Tectonic Therapeutic Inc. announced positive topline results from its Phase 1b Part B clinical trial evaluating TX45, a long-acting Fc-relaxin fusion protein, in patients with Group 2 pulmonary hypertension in heart failure with reduced ejection fraction (PH-HFrEF). The trial demonstrated that a single intravenous dose of TX45 was well tolerated and showed meaningful improvements in left heart function and pulmonary hemodynamics. No serious or severe adverse events, clinically significant changes in blood pressure, or immune-related reactions were reported. The company is also conducting the APEX Phase 2 trial of TX45 in patients with Group 2 pulmonary hypertension in heart failure with preserved ejection fraction (PH-HFpEF), with topline results expected in 2026. The Phase 1b results were presented by the company on October 29, 2025.