Whole recombinant yeast vaccine activates dendritic cells and elicits protective cell-mediated immunity

137

119

Cryptococcosis is a leading cause of death among individuals with compromised T cell function. Soluble Cryptococcus neoformans mannoproteins (MP) have emerged as promising vaccine candidates due to their capacity to elicit delayed-type hypersensitivity and Th type 1-like cytokines, both critical to the clearance of this pathogenic yeast. In this study, the mechanisms responsible for the potent immunostimulatory properties of MP were explored. Using Chinese hamster ovary cells expressing human macrophage mannose receptor (MMR), we determined that MP is a MMR ligand. Functionally, competitive blockade of multilectin mannose receptors (MR) on APCs diminished MP-dependent stimulation of primary T cells from immunized mice and the MP-reactive CD4+ T cell hybridoma, P1D6, by 72 and 99%, respectively. Removal of O-linked saccharides from MP by β-elimination inhibited MP-dependent stimulation of P1D6 and primary T cells by 89 and 90%, respectively. In addition, MP-dependent stimulation of P1D6 was abrogated after digestion with proteinase K, suggesting the protein core of MP contributed the antigenic moiety presented by APC. Stimulation of P1D6 by MP also was abolished using APC obtained from invariant chain-deficient mice, demonstrating Ag presentation was MHC class II restricted. Our data suggest that MP is a ligand for the MMR and that T cell stimulation is functionally inhibited either by competitive blockade of MR or by removal of carbohydrate residues critical for recognition. The demonstration that efficient T cell responses to MP require recognition of terminal mannose groups by MMR provides both a molecular basis for the immunogenicity of cryptococcal MP and support for vaccination strategies that target MR.

Section: Discussionmentioning

confidence: 81%

Optimal T Cell Responses to Cryptococcus neoformans Mannoprotein Are Dependent on Recognition of Conjugated Carbohydrates by Mannose Receptors

Mansour

Schlesinger

Levitz

2002

137

119

“…DCs also possess the unique ability to process particulate Ags efficiently into the MHC class I pathway, referred to as cross-presentation (42). Interestingly, it has been recently reported that whole recombinant yeast can activate DCs, which elicit protective cell-mediated antitumor immunity via CD4 ϩ and CD8 ϩ T lymphocytes (43). DC-SIGN binds yeast-derived mannan with a high affinity, indicating that DC-SIGN could be involved in yeast uptake.…”

Section: C-type Lectins As Ag Receptors On Dcsmentioning

confidence: 99%

The Dendritic Cell-Specific Adhesion Receptor DC-SIGN Internalizes Antigen for Presentation to T Cells

Engering¹,

Geijtenbeek²,

Vliet³

et al. 2002

569

500

Dendritic cells (DCs) capture Ags or viruses in peripheral tissue to transport them to lymphoid organs to induce cellular T cell responses. Recently, a DC-specific C-type lectin was identified, DC-specific ICAM-grabbing non-integrin (DC-SIGN), that functions as cell adhesion receptor mediating both DC migration and T cell activation. DC-SIGN also functions as an HIV-1R that captures HIVgp120 and facilitates DC-induced HIV transmission of T cells. Internalization motifs in the cytoplasmic tail of DC-SIGN hint to a function of DC-SIGN as endocytic receptor. In this study we demonstrate that on DCs DC-SIGN is rapidly internalized upon binding of soluble ligand. Mutating a putative internalization motif in the cytoplasmic tail reduces ligand-induced internalization. Detailed analysis using ratio fluorescence imaging and electron microscopy showed that DC-SIGN-ligand complexes are targeted to late endosomes/lysosomes. Moreover, ligands internalized by DC-SIGN are efficiently processed and presented to CD4+ T cells. The distinct pattern of expression of C-type lectins on DCs in situ and their nonoverlapping Ag recognition profile hint to selective functions of these receptors to allow a DC to recognize a wide variety of Ags and to process these to induce T cell activation. These data point to a novel function of the adhesion receptor DC-SIGN as an efficient DC-specific Ag receptor that can be used as a target to induce viral and antitumor immunity.

“…A recent study showed that yeast cells could act as an efficient vaccine and elicited protective cell-mediated immunity by virtue of their ability to induce DC maturation, IL-12 production, and efficient priming for MHC class I-or II-restricted Ag-specific T cell responses (59). We show in this work that not only the yeasts but yeast RNA could be an efficient trigger of DC maturation, IL-12 production, and induction of protective Ag-specific responses to Candida.…”

Section: Figurementioning

confidence: 99%

Dendritic Cells Pulsed with Fungal RNA Induce Protective Immunity toCandida albicansin Hematopoietic Transplantation

Bacci

Montagnoli

Perruccio

et al. 2002

120

Immature myeloid dendritic cells (DC) phagocytose yeasts and hyphae of the fungus Candida albicans and induce different Th cell responses to the fungus. Ingestion of yeasts activates DC for production of IL-12 and Th1 priming, while ingestion of hyphae induces IL-4 production and Th2 priming. In vivo, generation of antifungal protective immunity is induced upon injection of DC ex vivo pulsed with Candida yeasts but not hyphae. In the present study we sought to determine the functional activity of DC transfected with yeast or hyphal RNA. It was found that DC, from either spleens or bone marrow, transfected with yeast, but not hyphal, RNA 1) express fungal mannoproteins on their surface; 2) undergo functional maturation, as revealed by the up-regulated expression of MHC class II Ags and costimulatory molecules; 3) produce IL-12 but no IL-4; 4) are capable of inducing Th1-dependent antifungal resistance when delivered s.c. in vivo in nontransplanted mice; and 5) provide protection against the fungus in allogeneic bone marrow-transplanted mice, by accelerating the functional recovery of Candida-specific IFN-γ-producing CD4+ donor lymphocytes. These results indicate the efficacy of DC pulsed with Candida yeasts or yeast RNA as fungal vaccines and point to the potential use of RNA-transfected DC as anti-infective vaccines in conditions that negate the use of attenuated microorganisms or in the case of poor availability of protective Ags.