An alphavirus replicon-based human metapneumovirus vaccine is immunogenic and protective in mice and cotton rats

Abstract

Human metapneumovirus (hMPV) is a recently discovered paramyxovirus that causes upper and lower respiratory tract infections in infants, the elderly, and immunocompromised individuals worldwide. Here, we developed Venezuelan equine encephalitis virus replicon particles (VRPs) encoding hMPV fusion (F) or attachment (G) glycoproteins and evaluated the immunogenicity and protective efficacy of these vaccine candidates in mice and cotton rats. VRPs encoding hMPV F protein, when administered intranasally, induced F-specific virus-neutralizing antibodies in serum and immunoglobulin A (IgA) antibodies in secretions at the respiratory mucosa. Challenge virus replication was reduced significantly in both the upper and lower respiratory tracts following intranasal hMPV challenge in these animals. However, vaccination with hMPV G protein VRPs did not induce neutralizing antibodies or protect animals from hMPV challenge. Close examination of the histopathology of the lungs of VRP-MPV F-vaccinated animals following hMPV challenge revealed no enhancement of inflammation or mucus production. Aberrant cytokine gene expression was not detected in these animals. Together, these results represent an important first step toward the use of VRPs encoding hMPV F proteins as a prophylactic vaccine for hMPV.

FIG. 1.

Expression of hMPV proteins from VRP-infected BHK cells. BHK cells were either mock infected (A and C), infected at an MOI of 5 with VRP-MPV.F (B), or infected at an MOI of 5 with VRP-MPV.G (D). Cells then were fixed after 18 h and immunostained for hMPV F (A and B) or hMPV G (C and D) protein expression using guinea pig polyclonal anti-hMPV antibodies.

FIG. 2.

VRP-MPV.F induced hMPV-F- or hMPV-G-specific antibodies in the mucosal secretions of VRP-vaccinated mice. DBA/2 mice were vaccinated intranasally with 10⁶ infectious units of VRP-MPV.F or VRP-MPV.G on days 0 and 14. Nasal washes (A) or BAL fluids (B) were obtained from vaccinated mice 28 days postvaccination. An MPV-F- or MPV-G-specific enzyme-linked immunosorbent assay was performed on the samples with HRP-conjugated anti-mouse IgA antibodies. The amount of binding was determined from absorbance (optical density [OD]) of HRP-substrate complexes at 450 nm.