evidence: When the COVID-19 pandemic hit a year ago, two innovative young pharmaceutical companies decided to try to harness this role played by messenger RNA: the German company BioNTech, which formed a partnership with the U.S. company Pfizer; and Moderna, based in Cambridge, Mass. Their mission was to engineer messenger RNA carrying the code letters to make part of the coronavirus spike protein—a string that begins CCUCGGCGGGCA … —and to deploy it in human cells. [...] An mRNA vaccine has certain advantages over a DNA vaccine, which has to use a re-engineered virus or other delivery mechanism to make it through the membrane that protects the nucleus of a cell. The RNA does not need to get into the nucleus. It simply needs to be delivered into the more-accessible outer region of cells, the cytoplasm, which is where proteins are constructed. [...] The ability to code messenger RNA to do our bidding will transform medicine. As with the COVID vaccines, we can instruct mRNA to cause our cells to make antigens—molecules that stimulate our immune system—that could protect us against many viruses, bacteria, or other pathogens that cause infectious disease. In addition, mRNA could in the future be used, as BioNTech and Moderna are pioneering, to fight cancer. Harnessing a process called immunotherapy, the mRNA can be coded to produce molecules that will cause the body’s immune system to identify and kill cancer cells.