Replication and pathogenicity of attenuated human metapneumovirus F mutants in severe combined immunodeficiency mice

This study was to evaluate the replication and pathogenicity of attenuated human metapneumovirus (HMPV) mutants in severe combined immunodeficiency (SCID) mice. SCID mice were intranasally infected with either wild type GFP-rHMPV (WT), or mutant viruses (M1, M2 and M4) with the N-linked glycosylation(s) of the F protein removed. The organs were collected for viral isolation, titration, pulmonary histopathology and mRNA detection by PCR at different time points. WT or mutant viruses were successfully isolated from the lungs of infected mice after inoculation. The titers of WT and M1 peaked on 5th day and remained detectable until 14th day post-inoculation. M2 reached approximately 4 logs lower titer on 5th and 9th day post-inoculation as compared to WT and M1. M4 showed similar growth kinetics to M2. Viral signal was never detected from the heart, liver, spleen, kidney and brain on 5th day post-inoculation. The pulmonary pathology score in the M1 infected mice was similar to WT infected mice but higher than in M2 or M4 infected mice. WT and HMPV mutants can thus only replicate in the lungs of SCID mice. Attenuated M2 and M4 may be considered as candidates for the preparation of vaccine against HMPV.

► Wild-type HMPV and F mutants can only replicate in the lungs of SCID mice.
► Removal of N-linked carbohydrate in the F protein leads to attenuation of HMPV.
► Attenuated M2 and M4 may be considered as candidate vaccine strain.