Soluble recombinant human metapneumovirus G protein is immunogenic but not protective

Human metapneumovirus (HMPV) expresses the major surface glycoproteins F and G. We evaluated the protective efficacy of immunization with G. We generated a recombinant form of G ectodomain (G Delta TM) that was secreted from mammalian cells and purified by affinity chromatography. We tested the immunogenicity of G Delta TM in cotton rats. Animals were immunized with PBS, G Delta TM alone or adjuvanted, or were infected once with HMPV, and challenged with live HMPV at 28 days. Animals vaccinated with adjuvanted and non-adjuvanted G Delta TM developed high levels of serum antibodies to both recombinant and native G protein; however, vaccinated animals did not develop neutralizing antibodies and were not protected against virus challenge. Unlike the analogous non-fusion glycoproteins of other human paramyxoviruses, HMPV G does not appear to be a protective antigen. This represents an unusual feature of HMPV. (C) 2010 Elsevier Ltd. All rights reserved.