An engineered herpesvirus that provokes an immune response against cancer has become the first treatment of its kind to be approved for use in the United States, paving the way for a long-awaited class of therapies. On 27 October, the US Food and Drug Administration (FDA) approved a genetically engineered virus called talimogene laherparepvec (T-VEC) to treat advanced melanoma. Four days earlier, advisers to the European Medicines Agency had endorsed the drug.
With dozens of ongoing clinical trials of similar ‘oncolytic’ viruses, researchers hope that the approval will generate the enthusiasm and cash needed to spur further development of the approach. “The era of the oncolytic virus is probably here,” says Stephen Russell, a cancer researcher and haematologist at the Mayo Clinic in Rochester, Minnesota. “I expect to see a great deal happening over the next few years.”
Many viruses preferentially infect cancer cells. Malignancy can suppress normal antiviral responses, and sometimes the mutations that drive tumour growth also make cells more susceptible to infection. Viral infection can thus ravage a tumour while leaving abutting healthy cells untouched, says Brad Thompson, president of the pharmaceutical-development firm Oncolytics Biotech in Calgary, Canada.
Killer T cells (orange) are recruited to attack malignant cells (mauve) in the viral-based cancer therapy T-VEC.
And researchers continue to look for ways to improve T-VEC. In particular, they would like to be able to deliver the therapy systemically, so that the virus could target tumours in organs that are difficult to reach with an injection. This would require a technique to prevent the body from mounting an immune response to the virus prematurely, which would disable it before it could reach and kill tumour cells, says Howard Kaufman, a cancer researcher at Rutgers Cancer Institute of New Jersey.
To that end, those in the field are experimenting with a smorgasbord of viruses — from poxviruses to vesicular stomatitis virus, which does not normally infect humans but causes a blistering disease in cattle. Oncolytics Biotech is studying a virus that hitch-hikes through the body on certain blood cells, camouflaged from the immune system.
If cancer-killing viruses could be delivered to their targets through the bloodstream, rather than via injection directly into the tumour, they could be used to treat a greater range of cancers. Thompson envisions a day when physicians will be able to peruse a menu of oncolytic viruses and select the best fit. “Each virus interacts with the immune system differently,” he says. “They could have a role in pretty much all cancer therapy.”