Alethio Therapeutics has closed an oversubscribed $90 million Series A, providing runway for its lead program, ATX-011, into Phase I/IIa studies for essential thrombocythemia (ET). The University of Oxford spinout says the goal is to reach Phase III readiness after generating first-in-patient data. ATX-011 is designed as a first-in-class monoclonal antibody against G6B, a protein described as present on platelets and megakaryocytes. Alethio aims to lower platelet counts in ET by boosting platelet clearance and also highlights G6B expression on myeloproliferative neoplasm–initiating stem cells as part of a broader, mutation-agnostic mechanism. The company is positioning ATX-011 against current ET management, where options are limited and responses to hydroxyurea can be incomplete and slow. Alethio argues its approach could normalize hematopoiesis and reduce thrombotic risk while also targeting disease progression biology. Sofinnova Partners and RA Capital co-led the round, with Oxford Science Enterprises participating and Cancer Research Horizons and the University of Oxford providing additional support.