Washington: Scientists say they have identified a molecule that can be added to a cancer vaccine to boost the immune system's ability to fight skin cancer.


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A study, published in the journal PNAS, found that adding the molecule called Diprovocim to an existing vaccine can draw cancer-fighting cells to tumour sites.


Experiments in mice with melanoma suggest the therapy could increase chances of recovery in cases where a drug therapy alone is not working, researchers said.


Melanoma is a form of skin cancer that arises when pigment-producing cells known as melanocytes mutate and become cancerous.


"This co-therapy produced a complete response a curative response in the treatment of melanoma," said Dale Boger, a professor at the Scripps Research Institute in the US.


The vaccine also prompts the immune system to fight tumour cells should they ever return, a capability that could prevent cancer recurrence, researchers said.


"Just as a vaccine can train the body to fight off external pathogens, this vaccine trains the immune system to go after the tumour," Boger said.


Diprovocim works as an "adjuvant," a molecule added to a vaccine to fire up the body's immune response.


The molecule is easy to synthesise in the lab and easy to modify, which makes it attractive for use in medicine.


The researchers tested the vaccine design on mice with a form of notoriously aggressive melanoma.


All mice in the experiment were given the anti-cancer therapy anti-PD-L1.


The mice were then split into three group: eight received the cancer vaccine, eight received the cancer vaccine plus Diprovocim, and eight received the cancer vaccine plus an alternative adjuvant called alum.


The researchers observed a 100 per cent survival rate over 54 days in the mice given the cancer vaccine and Diprovocim. This was in contrast to a zero per cent survival rate in mice given only the cancer vaccine and a 25 per cent survival rate in mice given the cancer vaccine with alum.


"It was exciting to see the vaccine working simultaneously with a cancer immunotherapy like anti-PD-L1," said Boger.


Further experiments showed that using Diprovocim as an adjuvant boosts the vaccine's cancer-fighting potential by stimulating the immune system to make cells called tumour-infiltrating leukocytes.