Evaluation of vaccine assay system on human PBMC-grafted NOG-hIL-4 Tg mice with different antigens and adjuvant conditions

This study aimed to evaluate and optimize an in vivo vaccine assay model for detecting the enhancement of humoral immunity.Materials and Methods: Immunodeficient mice transgenic for human interleukin-4 were transplanted with human peripheral blood mononuclear cells and vaccinated with formulations containing either influenza hemagglutinin antigen with K3 and scleroglucan or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epitope antigen with AS01 and Lipid A. Results: Two weeks after human peripheral blood mononuclear cell transplantation, before the first vaccination, some mice showed elevated pre-existing antigen-reactive antibody levels.In the influenza experiment, antibody levels increased after vaccination in both the antigen-containing and control groups for each donor.In the SARS-CoV-2 experiment, antibody levels in the chemical-scaffold-based epitope vaccine group were significantly higher at weeks 6 and 8 compared with week 2.However, the carrier protein-conjugated epitope vaccine group did not show a statistically significant increase in antibody levels.In the experiment using CD8-positive cell-depleted human peripheral blood mononuclear cells, no mouse showed a high pre-vaccination antibody level, and the mean antibody level at week 8 was numerically higher than that at week 2, although the difference was not statistically significant.Conclusion: These findings indicate that antigen-reactive antibody kinetics can be monitored in this humanized mouse model.However, pre-vaccination antibody elevation and responses not clearly attributable to the administered antigen remain important limitations.Future studies should address these limitations by improving human T-B-cell interactions within lymphoid-like structures, thereby improving the relevance of this model for vaccine evaluation.