Conjugation of β-Glucan with the Hydrazone and Disulfide Linkers Markedly Improves the Immunogenicity of Zika Virus E Protein.

The diseases caused by Zika virus (ZIKV) have received widespread concerns. As a key viral element of ZIKV, E protein was an ideal antigen for vaccine development. However, the poor immunogenicity of E protein necessitated the formulation with adjuvants. Formulation of E protein by conjugation with β-glucan was a strategy to improve the immunogenicity of E protein, where β-glucan was a polysaccharide adjuvant that could activate macrophages and trigger intracellular processes. However, the antigenic epitopes of E protein and the immunomodulatory sites of β-glucan were shielded in the conjugate. Moreover, the conjugate might elicit the undesired immune response to β-glucan. Thus, the acidic-labile hydrazone and the thiol-sensitive disulfide bonds were used as the linkers between E protein and β-glucan. Hydrazone hydrolysis and disulfide reduction could sufficiently detach the two components in the immune cells to overcome the two disadvantages. As compared with the conjugate without the two linkers, the conjugate with the two linkers (E-PS-4) elicited high E protein-specific IgG titers and low β-glucan-specific IgG titers. E-PS-4 elicited high levels of IFN-γ, TNF-α, IL-2, and IL-10. Moreover, E-PS-4 greatly facilitated the activation of dendritic cells without significant toxicity to the organs. A pharmacokinetic study revealed that the serum duration of E-PS-4 was longer than that of E protein. Accordingly, conjugation of E protein with β-glucan by the hydrazone and disulfide linkers could promote a potent cellular and humoral immune response to E protein. Thus, our study could facilitate the development of an effective vaccine against ZIKV.