteins that control viral replication, structural gene expression and integration into the host genome, 

and cap, which codes for capsid structural proteins. At either end of the genome is a 145 bp terminal 

repeat (TR), containing a promoter: 

When used as a vector, the rep and cap genes are replaced by the transgene and its associated 

regulatory sequences. The total length of the insert cannot greatly exceed 4.7 kb, the length of the 

wild type genome 14 . Production of the recombinant vector requires that rep and cap are provided in 

trans, along with helper virus gene products (E1a, E1b, E2a, E4 and VA RNA from the adenovirus 

genome). The conventional method is to cotransfect two plasmids, one for the vector and another for 

rep and cap, into 293 cells infected with adenovirus 30 . This method, however, is cumbersome, low 

yielding (



possible using pharmaceutical techniques. Viral technique that is widely accepted is calcium 

phosphate-mediated transfection. 

Injection of Naked DNA is the simplest method of non-viral transfection. Clinical trials carried out 

of intramuscular injection of a naked DNA plasmid have occurred with some success; however, the 

expression has been very low in comparison to other methods of transfection. In addition to trials with 

plasmids, there have been trials with naked PCR product, which have had similar or greater success. 

Cellular uptake of naked DNA is generally inefficient. Research efforts focusing on improving the 

efficiency of naked DNA uptake have yielded several novel methods, such as electroporation, 

sonoporation, and the use of a "gene gun", which shoots gold-coated DNA particles into the cell using 

high-pressure gas. 

Chemical Methods to Enhance Delivery can be done via Oligonucleotides, Dendrines and lipolexes 

and polyplexes. The use of synthetic oligonucleotides in gene therapy is to inactivate the genes 

involved in the disease process. There are several methods by which this is achieved. One strategy 

uses antisense specific to the target gene to disrupt the transcription of the faulty gene. Another uses 

small molecules of RNA called siRNA to signal the cell to cleave specific unique sequences in the 

mRNA transcript of the faulty gene, disrupting translation of the faulty mRNA, and therefore 

expression of the gene. A further strategy uses double stranded oligodeoxynucleotides as a decoy for 

the transcription factors that are required to activate the transcription of the target gene. The 

transcription factors bind to the decoys instead of the promoter of the faulty gene, which reduces the 

transcription of the target gene, lowering expression 36 . Additionally, single stranded DNA 

oligonucleotides have been used to direct a single base change within a mutant gene. The 

oligonucleotide is designed to anneal with complementarily to the target gene with the exception of a 

central base, the target base, which serves as the template base for repair. This technique is referred to 

as oligonucleotide mediated gene repair, targeted gene repair, or targeted nucleotide alteration. 

The most common use of lipoplexes has been in gene transfer into cancer cells, where the supplied 

genes have activated tumor suppressor control genes in the cell and decrease the activity of 

oncogenes. Recent studies have shown lipoplexes to be useful in transfecting respiratory epithelial 

cells, so they may be used for treatment of genetic respiratory diseases such as cystic fibrosis. 

In particular, it is possible to construct a cationic dendrimer, i.e. one with a positive surface charge. 

When in the presence of genetic material such as DNA or RNA, charge complimentarity leads to a 

temporary association of the nucleic acid with the cationic dendrimer. On reaching its destination, the 

dendrimer-nucleic acid complex is then taken into the cell via endocytosis. 

Physical methods of delivery genes involves; electroporation, gene gun, sonoporation and 

magnetofection. Electroporation is a method that uses short pulses of high voltage to carry DNA 

across the cell membrane. This shock is thought to cause temporary formation of pores in the cell 

membrane, allowing DNA molecules to pass through. Electroporation is generally efficient and works 

across a broad range of cell types. However, a high rate of cell death following electroporation has 

limited its use, including clinical applications. The use of particle bombardment, or the gene gun, is 

another physical method of DNA transfection. In this technique, DNA is coated with gold particles 

and loaded into a device which generates a force to achieve penetration of DNA/gold into the cells. 

Sonoporation uses ultrasonic frequencies to deliver DNA into cells. The process of acoustic 

cavitation is thought to disrupt the cell membrane and allow DNA to move into cells. In a method 

termed magnetofection, DNA is complexed to magnetic particles, and a magnet is placed underneath 

the tissue culture dish to bring DNA complexes into contact with a cell monolayer. 




Hybrid method of gene transfer have it shortcomings, there have been some hybrid methods 

developed that combine two or more techniques 36 . Virosomes are one example; they combine 

liposome with an inactivated HIV or influenza virus. This has been shown to have more efficient gene 

transfer in respiratory epithelial cells than either viral or liposomal methods alone. Other methods 

involve mixing other viral vectors with cationic lipids or hybridizing viruses. 

POTENTIALS OF GENE THERAPY 

Gene therapy has much potential in the treatment of so many diseases ranging from genetic diseases 

and non-genetic diseases. In the nearest future gene-therapy will cut across nearly every area of 

medicine, which will make it potentials to be limitless. 

Gene Therapy for Cancer: cancer is caused because of multiple mutations that occur within a cell 

that cause it to proliferate out of control. Multiple gene therapy strategies have been developed to treat 

a wide variety of cancers, including suicide gene therapy, oncolytic virotherapy, anti-angiogenesis and 

therapeutic gene vaccines. Two-thirds of all gene therapy trials are for cancer and many of these are 

entering the advanced stage, including a Phase III trial of Ad.p53 for head and neck cancer and two 

different Phase III gene vaccine trials for prostate cancer and pancreas cancer. Currently gene therapy 

is being used to create recombinant cancer vaccines 39 . Unlike vaccines for infectious agents, these 

vaccines are not meant to prevent disease, but to cure or contain it by training the patient’s immune 

system to recognize the cancer cells by presenting it with highly antigenic and immunostimulatory 

cellular debris. Initially cancers cells are harvested from the patient or from established cancer cell 

lines and then are grown in vitro. These cells are then engineered to be more recognizable to the 

immune system by the addition of one or more genes, which are often cytokine genes that produce 

pro-inflammatory immune stimulating molecules, or highly antigenic protein genes. These altered 

cells are grown in vitro and killed, and the cellular contents are incorporated into a vaccine. 

Additionally, numerous Phase I and Phase II clinical trials for cancers in the brain, skin, liver, colon, 

breast and kidney among others, are being conducted in academic medical centers and biotechnology 

companies, using novel technologies and therapeutics developed on-site. Gene therapy may be used to 

treat cancer in the following ways: 

• Genes can be put into the cancer cells to make them more sensitive to treatments such as 

chemotherapy. 

• Genes may be put into cancer cells and then activated to produce a poisonous substance 

(toxin) that kills the cell. 

• Genes can be put into cancer cells which make those cells more obvious to the body's own 

defenses (the immune system), so that they are destroyed 'naturally' by the cells of our 

immune system. 

• Damaged genes may be replaced by the correctly working version. 

• New genes may be put into normal cells to make them more resistant to the side effects of 

treatment such as radiotherapy and chemotherapy. This protects the normal cells from the 

treatments so that higher doses can be given. At present, the risk of damage to normal cells 

often limits the doses that can be used. 

New research funded by the Irish Cancer Society at the Cork Cancer Research Centre has revealed 

that delivering beneficial human genes by means of a virus to breast cancer tumour cells causes genes 

to generate signals within the tumour to cut off its blood supply and stop its growth. The team says 

that the new type of gene therapy is novel because it uses genes from humans rather than from viruses 




-resulting in “significantly longer lasting therapy”. Although still in its infancy, the therapy targets 

breast cancer tumour cells without harming healthy cells, which is the ultimate aim for all cancer 

treatments. 

Gene therapy for HIV: HIV based vectors are recent development in gene therapy, the use of this 

vectors is focus in providing a cure for AIDS. The HIV vectors are used to selectively deliver 

therapeutic genes into HIV infected cells. The gene delivered into these cells is designed to kill any 

cell that is infected with HIV. The possible success in this focuses on the tat and rev genes found in 

the HIV genome, which are also found only in HIV, infected cells. The possible use of tat and rev 

induced promoter to drive the expression of a toxin gene in the HIV infected cell, any cell carrying the 

gene will be kill when it express the toxin gene. These will result to the termination of the HIV virus 

and the cell carrying the virus. There is fear that, there is a possibility of genetic recombination 

between the HIV vector and the HIV virus, which will cause the HIV vector to be an infectious 

particle in the system. The possible way to overcome this potential fear is by the inclusion of a suicide 

gene in the therapeutic vector. These suicide genes will make cells infected with HIV vector genome 

sensitive to a drug that will poison only those cells containing the HIV vector genome. Some of the 

advantages associated with this HIV vectors are; high transduction efficiency, the vector proteins are 

not expressed in the host, integrates into host genome resulting in sustained expression etc. 

Gene therapy Cures Retinitis Pigmentosa in Dogs: A new gene therapy method developed has the 

potentials to treat a common form of blindness that strikes both youngsters and adults. Scientist have 

shown that they prevent or even reverse, a blinding retinal disease, X-linked Retinitis pigmentosa, or 

XLRP, in dogs. The technique works by replacing a malfunctioning gene in the eye with a normal 

working copy that supplies a protein necessary for light-sensitive cells in the eye for them to function. 

The researchers tackled a condition called X-linked retinitis pigmentosa, a genetic defect that is 

passed from mother to sons. The X-linked form of retinitis pigmentosa addressed in the new study is 

the most common, and is caused by degeneration of light-sensitive cells in the eye known as 

photoreceptor cells. It starts early in life, so though affected children are often born seeing, they 

gradually lose their vision 40 . 

Advantages 

• Gene therapy will give a chance to somebody born with a genetic disease to live normal life, 

through the insertion of a normal gene to replace an abnormal or a non-functional gene. 

• A cancer patient can also get advantage of this technique by insertion of genetically altered 

vectors into human genome. 

Disadvantages 

• Gene therapy will increase the numbers of abortion that will be performed, because if an 

unborn child after a genetic test is found to be deficient of some genes that encode for a 

particular protein, which will result to that child suffering from a particular genetic disease 

condition, there will be tendency for the mother to opt for an abortion. 

• Problems with integrating therapeutic DNA into the genome and the rapidly dividing nature 

of many cells prevent gene therapy from achieving any long-term benefits. Patients will have 

to undergo multiple rounds of gene therapy. 

Chance of inducing a tumor (insertional mutagenesis) - If the DNA is integrated in the wrong place in 

the genome, for example in a tumor suppressor gene, it could induce a tumor. 




CONCLUSIONS 

Gene therapy is changing the world of medicine, by introducing new techniques that will help solve 

the problem of genetic disease. Many physicians are predicting that in twenty years gene therapy may 

change the practice of medicine from a treatment-based to a prevention-based practice. The genes are 

responsible for everything that happens in our cells. Our future is locked away inside of our genes; 

gene therapy is unlocking these doors. Researchers are starting to move away from developing new 

drugs, and towards finding an ultimate solution. That solution is to use gene therapy as a treatment for 

many genetic diseases. Researchers hope that in the coming years, every genetic disease will have 

gene therapy as its treatment. Gene therapy could be the last therapy that the human race will ever 

need as it stand a chance of tackling a broad range of diseases that are of genetic basics. 

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*Corresponding Author: Ighere D.A; National Centre for Genetic Resources and Biotechnology 

(NACGRAB), P.M.B 5382, Moor Plantation, Apata, Ibadan, Nigeria. 

Email: dighere@yahoo.com

Gene Therapy A Solution to Genetic Diseases - IJGHC

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