Complexes of peptide and major histocompatibility complex (MHC) class II are expressed on the surface of antigen-presenting cells but their molecular organization is unknown. Here we show that subsets of MHC class II molecules localize to membrane microdomains together with tetraspan proteins, the peptide editor HLA-DM and the costimulator CD86. Tetraspan microdomains differ from other membrane areas such as lipid rafts, as they enrich MHC class II molecules carrying a selected set of peptide antigens. Antigen-presenting cells deficient in tetraspan microdomains have a reduced capacity to activate CD4+ T cells. Thus, the organization of uniformly loaded peptide-MHC class II complexes in tetraspan domains may be a very early event that determines both the composition of the immunological synapse and the quality of the subsequent T helper cell response.

Abbreviations: ADA, anti-drug antibody; ADCC, antibody-dependent cellular cytotoxicity; ADME, absorption, distribution, metabolism and excretion; APC, antigen-presenting cell; AS, ankylosing spondylitis; CAPS, cropyrin-associated periodic syndromes; CD, cluster of differentiation; CDC, complement-dependent cytotoxicity; CDR, complementarity-determining region; CMV, cytomegalovirus; COPD, chronic obstructive pulmonary disease; CRA, cytokine release assay; CrD, Crohn disease; CRS, cytokine release syndrome; CTLA-4, cytotoxic T lymphocyte antigen-4; DAMPs, damage-associated molecular patterns; DC, dendritic cell; DTH, delayed-type hypersensitivity; EBV, Epstein Barr virus; EFD-PPND, embryo-fetal development and peri-/ post-natal development; EMA, European Medicines Agency; EPAR, European Public Assessment Report; EPO, erythropoietin; ESG, Expert Scientific Group; FDA, Food and Drug Administration; FIH, first-in-human; GD, gestation day; GLP, good laboratory practice; HED, human equivalent dose; HHV-8, human herpes virus-8; HLA, human leukocyte antigen; HSA, human serum albumin; HSP, heat shock protein; HTLV-1, human T cell leukemia virus-1; ICH, International Conference on Harmonization; IHC, immunohistochemistry; KLH, keyhole limpet hemocyanin; LCV, lymphocryptovirus; LFA-1, leukocyte function antigen-1; LPS, lipopolysaccharide; mAb, monoclonal antibody; MABEL, minimum anticipated biological effect level; MHC, major histocompatibility comlex; MoA, mechanism of action; MRSD, maximum recommended starting dose; MS, multiple sclerosis; NCE, new chemical entity; NHP, non-human primate; NK, natural killer; NLR, nod-like receptor; NOAEL, no observed adverse effect level; PAD, pharmacologically-active dose; PAMPs, pathogen-associated molecular patterns; PEG-MGDF, pegylated megakaryocyte growth and development factor; PD, pharmacodynamic; PHA, phytohemaglutinin; PK, pharmacokinetic; PML, progressive multifocal leukoencephalopathy; PsA, psoriatic arthritis; RA, rheumatoid arthritis; RMP, risk management plan; RO, receptor occupancy; RSV, respiratory syncytial virus; SBA, summary basis of approval; SLE, systemic lupus erythromatosus; SPC, summary of product characteristics; SRBC, sheep red blood cell; TCR, tissue cross reactivity; TDAR, T cell-dependent antibody response; TLR, toll-like receptor; TT, tetanus toxoid; UC, ulcerative colitis; VLA-4, very late antigen-4Most therapeutic monoclonal antibodies (mAbs) licensed for human use or in clinical development are indicated for treatment of patients with cancer and inflammatory/autoimmune disease and as such, are designed to directly interact with the immune system. A major hurdle for the development and early clinical investigation of many of these immunomodulatory mAbs is their inherent risk for adverse immune-mediated drug reactions in humans such as infusion reactions, cytokine storms, immunosuppression and autoimmunity. A thorough understanding of the immunopharmacology of a mAb in humans and animals is required to both anticipate the clinical risk of adverse immunotoxic...

Subvisible proteinaceous particles which are present in all therapeutic protein formulations are in the focus of intense discussions between health authorities, academics and biopharmaceutical companies in the context of concerns that such particles could promote unwanted immunogenicity via anti-drug antibody formation. In order to provide further understanding of the subject, this study closely examines the specific biological effects proteinaceous particles may exert on dendritic cells (DCs) as the most efficient antigen-presenting cell population crucial for the initiation of the adaptive immune response. Two different model IgG antibodies were subjected to three different types of exaggerated physical stress to generate subvisible particles in far greater concentrations than the ones typical for the currently marketed biotherapeutical antibodies. The aggregated samples were used in in vitro biological assays in order to interrogate the early DC-driven events that initiate CD4 T-cell dependent humoral adaptive immune responses – peptide presentation capacity and co-stimulatory activity of DCs. Most importantly, antigen presentation was addressed with a unique approach called MHC-associated Peptide Proteomics (MAPPs), which allows for identifying the sequences of HLA-DR associated peptides directly from human dendritic cells.The experiments demonstrated that highly aggregated solutions of two model mAbs generated under controlled conditions can induce activation of human monocyte-derived DCs as indicated by upregulation of typical maturation markers including co-stimulatory molecules necessary for CD4 T-cell activation. Additional data suggest that highly aggregated proteins could induce in vitro T-cell responses. Intriguingly, strong aggregation-mediated changes in the pattern and quantity of antigen-derived HLA-DR associated peptides presented on DCs were observed, indicating a change in protein processing and presentation. Increasing the amounts of subvisible proteinaceous particles correlated very well with the pronounced increase in the peptide number and clusters presented in the context of class II HLA-DR molecules, suggesting a major involvement of a mass-action mechanism of altering the presentation.

The chimeric antibodies anti-CD20 rituximab (Rtx) and anti-TNFα infliximab (Ifx) induce antidrug antibodies (ADAs) in many patients with inflammatory diseases. Because of the key role of CD4 T lymphocytes in the initiation of antibody responses, we localized the CD4 T cell epitopes of Rtx and Ifx. With the perspective to anticipate immunogenicity of therapeutic antibodies, identification of the CD4 T cell epitopes was performed using cells collected in healthy donors. Nine T cell epitopes were identified in the variable chains of both antibodies by deriving CD4 T cell lines raised against either Rtx or Ifx. The T cell epitopes often exhibited a good affinity for human leukocyte antigen (HLA)-DR molecules and were part of the peptides identified by MHC-associated peptide proteomics assay from HLA-DR molecules of dendritic cells (DCs) loaded with the antibodies. Two-third of the T cell epitopes identified from the healthy donors stimulated peripheral blood mononuclear cells from patients having developed ADAs against Rtx or Ifx and promoted the secretion of a diversity of cytokines. These data emphasize the predictive value of evaluating the T cell repertoire of healthy donors and the composition of peptides bound to HLA-DR of DCs to anticipate and prevent immunogenicity of therapeutic antibodies.

Protein reorganization at the interface of a T cell and an antigen-presenting cell (APC) plays an important role in T cell activation. Imaging techniques reveal that reorganization of particular receptor-ligand pairs gives rise to an intercellular junction, termed the immunological synapse. In this synapse antigenic peptides associated with major histocompatibility complex (MHC) molecules form multimolecular arrays on the APC side, engaging an equivalent number of clustered T cell receptors (TCRs) on the T cell. The accumulation of MHC molecules carrying cognate peptide in the APC-T cell interface was thought to depend on the specificity and presence of TCRs. Recent evidence, however, suggests that the APC is equipped to preorganize MHC-peptide complexes in the absence of T cells. To this end, MHC molecules become incorporated into two types of membrane microdomains: (i) cholesterol- and glycosphingolipid-enriched domains, denoted lipid rafts, that preconcentrate MHC class II molecules; and (ii) microdomains made up of tetraspan proteins, such as CD9, CD63, CD81 or CD82, that mediate enrichment of MHC class II molecules loaded with a select set of peptides. It follows that the integrity, composition and dynamics of these microdomains are candidate determinants favoring activation or silencing of T cells.