SAT0009 THE EFFECT OF FCGR3A POLYMORPHISM ON THE INITIAL DEPTH OF B-CELL DEPLETION BY RITUXIMAB, FUNCTIONAL NK-CELL MEDIATED KILLING AND CLINICAL RESPONSE IN SYSTEMIC LUPUS ERYTHEMATOSUS
Authors: Md Yuzaiful Md Yusof, James Robinson, Yasser El-Sherbiny, Andy C. Rawstron, Paul Emery, Ann Morgan, Edward Vital
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> Antibody-dependent cellular-mediated cytotoxicity (ADCC) is an important effector mechanism that contributes to the depletion of therapeutic antibody-opsonised cells <i>in vivo</i>. Rituximab (RTX) is an anti-CD20 antibody with a native IgG1 Fc, which crosslinks Fc receptors (FcγRs) expressed on immune effector cells. NK cells, which express FcγRIIIa, are believed to play an important role with less well-characterised contribution from monocytes/macrophages and neutrophils. A genetic variant in <i>FCGR3A</i> (158V) with an increased affinity for IgG1 has been reported to correlate with clinical response to RTX in RA[1]. Data in SLE are limited as the <i>FCGR</i> genetic locus is characterised by structural variation making genotyping challenging. <h3>Objectives:</h3> To assess the effect of <i>FCGR3A</i>-F158V polymorphism on (i) the initial depth of B-cell depletion by RTX; (ii) its functional effect on NK cell-mediated killing (iii) clinical response and (iv) 10-year RTX retention for the treatment of SLE. <h3>Methods:</h3> A prospective longitudinal study was conducted in RTX-treated SLE patients in Leeds. B-cells were measured at baseline and 6 weeks using highly sensitive flow cytometry. Complete depletion was defined as total B-cell count&lt;0.0001 x 10<sup>9</sup>/L. A major clinical response (MCR) was defined as improvement of all active BILAG-2004 domains to grade C/better and no A/B flare at 6 months. We measured qualitative polymorphism for <i>FCGR3A</i> using a multiplex ligation-dependent probe amplification as previously described[2]. Median expression of FcγRIIIa on NK cells (CD3-CD56+CD16+) and NK cell degranulation (CD107a) in the presence of RTX-coated Raji cells (B-lineage cell line) were assessed using flow cytometry. <h3>Results:</h3> 85 SLE patients with at least 2 x BILAG B were studied [Female: 82(96%); mean age (SD): 40(14) years; 60/85(71%) on concomitant DMARDs; ANA positive: 100%]. In cycle 1 RTX, 64/85(75%) achieved BILAG response [major=36%; partial=39%]. Both complete depletion and MCR were associated with carriage of the <i>FCGR3A</i>-158V allele (158FV or 158VV), OR 2.73 (95% CI 1.13-6.58) and 3.06 (95% CI 1.19-7.58) vs 158FF, respectively. Patients who had complete B-cell depletion post-RTX had higher level of FcγRIIIa on NK cells vs incomplete depletion; p=0.006. Comparing patients with <i>FCGR3A</i>-158V allele carriage vs FF genotype, there was a trend to higher expression of CD3-CD56+CD16+ in the former p=0.073. Moreover, degranulation as defined by ratio between%CD107a+NK cell in the presence of Raji cells + RTX and%CD107a+NK cell in Raji cells only, was higher in the V allele carriers vs FF genotype; p=0.024. Over 10-year follow-up, 27/85 (31.8%) had stopped RTX [primary inefficacy=7; secondary inefficacy=8; HACA=10; death=2]. <i>FCGR3A</i>-158FF genotype was associated with increased risk of RTX discontinuation; OR 2.36 (95% CI 1.08–5.18) after adjusting for age and DMARDs. <h3>Conclusion:</h3> An ADCC-enhancing FcγRIIIa variant was associated with initial complete B-cell depletion and MCR in RTX-treated SLE patients. This was supported by functional data on NK cell-mediated cytotoxicity and 10 year outcomes. These results elucidate one mechanism of resistance to rituximab in SLE and may guide development of more effective B-cell targeted strategies. With further validation, this polymorphism may be used to stratify SLE patients for therapy. <h3>References</h3> [1] Ruyssen-Witrand A et al. ARD 2012 [2] Nagelkerke S et al. Genes and Immunity 2015 <h3>Acknowledgement:</h3> This research was funded by NIHR (DRF-2014 07-155). The views expressed are those of authors &amp; not necessarily the NHS, NIHR or DOH. <h3>Disclosure of Interests:</h3> Md Yuzaiful Md Yusof: None declared, James Robinson: None declared, Yasser El-Sherbiny: None declared, Andy C Rawstron: None declared, Paul Emery Grant/research support from: Pfizer, MSD, AbbVie, Bristol-Myers Squibb, Roche, Consultant for: Pfizer, MSD, AbbVie, Bristol-Myers Squibb, UCB, Roche, Novartis, Gilead,Samsung, Sandoz and Lilly, Ann Morgan: None declared, Edward Vital Grant/research support from: He has received honoraria and research grant support from Roche, GSK and AstraZeneca.