The simultaneous isolation of multiple high and low frequent T-cell populations from donor peripheral blood mononuclear cells using the major histocompatibility complex I-Streptamer isolation technology.

BACKGROUND: Adoptive transfer of donor-derived T cells can be applied to improve immune reconstitution in immune-compromised patients after allogeneic stem cell transplantation. The separation of beneficial T cells from potentially harmful T cells can be achieved by using the major histocompatibility complex (MHC) I-Streptamer isolation technology, which has proven its feasibility for the fast and pure isolation of T-cell populations with a single specificity. We have analyzed the feasibility of the simultaneous isolation of multiple antigen-specific T-cell populations in one procedure by combining different MHC I-Streptamers. METHODS: First, the effect of combining different amounts of MHC I-Streptamers used in the isolation procedure on the isolation efficacy of target antigen-specific T cells and on the number of off-target co-isolated contaminating cells was assessed. The feasibility of this approach was demonstrated in large-scale validation procedures targeting both high and low frequent T-cell populations using the Good Manufacturing Practice (GMP)-compliant CliniMACS Plus device. RESULTS: T-cell products targeting up to 24 different T-cell populations could be isolated in one, simultaneous MHC I-Streptamer procedure, by adjusting the amount of MHC I- Streptamers per target antigen-specific T-cell population. Concurrently, the co-isolation of potentially harmful contaminating T cells remained below our safety limit. This technology allows the reproducible isolation of high and low frequent T-cell populations. However, the expected therapeutic relevance of direct clinical application without in vitro expansion of these low frequent T-cell populations is questionable. DISCUSSION: This study provides a feasible, fast and safe method for the generation of highly personalized MHC I-Streptamer isolated T-cell products for adoptive immunotherapy.

A Good Manufacturing Practice procedure to engineer donor virus-specific T cells into potent anti-leukemic effector cells.

A sequential, two-step procedure in which T-cell-depleted allogeneic stem cell transplantation is followed by treatment with donor lymphocyte infusion at 6 months can significantly reduce the risk and severity of graft-versus-host disease, with postponed induction of the beneficial graft-versus-leukemia effect. However, patients with high-risk leukemia have a substantial risk of relapse early after transplantation, at a time when administration of donor lymphocytes has a high likelihood of resulting in graft-versus-host disease, disturbing a favorable balance between the graft-versus-leukemia effect and graft-versus-host disease. New therapeutic modalities are, therefore, required to allow early administration of T cells capable of exerting a graft-versus-leukemia effect without causing graft-versus-host disease. Here we describe the isolation of virus-specific T cells using Streptamer-based isolation technology and subsequent transfer of the minor histocompatibility antigen HA-1-specific T-cell receptor using retroviral vectors. Isolation of virus-specific T cells and subsequent transduction with HA-1-T-cell receptor resulted in rapid in vitro generation of highly pure, dual-specific T cells with potent anti-leukemic reactivity. Due to the short production procedure of only 10-14 days and the defined specificity of the T cells, administration of virus-specific T cells transduced with the HA-1-T-cell receptor as early as 8 weeks after allogeneic stem cell transplantation is feasible. (This clinical trial is registered at www.clinicaltrialsregister.eu as EudraCT number 2010-024625-20).

Combined CD8+ and CD4+ adenovirus hexon-specific T cells associated with viral clearance after stem cell transplantation as treatment for adenovirus infection.

BACKGROUND: Human adenovirus can cause morbidity and mortality in immunocompromised patients after allogeneic stem cell transplantation. Reconstitution of adenovirus-specific CD4(+) T cells has been reported to be associated with sustained protection from adenovirus disease, but epitope specificity of these responses has not been characterized. Since mainly CD4(+) T cells and no CD8(+) T cells specific for adenovirus have been detected after allogeneic stem cell transplantation, the relative contribution of adenovirus-specific CD4(+) and CD8(+) T cells in protection from adenovirus disease remains to be elucidated. DESIGN AND METHODS: The presence of human adenovirus hexon-specific T cells was investigated in peripheral blood of pediatric and adult allogeneic stem cell transplant recipients, who showed spontaneous resolution of disseminated adenovirus infection. Subsequently, a clinical grade method was developed for rapid generation of adenovirus-specific T-cell lines for adoptive immunotherapy. RESULTS: Clearance of human adenovirus viremia coincided with emergence of a coordinated CD8(+) and CD4(+) T-cell response against adenovirus hexon epitopes in patients after allogeneic stem cell transplantation. Activation of adenovirus hexon-specific CD8(+) and CD4(+) T cells with a hexon protein-spanning peptide pool followed by interferon-γ-based isolation allowed rapid expansion of highly specific T-cell lines from healthy adults, including donors with very low frequencies of adenovirus hexon-specific T cells. Adenovirus-specific T-cell lines recognized multiple MHC class I and II restricted epitopes, including known and novel epitopes, and efficiently lysed human adenovirus-infected target cells. CONCLUSIONS: This study provides a rationale and strategy for the adoptive transfer of donor-derived human adenovirus hexon-specific CD8(+) and CD4(+) T cells for the treatment of disseminated adenovirus infection after allogeneic stem cell transplantation.

Co-ordinated isolation of CD8(+) and CD4(+) T cells recognizing a broad repertoire of cytomegalovirus pp65 and IE1 epitopes for highly specific adoptive immunotherapy.

BACKGROUND AIMS: Adoptive transfer of cytomegalovirus (CMV)-specific memory T cells can be used for treatment of CMV reactivation after allogeneic stem cell transplantation. As co-ordinated CD8(+) and CD4(+) T cells specific for a broad repertoire of CMV epitopes may be most effective for adoptive immunotherapy, the aim of this study was to isolate these cells from peripheral blood of CMV seropositive donors, irrespective of their HLA type. METHODS: Activation of CMV-specific CD8(+) and CD4(+) T cells was compared after stimulation of donor peripheral blood with minimal epitope peptides, pools of overlapping 15-mer peptides or full-length protein. Furthermore, the kinetics of interferon (IFN)-γ production after stimulation was analyzed to determine the optimal time-point for IFN-γ-based isolation of CMV-specific T cells. The specificity, phenotype and functionality of generated T-cell lines were analyzed. RESULTS: CMV protein-spanning 15-mer peptide pools induced simultaneous activation of both CD8(+) and CD4(+) CMV-specific T cells, while full-length CMV protein only efficiently activated CD4(+) CMV-specific T cells. Isolation of IFN-γ-secreting cells at the peak of the IFN-γ response after 4-h stimulation with CMV pp65 and IE1 peptide pools resulted in efficient enrichment of CMV-specific T cells. The T-cell lines contained high frequencies of CD8(+) and CD4(+) T cells recognizing multiple CMV pp65 and IE1 epitopes, and produced IFN-γ and tumor necrosis factor (TNF)-α upon specific restimulation. CONCLUSIONS: This study provides a feasible strategy for the rapid generation of clinical-grade CD8(+) and CD4(+) T-cell lines with high specificity for multiple CMV pp65 and IE1 epitopes, which may be used for effective adoptive immunotherapy.

Generation and infusion of multi-antigen-specific T cells to prevent complications early after T-cell depleted allogeneic stem cell transplantation-a phase I/II study.

Prophylactic infusion of selected donor T cells can be an effective method to restore specific immunity after T-cell-depleted allogeneic stem cell transplantation (TCD-alloSCT). In this phase I/II study, we aimed to reduce the risk of viral complications and disease relapses by administrating donor-derived CD8pos T cells directed against cytomegalovirus (CMV), Epstein-Barr virus (EBV) and adenovirus antigens, tumor-associated antigens (TAA) and minor histocompatibility antigens (MiHA). Twenty-seven of thirty-six screened HLA-A*02:01pos patients and their CMVpos and/or EBVpos donors were included. Using MHC-I-Streptamers, 27 T-cell products were generated containing a median of 5.2 × 106 cells. Twenty-four products were administered without infusion-related complications at a median of 58 days post alloSCT. No patients developed graft-versus-host disease during follow-up. Five patients showed disease progression without coinciding expansion of TAA/MiHA-specific T cells. Eight patients experienced CMV- and/or EBV-reactivations. Four of these reactivations were clinically relevant requiring antiviral treatment, of which two progressed to viral disease. All resolved ultimately. In 2/4 patients with EBV-reactivations and 6/8 patients with CMV-reactivations, viral loads were followed by the expansion of donor-derived virus target-antigen-specific T cells. In conclusion, generation of multi-antigen-specific T-cell products was feasible, infusions were well tolerated and expansion of target-antigen-specific T cells coinciding viral reactivations was illustrated in the majority of patients.

DC-SIGN mediates adhesion and rolling of dendritic cells on primary human umbilical vein endothelial cells through LewisY antigen expressed on ICAM-2.

Immature dendritic cells (DCs) are recruited from blood into tissues to patrol for foreign antigens. After antigen uptake and processing, DCs mature and migrate to the secondary lymphoid organs where they initiate immune responses. DC-SIGN is a DC-specific C-type lectin that acts both as a pattern recognition receptor and as an adhesion molecule. As an adhesion molecule, DC-SIGN is able to mediate rolling and adhesion over endothelial cells under shear flow. In this study, we show that the binding partner of DC-SIGN on endothelial cells is the glycan epitope Lewis(Y) (Le(Y)), expressed on ICAM-2. The interaction between DC-SIGN on dendritic cells and ICAM-2 on endothelial cells is strictly glycan-specific. ICAM-2 expressed on CHO cells only served as a ligand for DC-SIGN when properly glycosylated, underscoring its function as a scaffolding protein. The expression of Le(Y) in endothelial cells is directed by the enzyme FUT1. Silencing of FUT1 results in a decrease in the rolling and adhesion of immature DCs over endothelial cells. The identification of Le(Y) as the carbohydrate ligand of DC-SIGN in endothelial cells opens new possibilities for the manipulation of DC migration.

Schistosoma mansoni soluble egg antigens are internalized by human dendritic cells through multiple C-type lectins and suppress TLR-induced dendritic cell activation.

In schistosomiasis, a parasitic disease caused by helminths, the parasite eggs induce a T helper 2 cell (T(H)2) response in the host. Here, the specific role of human monocyte-derived dendritic cells (DCs) in initiation and polarization of the egg-specific T cell responses was examined. We demonstrate that immature DCs (iDCs) pulsed with schistosome soluble egg antigens (SEA) do not show an increase in expression of co-stimulatory molecules or cytokines, indicating that no conventional maturation was induced. The ability of SEA to affect the Toll-like receptor (TLR) induced maturation of iDCs was examined by copulsing the DCs with SEA and TLR-ligands. SEA suppressed both the maturation of iDCs induced by poly-I:C and LPS, as indicated by a decrease in co-stimulatory molecule expression and production of IL-12, IL-6 and TNF-alpha. In addition, SEA suppressed T(H)1 responses induced by the poly-I:C-pulsed DCs, and skewed the LPS-induced mixed response towards a T(H)2 response. Immature DCs rapidly internalized SEA through the C-type lectins DC-SIGN, MGL and the mannose receptor and the antigens were targeted to MHC class II-positive lysosomal compartments. The internalization of SEA by multiple C-type lectins may be important to regulate the response of the iDCs to TLR-induced signals.

Specificity of DC-SIGN for mannose- and fucose-containing glycans.

The dendritic cell specific C-type lectin dendritic cell specific ICAM-3 grabbing non-integrin (DC-SIGN) binds to "self" glycan ligands found on human cells and to "foreign" glycans of bacterial or parasitic pathogens. Here, we investigated the binding properties of DC-SIGN to a large array of potential ligands in a glycan array format. Our data indicate that DC-SIGN binds with K(d)<2muM to a neoglycoconjugate in which Galbeta1-4(Fucalpha1-3)GlcNAc (Le(x)) trisaccharides are expressed multivalently. A lower selective binding was observed to oligomannose-type N-glycans, diantennary N-glycans expressing Le(x) and GalNAcbeta1-4(Fucalpha1-3)GlcNAc (LacdiNAc-fucose), whereas no binding was observed to N-glycans expressing core-fucose linked either alpha1-6 or alpha1-3 to the Asn-linked GlcNAc of N-glycans. These results demonstrate that DC-SIGN is selective in its recognition of specific types of fucosylated glycans and subsets of oligomannose- and complex-type N-glycans.

Differential regulation of C-type lectin expression on tolerogenic dendritic cell subsets.

Antigen presenting cells (APC) express high levels of C-type lectins, which play a major role in cellular interactions as well as pathogen recognition and antigen presentation. The C-type lectin macrophage galactose-type lectin (MGL), expressed by dendritic cells (DC) and macrophages, mediates binding to glycoproteins and lipids that contain terminal GalNAc moieties. To investigate MGL expression patterns in more detail, we generated two new monoclonal antibodies and set up a quantitative real-time PCR analysis to determine MGL mRNA levels. MGL is not expressed by blood-resident plasmacytoid DC and thus represents an exclusive marker for myeloid-type APC. Dexamethasone treatment upregulated MGL expression on DC both at the protein and mRNA level in a time- and dose-dependent manner. In contrast, DC generated in the presence of IL-10 did not display enhanced MGL levels. Furthermore, dexamethasone and IL-10 also differentially regulated expression of other C-type lectins, such as DC-SIGN and Mannose Receptor. Our results demonstrate that depending on the local microenvironment, DC can adopt different C-type lectin profiles, which could have major influences on cell-cell interactions, antigen uptake and presentation.

Efficiency and mechanism of antigen-specific CD8+ T-cell activation using synthetic long peptides.

Synthetic long peptides that contain immunogenic T-cell epitopes have been used to induce activation of antigen-specific CD8 T cells in vitro for immune monitoring or adoptive transfer, or in vivo after peptide vaccination. However, the efficiency and mechanisms of presentation of exogenous long peptides in human leukocyte antigen (HLA) class I remain to be elucidated. In this study, we demonstrated that the efficiency of antigen-specific CD8 T-cell activation using extended peptide variants of common viral epitopes is variable. We demonstrated that processing and HLA class I presentation of the long peptides were not dependent on the proteasome and transporter associated with antigen processing, illustrating that the classic route of HLA class I presentation was not required for activation of specific CD8 T cells by exogenous synthetic long peptides. Although long peptides were shown to bind to the relevant HLA class I molecules, peptide trimming was likely to be essential for optimal HLA class I presentation and T-cell activation. As the proteasome was not required for processing of exogenous peptides, it is very likely that peptide trimming was mediated by peptidases, which may be located extracellularly at the cell surface, in the cytosol, endoplasmic reticulum, or in endosomal and lysosomal compartments. Furthermore, the results suggested that processing of the correct minimal peptides was facilitated by binding in HLA class I molecules. This mechanism of HLA-guided processing may be important in HLA class I presentation of exogenous long peptides to induce activation of specific CD8 T cells.

Effective treatment of refractory CMV reactivation after allogeneic stem cell transplantation with in vitro-generated CMV pp65-specific CD8+ T-cell lines.

To treat patients with refractory cytomegalovirus (CMV) reactivation after allogeneic stem cell transplantation, a phase I/II clinical study on adoptive transfer of in vitro-generated donor-derived or patient-derived CMV pp65-specific CD8* T-cell lines was performed. Peripheral blood mononuclear cells from CMV seropositive donors or patients were stimulated with HLA-A*0201-restricted and/or HLA-B*0702-restricted CMV pp65 peptides (NLV/TPR) and 1 day after stimulation interferon-γ)-producing cells were enriched using the CliniMACS Cytokine Capture System (interferon-γ), and cultured with autologous feeders and low-dose interluekin-2. After 7-14 days of culture, quality controls were performed and the CMV-specific T-cell lines were administered or cryopreserved. The T-cell lines generated contained 0.6-17 × 10(6) cells, comprising 54%-96% CMV pp65-specific CD8 T cells, and showed CMV-specific lysis of target cells. Fifteen CMV-specific T-cell lines were generated of which 8 were administered to patients with refractory CMV reactivation. After administration, no acute adverse events and no graft versus host disease were observed and CMV load disappeared. In several patients, a direct relation between administration of the T-cell line and the in vivo appearance of CMV pp65-specific T cells could be documented. In conclusion, administration of CMV pp65-specific CD8* T-cell lines was found to be feasible and safe, and enduring efficacy of administered CMV pp65-specific CD8* T-cell lines could be demonstrated.

Simultaneous isolation of CD8(+) and CD4(+) T cells specific for multiple viruses for broad antiviral immune reconstitution after allogeneic stem cell transplantation.

Opportunistic viral infections can cause serious morbidity and mortality in immunocompromised patients after allogeneic stem cell transplantation. Clinical studies have shown that adoptive transfer of donor-derived T cells specific for cytomegalovirus (CMV), Epstein-Barr virus (EBV), or human adenovirus (HAdV) can be a safe and effective treatment of infections with these major viral pathogens. The aim of this study was to develop a method for the simultaneous isolation of coordinated CD8(+) and CD4(+) memory T-cell responses against a broad repertoire of viral epitopes. To ensure that the method was applicable to a wide variety of virus-specific T cells that may differ in phenotypic and functional properties, we focused on T cells specific for the persistent viruses, CMV and EBV, and T cells specific for HAdV and influenza (FLU), which are not repetitively activated in vivo after initial viral clearance. Following in vitro activation, nearly all T cells specific for these viruses produced interferon γ (IFN-γ) and tumor necrosis factor α, and expressed CD137, whereas the populations varied in the production of interleukin-2, degranulation, and expression of phenotypic markers. Different kinetics of IFN-γ production were observed in CMV/EBV-specific T cells and HAdV/FLU-specific T cells. However, after the stimulation of peripheral blood from seropositive donors with viral protein-spanning peptide pools, the activated virus-specific CD8(+) and CD4(+) T cells could be simultaneously isolated by either IFN-γ-based or CD137-based enrichment. This study provides an efficient and widely applicable strategy for the isolation of virus-specific T cells, which may be used for the reconstitution of virus-specific immunity in allogeneic stem cell transplantation recipients.

DC-SIGN mediates binding of dendritic cells to authentic pseudo-LewisY glycolipids of Schistosoma mansoni cercariae, the first parasite-specific ligand of DC-SIGN.

During schistosomiasis, parasite-derived glycoconjugates play a key role in manipulation of the host immune response, associated with persistence of the parasite. Among the candidate host receptors that are triggered by glycoconjugates are C-type lectins (CLRs) on dendritic cells (DCs), which in concerted action with Toll-like receptors determine the balance in DCs between induction of immunity versus tolerance. Here we report that the CLR DC-SIGN mediates adhesion of DCs to authentic glycolipids derived from Schistosoma mansoni cercariae and their excretory/secretory products. Structural characterization of the glycolipids, in combination with solid phase and cellular binding studies revealed that DC-SIGN binds to the carbohydrate moieties of both glycosphingolipid species with Galbeta1-4(Fucalpha1-3)GlcNAc (Lewis(X)) and Fucalpha1-3Galbeta1-4(Fucalpha1-3)GlcNAc (pseudo-Lewis(Y)) determinants. Importantly, these data indicate that surveying DCs in the skin may encounter schistosome-derived glycolipids immediately after infection. Recent analysis of crystals of the carbohydrate binding domain of DC-SIGN bound to Lewis(X) provided insight into the ability of DC-SIGN to bind fucosylated ligands. Using molecular modeling we showed that the observed binding of the schistosome-specific pseudo-Lewis(Y) to DC-SIGN is not directly compatible with the model described. To fit pseudo-Lewis(Y) into the model, the orientation of the side chain of Phe(313) in the secondary binding site of DC-SIGN was slightly changed, which results in a perfect stacking of Phe(313) with the hydrophobic side of the galactose-linked fucose of pseudo-Lewis(Y). We propose that pathogens such as S. mansoni may use the observed flexibility in the secondary binding site of DC-SIGN to target DCs, which may contribute to immune escape.

Carbohydrate profiling reveals a distinctive role for the C-type lectin MGL in the recognition of helminth parasites and tumor antigens by dendritic cells.

Dendritic cells (DCs) are key to the maintenance of peripheral tolerance to self-antigens and the orchestration of an immune reaction to foreign antigens. C-type lectins, expressed by DCs, recognize carbohydrate moieties on antigens that can be internalized for processing and presentation. Little is known about the exact glycan structures on self-antigens and pathogens that are specifically recognized by the different C-type lectins and how this interaction influences DC function. We have analyzed the carbohydrate specificity of the human C-type lectin macrophage galactose-type lectin (MGL) using glycan microarray profiling and identified an exclusive specificity for terminal alpha- and beta-linked GalNAc residues that naturally occur as parts of glycoproteins or glycosphingolipids. Specific glycan structures containing terminal GalNAc moieties, expressed by the human helminth parasite Schistosoma mansoni as well as tumor antigens and a subset of gangliosides, were identified as ligands for MGL. Our results indicate an endogenous function for DC-expressed MGL in the clearance and tolerance to self-gangliosides, and in the pattern recognition of tumor antigens and foreign glycoproteins derived from helminth parasites.

Role of the N-terminus of epidermal growth factor in ErbB-2/ErbB-3 binding studied by phage display.

Epidermal growth factor (EGF) binds with high affinity to the EGF receptor, also known as ErbB-1, but upon replacement of the N-terminal linear region by neuregulin (NRG) 1 or transforming growth factor (TGF) alpha sequences it gains in addition high affinity for ErbB-2/ErbB-3 heterodimers. However, these chimeras weakly bind to ErbB-3 alone. To further dissect the ligand binding selectivity of the ErbB network, we have applied the phage display technique to examine the role of the linear N-terminal region in EGF for interaction with ErbB-2/ErbB-3 heterodimers. A library of EGF variants was constructed in which residues 2, 3, and 4 were randomly mutated, followed by selection for binding to intact MDA-MB-453 cells that overexpress ErbB-2 and ErbB-3 but lack ErbB-1. Analysis of the selected phage EGF variants revealed clones with high binding affinity to ErbB-2/ErbB-3 while maintaining high affinity to ErbB-1. In these variants, Trp (or alternatively His) was almost exclusively present at position 2, while specific combinations of hydrophobic, basic, and small residues were found at positions 3 and 4. The mitogenic activity of the phage EGF variants corresponded with their relative binding affinity. Two of the selected EGF variants, EGF/WVS and EGF/WRS, were further characterized as recombinant proteins. In contrast to previously characterized chimeras of EGF with NRG-1 or TGF-alpha, these variants did not only show high binding affinity for ErbB-2/ErbB-3 heterodimers but also for ErbB-3 alone. These data show that the linear N-terminal region of EGF-like growth factors is directly involved in binding to ErbB-3.

Molecular basis of the differences in binding properties of the highly related C-type lectins DC-SIGN and L-SIGN to Lewis X trisaccharide and Schistosoma mansoni egg antigens.

The dendritic cell-specific C-type lectin DC-SIGN functions as a pathogen receptor that recognizes Schistosoma mansoni egg antigens through its major glycan epitope Galbeta1,4(Fucalpha1,3)GlcNAc (Lex). Here we report that L-SIGN, a highly related homologue of DC-SIGN found on liver sinusoidal endothelial cells, binds to S. mansoni egg antigens but not to the Lex epitope. L-SIGN does bind the Lewis antigens Lea, Leb, and Ley, similar as DC-SIGN. A specific mutation in the carbohydrate recognition domain of DC-SIGN (V351G) abrogates binding to all Lewis antigens. In L-SIGN Ser363 is present at the corresponding position of Val351 in DC-SIGN. Replacement of this Ser into Val resulted in a "gain of function" L-SIGN mutant that binds to Lex, and shows increased binding to the other Lewis antigens. These data indicate that Val351 is important for the fucose specificity of DC-SIGN. Molecular modeling and docking of the different Lewis antigens in the carbohydrate recognition domains of L-SIGN, DC-SIGN, and their mutant forms, demonstrate that Val351 in DC-SIGN creates a hydrophobic pocket that strongly interacts with the Fucalpha1,3/4-GlcNAc moiety of the Lewis antigens. The equivalent amino acid residue Ser363 in L-SIGN creates a hydrophilic pocket that prevents interaction with Fucalpha1,3-GlcNAc in Lex but supports interactions with the Fucalpha1,4-GlcNAc moiety in Lea and Leb antigens. These data demonstrate for the first time that DC-SIGN and L-SIGN differ in their carbohydrate binding profiles and will contribute to our understanding of the functional roles of these C-type lectin receptors, both in recognition of pathogen and self-glycan antigens.

The dendritic cell-specific adhesion receptor DC-SIGN internalizes antigen for presentation to T cells.

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.