ParcelBio raised $13 million in seed funding to develop its APEXm platform, aimed at producing higher and more durable protein expression from mRNA. The round was led by Breyer Capital with participation from General Catalyst, Y Combinator, Metaplanet, and other investors, supporting platform development and advancement of a pipeline that includes an in vivo CAR T program for autoimmune disease. ParcelBio plans to debut APEXm and share preclinical data at ASGCT, claiming its engineered RNA can produce more complete target cell depletion in in vivo CAR T models and improve expression durability versus other clinical mRNA designs. The company describes APEXm as a linear RNA architecture designed to recruit native RNA-stabilizing machinery to increase both potency and persistence. The financing reinforces investor interest in next-generation mRNA formats aimed at overcoming the expression-duration limits of conventional designs, particularly where durable pharmacology is critical to therapeutic effect.