ABSTRACT
Antibodies to cell-surface antigens trigger activatory Fcγ receptor (FcγR)-mediated retrograde signals in leukocytes to control immune effector functions. Here, we uncover an FcγR mechanism that drives antibody-dependent forward signaling in target cells. Agonistic antibodies to death receptor 5 (DR5) induce cancer-cell apoptosis and are in clinical trials; however, their mechanism of action in vivo is not fully defined. Interaction of the DR5-agonistic antibody drozitumab with leukocyte FcγRs promoted DR5-mediated tumor-cell apoptosis. Whereas the anti-CD20 antibody rituximab required activatory FcγRs for tumoricidal function, drozitumab was effective in the context of either activatory or inhibitory FcγRs. A CD40-agonistic antibody required similar FcγR interactions to stimulate nuclear factor-κB activity in B cells. Thus, FcγRs can drive antibody-mediated receptor signaling in target cells.
Subject(s)
Antibodies, Monoclonal/metabolism , Neoplasms/metabolism , Receptors, IgG/metabolism , Receptors, TNF-Related Apoptosis-Inducing Ligand/metabolism , Signal Transduction/immunology , Animals , Antibodies, Monoclonal/genetics , Antibodies, Monoclonal/immunology , Antibodies, Monoclonal/pharmacology , Antibodies, Monoclonal/therapeutic use , Antibodies, Monoclonal, Humanized , Apoptosis/immunology , B-Lymphocytes/drug effects , B-Lymphocytes/metabolism , CD40 Antigens/agonists , CD40 Antigens/immunology , Cell Line, Tumor , Female , HCT116 Cells , Humans , Immunoglobulin Fc Fragments/genetics , Immunoglobulin G/genetics , Immunoglobulin G/immunology , Immunoglobulin G/pharmacology , Killer Cells, Natural/immunology , Leukocytes/immunology , Leukocytes/metabolism , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Mice, Knockout , Mutation/genetics , Mutation/immunology , Myeloid Cells/immunology , NF-kappa B/metabolism , Neoplasms/drug therapy , Neoplasms/pathology , Polymorphism, Single Nucleotide/genetics , Polymorphism, Single Nucleotide/immunology , Protein Binding/genetics , Protein Binding/immunology , Receptor Aggregation/immunology , Receptors, IgG/genetics , Receptors, TNF-Related Apoptosis-Inducing Ligand/agonists , Receptors, TNF-Related Apoptosis-Inducing Ligand/immunology , Xenograft Model Antitumor AssaysABSTRACT
Clinical response to the anti-CD20 antibody rituximab has been demonstrated to correlate with the polymorphism in the FcγRIIIa receptor where patients homozygous for the higher affinity V158 allotype showed a better response rate. This finding suggests that engineering of anti-CD20 for increased FcγRIIIa affinity could result in improved clinical outcome. To identify variants with increased affinity to FcγRIIIa, we developed quantitative assays using soluble receptors as well as engineered cell lines expressing FcγRI or FcγRIIIa on the cell surface. We assayed a set of anti-CD20 IgG(1) variants that had identical Fab regions, but alterations in the Fc regions, in both the soluble receptor-based and cell-based FcγRIIIa binding assays. We obtained similar relative binding affinity increases and assay precisions. The increase in affinity for FcγRIIIa correlated with the increase in activity in the antibody-dependent cellular cytotoxicity assay. These variants had unaltered FcγRI binding. In addition to Fcγ receptors, IgG also binds to FcRn, the receptor responsible for the long circulating half-life of IgG. The mutations in the anti-CD20 variants were previously found not to affect FcRn binding in the soluble receptor-based assays; consequently, we used anti-Her2 variants with different binding affinities to FcRn to study FcRn binding assays. We generated a cell line expressing FcRn on the cell surface to measure IgG binding and obtained similar ranking of these anti-Her2 variants in the cell-based and the soluble receptor-based FcRn binding assays. In conclusion, both the soluble receptor-based and cell-based binding assays can be used to identify IgG(1) variants with increased affinity to FcγRIIIa and unaltered affinity to FcγRI and FcRn.
