Glycosylation of the immunoglobulin G (IgG)-Fc tail is required for binding to Fc-gamma receptors (FcγRs) and complement-component C1q. A variety of IgG1-glycoforms is detected in human sera. Several groups have found global or antigen-specific skewing of IgG glycosylation, for example in autoimmune diseases, viral infections, and alloimmune reactions. The IgG glycoprofiles seem to correlate with disease outcome. Additionally, IgG-glycan composition contributes significantly to Ig-based therapies, as for example IVIg in autoimmune diseases and therapeutic antibodies for cancer treatment. The effect of the different glycan modifications, especially of fucosylation, has been studied before. However, the contribution of the 20 individual IgG glycoforms, in which the combined effect of all 4 modifications, to the IgG function has never been investigated. Here, we combined six glyco-engineering methods to generate all 20 major human IgG1-glycoforms and screened their functional capacity for FcγR and complement activity. Bisection had no effect on FcγR or C1q-binding, and sialylation had no- or little effect on FcγR binding. We confirmed that hypo-fucosylation of IgG1 increased binding to FcγRIIIa and FcγRIIIb by ~17-fold, but in addition we showed that this effect could be further increased to ~40-fold for FcγRIIIa upon simultaneous hypo-fucosylation and hyper-galactosylation, resulting in enhanced NK cell-mediated antibody-dependent cellular cytotoxicity. Moreover, elevated galactosylation and sialylation significantly increased (independent of fucosylation) C1q-binding, downstream complement deposition, and cytotoxicity. In conclusion, fucosylation and galactosylation are primary mediators of functional changes in IgG for FcγR- and complement-mediated effector functions, respectively, with galactose having an auxiliary role for FcγRIII-mediated functions. This knowledge could be used not only for glycan profiling of clinically important (antigen-specific) IgG but also to optimize therapeutic antibody applications.

Major histocompatibility complex (MHC) class I molecules present peptide ligands on the cell surface for recognition by appropriate cytotoxic T cells. MHC-bound peptides are critical for the stability of the MHC complex, and standard strategies for the production of recombinant MHC complexes are based on in vitro refolding reactions with specific peptides. This strategy is not amenable to high-throughput production of vast collections of MHC molecules. We have developed conditional MHC ligands that form stable complexes with MHC molecules but can be cleaved upon UV irradiation. The resulting empty, peptide-receptive MHC molecules can be charged with epitopes of choice under native conditions. Here we describe in-depth procedures for the high-throughput production of peptide-MHC (pMHC) complexes by MHC exchange, the analysis of peptide exchange efficiency by ELISA and the parallel production of MHC tetramers for T-cell detection. The production of the conditional pMHC complex by an in vitro refolding reaction can be achieved within 2 weeks, and the actual high-throughput MHC peptide exchange and subsequent MHC tetramer formation require less than a day.

Major histocompatibility complex (MHC) class I multimer technology has become an indispensable immunological assay system to dissect antigen-specific cytotoxic CD8 ؉ T cell responses by flow cytometry. However, the development of high-throughput assay systems, in which T cell responses against a multitude of epitopes are analyzed, has been precluded by the fact that for each T cell epitope, a separate in vitro MHC refolding reaction is required. We have recently demonstrated that conditional ligands that disintegrate upon exposure to long-wavelength UV light can be designed for the human MHC molecule HLA-A2. To determine whether this peptide-exchange technology can be developed into a generally applicable approach for high throughput MHC based applications we set out to design conditional ligands for the human MHC gene products HLA-A1, -A3, -A11, and -B7. Here, we describe the development and characterization of conditional ligands for this set of human MHC molecules and apply the peptide-exchange technology to identify melanoma-associated peptides that bind to HLA-A3 with high affinity. The conditional ligand technology developed here will allow high-throughput MHC-based analysis of cytotoxic T cell immunity in the vast majority of Western European individuals.M HC Class I molecules are heterotrimeric complexes consisting of an invariant light chain called ␤2-microglobulin (␤2m), a polymorphic heavy chain (HC) and an Ϸ8-to 11-aa peptide ligand. These peptide-MHC (pMHC) complexes are recognized by the T cell receptor (TCR) of CD8 ϩ T cells in a peptide-specific fashion, and this interaction forms the molecular basis of antigen recognition by CD8 ϩ T cells. In the past decade, the mapping of pathogen-specific and autoimmune-or cancer-associated T cell epitopes has been a major driving force in the development of assay systems for immunomonitoring. In addition, knowledge of such T cell epitopes forms a cornerstone in the development of vaccine-based or adoptive T cell therapies. As a first step in the mapping of disease-associated T cell epitopes, peptide fragments of disease-associated proteomes may be analyzed for binding to MHC molecules of interest, and subsequent assays can then be used to determine whether T cell reactivity against such pMHC complexes does occur. As demonstrated in a landmark study by Altman and colleagues (1), such antigen-specific T cell reactivity can efficiently be detected by the staining of T cell populations with recombinant fluorescent multimeric MHC molecules.There is an increasing interest in the development of assay systems, such as MHC-based microarrays, that can monitor a multitude of T cell responses in parallel (2-4). Unfortunately, current technology does not allow for the high-throughput generation of different pMHC complexes, thereby limiting the utility of these techniques. Specifically, because MHC class I complexes that are devoid of peptide are markedly unstable (5, 6), current production processes for recombinant MHC complexes require inclusion of a specific T cell epi...

Objective To understand the regulation of anti–citrulline‐containing peptide antibody (anti‐CCP) production in rheumatoid arthritis (RA), production of anti‐CCP by B cells derived from peripheral blood (PB), bone marrow (BM), and synovial fluid (SF) was examined. Methods Purified PB and SF B cells were isolated by negative selection and then cultured in the absence or presence of L–CD40 ligand cells and interleukin‐10 or anti‐CD3–activated T cells. Total IgM and IgM–anti‐CCP were detected after 14 days of culture by enzyme‐linked immunosorbent assay. Enzyme‐linked immunospot assays were performed to analyze the frequency of cells that spontaneously produced IgM–anti‐CCP in BM and SF B cells. Results IgM–anti‐CCP autoantibodies were induced in PB B cells from healthy controls and RA patients following coculture with activated T cells or application of the CD40 activation system, whereas no production could be detected when PB B cells were cultured in the absence of a stimulus. SF and BM B cells from anti‐CCP–seropositive RA patients, but not anti‐CCP–seronegative patients, actively produced IgM–anti‐CCP without stimulation. The frequency of spontaneous production of IgM–anti‐CCP among the IgM‐secreting cells ranged from 2.2% to 25%. Conclusion These results indicate the presence of B cell precursors for anti‐CCP autoantibodies that are able to produce antibodies upon stimulation in the PB B cell repertoire of healthy controls and patients with RA. In contrast, B cells that actively secreted anti‐CCP were specifically present in the BM and SF compartment of anti‐CCP–seropositive RA patients. The local presence of anti‐CCP–secreting cells in the inflamed joints provides evidence for an antigen‐driven maturation of CCP‐specific B cells at the site of inflammation in RA.

Virus-specific CD8 T cell response seems to play a significant role in the outcome of hepatitis delta virus (HDV) infection. However, the HDV-specific T cell epitope repertoire and mechanisms of CD8 T cell failure in HDV infection have been poorly characterized. We therefore aimed to characterize HDV-specific CD8 T cell epitopes and the impacts of viral mutations on immune escape. In this study, we predicted peptide epitopes binding the most frequent human leukocyte antigen (HLA) types and assessed their HLA binding capacities. These epitopes were characterized in HDV-infected patients by intracellular gamma interferon (IFN-γ) staining. Sequence analysis of large hepatitis delta antigen (L-HDAg) and HLA typing were performed in 104 patients. The impacts of substitutions within epitopes on the CD8 T cell response were evaluated experimentally and by studies. We identified two HLA-B*27-restricted CD8 T cell epitopes within L-HDAg. These novel epitopes are located in a relatively conserved region of L-HDAg. However, we detected molecular footprints within the epitopes in HLA-B*27-positive patients with chronic HDV infections. The variant peptides were not cross-recognized in HLA-B*27-positive patients with resolved HDV infections, indicating that the substitutions represent viral escape mutations. Molecular modeling of HLA-B*27 complexes with the L-HDAg epitope and its potential viral escape mutations indicated that the structural and electrostatic properties of the bound peptides differ considerably at the T cell receptor interface, which provides a possible molecular explanation for the escape mechanism. This viral escape from the HLA-B*27-restricted CD8 T cell response correlates with a chronic outcome of hepatitis D infection. T cell failure resulting from immune escape may contribute to the high chronicity rate in HDV infection. Hepatitis delta virus (HDV) causes severe chronic hepatitis, which affects 20 million people worldwide. Only a small number of patients are able to clear the virus, possibly mediated by a virus-specific T cell response. Here, we performed a systematic screen to define CD8 epitopes and investigated the role of CD8 T cells in the outcome of hepatitis delta and how they fail to eliminate HDV. Overall the number of epitopes identified was very low compared to other hepatotropic viruses. We identified, two HLA-B*27-restricted epitopes in patients with resolved infections. In HLA-B*27-positive patients with chronic HDV infections, however, we detected escape mutations within these identified epitopes that could lead to viral evasion of immune responses. These findings support evidence showing that HLA-B*27 is important for virus-specific CD8 T cell responses, similar to other viral infections. These results have implications for the clinical prognosis of HDV infection and for vaccine development.