How polio can fight cancer
A modified form of
poliovirus attacks cancer cells and also recruits the body’s immune system to
the cause, writes Andrew Masterson.
A protein common on some types of cancer cell turns out to be
the same one that in other circumstances allows the poliovirus to latch on to
its host.
The discovery that the protein –
known as CD155 – plays a role in both diseases has led to a leap forward in
explaining earlier research that found that a modified poliovirus – the type
used in the manufacture of vaccines – attacks tumour cells.
The ability of modified
polioviruses to both attack tumour cells and simultaneously induce the body’s
own immune response was first noted some years ago. It and several other
modified viruses, including herpes simplex type 1, adenovirus and measles, are
the subject of much research to determine their effectiveness at tackling brain
cancer.
A 2016 book, Neurotropic Viral Infections,
written by Dipongkor Saha of the Harvard Medical School and others, concluded
that the field “has great promise as an avenue toward effective therapy for
these deadly tumors”.
Despite the promise, however, the
molecular process by which modified viruses attacked cancer cells has remained
subject to conjecture – until now.
“We have had a general
understanding of how the modified poliovirus works, but not the mechanistic
details at this level,” says neurosurgeon Matthias Gromeier of the Duke
University Medical Centre in North Carolina, US.
In a study published in the journal Science Translational Medicine,
Gromeier and his colleagues describe how the virus’s cancer-fighting properties
manifest in two phases.
First, the poliovirus attaches to
the CD155 protein, infecting and killing many tumour cells. This prompts the
tumour cells to release antigens.
The immune system response to this
is modified and amplified by the second stage of the poliovirus assault. The
virus confronts dendritic cells and phages. The dendritic cells prompt T-cells
to launch a defensive action against the polio-infected tumour cells.
The antibodies thus formed also latch onto and attack uninfected
tumour cells – which until the polio invasion had been invisible to the body’s
defences.
“This is hugely important to us,”
says Gromeier.
“Knowing the steps that occur to
generate an immune response will enable us to rationally decide whether and
what other therapies make sense in combination with poliovirus to improve
patient survival.”
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