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There was just one problem: It was only a theory. No one had ever actually made an mRNA vaccine. What's more, most people in the field thought it was crazy to even try, not least because mRNA is inherently unstable and prone to degrading quickly. It was far from obvious that you could keep your modified mRNA together long enough to do its job. Also, cells have evolved to avoid being hijacked by foreign mRNA, and there would need to be a way of getting around this defense system. In 1993, while doing research at the University of Pennsylvania, Karikó and her boss managed a feat that told them they were on to something: They got a human cell to produce a tiny amount of new proteins using a modified version of mRNA that had been cleverly altered so it could get past the cell's defense system. This was a breakthrough, because it meant that if they could scale up the production dramatically, the would be able to make a vaccine. In theory, it would be possible to make mRNA vaccines not just for flu or coronaviruses, but also for various forms of cancer. Unfortunately, their work lost momentum when Karikó's boss left academia for a biotech firm. She no longer had a lab or financial support for her work; although she applied for grant after grant, every application was rejected. The year 1995 Nineteen ninety-five was particularly dispiriting: She had a cancer scare, she was taken off the tenure track at work, and her husband was stuck in Hungary because of a problem with his visa. But Karikó was undeterred. In 1997, she began working with Drew Weissman, a new colleague who came to Pennsylvania with a promising background; he had done a fellowship at NIH under the supervision of Anthony Fauci.