• Financing led by Breyer Capital with participation from General Catalyst, Y Combinator, Metaplanet, SurgePoint Capital, ZAKA VC, and other investors
• Proceeds will advance APEXm™ platform and in vivo CAR-T programs for autoimmune disease

SAN FRANCISCO–(BUSINESS WIRE)–ParcelBio, a biotechnology company developing a new class of potent and durable mRNA medicines, today announced it has raised $13 million in seed financing led by Breyer Capital, with participation from General Catalyst, Y Combinator, Metaplanet, SurgePoint Capital, ZAKA VC, and other investors.

The financing will support development of ParcelBio’s proprietary APEXm™ (Amplified and Prolonged EXpression mRNA) platform and advance its pipeline, including its lead in vivo CAR-T program for autoimmune disease, as well as additional programs in oncology and encoded protein therapeutics.

Current mRNA technologies are limited in their ability to achieve both high protein expression and sustained durability, often requiring tradeoffs between potency, duration, and manufacturability. These constraints have restricted the broader application of mRNA beyond vaccines and short-acting therapeutics.

ParcelBio is developing a new category of mRNA medicines designed to overcome these limitations. Its proprietary APEXm™ platform engineers RNA molecules to actively recruit the cell’s native RNA-stabilizing machinery, enabling significantly higher and more durable protein expression. This approach leads to a step-change in biological performance, reaching therapeutic thresholds that have historically been out of reach for mRNA.

“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, Ph.D., Chief Executive Officer and Co-Founder of ParcelBio. “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.”

Unlike circular RNA and other next-generation approaches that often introduce manufacturing complexity or reduce peak output, ParcelBio’s platform maintains a simple, linear mRNA architecture while delivering both high peak expression and sustained activity. The platform is modular and broadly applicable across proteins and cell types, enabling diverse therapeutic applications ranging from immune reprogramming to protein replacement.

ParcelBio’s lead program focuses on in vivo CAR-T therapies targeting 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 with curative potential. Additional programs are in development in oncology and encoded protein therapeutics.

Preclinical data demonstrate that ParcelBio’s APEXm™ RNA drives significantly higher and more durable protein expression compared to a leading clinical mRNA design, translating into deeper biological responses, including more complete target cell depletion in in vivo CAR-T models. The company will be debuting the APEXm™ platform and preclinical data in an oral presentation at the American Society of Gene & Cell Therapy (ASGCT) Annual Meeting on May 14, 2026.

“ParcelBio’s durable, tunable expression is designed to collapse the tradeoffs that have constrained mRNA in chronic, deep-tissue disease, bringing durable, controllable immune reset within reach in refractory autoimmunity and beyond,” said Dr. Morgan Cheatham, Partner and Head of Healthcare and Life Sciences at Breyer Capital. “Breyer Capital’s life sciences thesis is organized around the technologies that redefine what medicine can reach: programmable biology, controllable expression, and durable therapeutic impact. ParcelBio is built to advance all three.”

“Most RNA platforms force a tradeoff between potency, durability, and manufacturability,” said Chris Carlson, Ph.D., 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.”

About ParcelBio

ParcelBio is engineering a new class of mRNA medicines designed to deliver unprecedented potency and durability. Its proprietary APEXm™ platform uses novel RNA domains to enhance protein expression and extend activity, enabling therapies that reach the thresholds required for meaningful, and potentially curative, clinical outcomes. The company is advancing programs in autoimmune disease, oncology, and encoded protein therapeutics.

Contacts

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