Lesson 6 — The mRNA Revolution

Understanding the Complex: How Do Vaccines Actually Work?

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In 1989, Katalin Karikó was a junior researcher at the University of Pennsylvania. She had come from Hungary with a suitcase, $900 hidden in a stuffed bear (circumventing Hungarian currency restrictions), and a conviction that mRNA could be used as medicine. She wanted to use synthetic mRNA to instruct cells to produce therapeutic proteins — to essentially program the body to make its own drugs.

Her grant applications were rejected repeatedly. Her department demoted her, stripping her of her tenured position because she was not bringing in enough funding. She was nearly deported when her visa required institutional sponsorship. She kept working.

For nearly two decades, the scientific establishment remained largely uninterested in her ideas — partly because the central technical problem seemed insurmountable. When you inject synthetic mRNA into a living organism, the immune system treats it as a threat. It attacks it. The mRNA is degraded before it can do anything useful, and the immune reaction itself can cause dangerous inflammation.

In 2005, Karikó and her colleague Drew Weissman discovered the solution. They found that by replacing a specific building block in the mRNA — a nucleoside called uridine — with a modified version called pseudouridine, the mRNA became essentially invisible to the immune system's alarm system. It could slip into cells, be read by ribosomes, produce protein — without triggering the inflammatory response that had made earlier attempts unworkable.

The paper they published in Immunity in 2005 was not widely celebrated. It was cited occasionally, then more frequently, then — after COVID — it was recognized as one of the most consequential papers in the history of vaccinology. In 2023, Karikó and Weissman received the Nobel Prize in Physiology or Medicine.

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From lab to mass production

The path from Karikó and Weissman's 2005 paper to the COVID vaccine authorization in December 2020 required two more pieces.

One was the lipid nanoparticle delivery system — years of work by researchers including Pieter Cullis at the University of British Columbia, developing the fat-sphere packaging that would protect the mRNA in transit and deliver it into cells.

The other was BioNTech's platform strategy. Ugur Sahin and Özlem Türeci — both children of Turkish immigrants who had come to Germany as gastarbeiter — had built BioNTech not primarily as a vaccine company but as a cancer immunotherapy company. They were using mRNA to try to teach the immune system to recognize and attack tumor cells. The COVID pivot in January 2020 was radical but not random: they had been working on the same basic technology for years.

The leap from laboratory to manufacturing at scale — producing hundreds of millions of doses in months rather than years — required an enormous collaboration with Pfizer, which provided manufacturing infrastructure and global distribution. Even so, it was achieved. The timeline that had previously required a decade was compressed to under a year.

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Cancer vaccines: the next chapter

The most consequential application of the mRNA platform may not be COVID — or any infectious disease. It may be cancer.

Tumors accumulate mutations. Those mutations cause cells to produce abnormal proteins — neoantigens — that healthy cells do not have. The immune system can, in principle, recognize those neoantigens and attack the tumor. But in practice, tumors are remarkably good at evading immune detection: they suppress immune responses, hide their neoantigens, and create an immunosuppressive environment.

The idea behind personalized mRNA cancer vaccines is this: sequence the DNA of a patient's tumor, identify the specific mutations it carries, design an mRNA vaccine encoding those mutant proteins, and inject it to prime the immune system to recognize and attack the tumor's specific cells.

In 2022, Moderna and MSD (Merck) presented Phase 2 data from a trial in melanoma patients. Patients who received the personalized mRNA vaccine (mRNA-4157, also called V940) alongside the immunotherapy drug pembrolizumab showed approximately 44% lower risk of recurrence or death compared to patients who received pembrolizumab alone. The trial was small — 107 patients — and Phase 3 trials are required before any regulatory approval. But the signal was strong enough that the trial was immediately extended and Phase 3 was initiated.

Similar approaches are being tested in colorectal cancer, non-small-cell lung cancer, and other tumor types. The fundamental challenge — manufacturing a genuinely personalized vaccine for each patient within weeks — is significant. But it is, for the first time, technically feasible.

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Next lesson: Who does what? Why? Who pays? — The funding landscape behind vaccine development.

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Reading time: approx. 10–11 minutes