Apart targeting the tumour cells. This can

Apart from DNA, oncolytic
viruses are also used for vaccination purposes (Bartlett, et
al., 2013).
They can also be armed with immune modulatory transgenes or used in combination
with other immunotherapies (Chiocca & Rabkin, 2014). This therapy makes
use of the ability of the viruses to replicate in cancer cells and subsequently
spreading within a tumour without the destruction of normal tissues (Russell, et
al., 2012).
OVs that are used include a variety DNA and RNA viruses that can be genetically
engineered or naturally cancer-selective. An example includes onyx-15 which is
the world first oncolytic virus that had been approved by China for cancer
treatment (Ken, 2006). The main objective
of OV-mediated immunotherapy is to make use of the body’s innate and adaptive
immunity directed towards the tumour
(Figure 7).

Figure 7. OV-mediated effects
resulting in destruction of tumour cells. 1st phase: Administration of OV can be delivered
through intratumorally or systemically. The process starts by the virus
infecting the tumour cell. The virus then replicates, spreads itself within the
tumour cells and induce tumour cell death through the recruitment of other
immune cells. This process spreads throughout the tumour leading to an
inflammatory response. Immunomodulatory transgene is expressed when an armed OV
is used. Transgene products can further enhance the anti-tumour responses. The
process of OV-infection, replication and spreading can also inhibited by
different immune mechanisms. 2nd
Phase: The spread of the OV within the tumour cells will lead to a series of
signaling cascade due to the inflammation occurring. Dendritic cells will be
recruited and will present the TAAs on its surface resulting in an adaptive
immune response which targeting the tumour cells. This can be inhibited by Treg
cells. Source: (Chiocca & Rabkin, 2014)

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use of OVs as a cancer treatment strategy have several features that makes it
advantageous as compared to other current cancer treatment strategies. Firstly,
the use of OVs will not generate resistance against the tumour cells as it uses
various oncogenic pathways in order to induce cytotoxity to the tumour cells.
In addition, they are non-pathogenic and able to replicate only within a
tumour-selective environment. However, drawbacks such as the presence of
anti-OV antibodies that can be induced by multiple administrations may cause
clearance of the virus by immune system before the therapeutic effects are
elicited (Gong, et al., 2016). Recent clinical
trials have demonstrated the use of OVs expressing GM-CSF to be efficient in
inducing an anti-tumour immune response with minimal toxicity (Heo, et al.,