Stabilization of prefusion hMPV F improves manufacturability and protective immunity across hMPV lineages

Human metapneumovirus (hMPV) is a major cause of pediatric acute lower respiratory tract infections (ALRTIs), yet vaccine development has been hindered by the intrinsic metastability of the prefusion F glycoprotein (pre-F). Here, we used a structure-based design strategy to stabilize hMPV pre-F while preserving neutralization-sensitive epitopes. By applying combined stabilizing elements, including disulfide bonds, a designed salt bridge, and a trimer-interface sequence swap, we generated VM-874, a pre-F-stabilized trimer that was expressed at high levels in 293F cells and exhibited improved thermal stability and stress-resistant antigenicity. VM-874 also retained binding to multiple conformation-sensitive monoclonal antibodies following thermal and storage stress. VM-874 elicited high serum neutralizing titers against both hMPV A2 and B1 strains and conferred protection in BALB/c mice and cotton rats, as evidenced by reduced pulmonary viral burden and attenuated lung pathology after challenge. Although VM-874 elicited antibodies that cross-bound respiratory syncytial virus (RSV) F protein, no RSV-neutralizing activity was detected, underscoring the need to distinguish cross-reactivity from heterologous protection in combined RSV/hMPV vaccine strategies.