COMPREHENSIVE GENETIC AND FUNCTIONAL ANALYSES OF FC GAMMA RECEPTORS EXPLAIN RESPONSE TO RITUXIMAB THERAPY FOR AUTOIMMUNE RHEUMATIC DISEASES

Abstract Background/Aims Rituximab is widely used to treat rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) but clinical response varies. Efficacy is determined by the efficiency of depletion, which may depend on a variety of Fc gamma receptor (FcγR)-dependent mechanisms. Previous research was limited by complexity of the FCGR locus, not integrating copy number variation with functional SNP, and small sample size. Here, we aimed to assess the effect of the full range of FcγRs variants on depletion, clinical response and functional effect on NK-cell-mediated killing in two rheumatic diseases with a view to personalised B-cell depleting therapies. Methods A prospective longitudinal study was conducted in 873 patients (RA = 611; SLE=262) from four cohorts (BSRBR-RA, BILAG-BR, Leeds RA and Leeds SLE Biologics). For RA, the outcome measures were 3C-DAS28CRP and 2C-DAS28CRP at 6 (+/-3) months post-rituximab (adjusted for baseline DAS28). For SLE, major clinical response (MCR) was defined as improvement of active BILAG-2004 domains to grade C/better at 6 months. B-cell depletion was evaluated by highly-sensitive flow cytometry. Qualitative and quantitative polymorphisms for five major FcγRs were measured using a commercial multiplex ligation-dependent probe amplification. Median NK cell FcγRIIIa expression (CD3-CD56+CD16+) and NK-cell degranulation (CD107a) in the presence of rituximab-coated Daudi/Raji B-cell lines were assessed using flow cytometry. Results In RA, for FCGR3A, carriage of V allele (coefficient -0.25 [SE 0.11]; p = 0.02) and increased copies of V allele (-0.20 [0.09]; p = 0.02) were associated with better 2C-DAS28 response. Irrespective of FCGR3A genotype, increased gene copies were associated with a better response. In SLE, 177/262 (67.6%) achieved BILAG response (MCR=34.4%; Partial=33.2%). MCR was associated with increased copies of FCGR3A-158V allele, OR 1.64 (95% CI 1.12-2.41) and FCGR2C-ORF allele 1.93 (1.09-3.40). Of patients with B-cells data in the combined cohort, 236/413 (57%) achieved complete depletion post-rituximab. Only homozygosity for V allele and higher copies of FCGR3A V allele were associated with increased odds of depletion. Patients with complete depletion had higher NK cell FcγRIIIa expression at rituximab initiation than those with incomplete depletion (p = 0.04) and this higher expression was associated with improved EULAR response in RA. Moreover, for FCGR3A, degranulation activity was increased in V allele carriers vs FF genotype in the combined cohort; p = 0.02. Conclusion FcγRIIIa is the major low affinity FcγR and increased copies of the FCGR3A-158V allele, encoding the allotype with a higher affinity for IgG1, was associated with clinical and biological responses to rituximab in two autoimmune diseases. This was supported by functional data on NK cell-mediated cytotoxicity. In SLE, increased copies of the FCGR2C-ORF allele was also associated with improved response. Our findings indicate that enhancing FcγR-effector functions could improve the next generation of CD20-depleting therapies and genotyping could stratify patients for optimal treatment protocols. Disclosure M. Md Yusof: None. J. Robinson: None. V. Davies: None. D. Wild: None. M. Morgan: None. J. Taylor: None. Y. El-Sherbiny: None. D. Morris: None. L. Liu: None. A. Rawstron: None. M. Buch: None. D. Plant: None. H. Cordell: None. J. Isaacs: None. I. Bruce: None. P. Emery: Grants/research support; PE has received consultancy fees and funding for research from Roche within the last 3 years. A. Barton: None. T. Vyse: None. J. Barrett: None. E. Vital: Grants/research support; EMV has received consultancy fees and funding for research from Roche within the last 3 years. A. Morgan: None.