The notion of using viruses to attack cancer has been around nearly as long as we’ve known about viruses themselves. But several roadblocks-- viruses attacking patients’ immune systems, or, not effectively targeting tumors--have led to slow growth in this area of research. Until now.
Earlier this month, a team led by Dr. Stephen Russell at Minnesota’s Mayo Clinic announced that a patient with previously unresponsive, blood-borne cancer (multiple myeloma) had gone into complete remission after being treated with a massive dose of a modified measles virus. A second patient given a similar dose (10 million times the amount in the common measles vaccine) didn’t respond as dramatically to the treatment, but the patient’s tumors did shrink, indicating the virus was at least attacking the targeted areas.
In a separate study that hasn’t yet made it to human trials, a team led by Dr. Khalid Shah at the Harvard Stem Cell Institute (HSCI) at Massachusetts General Hospital has made progress in attacking brain tumor cells in mice using the herpes virus.
Shah’s team packed the virus inside a type of human stem cell which, unlike some previous vehicles, is amenable to carrying modified viruses and doesn’t trigger a significant immune response. The team’s second trick: They wrapped the herpes-loaded stem cells inside a biocompatible gel to help keep the virus in place and attacking tumor cells for a longer period of time. According to the team, mice treated in this way had significantly improved survival.
The victories come more than half a century after work on cancer-fighting viruses (known in the field as oncolytic virotherapy) began in earnest in the 1950s, when scientists began attempting to engineer the evolution of viruses to make them more effective at fighting specific types of cancer. But that initial surge of research mostly fizzled, resulting in little success, and other promising areas of cancer treatment lured researchers elsewhere.
So what’s behind the recent promising research in cancer-fighting contagions? For Russell at the Mayo Clinic, the difference has been incremental, parallel advancements.
“The field has finally reached a stage … where many of the fundamental problems have been partially addressed,” Russell says. “The parallel evolution of knowledge in virology, oncology and immunology have all had a major impact.”
For Shah and his team, advancements in virology are key to their success with brain tumors. His team was able to load the herpes with another agent (TRAIL) that specifically targets the tumor cells.
“If you put the virus and that agent together, it basically is a double kill,” Shah says. “One sensitizes the other for therapeutic efficiency.”
While this method requires the bulk of the tumor to be surgically removed first, Shah says this method can kill the remaining cells, as well as those that are resistant to other treatments as well.
As for what makes a specific virus fit to fight a particular kind of cancer, it’s all about how the virus functions in the wild. Russell says Herpes is a good at tackling brain tumors because it hangs around in nerve cells (creating cold sores in the process). That allows it to hide from your immune system—a tactic that keeps the virus from spreading elsewhere. Measles, on the other hand, naturally attacks the immune system, which makes it a good option for fighting cancers in the blood.
But if a patient has already been exposed to a virus that’s being used for treatment, the body’s immune system will attack the virus before it can do its job. This will also pose a problem if the treatment shows initial success, but the cancer eventually returns (as happened with the second patient in Russell’s trial).
“The only way we know how to use the virus when the patient is immune,” Russell says, “is to put it inside cell carriers and use them as Trojan Horses to deliver it to the target site.” He says this method has worked in mice, but hasn’t yet been tested on humans.
Both Shah and Russell believe their teams’ recent successes will lead to increased interest in the field, and likely more breakthroughs.
As for when this type of treatment will go from research and limited human testing to approval for widespread use, it's not clear.
“The biggest player at the moment is Amgen,” says Russell, “with a herpes virus that is about to be approved by FDA—we think—for melanoma therapy.”
The measles success is cause for with hope, but cool heads are calling for caution until more results become available. The technique will likely encounter other hurdles when it's tried on more human patients. For something like this to be brought to the masses, it would have to go through "large randomized clinical trials," the Washington Post pointed out in its coverage of the concept—a process that will likely take years.
For now, Peter Lipson of Forbes Magazine said, the study is "a promising proof of concept, but a very early one."
"This has been tried in two patients, neither of whom are cured, and the therapy was not without dangers," Lipson wrote. It may not be a cure and instead another step "toward an eventual treatment."
"Either way," though, he wrote, "it’s good science."