By Gnaneshwar Rajan and Gursimran Mehar (Reuters) -The U.S. health regulator said on Monday companies will be required to add a serious warning on the prescribing information for cancer therapies known as CAR-T, made by Gilead Sciences, Johnson & Johnson, Novartis and others. The other cancer therapies include Bristol Myers Squibb’s Breyanzi and its partnered therapy, Abecma, with 2seventy bio, J&J unit Janssen and Legend Biotech’s Carvykti, Novartis AG’s Kymriah, and Gilead unit Kite’s Tecartus and Yescarta. Novartis said it will update the prescribing information for its CAR-T cell therapy K…