Diagonal Therapeutics closed a $125 million Series B co‑led by Sanofi Ventures to advance DIAG723—its clustering antibody designed for hereditary hemorrhagic telangiectasia (HHT) and pulmonary arterial hypertension—into first‑in‑human studies. The company said the round was oversubscribed and will also support other pipeline programs across hematology, hepatology and nephrology. Diagonal’s approach uses antibodies engineered to restore or normalize receptor clustering and signaling in diseases driven by impaired receptor dynamics; preclinical models reportedly showed disease‑modifying activity. Sanofi Ventures’ participation included a board seat and underscores big‑pharma interest in novel biologic modalities for rare and high‑value indications. The company expects to begin human dosing in the first half of the year and will use the funding to expand manufacturing and clinical operations ahead of translational studies.