A new study explains why a small group of women with advanced breast cancer lived more than 20 years after receiving an experimental cancer vaccine. Researchers discovered that these long-term survivors shared a special immune “memory” marker called CD27, which helps the immune system remember and fight cancer for decades. This finding is unusual because long-term survival is rare in metastatic breast cancer.
The study found that CD27 plays a key role in activating CD4+ “helper” T cells, not just the CD8+ “killer” T cells that most cancer research focuses on. When CD27 is activated, these helper T cells strongly support long-lasting anti-cancer immunity. In animal studies, adding a CD27-activating antibody to a HER2 cancer vaccine increased complete tumor disappearance from 6% to 40. When researchers further boosted killer T cells, tumor rejection rose to nearly 90%.
This discovery matters because the CD27 antibody may only need to be given once together with a vaccine, making it simple and practical. Scientists believe this approach could work well alongside existing immunotherapies, such as checkpoint inhibitors, and may help make cancer vaccines far more effective for many patients, not just a few rare responders.