QnAs with Katalin Karikó

Katalin Karikó’s path to scientific excellence was as peripatetic as her rise to fame in the midst of a pandemic was meteoric. Born in Hungary, Karikó emigrated with her family to the United States in 1985, hoping to scale the ranks of academia and settle into a scientific career. Early on, she developed an obsessive interest in using messenger RNA (mRNA)—a molecule that serves as a manual for making proteins in cells—to treat a range of human ailments. However, her failure to secure routine research grants to pursue unorthodox ideas written off as unrealistic left her without a viable path to a faculty position in the United States. So, in 2013, she left for Mainz, Germany, where she joined BioNTech, a little-known biotech firm specializing in RNA pharmaceuticals that has now made headlines around the world with a spectacularly successful COVID-19 vaccine, developed in partnership with the drug company Pfizer. At the center of the vaccine’s tangled origin story is Karikó’s plot-propelling breakthrough, made in the mid-2000s together with immunologist Drew Weissman at the University of Pennsylvania. For forging a path that has given the world life-saving vaccines to combat the COVID-19 pandemic, Karikó, now senior vice president at BioNTech, has won the 2022 Vilcek Prize for Excellence, an honor bestowed by the New York City–based Vilcek Foundation, which recognizes immigrant contributions to biomedical science and the arts (1). Among the long list of other prominent honors recently bestowed on Karikó, are Spain’s Princess of Asturias Award for technical and scientific research, a Breakthrough Prize in life sciences, and the Lasker-DeBakey Clinical Medical Research Award. Karikó sat down with PNAS to retrace her path from the sidelines to the headlines.

Katalin Karikó at BioNTech. Image credit: BioNTech SE 2021.

BioNTech, Mainz, Germany. Image credit: BioNTech SE 2021.

PNAS: Where did you grow up and when did you first become interested in biology?

Karikó: I was raised in Kisújszállás, a small town of around 10,000 people in the middle of Hungary. I had great teachers in elementary and high school who inspired an early interest in nature and biology. In eighth grade, I participated in a national biology competition and was recognized as the third-best in the country. And, in high school, I already knew I wanted to be a scientist. As a student at the University of Szeged, I worked in a lipid group at the Biological Research Center of the Hungarian Academy of Sciences. We isolated from cow brain a mixture of phospholipids used to prepare liposomes for delivery of plasmid DNA into cells. I was excited about the results we published (2). In 1978, I joined a group of organic chemists working on 2′-5′-oligoadenylates, which are short RNA molecules. Specifically, I was working on RNA delivery into cells for the eventual development of antiviral compounds. For my thesis, I used cordycepin, a modified nucleoside, and generated short 2′-5′-linked RNA molecules but soon realized the challenges tied to delivering a negatively charged, large molecule into cells. Before long, we ran out of funding.

PNAS: Tell me about your move to the United States and how you landed at the University of Pennsylvania.

Karikó: I never wanted to leave Hungary; I was very happy there. But when it came time to apply for jobs, I knew I had to leave. I sent out letters to labs in Europe and the United States, and Professor Robert Suhadolnik, who was working on 2′-5′-linked oligoadenylates at Temple University in Philadelphia, responded with an invitation to work in his lab. Back then, in 1985, there was a lot of rationing in Hungary, and we were allowed to leave with just $100. So, I smuggled around $1,200 in my two-and-a-half-year-old daughter’s teddy bear and set off for Philadelphia with my daughter and husband. My mother joined us a while later, and the four of us lived on my starting salary of $17,000 per year. Still, the money was not a major issue because I was thankful for the opportunity to learn and perform experiments.

I left Temple in 1988 to work at the Uniformed Services University of the Health Sciences in Bethesda, Maryland for almost a year. There, I learned basic molecular biology and immunology techniques. I remember being excited to learn about lipofectin, a positively charged lipid that can be easily mixed with nucleic acids for transfection into cells; I thought back to the laborious process of making the liposomes back in Hungary.

In 1989 I accepted a research assistant professor position—a nontenured faculty position—at the University of Pennsylvania in Philadelphia, thanks to Elliot Barnathan, an assistant professor in cardiology who had the grants to pay my salary. That’s when I began to work on mRNA.

PNAS: And you began by focusing on the therapeutic potential of RNA. Can you provide a brief overview of the field of RNA vaccines and drugs in the mid-to-late 1990s?

Karikó: Back then, in the early 1990s, there were a handful of groups working on mRNA vaccines; one group, for example, was working on a cancer vaccine and another on an influenza vaccine. Though I followed what little literature there was on mRNA vaccines, my main focus was on mRNA therapeutics, and I had mostly been working in potential applications in heart disease and stroke. Moreover, I knew little immunology and vaccine biology at the time; I learned most of it from Drew Weissman. I met Drew around 1997, when he had just been hired as an assistant professor at Penn Medicine. I told him I had been working with mRNA for almost 10 years, and he told me he’d been working in Tony Fauci’s lab. I didn’t know who Tony Fauci was at the time; I was not from his field, and Fauci was not on the television every day.

PNAS: At this stage in your career, you met with more than a fair share of rejection. What made you stay the course?

Karikó: The main reason I stayed at Penn, despite the lack of a permanent faculty position, was that the enthusiasm of Elliot Barnathan and David Langer for our experiments in mRNA therapeutics matched mine. Later, we collaborated with Drew Weissman. While performing experiments on human dendritic cells, we discovered that the mRNA I was making was immunogenic and induced the production of inflammatory cytokines. It was devastating to hear from Drew that the mRNA I was making was no good for the therapeutic applications I intended. So we did further experiments, proving that mRNA delivered from outside to the immune cell is indeed immunogenic; after all, mRNA made in the nuclei of living cells ends up in the cytoplasm and, under normal conditions, never gets outside the cells or encounters immune cells in the body.

PNAS: When you met Weissman at Penn, he was working on HIV vaccines. That fateful meeting led to a breakthrough in the mid 2000s. What was the breakthrough? How did it come about? What were the key papers?

Karikó: The breakthrough, as you put it, we first sent to a Nature journal, and within 24 h, they rejected it as an incremental contribution. I started learning English only at university, so I had to look up the meaning of the word incremental! Anyway, we then sent it to Immunity, and they accepted it (3). We literally did all the work ourselves, Drew and I. Even at the age of 58, I didn’t have much help or funding to perform the experiments, so I did them with my own hands. It took us a while to publish the follow-up paper in Molecular Therapy in 2008, where we presented data on the superior translation of the pseudouridine-containing mRNA and the lack of immune activation in mice (4).

Back to this idea: in 2004, it struck me that transfer RNA does not trigger the immune system. So we performed a critical experiment showing that transfer RNA, which is made inside the cell, is indeed not immunogenic. This led to the idea that the nucleosides in mRNA need to be modified to get past the immune system. I shared this idea with Drew, and we decided to try using modified nucleosides in mRNA. On the recommendation of János Ludwig, a compatriot with whom I had been a fellow grad student and who was then working in Germany, I ordered triphosphate-derivatives of different modified nucleosides from the company TriLink. In the modified mRNA molecules, the nucleoside uridine is replaced with pseudouridine, which, as was shown later, naturally occurs in mRNA along with other short forms of RNA in cells. The modification solved the problem of immunogenicity and, additionally, improved the stability of the mRNA and the protein yield. It was more than a year of struggle to prove that the original idea was correct. The modified nucleosides suppressed the immunogenicity of the RNA.

PNAS: Was this your idea?

Karikó: One of my hobbies is reading really old scientific papers. When I realized that uridine in RNA sets off immune cells, resulting in inflammation and interferon production, I wondered whether anyone had noticed this before. So I went back to the literature. Sure enough, I found a 1963 paper in which the authors reported that RNA isolated from mammalian cells does not induce the production of interferon (5). However, when the RNA was treated with nitrous acid, which deaminates all of the cytidines to uridines, it induced interferons. It gave me great pleasure to see that these researchers had stumbled upon this observation years before. [The history of mRNA vaccines can be traced back to the 1960s and involves dozens of researchers working on individual steps that eventually led to safe and effective products for clinical use. For an overview of this crowded playing field, see refs. 6 and 7.]

PNAS: How did that breakthrough form the basis of the Pfizer-BioNTech COVID-19 vaccine?

Karikó: In 2013, I left Philadelphia to join BioNTech, where I continued to improve the mRNA and its formulation. Two years later, our CEO Uğur Şahin, a visionary scientist, announced that the company had a moral obligation to begin vaccine development against infectious pathogens. Later, in 2018, we partnered with Pfizer to develop mRNA vaccines, specifically against the influenza virus. By the end of 2019, we were poised to begin clinical trials, when the coronavirus pandemic struck. In January 2020, Uğur realized that we had to pivot to developing a vaccine for SARS-CoV-2, given the news from Wuhan, China. He designed the coding sequence for the mRNA vaccine based on the information coming from Wuhan. In prior years, my basic science team at BioNTech had improved the mRNA construct and identified the right cap structure and formulation used in the vaccine. Pfizer soon came on board, even though our initial agreement was for an influenza vaccine.

PNAS: Given the checkered history of mRNA vaccine attempts and the fact that no mRNA vaccine had won regulatory approval, what was your outlook when the COVID-19 vaccine trials began? What kind of results did you expect?

Karikó: We had already seen in preclinical studies that even small amounts of 1-methylpseudouridine–modified, lipid nanoparticle-formulated mRNA vaccine was potent and protective in monkeys against Zika (8), influenza, and so forth. There was quite a bit of data from various research labs to suggest that this kind of vaccine would be effective. Additionally, there was enough data to suggest that nucleoside-modified RNA would not induce the production of interferons, which can lead to inflammation and prevent antibody production against the virus. Given this background in animal studies, and the high levels of antibody triggered in vaccinated individuals in the phase I/II human trial, I was not surprised with the results (9). I was happy that we were on our way to delivering a product that would help save countless lives.

PNAS: What are some of the major advantages of mRNA vaccines over traditional vaccines?

Karikó: Speed of manufacture is perhaps the biggest advantage of mRNA vaccines. You can order and receive a gene of interest in 1 to 2 days, and use it as a template to make mRNA in a few hours. Considering that the speed of translation is roughly 6 amino acids per second, a significant amount of protein is produced in cells from the transfected mRNA. As for the cost, modifying the RNA, or using pseudouridine, does not increase the cost much. The scalability of RNA vaccines is another major advantage; these are relatively simple to synthesize in one pot. The lipid nanoparticle formulation, however, is tricky to synthesize and scale, but experts have optimized that, too.

PNAS: In some ways, the success of these two mRNA vaccines represents a hinge moment in the history of vaccines, as some have observed (10). What are your thoughts?

Karikó: The vaccines opened up the world of mRNA, including therapeutics, to everyone. In 2013, Ingmar Hoerr, the founder of CureVac, organized the first mRNA therapy meeting, and we’ve been meeting alternately in Berlin and Boston every year since. If you attended these meetings, you’d realize that companies working on mRNA therapies are numerous, and some candidate mRNA molecules are in fairly advanced stages of clinical development. CureVac, for instance, began work on an mRNA vaccine for cancer treatment two decades ago, and when I joined BioNTech, they already had a trial running for an mRNA-based cancer vaccine. In fact, many people don’t know that Moderna had already run a clinical trial in Germany with nucleoside-modified, 1-methylpseudouridine–containing, lipid nanoparticle-formulated mRNA vaccine against influenza virus even before the SARS-CoV-2 pandemic (11). To people outside the field, these COVID-19 vaccines seem like a watershed moment, but those in the field have watched these developments take shape and the field of mRNA mature over the years (7).

PNAS: What other diseases are within reach of mRNA vaccines in the next 10 years? At least nine candidates are in development or early-stage trials, such as HIV, Nipah, Zika, dengue, and malaria vaccines. Which of these is low-hanging fruit?

Karikó: SARS-CoV-2 was in many ways brand new to the world, so it was possible to run a trial. With influenza, on the other hand, for which there is significant progress on an mRNA vaccine, it is difficult to run a trial because large sections of the population have been infected and already carry antibodies. Still, influenza is among the leading target candidates. Malaria, some bacterial pathogens, including tuberculosis, are also candidates.

PNAS: Your journey in science has taken you from relative obscurity to the relentless glare of the limelight. How do you feel about your newfound celebrity, given that it came during a pandemic that has taken a terrible human toll?

Karikó: Honestly, I wish my old life back; the attention is exhausting. Every day, I end up rejecting interview requests because there simply isn’t enough time. I was quite happy without all this recognition. I didn’t even get an R01 grant in my career and, for nearly 40 years, I received virtually no awards; yet, I was glad to just to keep doing experiments. That said, I try to use this opportunity to emphasize the importance of science funding and science education and science teachers, in particular, and focusing on your own research rather than rewards and recognition.

PNAS: The story of your career in science is a tale of success against the odds. Do you have a message for early-career scientists who might be struggling to get their unconventional ideas validated?

Karikó: In science, you are often working without any certainty of getting results. I often compare doing science with my daughter’s rowing: you are in a boat going backward without a clear view of how far the finish line is [Karikó’s daughter, Susan Francia, is a two-time US Olympic rowing champion and gold medalist]. So, I think, passion, single-minded focus, and a sense of mission are the key ingredients for fulfillment in a research career. At least, they are, in my case.

PNAS: How do you feel about being selected for the Vilcek Prize?

Karikó: The Vilcek Prize is a wonderful recognition of the aspirations, sacrifices, and struggles of immigrant scientists. As an immigrant scientist, I am deeply honored to receive the prize.