Evaluation of the immunogenicity of an mRNA vectored Nipah virus vaccine candidate in pigs

Abstract

Nipah virus (NiV) poses a significant threat to human and livestock populations across South and Southeast Asia. Vaccines are required to reduce the risk and impact of spillover infection events. Pigs can act as an intermediate amplifying host for NiV and, separately, provide a preclinical model for evaluating human vaccine candidate immunogenicity. The aim of this study was therefore to evaluate the immunogenicity of an mRNA vectored NiV vaccine candidate in pigs. Pigs were immunized twice with 100 μg nucleoside-modified mRNA vaccine encoding soluble G glycoprotein from the Malaysia strain of NiV, formulated in lipid nanoparticles. Potent antigen-binding and virus neutralizing antibodies were detected in serum following the booster immunization. Antibody responses effectively neutralized both the Malaysia and Bangladesh strains of NiV but showed limited neutralization of the related (about 80% amino acid sequence identity for G) Hendra virus. Antibodies were also capable of neutralizing NiV glycoprotein mediated cell-cell fusion. NiV G-specific T cell cytokine responses were also measurable following the booster immunization with evidence for induction of both CD4 and CD8 T cell responses. These data support the further evaluation of mRNA vectored NiV G as a vaccine for both pigs and humans.

Keywords: Nipah virus; immunogenicity; mRNA; pig; vaccine.

Figure 1

Antibody responses following immunization of pigs with mRNA vectored Nipah virus G protein. Pigs were immunized on 0 (prime) and 21 (boost) dpv. Recombinant NiV sG protein was used in ELISAs to assess antigen-specific antibody responses longitudinally (A) and end-point titers were determined in sera collected on 21 and 42 dpv (B). Neutralizing antibody responses were assessed by classical VNT; longitudinal serum samples were assessed for neutralization of NiV-M (C) and day 42 sera tested for cross-neutralization of NiV-M, NiV-B, and HeV (D). NiV neutralizing antibody titers were additionally assessed using NiV-M and NiV-B pseudoviruses (E) and presented as the reciprocal serum dilution to inhibit pseudovirus entry by 90% (IC₉₀). Sera was assessed for inhibition of NiV-M and -B glycoprotein mediated cell–cell fusion (F). Each data point represents individual pig sera with lines denoting the median. *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 2

Evaluation of NiV antigen-specific T cell responses following immunization of pigs with mRNA vectored Nipah virus G protein. Pigs were immunized on 0 (prime) and 21 (boost) dpv. Responses of PBMC to stimulation with a NiV G peptide pool were monitored weekly by IFN-γ ELISpot assay and responding cells phenotyped by intracellular cytokine staining (ICS) assays. ELISpot data are presented as the unstimulated condition-corrected number of IFN-γ spot forming cells (S-C) per million PBMC (A) and ICS data shown as the unstimulated condition-corrected % cytokine expressing (IFN-γ and/or TNF-α) CD4⁺ (B) and CD8⁺ T cells (C). Each data point represents individual pig PBMC responses with bars denoting the mean for each timepoint.