FcRn regulates antigen presentation in dendritic cells downstream of DEC205-targeted vaccines.

Dendritic cell (DC)-targeted vaccination is a new mode of antigen delivery that relies on the use of monoclonal antibodies (mAb) to target antigen to specific DC subsets. The neonatal Fc receptor (FcRn) is a non-classical Fc receptor that binds to immunoglobulin G (IgG) in acidified endosomes and controls its intracellular transport and recycling. FcRn is known to participate in the antigen presentation of immune complexes, however its contribution to DC-targeted vaccination has not previously been examined. Here we have investigated the role of FcRn in antigen presentation using antigen conjugated to IgG mAb which target specific DC receptors, including DEC205 and Clec9A expressed by the conventional DC 1 (cDC1) subset. We show that FcRn is expressed at high levels by cDC1, both at steady-state and following activation and plays a significant role in MHC I cross-presentation and MHC II presentation of antigens that are targeted to cDC1 via mAb specific for DEC205. This effect of FcRn is intrinsic to cDC1 and FcRn impacts the efficacy of anti-DEC205-mediated vaccination against B cell lymphoma. In contrast, FcRn does not impact presentation of antigens targeted to Clec9A and does not regulate presentation of cell-associated antigen. These data highlight a new and unique role of FcRn in controlling the immunogenicity of anti-DEC205-based vaccination, with consequences for exploiting this pathway to improve DC-targeted vaccine outcomes.

In vivo assembly of epitope-coated biopolymer particles that induce anti-tumor responses.

There is an unmet need for antigen delivery systems that elicit efficient T cell priming to prevent infectious diseases or for treatment of cancers. Here, we explored the immunogenic potential of biologically assembled biopolymer particles (BPs) that have been bioengineered to display the antigenic MHC I and MHC II epitopes of model antigen ovalbumin (OVA). Purified dendritic cells (DCs) captured BP-OVA and presented the associated antigenic epitopes to CD4+ T cells and CD8+ T cells. Vaccination with BP-OVA in the absence of adjuvant elicited antigen presentation to OVA-specific CD8+ and CD4+ T cells and cross-primed effective cytotoxic T lymphocyte (CTL) killers. BP-OVA induction of CTL killing did not require CD4+ T cell help, with active CTLs generated in BP-OVA vaccinated I-Ab-/- and CD40-/- mice. In contrast, IL-15 and type I IFN were required, with abrogated CTL activity in vaccinated IL-15-/- and IFNAR1-/- mice. cDC1 and/or CD103+ DCs were not essential for BP-OVA specific CTL with immunization eliciting responses in Batf3-/- mice. Poly I:C, but not LPS or CpG, co-administered as an adjuvant with BP-OVA boosted CTL responses. Finally, vaccination with BP-OVA protected against B16-OVA melanoma and Eµ-myc-GFP-OVA lymphoma inoculation. In summary, we have demonstrated that epitope-displaying BPs represent an antigen delivery platform exhibiting a unique mechanism to effectively engage T cell immune responses.

Targeting dendritic cells to advance cross-presentation and vaccination outcomes.

Dendritic cells (DCs) are a complex network of specialised antigen-presenting cells that are critical initiators of adaptive immunity. Targeting antigen directly to DCs in situ is a vaccination strategy that selectively delivers antigen to receptors expressed by DC subtypes. This approach exploits specific DC subset functions of antigen uptake and presentation. Here, we review DC-targeted vaccination strategies that are designed to elicit effective cross-presentation for CD8+ T cell immunity. In particular, we focus on approaches that exploit receptors highly expressed by mouse and human cDCs equipped with superior cross-presentation capacity. These receptors include DEC205, Clec9A and XCR1. Targeting DC receptors Clec12A, Clec4A4 and mannose receptor is also reviewed. Outcomes of DC-targeted vaccination in mouse models through to human clinical trials is discussed. This is a promising new vaccination approach capable of directly targeting the cross-presentation pathway for prevention and treatment of tumours and infectious diseases.

MHC Class II Ubiquitination Regulates Dendritic Cell Function and Immunity.

MHC class II (MHC II) Ag presentation by dendritic cells (DCs) is critical for CD4+ T cell immunity. Cell surface levels of MHC II loaded with peptide is controlled by ubiquitination. In this study, we have examined how MHC II ubiquitination impacts immunity using MHC IIKRKI/KI mice expressing mutant MHC II molecules that are unable to be ubiquitinated. Numbers of conventional DC (cDC) 1, cDC2 and plasmacytoid DCs were significantly reduced in MHC IIKRKI/KI spleen, with the remaining MHC IIKRKI/KI DCs expressing an altered surface phenotype. Whereas Ag uptake, endosomal pH, and cathepsin protease activity were unaltered, MHC IIKRKI/KI cDC1 produced increased inflammatory cytokines and possessed defects in Ag proteolysis. Immunization of MHC IIKRKI/KI mice identified impairments in MHC II and MHC class I presentation of soluble, cell-associated and/or DC-targeted OVA via mAb specific for DC surface receptor Clec9A (anti-Clec9A-OVA mAb). Reduced T cell responses and impaired CTL killing was observed in MHC IIKRKI/KI mice following immunization with cell-associated and anti-Clec9A-OVA. Immunization of MHC IIKRKI/KI mice failed to elicit follicular Th cell responses and generated barely detectable Ab to anti-Clec9A mAb-targeted Ag. In summary, MHC II ubiquitination in DCs impacts the homeostasis, phenotype, cytokine production, and Ag proteolysis by DCs with consequences for Ag presentation and T cell and Ab-mediated immunity.