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Objectives The frequency and consequences of anti-drug antibodies to rituximab (RTX-ADA) are not well known in RA and even less in other systemic auto-immune diseases (sAID). We aimed to evaluate the frequency, consequences and predictive factors of RTX-ADA in RA and sAID. Methods All patients presenting with RA or other sAID treated with RTX from 2012 to 2017 in our tertiary reference centre for sAID were retrospectively studied. Patients who were tested for RTX-ADA were identified. Results One hundred and ninety-nine patients were treated with RTX (RA: 124, other sAID: 75). Among 62/199 (31.1%) tested for RTX-ADA, 14 were positive: 3/35 RA (8.6%) and 11/27 (40.7%) other sAID, (P = 0.0047). Among the whole RTX-treated populations, the frequency of RTX-ADA was 2.4% and 14.7% (P = 0.0026) in RA and sAID, respectively. Most of the immunized patients had infusion reactions to second or subsequent RTX cycles (11/14) and loss of efficacy (2/14). Predictive factors of immunization were sAID vs RA (78.6% vs 21.4%, P = 0.026, adjusted odds ratio (OR) = 5.35[1.43—54.75]) and African ethnicity (57.1% vs 4.2%, P < 0.001, adjusted OR = 9.25 [5.08—302.12]). Associated immunosuppressive therapy did not protect against immunization. Three patients with pSS immunized against RTX were treated with ofatumumab with complete remission of their disease. Conclusion Immunization against RTX is more frequent in other sAID than in RA. Testing for RTX-ADA must be performed in patients with infusion reactions or loss of efficacy especially if they are of African origin. Immunized patients might be treated efficiently and safely with ofatumumab. This alternative should be further evaluated for sAID. [ABSTRACT FROM AUTHOR]

Objective. To investigate maintenance of rituximab (RTX) in RA patients re-treated with reduced doses compared with standard dose in a real life setting. Methods. The Autoimmunity and Rituximab (AIR) registry is a nationwide prospective observational cohort investigating the long-term safety and efficacy of RTX in RA. The present study included patients from the AIR registry that have been re-treated with RTX after a first course of RTX standard dose (1000 mg x 2). Two groups were defined according to dose of RTX of the first retreatment course (i.e. second course): standard dose group and reduced dose group. Five years' maintenance and rate of serious infections of the retreatment period were compared between standard dose and reduced dose groups. Analyses used the inverse probability of treatment weighting propensity score adjusted method. Results. Among the 1986 patients from the AIR registry, 1278 were included, 1093 (85.5%) treated with standard dose and 185 (14.5%) with reduced doses. Maintenance of RTX at 5 years in the standard and reduced groups was 55.5 and 53.8%, respectively, and did not significantly differ between groups in adjusted analyses (hazard ratio = 1.03; 95% CI: 0.81, 1.30), but the cumulative RTX dose received for retreatment [1.4 (0.6) vs 2.3 (1.0) g/year, P < 0.001] and the rate of serious infections were significantly lower in the reduced dose group (adjusted hazard ratio = 0.50; 95% CI: 0.27, 0.92; P = 0.02). Conclusion. Use of reduced doses of RTX for retreatment did not alter the maintenance of RTX at 5 years in RA patients, but allowed a 39% total dose reduction and a lower rate of serious infections. [ABSTRACT FROM AUTHOR]