Primary Sjögren’s Syndrome (pSS) is an autoimmune disease in which the immune system attacks cells in the body that secrete fluids, such as tear ducts and salivary glands. Symptoms include itchy eyes, a dry mouth, joint and muscle pain, difficulty concentrating, and disabling fatigue. Around a third of patients also experience other health problems such as arthritis, fever, vasculitis, kidney disease, and lung disease. Finally, people with pSS are at a greater risk of developing B-cell lymphomas. Although there are treatments to alleviate some symptoms of pSS, there is no cure. The aim of NECESSITY is to identify sensitive clinical endpoints that could be used in clinical trials to determine whether a new pSS medicine works or not. In addition, the project aims to identify biological markers that could be used to identify specific subgroups of patients with different types of pSS. Finally, the project plans to run an innovative clinical trial (a multi-arm, multi-stage platform trial) to validate both the newly-defined pSS endpoints and the subgroups identified. Ultimately, the project results will contribute to the development of much-needed new treatments for pSS. In addition, many of the tools and methodologies developed by the project will also be useful for other autoimmune diseases.