U.S. scientists say they have harnessed the killer instinct of a virus to destroy cancer cells in animals and human tissue in laboratory tests.

In a study published Friday in the Journal of Clinical Investigation, scientists at Jennerex Biotherapeutics in San Francisco genetically engineered a strain of the virus used to vaccinate people against smallpox to make it zero in on tumours in both rabbits and mice.

In tests on rabbits and mice, scientists found that the virus had the ability to remain in the tumours for at least 10 days, showing that the hosts' antiviral immune response did not destroy it.
(CBC)

Known as poxvirus, the lab-grown virus can spread extremely quickly within tissues in the body.

The virus was engineered to attack certain cancer cells that have a specific protein, EGFR. The modified virus was then injected under the skin of lab animals with cancer tumours. Scientists found that the virus remained in the tumours for at least 10 days, showing that the hosts' antiviral immune responses did not destroy it.

They also discovered that the normal tissues in the animals' bodies were not infected with the virus.

"Dramatic therapeutic effects against large primary tumours were demonstrated following systemic delivery," reads the report.

The researchers cautioned that repeated use of the virus in one patient as an anti-tumour agent may not work if a cancer patient has had previous exposure to the virus and developed antibodies to it.

However, they are buoyed by the fact that a repeat injection of the virus into animals six weeks after the initial injection decreased the size of the tumours in three of the four test subjects.

"Initial results indicate that an anti-tumour effect is feasible in previously immunized individuals," reads the report.

Tests on human samples in the lab, which included ovarian, muscle, pancreatic, breast, and lung cancer cells, also showed the virus killed cancerous cells rapidly.

Researchers believe the treatment holds promise for human cancers and suggest clinical trials in humans go ahead.