Oncolytic Virus Elevates Breast Cancer Immunotherapy Efficacy

The Maraba virus combined with an immune checkpoint inhibitor increased triple-negative breast cancer survival in mice.

It is no secret that immunotherapy may represent the future of cancer treatment and has dramatically shifted the oncology landscape thus far. Immunotherapy has shown significant progress treating the disease, however, many types of cancer do not respond to these treatments.

Researchers may have found a way to overcome the challenge of treatment resistance via a combination of oncolytic viruses and checkpoint inhibitors, a strategy that holds promise in other cancer types, according to a new study published by Science Translational Medicine.

“It was absolutely amazing to see that we could cure cancer in most of our mice, even in models that are normally very resistant to immunotherapy,” said lead author Marie-Claude Bourgeois-Daigneault, PhD. “We believe that the same mechanisms are at work in human cancers, but further research is needed to test this kind of therapy in humans.”

The researchers explored the new combination therapy in mice models with triple-negative breast cancer, the most aggressive subtype of the disease. The authors noted that all animals were resistant to checkpoint inhibitors.

The Maraba oncolytic virus was observed to replicate inside tumors and help the immune system recognize and kill cancer cells; however, the virus itself was not able to improve patient survival.

Then, the investigators tested the virus-immunotherapy combination in mouse models of breast cancer that metastasized postsurgery.

The combination was found to cure 60% to 90% of mice compared with 0% for the checkpoint inhibitor monotherapy, according to the study. Only 20% to 30% of mice that received the Maraba virus were cured.

These findings suggest that the Maraba virus may dramatically increase the efficacy of immunotherapy and breast cancer survival, according to the authors.

Prior research has shown the potential for the Maraba virus in melanoma, but the authors note this is the first study to demonstrate its potential in breast cancer.

There are other ongoing clinical trials examining the potential of oncolytic viruses plus checkpoint inhibitors for cancer, according to the authors. Another study also found that the Maraba virus has the ability to kill HIV-infected cells that current antiretroviral therapies cannot target.

“Our immune system is constantly trying to recognize and kill cancer cells, but the cancer cells are always trying to hide from it,” Dr Bell said. “When you infect a cancer cell with a virus, it raises a big red flag, which helps the immune system recognize and attack the cancer. But in some kinds of cancer this still isn’t enough. We found that when you add a checkpoint inhibitor after the virus, this releases all the alarms and the immune system sends in the full army against the cancer.”