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

Study Description: As a primary objective, this study represents an innovative investigative measure of the safety and tolerability of JAK inhibition in participants with primary Sjogren's syndrome. Secondary objectives will include investigating the effects of Tofacitinib on target tissues (e.g., salivary glands), systemic inflammation, and on vascular function in SS participants. We also aim to identify biomarkers of response that may be useful as endpoints in future studies. Objectives: Primary Objective: -To determine the safety and tolerability of Tofacitinib in participants with SS and mild to moderate disease activity. Secondary Objectives: * To assess clinical improvement after treatment with Tofacitinib as measured by changes in the European League Against Rheumatism (EULAR) Sjogren's syndrome Disease Activity Index (ESSDAI) and no worsening on the Physician s Global assessment Scale (PGA). * To demonstrate that treatment with Tofacitinib is effective clinically and biologically in SS individuals with mild to moderate disease. * To investigate the effects of Tofacitinib on systemic biomarkers of SS as measures biological effects that can be used as outcome measures to power a larger Clinical Trial. Endpoints: Primary Endpoint: -Safety and tolerability will be measured by assessment of adverse events (AEs) and clinical safety laboratory tests throughout the study. Toxicity is defined as any study drug-related Grade 3 adverse event or higher (as measured by the National Cancer Institute (NCI), Common Terminology Criteria for Adverse Events (CTCAE), Version 5.0). Secondary Endpoints: Preliminary assessments of clinical response will be measured by: * Changes in the ESSDAI score between Baseline and Day 168 (end of treatment) * Changes in the Physician's Global Assessment (PGA) scores between baseline and study day 168.