ParcelBio raised $13 million in seed financing to build its APEXm platform for durable protein expression and to advance an in vivo CAR T program for autoimmune disease. The round was led by Breyer Capital with participation from General Catalyst, Y Combinator, and other investors. ParcelBio said APEXm is designed to increase both potency and durability of protein expression compared with other RNA designs, supported by preclinical work planned for presentation at ASGCT. The company also emphasized manufacturability and a linear RNA architecture. The funding positions the company to deepen preclinical development and move toward additional pipeline programs spanning oncology and encoded protein therapeutics.