Rallybio, LLC

Rallybio, LLC is a Connecticut-based biotechnology company focused on discovering, developing and commercializing therapies for patients with severe and rare diseases. Its work spans small molecules, engineered proteins and antibodies [1], and its publicly described pipeline centers on complement dysregulation and hematology [0]. A lead asset, RLYB116, is a C5 inhibitor being evaluated in a confirmatory PK/PD study intended to support its positioning for patients with complement-mediated diseases [0].

The company was launched publicly in April 2018 by a leadership team drawn from Alexion Pharmaceuticals, and at launch stated it would license assets for development, applying a framework based on understanding the underlying biology, how an asset translates to pathology, how it addresses clinical symptoms, and whether it can be developed into a drug that improves quality of life or survival [4]. Rallybio Corporation is now a listed company (ticker RLYB) that advances its pipeline through partnerships, licensing and potential mergers and acquisitions [6].

Founding story

Rallybio, LLC was co-founded in January 2018 by Martin Mackay, Stephen Uden and Jeffrey Fryer, all of whom had worked at Alexion Pharmaceuticals until 2017. Mackay had been Alexion's global head of research and development, with prior R&D leadership roles at AstraZeneca and Pfizer Pharmatherapeutics; Uden had led research at Alexion, where he expanded the research portfolio to more than 30 pre-clinical and clinical programs, following earlier roles leading Wyeth and Novartis Oncology development groups in Japan and positions at Pfizer and Neurogen; Fryer had served as Alexion's chief tax officer. The company emerged publicly on April 25, 2018 with $37 million in financing and occupied space at the University of Connecticut's Technology Incubation Program [4].

Business model

Rallybio develops rare-disease drug candidates, licensing in assets for development and advancing its pipeline through strategic partnerships, licensing and potential mergers and acquisitions [4][6].

Traction

RLYB116, a C5 inhibitor, is in a confirmatory PK/PD study [0]. As of May 2026 the listed company had a market capitalization of approximately $49.78 million and average trading volume of about 152,931 shares [6].

Latest developments

On March 1, 2026 Rallybio Corporation signed a merger agreement to acquire Candid Therapeutics via a wholly owned subsidiary. Candid terminated the agreement on May 3, 2026 after entering an alternative agreement with UCB S.A. Rallybio will receive a $50 million termination fee, agreed mutual releases of claims with Candid and UCB under a May 1 waiver, and plans to withdraw the related Form S-4 registration statement filed in March and amended in April 2026 [6].