The same messenger RNA technology that delivered life-saving COVID-19 vaccines is now being adapted to fight cancer. Experimental mRNA vaccines are already in clinical trials for melanoma, small cell lung cancer, bladder cancer, and other malignancies. But exactly how these vaccines mobilize the immune system against tumors has remained incompletely understood — until now.
A study published in Nature by researchers at WashU Medicine reveals an unexpected layer of complexity. Scientists had long assumed that a specific type of immune cell called cDC1 — a classical type 1 dendritic cell — was the essential driver of the anti-tumor response after mRNA vaccination. cDC1 cells are expert teachers that prime T cells, the immune system's killer cells, to recognize and destroy targets presenting the vaccine's protein fragments.
To test this assumption, the research team led by Dr. Kenneth Murphy and Dr. William Gillanders created mouse models that lacked cDC1 cells. To their surprise, mice vaccinated with an mRNA cancer vaccine still generated strong T-cell responses and successfully eliminated sarcoma tumors even without cDC1. This meant another cell type was filling the gap.
That cell turned out to be cDC2, a closely related dendritic cell subtype. The study found that cDC2 cells can also activate T cells and stimulate tumor destruction, albeit through a different mechanism. While cDC1 cells process and present vaccine protein fragments directly, cDC2 relies on a process called "cross-dressing" — receiving pre-processed protein fragments from other cells and presenting them to T cells. Crucially, the T cells activated by cDC1 and cDC2 displayed subtly different molecular fingerprints, suggesting they perform complementary roles in fighting cancer.
The discovery has significant implications for vaccine design. If mRNA vaccines can leverage both dendritic cell pathways simultaneously, they may produce stronger and more durable anti-tumor immunity. The backup system also explains why some patients respond to mRNA cancer vaccines even when their cDC1 pathway is compromised. For vaccine developers, these findings offer a new toolkit: future vaccines could be engineered to deliberately engage both cDC1 and cDC2 pathways, potentially improving response rates across a broader range of cancer types.
Knowledge takeaway: mRNA cancer vaccines activate both cDC1 and cDC2 dendritic cells, not just cDC1 as previously believed; cDC2 uses a "cross-dressing" mechanism to present tumor antigens and activate T cells; T cells activated by each pathway carry different molecular markers, suggesting they play complementary roles; this dual-pathway mechanism could help design more effective cancer vaccines that work even when one immune pathway is compromised.