Quantitation of norovirus-specific IgG before and after infection in immunocompromised patients

Polyethylenimine-Conjugated Au-NPs as an Efficient Vehicle for in vitro and in vivo DNA Vaccine Delivery

Purpose

This study aimed to develop green-synthesized gold nanoparticles (Au-NPs) conjugated with polyethyleneimine (PEI) to overcome challenges in intracellular DNA vaccine delivery, focusing on enhancing cellular uptake and immune responses against the human norovirus (HuNoV) GII.4 variants.

Methods

Au-NPs were synthesized using a citrate-ion-mediated green approach, with size and morphology analyzed via UV-vis spectroscopy and transmission electron microscopy (TEM). Stability was evaluated through zeta potential measurements. PEI conjugation was employed to modify surface charge. After in vitro evaluation of pDNA delivery efficiency and cytotoxicity in HEK293 cells, PEI-coated Au-NPs loaded with a HuNoV GII.4 pDNA vaccine (AuPEI-NPs-pDNA) were assessed for the immune responses in mice.

Results

UV-vis spectroscopy and TEM confirmed successful Au-NP synthesis. Zeta potential shifted from -31.38 mV to -20.60 mV, reflecting stable but slightly reduced colloidal stability with larger sizes. PEI conjugation reversed surface charge to positive, enabling 100% transfection efficacy in HEK293 cells by day two without cytotoxicity. The AuPEI-NPs-pDNA induced significantly higher NoV-specific IgG antibodies and T-cell responses compared to unmodified Au-NPs, highlighting the role of positive charge in enhancing cellular uptake and immune activation. These results underscore PEI-coated Au-NPs as a biocompatible, efficient platform for DNA vaccine delivery.

Conclusion

PEI-coated Au-NPs demonstrate exceptional potential as non-toxic, high-efficiency carriers for DNA vaccines, enabling robust humoral and cellular immune responses. This strategy holds promises for advancing gene therapy and combating rapidly evolving pathogens like HuNoV, with broader applications in targeted drug delivery.

Prolonged norovirus infections correlate to quasispecies evolution resulting in structural changes of surface-exposed epitopes

In this study, we analyzed norovirus (NoV) evolution in sequential samples of six chronically infected patients. The capsid gene was amplified from stool samples, and deep sequencing was performed. The role of amino acid flexibility in structural changes and ligand binding was studied with molecular dynamics (MD) simulations. Concentrations of capsid-specific antibodies increased in sequential sera. Capsid sequences accumulated mutations during chronic infection, particularly in the surface-exposed antigenic epitopes A, D, and E. The number of quasispecies increased in infections lasting for >1 month. Interestingly, high genetic complexity and distances were followed by ongoing NoV replication, whereas lower genetic complexity and distances preceded cure. MD simulation revealed that surface-exposed amino acid substitutions of the P2 domain caused fluctuation of blockade epitopes. In conclusion, the capsid protein accumulates numerous mutations during chronic infection; however, only those on the protein surface change the protein structure substantially and may lead to immune escape.

Linear B-Cell Epitopes in Human Norovirus GII.4 Capsid Protein Elicit Blockade Antibodies

Human norovirus (HuNoV) is the leading cause of nonbacterial gastroenteritis worldwide with the GII.4 genotype accounting for over 80% of infections. The major capsid protein of GII.4 variants is evolving rapidly, resulting in new epidemic variants with altered antigenic potentials that must be considered for the development of an effective vaccine. In this study, we identify and characterize linear blockade B-cell epitopes in HuNoV GII.4. Five unique linear B-cell epitopes, namely P2A, P2B, P2C, P2D, and P2E, were predicted on the surface-exposed regions of the capsid protein. Evolving of the surface-exposed epitopes over time was found to correlate with the emergence of new GII.4 outbreak variants. Molecular dynamic simulation (MD) analysis and molecular docking revealed that amino acid substitutions in the putative epitopes P2B, P2C, and P2D could be associated with immune escape and the appearance of new GII.4 variants by affecting solvent accessibility and flexibility of the antigenic sites and histo-blood group antigens (HBAG) binding. Testing the synthetic peptides in wild-type mice, epitopes P2B (336-355), P2C (367-384), and P2D (390-400) were recognized as GII.4-specific linear blockade epitopes with the blocking rate of 68, 55 and 28%, respectively. Blocking rate was found to increase to 80% using the pooled serum of epitopes P2B and P2C. These data provide a strategy for expanding the broad blockade potential of vaccines for prevention of NoV infection.