Medical Technology

Types of Retroviral Vectors

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Viral vectors are tools used by molecular scientists to transport genetic material into a cell and make permanent alterations in the cellular genetic makeup. The process is called ‘transduction’ and the cells which are subjected to this process are described as being ‘transduced’. Retrovirus is one of the main viruses made use of as viral vectors and is often the preferred choice for gene therapy techniques.

What is a retrovirus?

Retrovirus is a RNA virus which has the ability to duplicate within a host cell. It achieves this by using an enzyme known as reverse transcriptase which it uses to produce DNA from the viral RNA genome. The synthesized DNA is them integrated into the host genome which allows it to replicate as part of the host cell DNA. This impressive modality of replication and the relative specificity towards targeted cells make retroviruses a perfect tool for gene therapy techniques.

What is a gamma-retroviral vector?

In gene therapy research, around 21% of the clinical trials have been carried out using this type of retroviral vectors which are formed based on Moloney murine leukemia virus. The gamma-retroviral vector usually is a ‘replication defective’ virus which does not have the ability to replicate when it integrates or infects a targeted cell. This prevents the unwanted propagation of the virus following its introduction as a therapeutic measure.

What are the problems associated with gamma-retroviral vectors?

In order to function properly, retroviral vectors require dividing cells and this may hinder its usability for therapeutic measures of non-dividing cell structures. This is mostly noticeable in nerve cells as they resist infections from retroviruses because they do not divide as does many other cells in the body. Thus, it was necessary to develop newer retroviral vectors which do not require such circumstances in delivering their pay-load into target cells with minimum side effects at all times.

What are Lentivirus and its usefulness in gene therapy?

Lentivirus is a subclass of retroviruses and is used in gene therapy trials from recent past. The unique feature in Lentivirus is its ability to integrate replicated DNA sequences into the cellular genome without having to wait for cell replication as in the case of gamma-retroviral vectors. Thus, once entered into the cell, the lentiviral vector will use its reverse transcriptase enzyme to produce the necessary DNA from its RNA payload and will insert the DNA sequence at random points of the cellular genome.

At the same time, following integration into the cellular genome, the viral vector remains as a ‘pro-virus’ within the genome and could influence the replication and the cellular processes further. Promotion of oncogenes is one side effect when such viruses are used although research does not seem to show much significance in this probability.

More about this author: Dr Pandula Siribaddana

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