Design and Evaluation of a Multi-Epitope Peptide of Human Metapneumovirus.

No licensed vaccines or therapeutic agents for human metapneumovirus (hMPV) infection exist to date. We aimed to construct a multi-epitope peptide (MEP) of hMPV to show promising results for epitope-based vaccine development. Six independent algorithms were screened to predict B-cell epitopes of hMPV, and three algorithms were used to predict cytotoxic T lymphocyte and T helper (Th) lymphocyte epitopes. Predicted epitopes were assembled in series with the spacers GPGPG and KK introduced, termed MEP. Recombinant mep genes were inserted into pET32a(+) plasmid and expressed in Escherichia coli strain BL21 (DE3). BALB/c mice were immunized with MEP with different adjuvants. Antibody titer, lymphocyte proliferation, cytotoxic T lymphocyte (CTL) activity and splenocyte cytokines were detected 2 weeks later after the last immunization. Microneutralization assay was used to detect neutralizing antibodies. Six B-cell epitopes, four CTL epitopes and two Th epitopes were screened to construct the mep gene. Expressed MEP induced >104 antibodies in BALB/c mice, and produced anti-MEP antibody reacting with hMPV strains specifically as detected in indirect fluorescent assay (the titer was 160). The lymphocyte proliferation index, CTL activity and splenocyte cytokines of the MEP immunization groups were higher than in the control group (p < 0.05). Both IgG1 and IgG2a antibodies could be detected in the different groups, and balanced Th1/Th2 cytokines were secreted by splenocytes in these groups. The mean neutralizing titers of the MEP+CpG ODN, MEP+Alum and MEP+Alum+ CpG ODN groups were 87 (95% CI 50-126), 93 (95% CI 67-121) and 96 (95% CI 69-147), respectively. MEP of hMPV elicited both strong humoral immunity and cell-mediated immunity in mice. The anti-MEP serum could neutralize hMPV infection in vitro. Joint use of CpG ODN and aluminum hydroxide adjuvants obtained the best immune effects. This study may contribute to hMPV epitope-based vaccine development.