Antigen-loaded exosomes alone induce Th1-type memory through a B-cell-dependent mechanism

Area of Science:

• Immunology
• Nanomedicine
• Vaccinology

Background:

• Exosomes are nanovesicles involved in intercellular communication.
• They carry proteins crucial for antigen presentation and immune modulation.
• Understanding exosome loading strategies is key for therapeutic applications.

Purpose of the Study:

• To compare the immunogenicity of directly peptide-loaded exosomes (Pep-Exo) versus antigen-pulsed dendritic cell-derived exosomes (OVA-Exo).
• To investigate the in vitro and in vivo T-cell proliferation induced by these exosomes.
• To elucidate the role of B cells and adjuvant effects in exosome-mediated immune responses.

Main Methods:

• In vitro and in vivo T-cell proliferation assays using transgenic T-cells.
• Immunization of mice with Pep-Exo and OVA-Exo, with and without whole antigen.
• Analysis of cytokine production (interferon-gamma) and antibody responses (IgG2a).
• Assessment of immune responses in Bruton tyrosine kinase-deficient mice.

Main Results:

• Both Pep-Exo and OVA-Exo induced in vitro T-cell proliferation, with Pep-Exo being more potent.
• Only OVA-Exo induced significant in vivo T-cell responses, demonstrating the advantage of indirect loading.
• OVA-Exo promoted Th1-type shifts, antibody production, and T-cell responses independently of whole antigen co-administration.
• B cells, mediated by Bruton tyrosine kinase, were essential for exosome-induced T-cell stimulation.

Conclusions:

• Indirect exosome loading strategies (OVA-Exo) are superior for inducing robust in vivo immune responses compared to direct peptide loading (Pep-Exo).
• Exosomes act as potent immune regulators, capable of driving adaptive immunity and influencing T-cell polarization.
• B cells play a critical role in mediating exosome-based immune stimulation, suggesting their utility in vaccine adjuvant and immunotherapy design.