Steve Gschmeissner/Science Photo Library
Researchers are testing personalized vaccines to treat melanoma (shown here).
It is precision medicine taken to the extreme: cancer-fighting vaccines that are custom designed for each patient according to the mutations in their individual tumours. With early clinical trials showing promise, that extreme could one day become commonplace — but only if drug developers can scale up and speed up the production of their tailored medicines.
The topic was front and centre at the American Association for Cancer Research (AACR) annual meeting in New Orleans, Louisiana, on 16–20 April. Researchers there described early data from clinical trials suggesting that personalized vaccines can trigger immune responses against cancer cells. Investors seem optimistic that those results will translate into benefits for patients; over the past year, venture capitalists have pumped cash into biotechnology start-ups that are pursuing the approach.
But some researchers worry that the excitement is too much, too soon for an approach that still faces many technical challenges. “What I do really puzzle at is the level of what I would call irrational exuberance,” says Drew Pardoll, a cancer immunologist at Johns Hopkins University in Baltimore, Maryland.

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The concept of a vaccine to treat cancer has intrinsic appeal. Some tumour proteins are either mutated or expressed at different levels than in normal tissue. This raises the possibility that the immune system could recognize these unusual proteins as foreign — especially if it were alerted to their presence by a vaccine containing fragments of the mutated protein. The immune system’s army of T cells could then seek out and destroy cancer cells bearing the protein.
Decades of research into cancer-treatment vaccines have thus far yielded disappointing clinical trial results, but recent advances — including a suite of drugs that may amplify the effects of cancer vaccines — have rekindled hope for the field. And DNA sequencing of tumour genomes has revealed a staggering diversity of mutations, producing proteins that could serve as ‘antigens’ by alerting the immune system.
Last year, researchers reported that they had triggered an immune response in three patients with melanoma by administering a vaccine tailored to their potential tumour antigens1. The vaccines' effects on tumour growth are not yet clear, but by the end of 2015, several companies had announced their intention to enter the field. Gritstone Oncology, a start-up firm in Emeryville, California, raised US$102 million to pursue the approach, and Neon Therapeutics of Cambridge, Massachusetts, raised $55 million. A third company, Caperna, spun out of a prominent biotechnology company called Moderna Therapeutics, also in Cambridge.