Hepatitis C virus modified _SE2_F442NYT-mRNA-LNP candidate vaccine promotes helper CXCR5⁺T cells

T cells play an important role in initiating antibody responses by instructive signals of cell-cell contacts and secretion of soluble cytokines as mediators. We investigated the role of the modified soluble E2 (sE2_F442NYT) antigen from hepatitis C virus (HCV) on healthy human peripheral blood mononuclear cell (PBMC)-derived immune cells or immunized mouse cells to understand the mechanisms of immune regulation by the candidate vaccine antigen. HCV E2 and E2_F442NYT displayed a role in inducing type 17 T-helper cell (Th17) phenotype, as indicated by interleukin-17 (IL-17) expression and signal transducer and activator of transcription 3 (Stat3) phosphorylation. The spleen cells from sE2-mRNA-lipid nanoparticles (LNPs) or sE2_F442NYT-mRNA-LNP-immunized mice exhibited similar IL-17A mRNA levels, and Th17 (CXCR3^-CCR6⁺) cells in CD4⁺CD44⁺ spleen cells, supporting both sE2 and modified sE2_F442NYT^-induced Th17 polarization. Immunohistochemical and multiplex immunofluorescence imaging studies revealed abundant CD4⁺CXCR5⁺T cells co-localized with BCL6 in sE2_F442NYT-mRNA-LNP immunized mouse spleen cells than unmodified sE2-mRNA-LNP immunized animals, suggesting sE2_F442NYT induces stronger follicular helper T cell generation. We previously demonstrated increased total IgG production and isotype switching from IgG1 to IgG2a and IgG2b in sE2_442NYT immunized mice. The stronger B and T cell responses observed from modified sE2_F442NYT support the overall in vivo outcome of the study toward a higher B helper T cell generation from sE2_F442NYT-mRNA-LNP immunization as compared to unmodified sE2-mRNA-LNP.IMPORTANCEThe study will help rationalize HCV vaccine antigen selection for an effective immune response. Extension by additional strategies may be useful to direct stronger B helper T cell generation for prolonged vaccine-associated protection.