A molecule derived from vitamin A may be quietly helping cancers escape the body’s immune defenses, according to new research from the Ludwig Institute for Cancer Research.

The studies, published in Nature Immunology and iScience, found that all-trans retinoic acid; a byproduct of vitamin A, can dampen the activity of immune cells that normally attack tumors. In doing so, it may also weaken the effectiveness of certain cancer vaccines.

Scientists involved in the research developed an experimental drug, known as KyA33, designed to block this immune-suppressing pathway. In animal studies, the drug boosted immune responses, improved vaccine performance, and slowed tumor growth.

The findings may help resolve a long-standing puzzle in cancer research: while vitamin A has shown anti-cancer effects in laboratory experiments, high levels have been associated with poorer outcomes in clinical studies. Researchers say some tumors may exploit retinoic acid to suppress immune responses and survive.

The team has since launched a biotechnology company to move the drug toward human trials, with hopes it could lead to new cancer immunotherapies and treatments for other immune-related diseases.