OP0279 A UNIQUE IL-21 SIGNATURE CHARACTERIZES LESIONAL AND CIRCULATING T-FOLLICULAR HELPER CELLS IN SJÖGREN’S SYNDROME PATIENTS WITH ECTOPIC GERMINAL CENTRES AND MALT LYMPHOMA
Authors: Elena Pontarini, William Murray Brown, Cristina Croia, Davide Lucchesi, Felice Rivellese, Liliane Fossati-Jimack, Piero Ruscitti, Edoardo Prediletto, Elisa Corsiero, Francesca Barone, Benjamin Fisher, Serena Colafrancesco, Ilaria Puxeddu, Roberto Giacomelli, Roberta Priori, Chiara Baldini, Costantino Pitzalis, Michele Bombardieri
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> B/T cell aggregates in the salivary glands (SG) of Sjögren's syndrome (SS) can form ectopic lymphoid structures (ELS) with germinal centers (GC), which are linked to MALT lymphoma (MALT-L) development. T follicular-helper cells (Tfh), main producers of IL21, are crucial for affinity maturation and class-switching of GC B cells, and may be responsible for onset of autoimmunity. <h3>Objectives</h3> To characterize the cytokine production in circulating T cells alongside the Tfh infiltration and the expression of IL21/IL21 receptor (IL21R) in the SGs of SS patients, in the context of ectopic GCs and MALT-L. <h3>Methods</h3> SG biopsies with matching histology and RNA from 37 SS and 38 non-specific chronic sialadenitis (NSCS) patients were stratified as ELS-/ELS+ based on CD3/CD20/CD21/CD138 immunostaining (IHC). Histological samples and mRNA from 12 parotid MALT-L were also analyzed. Gene expression was measured by Taqman RT-PCR. Multicolor immunofluorescence/confocal microscopy for CD3, CD4, CD45RO, ICOS, PD1, BCL6 identify Tfh cells in SG and MALT-L tissues. FACS analysis for CD4, CD8, INFγ, IL17, IL21, Granzyme-B, IL10, CD25, Foxp3, CXCR5, ICOS, PD1, was performed on peripheral blood mononuclear cells from 20 SS and 10 NSCS patients with matched SG histology for the characterization of T CD4+ cells cytokines production. <h3>Results</h3> IL21 and IL21R expression, together with CD4<sup>+</sup>CD45RO<sup>+</sup>PD1<sup>+</sup>ICOS<sup>+</sup> Tfh cells were strongly enriched in ELS+ vs ELS- SS SGs. Tfh cells densely infiltrated B cell rich areas and, within ectopic GC, acquired BCL6 expression, both in ELS+ and MALT-L. Tfh infiltration significantly correlated with SG IL21 mRNA level, which in turn was associated with high T (CD3+), B (CD20+) and plasma cells (CD138+) IHC scores and significantly correlated with CXCL13, LTβ, BAFF, AID and Pax5 gene expression. MALT-L samples displayed 10-fold higher IL21 mRNA and twice as much PD1<sup>+</sup>ICOS<sup>+</sup>BCL6<sup>+</sup> Tfh-cells/field in comparison to ELS+ SS samples. Within the SGs, IL21 and INFγ were the most abundant cytokines produced by infiltrating CD4 T cells and CXCR5+ Tfh cells frequently displayed double IL21/INFγ production. Similarly, IL21, IL17 and IFNγ producing ICOS+CXCR5+ circulating Tfh cells were significantly increased in the peripheral blood of SS patients compared to sicca, but only IL21+ Tfh cells were associated with the presence of ectopic GC in SG. IL21, IL17 and IFNγ production by Tfh in the peripheral compartment showed a positive correlation with IgG serum levels. <h3>Conclusion</h3> Within the SG of SS patients Tfh cells closely segregate with lesional IL21 expression, localize within ELS and are strongly enriched during MALT-L development, which is supporting their role in sustaining B cell activation and malignant transformation. High production of IL21 by Tfh in peripheral blood selectively identifies SS patient with ectopic GC in the SG, suggesting a role for IL21+ Tfh cells as surrogate markers of SG histopathology in SS. <h3>Acknowledgement</h3> This work was supported by project grants from the Medical Research Council (MR/N003063/1 to MB) and&nbsp;Versus&nbsp;Arthritis (grant&nbsp;21753&nbsp;to EP). <h3>Disclosure of Interests</h3> Elena Pontarini: None declared, William Murray Brown: None declared, Cristina Croia: None declared, Davide Lucchesi: None declared, Felice Rivellese: None declared, Liliane Fossati-Jimack: None declared, Piero Ruscitti Grant/research support from: Pfizer, Speakers bureau: MSD, BMS, Lilly, Sobi, Edoardo Prediletto: None declared, Elisa Corsiero: None declared, Francesca Barone Grant/research support from: GlaxoSmithKline, Roche, UCB Pharma, Actelion, ONO Pharmaceutical, Consultant for: GlaxoSmithKline, Roche, Actelion, ONO Pharmaceutical, Benjamin Fisher Consultant for: Novartis, Roche, MedImmune, Bristol-Myers Squibb, Serena Colafrancesco: None declared, Ilaria Puxeddu: None declared, Roberto Giacomelli Grant/research support from: Pfizer, Actelion, Speakers bureau: Actelion, Bristol-Myers Squibb, Merck Sharp &amp; Dohme, Abbvie, Pfizer, Sobi, Roche, Roberta Priori: None declared, Chiara Baldini: None declared, Costantino Pitzalis Grant/research support from: Celgene, Michele Bombardieri Grant/research support from: Celgene, Consultant for: Medimmune