Anti-FCGR2A monoclonal antibody, clone AT10 [Biotin]

Introduction: The Fc gamma RIIa receptor is responsible for the clearance of large immune complexes and recently has been proved to be a C-reactive protein (CRP) receptor as well. A polymorphism in the corresponding FCG2RA gene resulting in an amino acid change (R131H) has been implicated, with conflicting results in the pathogenesis of various autoimmune or inflammatory disorders (e. g., atherosclerosis and coronary artery disease [CAD]). Methods: We recently developed a real-time polymerase chain reaction and melting curve analysis method for the genotyping of the above polymorphism. We further looked at its validity with bioinformatics study and DNA sequencing. Then we genotyped 134 CAD patients and 45 angiographically normal controls and determined serum high-sensitivity CRP by nephelometry (Dade-Behring). Also, we used apparently healthy platelet donors (n = 206) as a larger control group. Results: Our method is accurate and devoid of problems with homologs and copy number variants. The need for reference materials is stressed. There were statistically significant differences (p < 0.05) between the CAD patients and each of the two other control groups, with the percentage of RR genotype rising from 6.5% and 11% in the control groups to an average of 19% in all CAD patients (17%, 24%, and 18.5% in stable angina, unstable angina, and myocardial infarction, respectively). In a logistic regression model that included known risk factors for CAD including CRP, the RR genotype remained a significant predictor for CAD (odds ratio: 6.3 [1.1-36.3]). Also after linear regression analysis, CRP levels were reduced in the RR carriers (vs. HH + HR), controlling for age, sex, and disease (marginal p = 0.07). Conclusions: With our accurate genotyping method, the RR genotype was correlated with atherothrombotic CAD events. The inverse correlation found between CRP levels and genotype supports the in vitro data of RR cells binding CRP stronger than HH.

Engaging inhibitory FcRIIb by Fc region has been recently reported to be an attractive approach for improving the efficacy of antibody therapeutics. However, the previously reported S267E/L328F variant with enhanced binding affinity to FcRIIb, also enhances binding affinity to FcRIIa(R131) allotype to a similar degree because FcRIIb and FcRIIa(R131) are structurally similar. In this study, we applied comprehensive mutagenesis and structure-guided design based on the crystal structure of the Fc/FcRIIb complex to identify a novel Fc variant with selectively enhanced FcRIIb binding over both FcRIIa(R131) and FcRIIa(H131). This novel variant has more than 200-fold stronger binding affinity to FcRIIb than wild-type IgG1, while binding affinity to FcRIIa(R131) and FcRIIa(H131) is comparable with or lower than wild-type IgG1. This selectivity was achieved by conformational change of the C(H)2 domain by mutating Pro to Asp at position 238. Fc variant with increased binding to both FcRIIb and FcRIIa induced platelet aggregation and activation in an immune complex form in vitro while our novel variant did not. When applied to agonistic anti-CD137 IgG1 antibody, our variant greatly enhanced the agonistic activity. Thus, the selective enhancement of FcRIIb binding achieved by our Fc variant provides a novel tool for improving the efficacy of antibody therapeutics.