Mature Dendritic Cell-Derived Extracellular Vesicles are Potent Mucosal Adjuvants for Influenza Hemagglutinin Vaccines.

Immune cell-derived extracellular vesicles (EVs) possess intrinsic immunomodulatory properties, making them potential vaccine adjuvants. Here, we show that EVs from mature bone marrow-derived dendritic cells (mDC-EVs), rather than those from immature dendritic cells (imDC-EVs), are potent mucosal adjuvants for influenza hemagglutinin (HA) vaccines. In vitro, mDC-EVs exhibited intriguing immune-stimulating effects on various antigen-presenting cells, including DCs, macrophages, and B cells. Furthermore, intranasal immunization with mDC-EVs-adjuvanted A/Aichi/2/1968 (H3N2) HA (H3+mDC-EVs) significantly enhanced and expanded both systemic and mucosal antibody and cellular immune responses in female Balb/c mice. These responses offered complete protection against bodyweight loss following homologous and heterologous virus challenges. Mechanistically, H3+mDC-EVs immunization promoted enhanced airway immune cell recruitment, distinct antigen cellular uptake, and rapid activation of B and T cells within 24 h. It also induced robust germinal center reactions and antigen-experienced memory T-cell responses in lung-draining mediastinal lymph nodes 14 days postimmunization. Given their biocompatibility and solid adjuvanticity, mDC-EVs represent a promising adjuvant candidate for mucosal vaccine development.