1.1 Introduction
According to Nature (2021), genetic vectors are vehicles for delivering foreign DNA into recipient cells. Vectors can replicate autonomously and typically include features to facilitate the manipulation of DNA as well as a genetic marker for their selective recognition. The most common vectors are DNA plasmids, viruses and artificial chromosomes (Nature, 2021).
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Limitations of the Study and Definition of technical terms.
1.2 Background of Study
Gene vector is a strategy based on using genes as pharmaceuticals. It can be used effectively for curing a vast spectrum of serious acquired or congenital diseases (Gardlík et al., 2005), such as cancerous diseases (Valenčáková et al., 2015), Acquired Immune Deficiency Syndrome (AIDS) (Yu et al., 1994), cardiovascular diseases (Dishart et al., 2003), infectious diseases, cystic fibrosis, familial hypercholesterolemia, muscular dystrophy (Bunnell et al., 1998), and X-linked severe immunodeficiency (X-linked SCID) (Kohn et al., 2003). Gene therapy is a simple method based on principles of transitioning a damaged gene for a healthy one, or by supplementing a missing gene, so expression of a required protein can be achieved (Zhang et al., 2004). Nevertheless, in practice it is a complex procedure, in which the transported gene (transgene) must overcome several obstacles for it to reach targeted nuclei of human cells, where the expression should finish accurately.
European medicine agency (EMA) defines a medicinal product in gene therapy as a biological-medicinal product meeting following descriptions:
- It consisting of an active substance containing or composed of recombinant deoxyribonucleic acid used or to be used in human beings with respect for regulation, correction, shift, completion or excision of gene sequence; its therapeutic, prophylactic or diagnostic effect is directly related to the sequence of recombinant deoxyribonucleic acid which it comprises of, or the gene expression product of this sequence.
Food and Drug Administration (FDA) defines vectors in gene therapy as agents mediating their effects by transcription and/or translation of transmitted genetic material and/or integration to host genome, and are administered as nucleic acids, viruses, or genetically modified microorganisms. Products can be used for cell reparation in vivo, or can be carried to cells ex vivo before delivery to the recipient (Wirth et al., 2013).
Gene therapy is one of the fastest developing fields in medicine. To this day, more than 1 800 approved clinical studies of gene therapy have been or are being published. The most common gene therapy is gene therapy of cancerous diseases. Worldwide, cancerous diseases represent over 60% of clinical studies concerning gene therapy, followed by monogenous and cardiovascular diseases (Wysocki et al., 2002).
1.3 Statement of Problems
The need for efficient transfer of potentially therapeutic genes to defined cell populations has stimulated the development of vectors based on viruses. To date, most effort has been spent on the RNA-containing retroviruses. These viruses, however, possess a number of problems including an inability to infect nondividing cells as well as having potential for oncogenicity and insertional mutagenesis of host cell genes due to random chromosomal integration. These problems have led to the development of vectors based on DNA-containing viruses such as adenovirus, herpes simplex virus and parvovirus. These viruses possess a number of attributes favourable to their use in gene therapy. Adenoviruses, for example, were first considered as potential vectors for the genetic treatment of lung conditions due to their natural affinity for respiratory epithelium. However, other features including their ability to be prepared at high titres, to direct high levels of foreign gene expression and their extrachromosomal existence has resulted in their development for the treatment of numerous other diseases(NIH, 2021b).
Virus vectors have been shown to efficiently infect target cell populations and to express proteins at therapeutic levels in the absence of significant toxicity. The ability of herpes simplex virus to reside in neurons in a latent state that does not appear to affect normal cellular physiology has sparked interest in this virus as a potential vector in the treatment of neurological disorders. A subgroup of parvoviruses, namely the adeno-associated viruses, have a prediliction for integration at a defined chromosomal location and may represent a safer alternative to retroviruses (NIH, 2021b).
1.4 Aim and Objectives of Study
The aim of this study is to examine the use of virus as gene vectors. In achieving this aim, the specific objectives were set out as follows;
- To determine the use of virus as genetic vectors,
- To provide adequate information about proteins at therapeutic levels in the absence of significant toxicity.
- To examine therapeutic effects of the use of virus as genetic vectors.
1.5 Scope of Study
This study focuses on the use of virus as gene vectors, which aimed at determining therapeutic effects and the uses of virus.
1.6 Limitations of the Study
During the course of this study, many things militated against its completion, some of which are:
- Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
- Establishment Policies: Establishment policies posed a serious limitation as most staffs are not ready to release information needed for this project work. There were lots of information needed from the staffs of this institution to enhance the study which took them time to release or they did not release at all for security purposes, hence the scope was reduced.
- Research material: availability of research material is a major setback to the scope of the study.
- Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
- Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials.
1.7 Significance of Study
This study, when completed, will serve as reference material for subsequent researcher in the field or related topics.
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