Abstract
The development of safe subunit vaccines requires adjuvants that augment immunogenicity of non-replicating protein-based antigens. Current vaccines against infectious diseases preferentially induce protective antibodies driven by adjuvants such as alum. However, the contribution of antibody to host defense is limited for certain classes of infectious diseases such as fungi, whereas animal studies and clinical observations implicate cellular immunity as an essential component of the resolution of fungal pathogens. Here, we decipher the structural bases of a newly identified glycoprotein ligand of Dectin-2 with potent adjuvancy, Blastomyces endoglucanase-2 (Bl-Eng2). We also pinpoint the developmental steps of antigen-specific CD4+ and CD8+ T responses augmented by Bl-Eng2 including expansion, differentiation and tissue residency. Dectin-2 ligation led to successful systemic and mucosal vaccination against invasive fungal infection and Influenza A infection, respectively. O-linked glycans on Bl-Eng2 applied at the skin and respiratory mucosa greatly augment vaccine subunit- induced protective immunity against lethal influenza and fungal pulmonary challenge.
Highlights
The lack of appropriate adjuvants is one major impediment to developing safe and effective vaccines against infections with viral and fungal pathogens
We recently demonstrated that fungal recognition by C-type lectin receptor (CLR) Dectin2 is required for the differentiation of protective, antifungal Th1 and Th17 cells [20]
We observed that digestion of the crude, water-soluble, cell wall extract (CWE) from Blastomyces vaccine yeast with either proteinase K or endo-mannosidases reduced Dectin-2 recognition as measured by reduced ligand activity by corresponding reporter cells [27], suggesting that both the protein and glycan moieties may contribute
Summary
The lack of appropriate adjuvants is one major impediment to developing safe and effective vaccines against infections with viral and fungal pathogens. There are no effective vaccines against fungi and respiratory viruses available, including broadly protective vaccines against seasonal influenza A viruses (IAV). IAV vaccines licensed in the USA rely on the generation of neutralizing antibodies targeting hemagglutinin (HA) antigens, which is the most frequently mutated IAV protein [1]. Cellular immunity mediated by CD8+ cytotoxic T lymphocytes (CTLs) target structural IAV epitopes such as nucleoprotein peptides. These targets are less mutable and broadly conserved, and they generate long-lived memory cells capable of mounting cross-protective recall responses to heterosubtypic influenza infection [5,6,7,8]
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