Engineering,Structure and Immunogenicity of the Human Metapneumovirus F Protein in the Postfusion Conformation

Human metapneumovirus (hmpv) is a paramyxovirus that is a common cause of bronchiolitis and pneumonia in children less than five years of age. the hmpv fusion (f) glycoprotein is the primary target of neutralizing antibodies and is thus a critical vaccine antigen. to facilitate structure-based vaccine design,we stabilized the ectodomain of the hmpv f protein in the postfusion conformation and determined its structure to a resolution of 3.3 å by x-ray crystallography. the structure resembles an elongated cone and is very similar to the postfusion f protein from the related human respiratory syncytial virus (hrsv). in contrast,significant differences were apparent with the postfusion f proteins from other paramyxoviruses,such as human parainfluenza type 3 (hpiv3) and newcastle disease virus (ndv). the high similarity of hmpv and hrsv postfusion f in two antigenic sites targeted by neutralizing antibodies prompted us to test for antibody cross-reactivity. the widely used monoclonal antibody 101f,which binds to antigenic site iv of hrsv f,was found to cross-react with hmpv postfusion f and neutralize both hrsv and hmpv. despite the cross-reactivity of 101f and the reported cross-reactivity of two other antibodies,54g10 and mpe8,we found no detectable cross-reactivity in the polyclonal antibody responses raised in mice against the postfusion forms of either hmpv or hrsv f. the postfusion-stabilized hmpv f protein did,however,elicit high titers of hmpv-neutralizing activity,suggesting that it could serve as an effective subunit vaccine. structural insights from these studies should be useful for designing novel immunogens able to induce wider cross-reactive antibody responses. © 2016 más et al.