The story of Katalin Kariko is one of the most remarkable in the history of modern science. For decades, she pursued a single idea -- that synthetic messenger RNA could be used to instruct human cells to produce therapeutic proteins -- while the scientific establishment repeatedly told her the idea was not worth funding. She was demoted, denied grants, and pushed to the margins of academic life. Then a global pandemic arrived, and the technology she had spent her career developing became the basis for vaccines that saved millions of lives. In 2023, she was awarded the Nobel Prize in Physiology or Medicine. Her journey from a small town in communist Hungary to Stockholm is a testament to the power of persistence and the danger of dismissing unconventional ideas.
Growing Up in Hungary
Katalin Kariko was born in 1955 in Kisujszallas, a small town on the Great Hungarian Plain. Her father was a butcher, and the family lived modestly in a home without running water, a refrigerator, or a television. Despite these humble circumstances, Kariko excelled academically and developed a passion for biology at an early age.
She studied biology at the University of Szeged, one of Hungary's leading research universities, and earned her PhD there in 1982, working on RNA and antiviral responses. After completing her doctorate, she took a position at the Biological Research Centre of the Hungarian Academy of Sciences, where she began working on the therapeutic potential of messenger RNA -- the molecular intermediary that carries genetic instructions from DNA to the cell's protein-making machinery.
The Teddy Bear and Emigration
By the mid-1980s, Hungary's economy was struggling, and Kariko's research funding was eliminated. She and her husband, Bela Francia, made the decision to leave for the United States, where she had secured a postdoctoral position at Temple University in Philadelphia. But Hungarian law severely restricted how much money citizens could take out of the country.
Kariko and her husband sold their car -- a Fiat -- and converted the proceeds into British pounds. They hid the cash inside their two-year-old daughter Susan's teddy bear. In 1985, the family emigrated to the United States with little more than the stuffed animal and a belief that mRNA could change medicine. Susan Francia would grow up to become an Olympic gold medal-winning rower -- a detail that adds an almost improbable richness to the family's story.
Decades of Rejection
At Temple University and then at the University of Pennsylvania, where she moved in 1989, Kariko devoted herself to developing mRNA as a therapeutic tool. The concept was straightforward in principle: if you could deliver synthetic mRNA into a patient's cells, those cells would produce whatever protein the mRNA encoded -- a vaccine antigen, a missing enzyme, a growth factor. Unlike gene therapy using DNA, mRNA would not integrate into the genome, reducing the risk of permanent genetic changes.
But in practice, mRNA therapy faced enormous obstacles. When synthetic mRNA was injected into animal cells, the immune system recognized it as foreign and mounted a violent inflammatory response, destroying the mRNA before it could do its job. Grant review panels consistently rejected Kariko's proposals, deeming the approach impractical. In 1995, UPenn denied her a tenure-track promotion, effectively demoting her to a lower-ranking research position. Most scientists in her situation would have abandoned the line of research entirely.
Kariko did not.
The Breakthrough with Drew Weissman
The turning point came through a chance encounter. In 1997, Kariko met Drew Weissman, an immunologist at UPenn, while they were both using the departmental copy machine. Weissman was interested in developing an HIV vaccine and was intrigued by the possibility of using mRNA to deliver antigens. He and Kariko began collaborating.
Together, they confronted the central problem head-on: why did synthetic mRNA provoke such a powerful inflammatory response? The answer, they discovered, lay in the nucleosides -- the chemical building blocks of RNA. Natural mRNA in human cells contains modified nucleosides, subtle chemical tweaks to the standard four RNA bases. Synthetic mRNA, produced in a laboratory, typically contained only unmodified nucleosides, and the immune system's toll-like receptors recognized these unmodified molecules as signatures of viral infection.
In a series of papers published between 2005 and 2010, Kariko and Weissman demonstrated that replacing one of the standard nucleosides -- uridine -- with a modified version called pseudouridine dramatically reduced the inflammatory response to synthetic mRNA. The modified mRNA was not only tolerated by the immune system but actually produced more protein than unmodified mRNA. They also showed that incorporating other modified nucleosides, such as N1-methylpseudouridine, further improved performance.
These papers, though groundbreaking in hindsight, were largely ignored at the time. The scientific mainstream remained skeptical of mRNA therapeutics, and the papers received modest citations for years.
BioNTech and the mRNA Revolution
The researchers who did pay attention were entrepreneurs. In 2013, Kariko was recruited by Ugur Sahin and Ozlem Tureci, the founders of BioNTech, a German biotechnology company focused on developing mRNA-based cancer immunotherapies. Kariko became BioNTech's Senior Vice President, bringing her expertise in modified nucleosides to the company's mRNA platform.
Separately, Derrick Rossi, a stem cell biologist at Harvard, had used Kariko and Weissman's modified mRNA technology to reprogram adult cells into induced pluripotent stem cells -- a finding that led him to co-found Moderna in 2010. Both BioNTech and Moderna built their entire platforms on the foundation of nucleoside-modified mRNA.
COVID-19: Vindication on a Global Stage
When the genetic sequence of SARS-CoV-2 was published in January 2020, the mRNA platform was ready. BioNTech, in partnership with Pfizer, and Moderna independently designed mRNA vaccines encoding the spike protein of the new coronavirus. Because mRNA vaccines require only the genetic sequence of the target -- not the virus itself -- the vaccines were designed within days and moved into clinical trials at unprecedented speed.
The Pfizer-BioNTech vaccine (BNT162b2) and the Moderna vaccine (mRNA-1273) both used N1-methylpseudouridine, the modified nucleoside that Kariko and Weissman had identified. Both vaccines demonstrated approximately 95 percent efficacy in their Phase 3 clinical trials -- extraordinary results that enabled emergency use authorizations by the end of 2020.
By early 2026, mRNA COVID-19 vaccines have been administered billions of times worldwide. They are estimated to have prevented millions of deaths and shortened the pandemic by years. The technology that grant reviewers had dismissed as impractical for decades had become the most important medical intervention of the twenty-first century.
The Nobel Prize
On October 2, 2023, Katalin Kariko and Drew Weissman were awarded the Nobel Prize in Physiology or Medicine "for their discoveries concerning nucleoside base modifications that enabled the development of effective mRNA vaccines against COVID-19." For Kariko, the award represented the ultimate vindication of a career spent fighting for an idea that few believed in.
In her Nobel lecture, Kariko reflected on the years of rejection with characteristic pragmatism. "I never thought of giving up," she said. "I just thought of the next experiment."
Implications for Gene Therapy and Beyond
The significance of Kariko's work extends far beyond vaccines. Modified mRNA is now being developed as a delivery mechanism for an extraordinary range of therapeutic applications:
- Cancer immunotherapy: mRNA encoding tumor-specific antigens can train the immune system to attack cancer cells. BioNTech has multiple mRNA cancer vaccines in clinical trials.
- Protein replacement therapy: For genetic diseases caused by missing or defective proteins, mRNA can instruct cells to produce the correct version temporarily, without altering the genome.
- Gene editing delivery: Modified mRNA can be used to deliver CRISPR-Cas9 components into cells, providing transient expression of the editing machinery without the risks associated with DNA-based delivery vectors. This approach was used in the development of Casgevy.
- Epigenetic reprogramming: mRNA encoding Yamanaka factors or other reprogramming transcription factors could potentially be used to deliver rejuvenation therapies, leveraging the transient nature of mRNA expression to avoid the cancer risks of permanent genetic modification.
Recent Developments (2025–2026)
Following her 2023 Nobel Prize, Karikó has focused on education and expanding mRNA applications. In May 2025, she was elected to the US National Academy of Sciences and delivered the prestigious Mendel Lecture at the European Society of Human Genetics Annual Meeting on clinical applications of mRNA therapeutics. She also received the ASIMOV Prize in May 2025.
She left BioNTech in 2022 to devote more time to research and has since become a professor at the University of Szeged in Hungary while maintaining an adjunct professorship in neurosurgery at the University of Pennsylvania. Her focus has shifted toward advocating for broader mRNA applications beyond vaccines — including mRNA-based gene therapy, cancer immunotherapy, and protein replacement therapies.
Research Lab & Companies
- University of Szeged — Professor (Hungary)
- University of Pennsylvania — Adjunct Professor of Neurosurgery
- BioNTech — Former SVP (2013–2022, developed mRNA vaccine platform)
- Nobel Prize in Physiology or Medicine 2023 — shared with Drew Weissman
A Story of Persistence
Katalin Kariko's career arc -- from a small Hungarian town to a Nobel Prize, through decades of rejection and marginalization -- has become one of the defining narratives of modern science. It is a story about the importance of funding basic research even when its applications are not immediately apparent. It is a story about the costs of a scientific culture that rewards trend-following over originality. And it is a story about one scientist's refusal to abandon an idea that she knew, in her bones, was right.
The mRNA platform she helped create is still in its infancy. As delivery methods improve, as modified nucleoside chemistry advances, and as the intersection with gene editing tools like CRISPR deepens, the full impact of Kariko's work will unfold over decades. But even now, the verdict is clear: her persistence changed the world.
