Rituximab (MabThera, Rituxan) is a chimeric IgG1 monoclonal antibody that specifically targets the CD20 surface antigen expressed on normal and neoplastic B-lymphoid cells. Rituximab is currently ...used in the treatment of both follicular and aggressive B-cell non-Hodgkin lymphomas. Despite its demonstrated clinical effectiveness, its in vivo mechanisms of action remain unknown and could differ by subtype of lymphoma. Rituximab has been shown to induce apoptosis, complement-mediated lysis, and antibody-dependent cellular cytotoxicity in vitro, and some evidence points toward an involvement of these mechanisms in vivo. Rituximab also has a delayed therapeutic effect as well as a potential “vaccinal” effect. Here, we review the current understanding of the mechanism of action of rituximab and discuss approaches that could increase its clinical activity. A better understanding of how rituximab acts in vivo should make it possible to develop new and more effective therapeutic strategies. (Blood. 2004;104:2635-2642)
Monoclonal antibodies are biopharmaceuticals with a very long half-life due to the binding of their Fc portion to the neonatal receptor (FcRn), a pharmacokinetic property that can be further improved ...through engineering of the Fc portion, as demonstrated by the approval of several new drugs. Many Fc variants with increased binding to FcRn have been found using different methods, such as structure-guided design, random mutagenesis, or a combination of both, and are described in the literature as well as in patents. Our hypothesis is that this material could be subjected to a machine learning approach in order to generate new variants with similar properties. We therefore compiled 1323 Fc variants affecting the affinity for FcRn, which were disclosed in twenty patents. These data were used to train several algorithms, with two different models, in order to predict the affinity for FcRn of new randomly generated Fc variants. To determine which algorithm was the most robust, we first assessed the correlation between measured and predicted affinity in a 10-fold cross-validation test. We then generated variants by in silico random mutagenesis and compared the prediction made by the different algorithms. As a final validation, we produced variants, not described in any patents, and compared the predicted affinity with the experimental binding affinities measured by surface plasmon resonance (SPR). The best mean absolute error (MAE) between predicted and experimental values was obtained with a support vector regressor (SVR) using six features and trained on 1251 examples. With this setting, the error on the log(K
) was less than 0.17. The obtained results show that such an approach could be used to find new variants with better half-life properties that are different from those already extensively used in therapeutic antibody development.
Given that the FcγRIIIa receptor 158V allotype displays a higher affinity for human immunoglobulin G1 and increased antibody-dependent cellular cytotoxicity, the aim of this study was to determine ...the influence of that FCGR3A polymorphism on the therapeutic response to rituximab, an anti-CD20 humanized immunoglobulin G1 increasingly used in the treatment of non-Hodgkin lymphomas. TheFCGR3A-158V/F genotype was determined in 49 patients having received rituximab for a previously untreated follicular non-Hodgkin lymphoma. The clinical response and the disappearance of theBCL2-JH gene rearrangement in both peripheral blood and bone marrow were evaluated at 2 months (M2) and at 1 year (M12). The study population consisted of 20% FCGR3A-158V homozygous patients, 35% FCGR3A-158F homozygous patients, and 45% heterozygous patients (FCGR3A-158F carriers). The objective response rates at M2 and M12 were 100% and 90%, respectively, inFCGR3A-158V homozygous patients compared with 67% (P = .03) and 51% (P = .03), respectively, in FCGR3A-158F carriers. A disappearance of theBCL2-JH gene rearrangement in both peripheral blood and marrow was observed at M12 in 5 of 6 of homozygousFCGR3A-158V patients compared with 5 of 17 ofFCGR3A-158F carriers (P = .03). The homozygous FCGR3A-158V genotype was confirmed to be the single parameter associated with clinical and molecular responses by multivariate analysis. This study showed an association between theFCGR3A genotype and clinical and molecular responses to rituximab. This finding will certainly give rise to new pharmacogenetic approaches to the management of patients with non-Hodgkin lymphomas.
Infliximab, a chimeric monoclonal antibody, has profoundly modified the treatment of several inflammatory diseases, but no satisfactory description of its pharmacokinetics is available. The objective ...of this study is to describe the pharmacokinetics of infliximab and to explore the sources of its interindividual variability. Thirty-three chronic inflammatory bowel disease patients were studied. Infliximab serum concentrations, obtained during therapeutic drug monitoring, were analyzed using a population approach. Influence of sex, weight, age, concomitant immunosuppressive treatment, and development of antibodies toward infliximab (ATI) on pharmacokinetic parameters was investigated. A two-compartment model with first-order distribution and elimination constants allowed a satisfactory description of infliximab serum concentrations. Mean population distribution and elimination half-lives were 4.3 and 18.5 days, respectively. Weight and sex were found to significantly influence volume of distribution of the central compartment, which increased with weight and was higher in men. Clearance was 2.7 times higher, and elimination half-life was 34% lower in the presence of ATI. In two patients, an increase in infliximab dose or a decrease in dosing interval lead to a decrease in infliximab clearance toward its value in patients without ATI. Infliximab pharmacokinetics are similar to those of other monoclonal antibodies, notably with an elimination half-life of approximately 3 weeks. Both body weight and sex were found to influence infliximab pharmacokinetics, and its clearance increased thrice in the presence of ATI.
The FcγRIIA/CD32A is mainly expressed on platelets, myeloid and several endothelial cells. Its affinity is considered insufficient for allowing significant binding of monomeric IgG, while its H131R ...polymorphism (histidine > arginine at position 131) influences affinity for multimeric IgG2. Platelet FcγRIIA has been reported to contribute to IgG-containing immune-complexe clearance. Given our finding that platelet FcγRIIA actually binds monomeric IgG, we investigated the role of platelets and FcγRIIA in IgG antibody elimination. We used pharmacokinetics analysis of infliximab (IgG1) in individuals with controlled Crohn’s disease. The influence of platelet count and FcγRIIA polymorphism was quantified by multivariate linear modelling. The infliximab half-life increased with R allele number (13.2, 14.4 and 15.6 days for HH, HR and RR patients, respectively). It decreased with increasing platelet count in R carriers: from ≈20 days (RR) and ≈17 days (HR) at 150 × 109/L, respectively, to ≈13 days (both HR and RR) at 350 × 109/L. Moreover, a flow cytometry assay showed that infliximab and monomeric IgG1 bound efficiently to platelet FcγRIIA H and R allotypes, whereas panitumumab and IgG2 bound poorly to the latter. We propose that infliximab (and presumably any IgG1 antibody) elimination is partly due to an unappreciated mechanism dependent on binding to platelet FcγRIIA, which is probably tuned by its affinity for IgG2.
Obinutuzumab (OBZ) is a recombinant type II anti-CD20 and immunoglobulin G1 Fc-optimized monoclonal antibody (mAb), recently approved in chronic lymphocytic leukemia (CLL; B-cell CLL) and follicular ...lymphoma (FL). Rituximab (RTX) is frequently considered as its “ancestor” and OBZ clinical development was justified by the importance of FcγRIIIA-mediated mechanisms in RTX clinical activity. However, RTX differs from OBZ in 2 critical independent properties: being a type I anti-CD20 mAb and not being Fc-optimized. Moreover, the use of a different dosing regimen for RTX and OBZ further complicates any interpretation of clinical results. The results obtained for OBZ in CLL provide new arguments for FcγRIIIA-mediated mechanisms when the target antigen is expressed at a low density. Results of OBZ in FL confirm the interest for FcγRIIIA-mediated mechanisms, with some limitations, some of them being possibly due to lack of OBZ-induced complement activation. The situation in diffuse large B-cell lymphoma is deceiving, as the possible gains of activity of OBZ appear to be annihilated by the lack of complement activation. Although RTX was by chance an anti-CD20 mAb with equilibrated pharmacodynamic properties, the reinforcement of some of these properties, which has been done at the expense of complement activation, has conferred an advantage in some B-cell disorders while restricting OBZ indications. The OBZ story nicely demonstrates that the future of naked mAbs is to design agents with optimized and tailored properties, and that this must be done step by step, with a full clinical validation.
Recently, it has been shown that FCGR3A-158 gene polymorphism is associated with biological and possibly clinical response to infliximab in Crohnʼs disease. We further assessed this association in a ...subset of 344 patients from the large and well-defined cohort of 573 patients with Crohnʼs disease from the ACCENT I study. No association could be observed between FCGR3A-158 gene polymorphism and the clinical response to infliximab, which was primarily defined as a decrease of ≥70 points in the Crohnʼs disease activity index or clinical remission (Crohnʼs disease activity index <150). We did, however, confirm a trend towards a greater decrease in C-reactive protein after infliximab in V/V homozygotes as compared with V/F heterozygotes and F/F homozygotes (−79.4, −76.5, and −64.3%, respectively, at week 6; P=0.085; one-tailed P=0.043). This finding has no immediate clinical impact but may enhance the understanding of the complex mechanisms of action of anti-tumor necrosis factor agents in Crohnʼs disease.
For twelve years, the oncology field has been revolutionized by antibodies targeting immune checkpoints. They must be considered as a heterogenous family of immunostimulatory antibodies displaying ...very different mechanisms of action, not only depending on the target or on the cells expressing it, but also on the IgG subclass or IgG variant that has been chosen. To dissect this complex landscape, the clinical experience has been confronted with a precise analysis of the heavy chain isotypes, referred as new Ge nomenclature. For antibodies targeting inhibitory receptors, anti-CTLA-4 antibodies (whose main effect is to kill regulatory T cells) will be distinguished from anti-PD-1 antibodies and other true antagonistic antibodies. Antibodies targeting ligands of inhibitory receptors (PD-L1, CD47) represent another different category, due to the antigen expression on tumors and a possible beneficial killing effect. The case of agonistic antibodies targeting lymphocyte activatory receptors, such as CD40 or 4-1BB, is still another “under construction” category because these products are less advanced in their clinical development. Altogether, it appears that choosing the right heavy chain is crucial to obtain the desired pharmacological effect in patients.
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