ParcelBio secured $13 million in seed financing to develop its APEXm (Amplified and Prolonged EXpression mRNA) platform and advance an in vivo CAR T program for autoimmune disease. The round was led by Breyer Capital and included participation from General Catalyst, Y Combinator, and other investors. ParcelBio said the technology is designed to overcome limitations in mRNA durability and protein output by engineering RNA that recruits the cell’s native RNA-stabilizing machinery. The company also emphasized manufacturability by keeping APEXm in a “simple, linear” architecture. It plans to debut APEXm and share preclinical data at the American Society of Gene and Cell Therapy annual meeting, with claims that the platform drives higher and more durable protein expression and improves target cell depletion in in vivo CAR T models.