Mereo BioPharma is a UK-based clinical-stage biopharmaceutical company focused on developing treatments for rare diseases. Mereo has no approved or marketed products and generates no product revenue. Its core strategy is to in-license drug candidates that large pharma companies have already advanced but deprioritized, then push those candidates through late-stage trials — leveraging existing data packages to reduce development time and cost. Mereo's two lead programs are setrusumab, an IV antibody for osteogenesis imperfecta (brittle bone disease), and alvelestat, an oral small molecule for alpha-1 antitrypsin deficiency-associated lung disease (AATD-LD). Setrusumab was licensed from Novartis and co-developed with Ultragenyx, which holds U.S. and rest-of-world rights while Mereo retains European and U.K. commercial rights. Phase 3 results announced in late 2025 were mixed — both studies missed the primary fracture rate endpoint, though both showed significant bone mineral density improvements, leaving the regulatory path uncertain. Alvelestat, licensed from AstraZeneca, inhibits neutrophil elastase and is taken orally twice daily, positioning it as a more convenient alternative to the current standard of care of weekly IV infusions. A Phase 3 is being designed pending financing. Mereo's current revenue model relies on upfront payments and milestones from partnerships, with longer-term potential from royalties and self-commercialization in Europe for approved products. The company has 39 employees, outsources manufacturing, and funds operations through partnership proceeds.