Abstract
Granzyme A (GzmA), together with perforin, are well-known for their cytotoxic activity against tumor or virus-infected cells. In addition to this cytotoxic function, GzmA stimulates several immune cell types and induces inflammation in the absence of perforin, however, its effect on the dendritic cell (DC) is unknown. In the current study, we showed that recombinant GzmA induced the phenotypic maturation of plasmacytoid DCs (pDCs) and conventional DCs (cDCs), but not their apoptosis. Particularly, GzmA made pDCs more functional, thus leading to production of type I interferon (IFN) via the TLR9-MyD88 pathway. We also demonstrated that GzmA binds TLR9 and co-localizes with it in endosomes. When co-administered with antigen, GzmA acted as a powerful adjuvant for eliciting antigen-specific cytotoxic CD8+ T lymphocytes (CTLs) that protected mice from tumor challenge. The induction of CTL was completely abolished in XCR1+ DC-depleted mice, whereas it was reduced to less than half in pDC-depleted or IFN-α/β receptor knockout mice. Thus, CTL cross-priming was dependent on XCR1+cDC and also type I IFN, which was produced by GzmA-activated pDCs. These results indicate that GzmA -stimulated pDCs enhance the cross-priming activity of cDCs in situ. We also showed that the adjuvant effect of GzmA is superior to CpG-ODN and LPS. Our findings highlight the ability of GzmA to bridge innate and adaptive immune responses via pDC help and suggest that GzmA may be useful as a vaccine adjuvant.
Highlights
Among the many attempts to develop new and improved vaccine strategies for infectious and cancer, a major obstacle is the lack of appropriate adjuvants that can safely drive potent cellular immunity [1]
After sorting, we found that Granzyme A (GzmA)-stimulated plasmacytoid dendritic cells (DCs) (pDCs) produced IFNα (Figure 1E), but little IFN-β (IFN-α 466.1 ± 107.2 pg/ml vs. IFN-β 44.1 ± 28.7 pg/ml)
When we evaluated IFN-α production by comparing GzmA with CpG-ODN, CpG-ODN-stimulated pDCs produced more IFN-α than GzmA-stimulated cells in vitro (Figure 1E)
Summary
Among the many attempts to develop new and improved vaccine strategies for infectious and cancer, a major obstacle is the lack of appropriate adjuvants that can safely drive potent cellular immunity [1]. The classical adjuvants, aluminum salts (alum) and incomplete Freund’s adjuvant (IFA), which are used clinically, promote humoral immunity and T helper type 2 (Th2) cell responses, but their ability to efficiently drive T helper 1 (Th1) responses and CTLs is limited [2]. In evaluating the activity of adjuvants, especially for the induction of T cell immunity, it is extremely useful to assess the in situ maturation of cDCs by adjuvants using several criteria [10,11,12]; [1] high expression of MHC class I and II, [2] up-regulation of costimulatory molecules, including CD80 and CD86 and [3] production of inflammatory cytokines such as IL-12, or chemokines [13,14,15,16]. In evaluating the activity of adjuvants, especially for the induction of T cell immunity, it is extremely useful to assess the in situ maturation of cDCs by adjuvants using several criteria [10,11,12]; [1] high expression of MHC class I and II, [2] up-regulation of costimulatory molecules, including CD80 and CD86 and [3] production of inflammatory cytokines such as IL-12, or chemokines [13,14,15,16]. [4] Another important factor is crosspresentation by DCs, i.e., whether T cell immunity in vivo occurs after co-administration of antigen plus adjuvant [17,18,19]
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