POS0680 BELIMUMAB ADD-ON THERAPY MOBILISES MEMORY B CELLS INTO THE CIRCULATION OF PATIENTS WITH SLE

Background:Belimumab (BLM), a recombinant human monoclonal antibody directed against B-cell activating factor (BAFF), is the first approved biological agent for patients with active severe systemic lupus erythematosus (SLE) and lupus nephritis (LN). There is clinical evidence that combining BLM with B cell depleting therapy can ameliorate disease activity in severe, refractory SLE patients1. Although BLM is a B cell directed therapy and has been shown to significantly decrease total B cells, flow cytometry observations suggest a rapid increase of circulating memory B cells (MBC)2.Objectives:To investigate dynamics of B-cell subsets in SLE patients treated with or without BLM, with a focus on assessing MBC characteristics.Methods:Extensive B cell subset phenotyping was performed by high-sensitivity (HS) flow cytometry (acquisition of 107 leukocytes; per EuroFlow protocols3) on samples from active LN or SLE patients with major organ involvement treated with standard of care (SOC) consisting of high dose steroids and mycophenolate mofetil combined with or without the addition of BLM. MBC gene expression profiles were characterized with single-cell RNA and V(D)J sequencing (ScRNA-SEQ).Results:By employing HS flowcytometry, we established that the absolute increase in circulating MBC in SLE and LN patients was significant for patients who initiated BLM (Figure 1). The increase was observed in a broad range of MBC subsets (Unswitched, IgG1+, IgG2+, IgA1+, IgA2+) at 2 and 4 weeks following initiation of BLM treatment. This rise in MBC could hypothetically be attributed to either proliferation of blood MBC, BLM induced migration of tissue-resident MBCs or BLM related retention of tissue-destined MBC in the blood. ScRNA-SEQ analysis of cell cycle gene-expression was performed and established in both groups a non-proliferating phenotype [in approximately ~94%] of MBC post-treatment, including absence of MKI67 as active proliferation marker. Clonal diversity analysis comparing week 2 with baseline revealed an unexpected decrease of the largest MBC clones in BLM, whereas no change in clonality was observed with SOC alone. Together these data indicate that proliferation is unlikely to be responsible for the observed increase in MBC by BLM. Furthermore, a clear difference was found in gene-expression levels between both treatment groups: BLM was responsible for the upregulation of 72 vs 10 genes in SOC, likewise 162 vs 32 genes were downregulated. Most importantly, a significant downregulation of the migration genes SELL (CD62L), CCR7, ITGB1, RAC2 and ICAM2, were specifically seen in BLM treated patients. This may reflect disrupted lymphocyte trafficking, preventing MBCs from transmigrating from the blood into tissue owing to reduced migration molecules, or preventing MBCs from being retained at the tissue level owing to reduction in tissue adhesion proteins.Conclusion:The addition of BLM to SOC significantly increases MBCs in patients with SLE independently of proliferation, accompanied by a strong modulation of gene expression, including reduced expression of migration markers pointing towards disrupted lymphocyte trafficking. These data may have important implications for improving treatment strategies in patients with LN or severe SLE, as a deeper depletion of autoreactive MBCs could be established by adding B-cell-depleting therapy after the initiation of BLM.Figure 1.Change in pre-germinal center and memory B cell counts from baseline to week 4 of patients with SLE or LN treated with SOC (n=8) or SOC+BLM (n=11).References:[1]Arends EJ et al. Long-term effects of combined B cell immunomodulation with rituximab and belimumab in severe, refractory systemic lupus erythematosus: 2-year results. Nephrol Dial Transplant. 2020 Jun 27 gfaa117.[2]Stohl W et al. Belimumab reduces autoantibodies, normalizes low complement levels, and reduces select B cell populations in patients with SLE. Arthritis Rheum. 2012;64(7):2328-2337.[3]Blanco et al, Age-associated distribution of B and plasma cell subsets in peripheral blood - J Allergy Clin Immunol 2018 141 2208-2219.Disclosure of Interests:Eline J. Arends: None declared, Mihaela Zlei: None declared, Christopher M. Tipton: None declared, Zgjim Osmani: None declared, Sylvia Kamerling: None declared, Ton Rabelink: None declared, Ignacio Sanz: None declared, Jacques J.M. van Dongen Paid instructor for: BD Biosciences: Educational Services (fees for LUMC), Consultant of: BD Biosciences and Cytognos (fees for LUMC), Grant/research support from: GSK (flow cytometry studies for GSK BLISS-BELIEVE study NCT03312907), Cees van Kooten: None declared, Y.K. Onno Teng Consultant of: Aurinia provided financial compensation for consultancy, Grant/research support from: GSK provided belimumab for free for the Synbiose-2 clinical trial and provided an unrestricted grant to conduct the study.

MO257BELIMUMAB ADD-ON THERAPY MOBILIZES MEMORY B CELLS INTO CIRCULATION OF SLE PATIENTS

Background and Aims Belimumab (BLM), a recombinant human IgG-1λ monoclonal antibody directed against B-cell activating factor (BAFF), is the first approved biological agent for patients with active severe systemic lupus erythematosus (SLE) and lupus nephritis (LN). There is clinical evidence that combining belimumab with B cell depleting therapy can ameliorate disease activity in severe, refractory SLE patients. Although BLM is a B cell directed therapy and has been shown to significantly decrease total B cells, flow cytometry observations suggest a rapid increase of circulating memory B cells. The present study investigated the dynamics of B cell subsets in patients treated with or without BLM, with a special focus on the memory compartment in order to assess the characteristics of these memory B cells. Method We first performed extensive B cell subset phenotyping by high sensitivity flowcytometry according to the Euroflow protocol on whole blood from active lupus nephritis or SLE patients with other major organ involvement treated with standard of care (SOC) consisting of high dose steroids and mycophenolate mofetil combined with or without the addition of BLM. Next we characterized memory B cell gene expression profiles with single-cell RNA and V(D)J sequencing (ScRNA-SEQ). Results By employing high sensitivity flowcytometry, we established that the absolute increase in circulating memory B cells in SLE and LN patients was significant for patients who initiated BLM but not for patients treated with standard of care (Figure 1). The increase was observed in a broad range of memory B cell subsets (Unswitched, IgG1+, IgG2+, IgA1+, IgA2+) at 2 and 4 weeks following initiation of BLM treatment. This rise in memory B cells could hypothetically be attributed to either proliferation or homeostatic modulation of tissue-resident memory B cells causing a release into the circulation. ScRNA-SEQ cell cycle gene-expression was performed and established in both groups a non-proliferating phenotype [in approximately ∼94%] of memory B cells post-treatment, including absence of MKI67 as active proliferation marker. Additionally, BLM treatment did not result in an increased, and even in a severe reduction of the largest memory B cells clones after two weeks. In contrast, no change in clonality was seen after treatment with SOC. Together these data indicate that proliferation is not likely to be responsible for the observed increase in memory B cells by BLM. Furthermore, a clear difference was found in gene-expression levels between both treatment groups: BLM was responsible for the upregulation of 72 vs 10 genes in SOC, likewise 162 vs 32 genes were downregulated. Most importantly, a significant downregulation of the migration genes SELL (CD62L), CCR7, ITGB1, RAC2 and ICAM2, were specifically seen in BLM treated patients, possibly reflecting disrupted lymphocyte trafficking preventing memory B cells to either transmigrate into tissue or be retained at the tissue level. Conclusion The addition of BLM compared to standard of care in SLE patients leads to an increase of memory B cells in the circulation which appeared independent of proliferation. The process was accompanied with a strong modulation of gene-expression levels including a reduced expression of migration markers pointing towards disrupted lymphocyte trafficking. Altogether, these data could have important implications to further improve treatment strategies in severe SLE or lupus nephritis patients, for instance by establishing a deeper depletion of (autoreactive) memory B cells by the addition of rituximab after the initiation of belimumab.

A Glimpse of the Structural Biology of the Metabolism of Sphingosine-1-Phosphate

As a key sphingolipid metabolite, sphingosine-1-phosphate (S1P) plays crucial roles in vascular and immune systems. It regulates angiogenesis, vascular integrity and homeostasis, allergic responses, and lymphocyte trafficking. S1P is interconverted with sphingosine, which is also derived from the deacylation of ceramide. S1P levels and the ratio to ceramide in cells are tightly regulated by its metabolic pathways. Abnormal S1P production causes the occurrence and progression of numerous severe diseases, such as metabolic syndrome, cancers, autoimmune disorders such as multiple sclerosis, and kidney and cardiovascular diseases. In recent years, huge advances on the structure of S1P metabolic pathways have been accomplished. In this review, we have got a glimpse of S1P metabolism through structural and biochemical studies of: sphingosine kinases, S1P transporters and S1P receptors, and the development of therapeutics targeting S1P signaling. The progress we summarize here could provide fresh perspectives to further the exploration of S1P functions and facilitate the development of therapeutic molecules targeting S1P signaling with improved specificity and therapeutic effects.

DOP64 Discovery of highly selective small-molecule oral inhibitors of integrin α4β7 for the treatment of inflammatory bowel diseases

Background Integrins play a key role in facilitating immune cell trafficking throughout the body and represent an important receptor family for therapeutic intervention. In particular, the α4β7 integrin is a clinically validated target for the treatment of inflammatory bowel diseases (IBD), as exemplified by the humanised monoclonal antibody vedolizumab, which blocks the interactions between α4β7-expressing lymphocytes and its ligand MAdCAM-1. This blockade leads to the inhibition of these circulating lymphocytes from exiting the bloodstream and entering intestinal mucosal tissues resulting in a decrease in mucosal inflammation in patients. While oral inhibitors of the α4β7 integrin are advantageous over biologics, the efforts have been impeded by challenges to achieve desired selectivity and optimal DMPK properties. The aim of this study was to develop and characterise orally bioavailable small-molecule inhibitors of the α4β7 integrin and to determine their therapeutic potential. Methods Oral small-molecule inhibitors targeting the α4β7 integrin were discovered using Morphic Integrin Technology (MInT) platform. These small-molecule inhibitors were tested for potency and selectivity against a broad panel of integrin family members in multiple biochemical and cell-based functional assays in a ligand-competitive fashion. An acute PD assay with CFSE-labelled lymphocytes was developed to evaluate the activity of the small-molecule compounds in blocking lymphocyte trafficking to gut-associated lymphoid tissues in mice. The in vivo activity was also examined through changes in circulating α4β7+ CD4+ T memory cells in a relevant non-human primate model. Results Key drug candidate small molecules demonstrated over 1000-fold selectivity in vitro against a broad panel of integrin family members, including the α4β1 integrin. These compounds effectively blocked lymphocyte trafficking to mesenteric lymph nodes and Peyer’s patches in the gut in a dose-dependent manner, similar to an α4β7-specific antibody, in an acute gut-homing assay in mice. Additionally, these inhibitors also demonstrated effective occlusion of immune trafficking in a relevant non-human primate model. The lead compound has favourable DMPK properties, good oral bioavailability and is projected to have sufficient exposure in humans to effectively block α4β7-expressing immune cells in circulation. Conclusion Potent, selective, oral small-molecule inhibitors of α4β7 integrin have been discovered that demonstrate on-target, mechanistic efficacy in two animal models relevant to human IBD. It has the potential to be an effective and safe therapeutic in monotherapy as well as serving as a backbone for combination with other IBD drugs.