Safety of Tofacitinib, an Oral Janus Kinase Inhibitor, in Primary Sjogren's Syndrome

Background: An autoimmune disease is one in which the immune system attacks a person's own body. Sjogren's syndrome (SS) is an autoimmune disease. It often involves multiple systems and organs of the body. Researchers are trying to find new, more effective and safe treatments for SS. Objective: To evaluate the safety and tolerance of tofacitinib in people with SS. Eligibility: Adults ages 18-75 with SS. Design: Participants will be screened on a separate protocol. They will undergo: * Medical and dental history * Physical exam * Medicine review * Electrocardiogram to test the heart s electrical activity (Participants will lay on a table. Sticky pads will be placed on their body.) * Eye exam and test for dry eyes * Oral, head, and neck exams * Plaque collection (Dental plaques and tongue and mucosal scrapings will be collected using a small tongue depressor.) * Salivary gland ultrasound * Blood and urine tests * Minor salivary gland biopsy (The lower lip will be numbed. Several tiny salivary glands will be removed through a small incision.) * Saliva collection * Disease assessment. Participants will repeat some of the screening tests during the study. Participants will take capsules of the study drug or a placebo by mouth for 168 days. Participants will have tests to measure blood pressure and the speed of blood flow through the organs. They will also have a test that examines the function and reaction of the blood vessels. For these tests, they will wear blood pressure cuffs and other sensors. Participants will complete questionnaires about their health. Participants will have 9 study visits over 28 weeks. They may be contacted by phone between study visits.