P007 Autoantibodies’ titre changes during anti-BLyS treatment in systemic lupus erythematosus
Authors: I Cavazzana, C Pozzari, R Kumar, R Ottaviani, M Fredi, S Piantoni, A Tincani, F Franceschini
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Career situation of first and presenting author</h3> Assistant. <h3>Introduction</h3> Belimumab, a human monoclonal antibody anti-soluble B lymphocytes stimulator, is the only biological drug approved for Systemic Lupus Erythematosus (SLE). It reduces disease activity and blocks damage progression.<sup>1 2</sup> Anyway, no definitive results have been published regarding its effect on autoantibodies' titre. <h3>Objectives</h3> To analyse the modulation of anti-dsDNA, anti-ENA and anti-phospholipid antibodies' titre by Belimumab in patients affected by SLE. <h3>Methods</h3> 50 SLE<sup>3</sup> patients starting Belimumab were enrolled. Sera were collected at baseline (T0) and every 6 months until 24th month. Clinical features and disease activity index (namely SLEDAI-2K)<sup>4</sup> were collected at any timepoints. AntidsDNA were analysed by radioimmunological method, anti-cardiolipin (aCL) and anti-β2 glycoprotein I (anti-β2GPI) were detected by home-made ELISA.<sup>4 5</sup> Anti-ENA were detected by ELISA; positive sera were further characterized by ELISA to identify anti-Ro, anti-La, anti-ribosomal P protein (ribP), anti-Sm and anti-U1RNP specificities. <h3>Results</h3> At T0 anti-dsDNA were positive in 86%, anti-ENA in 50%, a CL in 20% and antibeta2GPI in 28% of cases, respectively. A negative seroconversion was detected in 9/43 anti-dsDNA (21%); in 5/12 anti-beta2GPI IgG (40%) and in 3/10 aCL IgG (30%) sera, mostly at T6. Among anti-ENA specificities 6/10 (60%) anti-ribP and 3/17 (17,6%) anti-Sm positive sera became negative; while anti-Ro and anti-U1RNP antibodies resulted stable during treatment. A significant decrease of anti-dsDNA titre was observed at T6 (p 0,0011); T12 (p: 0,014); T18 (p: 0,0031) and T24 (p: 0,013). Anti-beta2GPI IgM isotype showed significant reduction at T6 (p: 0,0032), T12 (0,001), T18 (p: 0,002) and T24 (p: 0,011). ACL antibodies showed significant decrease only for IgG isotype at T18 (p: 0,001). Anti-ribP antibodies showed a significant titre decrease at T6 (p: 0,015) and T12 (p:0,0078), with complete negative seroconversion at T18. Anti-Sm antibodies significantly dropped down at T6 (p:0.032), than maintained a stable titre during time. A significant correlation between anti-dsDNA titre anti-ribP titre and between SLEDAI ratio (SLEDAI value/SLEDAI T0) and anti-ribP ratio (value/value T0) were found. <h3>Conclusions</h3> Belimumab treatment induced a significant reduction of high-affinity anti-dsDNA, anti-Sm and anti-ribP antibodies titre. The decrease of anti-ribP titre correlates with anti-dsDNA titre and disease activity. <h3>References</h3> Ginzler EM, <i>et al. J Rheumatol</i> 2014;41:2. Iaccarino L, <i>et al. Arthritis care Res</i> 2017;69:115–123. Petri M, <i>et al. Arthritis Rheum</i> 2012;64:2677–86. Gladman DD, <i>et al. J Rheumatol</i> 2002;29:288–91. Harris EN. <i>Ann J Clin Pathol</i> 1990;94:476–84. Balestrieri G, <i>et al. Lupus</i> 1995;4:122–30. <h3>Disclosure of Interest</h3> None declared.