Biotechnology company ParcelBio said this week that it has raised $13 million in a seed financing round led by Breyer Capital with participation from General Catalyst, Y Combinator, Metaplanet, SurgePoint Capital, ZAKA VC, and other investors. The financing will support the development of the company’s proprietary Amplified and Prolonged EXpression mRNA (APEXm) platform and advance its pipeline including an in vivo CAR T program for autoimmune disease, as well as additional programs in oncology and encoded protein therapeutics.

The company, which is developing what it describes as a new class of durable mRNA medicines, will debut APEXm and share some preclinical data at the American Society of Gene and Cell Therapy annual meeting. This year’s meeting is being held in Boston, Massachusetts and will run from May 11-15. The company claims that its data will demonstrate that ParcelBio’s APEXm RNA drives significantly higher and more durable protein expression compared to another clinical mRNA design, and yields more complete target cell depletion in in vivo CAR T models. 

“mRNA has transformed medicine, but today’s technologies are fundamentally limited in how much protein they can produce and for how long,” said David Weinberg, PhD, chief executive officer and co-founder of ParcelBio. His company’s proprietary technology addresses this problem by engineering RNA molecules to recruit the cell’s native RNA-stabilizing machinery, which enables higher and more durable protein expression. The company claims that its approach will result in medicines that reach thresholds that have historically been challenging for mRNA-based therapeutics. “We engineered RNA to work with the cell’s machinery rather than against it, enabling meaningful improvements in both expression and durability that we believe are essential for true disease modification,” Weinberg said. 

Furthermore, ParcelBio’s platform maintains a simple, linear RNA architecture unlike circular RNA and other approaches, whose structure introduces manufacturing complexity or reduces output. Its broad applicability across proteins and cell types makes it suited for various therapeutic applications including immune programming and protein replacement. 

“Most RNA platforms force a tradeoff between potency, durability, and manufacturability,” said Chris Carlson, PhD, chief scientific officer and co-founder of ParcelBio. “Our approach eliminates that tradeoff, enabling both higher peak expression and longer duration within a manufacturable system, and opening the door to entirely new classes of medicines.”

ParcelBio’s lead program focuses on in vivo CAR T therapies that target pathogenic B cells across autoimmune diseases, with the goal of achieving deep B-cell depletion for durable, drug-free remission. By enabling sustained CAR expression without viral delivery or ex vivo manufacturing, the company aims to develop scalable, off-the-shelf therapies. Additional programs leveraging the technology are currently in development in oncology and encoded protein therapeutics.

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