Scientists at Washington University School of Medicine in St. Louis have uncovered a hidden backup system in the immune system that could make mRNA cancer vaccines significantly more powerful — a discovery that overturns a long-held assumption about how these vaccines work.
Published in Nature, the study reveals that mRNA cancer vaccines engage not just one, but two distinct subtypes of dendritic cells — the immune system's master trainers — to launch tumor-killing T-cell responses.
For years, researchers assumed that a specific immune cell subtype called cDC1 (classical type 1 dendritic cell) was essential for mRNA vaccines to work. But when the Washington University team genetically removed cDC1s in mice, the mRNA vaccines still triggered strong cancer-killing responses. Mice lacking cDC1s were still able to clear sarcoma tumors, proving another cell type was stepping in.
That backup turned out to be cDC2 — a cousin subtype long thought uninvolved in vaccine responses. The study found that cDC2s activate T-cells through an unexpected "cross-dressing" mechanism: other cells process the mRNA instructions into protein fragments and then transfer the entire presenting complex to cDC2s, which then engage T-cells.
"This work uncovers a new way mRNA vaccines engage the immune system — through both cDC1 and cDC2 — which helps explain their power and gives researchers concrete targets for making future mRNA cancer vaccines more effective," said co-corresponding author Dr. William E. Gillanders, a surgical oncologist at WashU Medicine.
The researchers also discovered that T-cells activated by cDC1s and cDC2s carry slightly different molecular fingerprints, which could help scientists design more targeted vaccine strategies.
mRNA vaccines are already in clinical trials for melanoma, small cell lung cancer, bladder cancer, and other malignancies. This discovery provides immediate, actionable insights: vaccine developers can now optimize formulations to engage both dendritic cell pathways, potentially improving response rates in patients who don't respond well to current approaches.
"It could improve vaccine formulation and dosing, potentially explain why some patients respond better to vaccines than others, and guide strategies for making vaccines more effective," Gillanders said.
