OP0318 Use of an in Vitro Whole Blood Depletion Assay to Compare the Efficacy of B Cell Depleting Agents in Patients with Systemic Lupus Erythematosus
Authors: V. Reddy, G. Cambridge, D. Isenberg, M. Cragg, M. Leandro
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> Variability in clinical response to B-cell depletion therapy (BCDT) with the anti-CD20 mAb rituximab (RTX) has been well described in Systemic Lupus Erythematosus (SLE). Poor clinical response is associated with incomplete depletion which suggests that improving the efficiency of depletion might result in improved therapeutic outcome. GA101 is a recombinant, afucosylated fully human type II anti-CD20 mAb that has shown more effective depletion and clinical response in phase II trials in lymphoma. We have therefore compared the <i>in vitro</i> B-cell cytotoxicity (cytotoxicity index, CTI) of BHH2 (glycosylated GA101) with RTX, in lymphocytes from patients with SLE. <h3>Objectives</h3> To determine whether type II anti-CD20 antibodies are superior to type I anti-CD20 antibodies at inducing cytotoxicity <i>in vitro</i> of B cells from patients with SLE<i>.</i> <h3>Methods</h3> We included 23 patients with SLE, who met the American College of Rheumatology revised classification criteria. An <i>in vitro</i> autologous whole blood depletion assay (WBD) was used to assess the CTI. Briefly, 100µl of heparinised blood was incubated with either RTX, BHH2 or an isotype control, at a concentration of 1µg/ml at 37ºC, 5% CO<sub>2</sub> for 24 hours. Samples were then analysed by flow cytometry for CD45 (all lymphocytes), CD3 (T cells), and CD19 (B cells). The CTI was calculated using the formula: CTI of mAb = 100 - [(number of B:T cells in sample without antibody – number of B:T cells with mAb) / number of B:T cells in sample without antibody) X 100] and the mean from triplicate wells calculated. The relationship between the relative expression (mean fluorescence intensity; MFI) of CD20 and CD32B (FcgRIIB) on B cells and CTI was determined using spearman rank correlation. Concurrent clinical and laboratory parameters including anti-dsDNA and C3 were collected and assessed. <h3>Results</h3> The mean CTI of BHH2 was higher than RTX in all but one patient. Median CTI in 23 SLE patients was 30% (range 9-70) and 15% (range 1-42), for BHH2 and RTX, respectively (P=0.0002). CTI was &lt;25% in 5 (21%) and 16 (73%) patients, for BHH2 and RTX, respectively. The mean ± SD MFI of CD20 and CD32B on SLE-B cells was 9079±4025 and 4223±1587, respectively. The CTI of neither mAb correlated with the expression of CD20 (r2= -0.1898, 0.1258, for BHH2 and RTX, respectively) or CD32 (r2= -0.332, 0.204, for BHH2 and RTX, respectively). Also, there was no correlation between the CTI of mAbs and lymphocyte-count, CD19 cell count, serum creatinine, total IgG, C3, positivity for ENAs or anti-dsDNA. <h3>Conclusions</h3> These results indicate that BHH2 is superior to RTX at inducing cytotoxicity <i>in vitro</i> in B cells from patients with SLE. This study provides the preliminary data to consider type II mAbs (GA101-like) as an alternative BCD agent for SLE in a clinical trial setting. <h3>Disclosure of Interest</h3> None Declared