The FCGR3A gene dimorphism generates two allotypes: FcγRIIIa-158V and FcγRIIIa-158F. The genotype homozygous for FcγRIIIa-158V (VV) is associated with higher clinical response to rituximab, a chimeric anti-CD20 IgG1 used in the treatment of B lymphoproliferative malignancies. Our objective was to determine whether this genetic association relates to rituximab-dependent cytotoxicity mediated by FcγRIIIa/CD16a+ cells. The number of CD16+ circulating monocytes, T cells, and natural killer (NK) cells in 54 donors was first shown to be unrelated to FCGR3A polymorphism. We then demonstrated that FcγRIIIa-158V displays higher affinity for rituximab than FcγRIIIa-158F by comparing rituximab concentrations inhibiting the binding of 3G8 mAb (anti-CD16) with VV NK cells and NK cells homozygous for FcγRIIIa-158F (FF). VV and FF NK cells killed Daudi cells similarly after FcγRIIIa engagement by saturating concentrations of rituximab or 3G8. However, the rituximab concentration resulting in 50% lysis (EC₅₀) observed with NK cells from VV donors was 4.2 times lower than that observed with NK cells from FF donors (on average 0.00096 and 0.00402 μg/ml, respectively, P = 0.0043). Finally, the functional difference between VV and FF NK cells was restricted to rituximab concentrations weakly sensitizing CD20. This study supports the conclusion that FCGR3A genotype is associated with response to rituximab because it affects the relationship between rituximab concentration and NK cell-mediated lysis of CD20+ cells. Rituximab administration could therefore be adjusted according to FCGR3A genotype.

Hereditary hemorrhagic telangiectasia (HHT) (Online Mendelian Inheritance in Man [OMIM] #187300) is a dominantly inherited genetic vascular disorder characterized by recurrent epistaxis; cutaneous telangiectasia; and visceral arteriovenous malformations (AVMs) that affect many organs, including the lungs, gastrointestinal tract, liver, and brain. Diagnosis is based on the Curaçao criteria and is considered definite if at least 3 of 4 criteria are fulfilled.¹ The criteria are spontaneous and recurrent epistaxis, telangiectasia, family history, and visceral lesions.

Summary: Aim : To test the hypothesis of an association between polymorphism in FCGR3A (the gene coding for FcγRIIIa, which is expressed on macrophages and natural killer cells, is involved in antibody‐dependent cell‐mediated cytotoxicity and has recently been associated with a positive response to rituximab, a recombinant immunoglobulin G1 antibody used in non‐Hodgkin's lymphomas) and response to infliximab in Crohn's disease.Methods : FCGR3A‐158 polymorphism was determined using an allele‐specific polymerase chain reaction assay in 200 Crohn's disease patients who had received infliximab for either refractory luminal (n = 142) or fistulizing (n = 58) Crohn's disease. Clinical and biological responses (according to C‐reactive protein levels) were assessed in 200 and 145 patients, respectively.Results : There were 82.9% clinical responders in V/V patients vs. 72.7% in V/F and F/F patients (N.S.). Globally, the decrease in C‐reactive protein was significantly higher in V/V patients than in F carriers (P = 0.0078). A biological response was observed in 100% of V/V patients, compared with 69.8% of F carriers (P = 0.0002; relative risk, 1.43; 95% confidence interval, 1.27–1.61). In the sub‐group of patients with elevated C‐reactive protein before treatment, the multivariate analysis selected the use of immunosuppressive drugs and FCGR3A genotype as independent factors influencing the clinical response to infliximab (P = 0.003).Conclusion : Crohn's disease patients with FCGR3A‐158 V/V genotype have a better biological and, possibly, clinical response to infliximab.