An experimental immunotherapy can temporarily reprogram patients’ immune cells to attack a specific target via only a single injection of messenger RNA (mRNA), similar to the mRNA-based COVID-19 vaccines, according to a new study from researchers in the Perelman School of Medicine at the University of Pennsylvania. The researchers, whose work was published on January 6, 2022 in Science, demonstrated the new approach with an mRNA preparation that reprograms T cells—a powerful type of immune cell—to attack heart fibroblast cells. Heart failure is often driven in part by these fibroblast cells, which respond to heart injury and inflammation by chronically overproducing fibrous material that stiffens the heart muscle, impairing heart function—a condition called fibrosis. In experiments in mice that model heart failure, the reduction in cardiac fibroblasts caused by the reprogrammed T cells led to a dramatic reversal of fibrosis. The article is titled “CAR T Cells Produced in Vivo to Treat Cardiac Injury.”