Title: Chimaeric auto-antigen receptor immunotherapy for antiphospholipid syndrome
Funder: Versus Arthritis

Abstract: The procoagulant diathesis characteristic of antiphospholipid syndrome (APS) predisposes patients to recurrent thrombotic episodes including stroke, myocardial infarction, pulmonary embolism, and deep vein thrombosis. Current treatments are limited to long-term anticoagulation with vitamin K antagonists such as warfarin rather targeting the pathogenic antiphospholipid antibodies (aPL). Despite adequate anticoagulation with warfarin, and in some cases with additional immunosuppressive therapy, APS patients may suffer recurrent life-threatening thrombotic events. The anti-CD20 drug rituximab is the only treatment shown to reduce aPL in some patients. Despite its drawbacks, such as risk of infection, the ability of rituximab to reduce autoantibody levels in many autoimmune rheumatic diseases supports the backbone of our proposed research – to develop a targeted treatment for APS that specifically depletes aPL-expressing B cells. Chimaeric antigen receptor T cell (CAR-T) immunotherapy is a ground-breaking therapy licensed for B cell malignancies. The basis of CAR-T is the introduction of a synthetic molecule – the CAR – into patient-derived CD3+T cells. For B cell malignancies, the CAR is designed to bind cell surface molecules (e.g.CD19) via an antibody or ligand-derived ectodomain. Converting the antigen-binding ectodomain into an autoantibody-binding ectodomain enables the targeting of autoantibody-producing B cells. Indeed, chimaeric autoantibody receptor T cell (CAAR-T) therapy depleted pathogenic, autoreactive B cells in a mouse model of the autoimmune skin disease pemphigus. CAAR-T therapy could therefore be a feasible strategy for treating autoimmune rheumatic disease. We propose to test CAAR-T therapy for APS in the first instance due to the real, unmet need for better, more effective therapies, and because CAAR-T therapy is best suited for diseases where the pathogenic role of both the autoantibody population (aPL) and the autoantigen (β2-glycoprotein I, β2GPI) is firmly established. Our primary objective is to create β2GPI-containing CAAR-T cells that are capable of killing B cells expressing surface anti-β2GPI aPL (aβ2GPI). We will synthesise three different CAARs that contain regions of conformationally correct β2GPI within the CAAR ectodomain. Two of these CAARs will contain the immunodominant region that aPL recognise. The CAARs will be lentivirally transfected in T cells isolated from patients with APS and healthy controls and tested for their ability to generate a response against (a) monoclonal aPL-expressing 293T cells, and (b) patient-derived aβ2GPI-positive B cells. The CAAR-T response will be monitored in assays of cytotoxicity, cytokine release, and real-time monitoring of effector T cells, and target cell cytolysis. Importantly, our research will also enable identification, visualisation and enumeration of blood β2GPI-specific B cells for the first time in APS, using fluorescently labelled tetramers of the three β2GPI variants used to create the CAARs. This novel proposal is aims to only eliminate autoantibody-producing B cells whilst maintaining protective immunity. Our research is clearly translational, bridging between discovery and experimental medicine pathways. Future proposals will focus on pre-clinical testing in humanised animal models of APS. If our research is fruitful, CAAR-T therapy could prove to be a game-changer for APS and set a precedent for a new era of personalised medicine and targeted treatments for autoimmune rheumatic diseases.


Research activity codes: 2.1 BIOLOGICAL AND ENDOGENOUS FACTORS;4.1 DISCOVERY AND PRECLINICAL TESTING OF MARKERS AND TECHNOLOGIES
Health categories: BLOOD;CARDIOVASCULAR