ParcelBio secured $13 million in seed financing to develop its Amplified and Prolonged EXpression mRNA (APEXm) platform and advance an in vivo CAR T program for autoimmune disease. The round was led by Breyer Capital with participation from General Catalyst, Y Combinator, Metaplanet, SurgePoint Capital, ZAKA VC, and other investors. ParcelBio said it will debut APEXm and share preclinical data at ASGCT, describing higher and more durable protein expression than comparator mRNA designs and improved target cell depletion in in vivo CAR T models. The company’s approach focuses on engineering RNA to recruit native RNA-stabilizing machinery, aiming to address protein output and duration limitations. Alongside the autoimmune CAR-T program, the company pointed to additional pipeline assets in oncology and encoded protein therapeutics. Seed funding at this stage signals continued investor appetite for next-generation mRNA designs that can compete on durability and potency, not just delivery.