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

* INCLUSION CRITERIA: Adult primary SS participants with mild-to-moderate disease activity will be eligible for this study. Enrolled participants can be naïve or failed immunosuppressive therapy beyond antimalarials and glucocorticoids; to prevent bias in the cohort of participants with more recalcitrant disease. We expect that Tofacitinib is a potential second line therapy, in addition to antimalarials and glucocorticoids, depending on the participant's initial presentation and response. Women and members of minority groups, if eligible, will be included in accordance with the NIH Policy on Inclusion of Women and Minorities as Participants in Research Involving Human Participants. In order to be eligible to participate in this study, an individual must meet all of the following criteria: 1. Ability of participant to understand and the willingness to sign a written informed consent document. 2. Participation and enrollment in companion protocol, 15-D-0051, Characterization of Diseases with Salivary Gland Involvement. 3. Stated willingness to comply with all study procedures and availability for the duration of the study 4. Male or female, aged between 18-75 years 5. In good general health as evidenced by medical history 6. Meets the 2002 American European Consensus Group classification criteria for primary Sjogren's Syndrome or 2016 American College of Rheumatology/European League against Rheumatism Classification Criteria (ACR-EULAR) with mild to moderate disease activity defined as ESSDAI between 0 to 13 at the screening visit and \>0 ml/min/gland stimulated saliva flow. 7. Ability to take oral medication and be willing to adhere to the study intervention regimen 8. If on glucocorticoids, the dose must be less than 10 mg daily and stable for the 4 weeks (28 days) prior to screening visit. 9. If on hydroxychloroquine or other antimalarials such as chloroquine or quinacrine, the dose must have been stable for the 12 weeks (96 days) prior to screening visit. The maximum allowed dose is hydroxychloroquine up to 400 mg/day or 6.5 mg/kg/day if more than 400 mg/day. The maximum allowed dose for chloroquine phosphate is up to 500 mg daily and for quinacrine up to 100 mg daily. 10. Participants may be on lipid lowering medications if initiated at least 3 months prior to the screening visit and dose must be stable for 4 weeks (28 days) prior to study entry. 11. Males and females with potential for reproduction must agree to practice effective birth control measures. Females should be on adequate contraception if they are of child-bearing potential documented by a clinician, unless participants or spouse have previously undergone a sterilization procedure. Adequate birth control measures are: intrauterine device (IUD) alone or hormone implants, hormone patches, injectable, or oral contraceptives plus a barrier method (male condom, female condom or diaphragm), abstinence or a vasectomized partner. 12. Agreement to adhere to Lifestyle Considerations throughout study duration EXCLUSION CRITERIA: In order to be eligible to participate in this study, an individual must not meet any of the following criteria: 1. Current or prior treatment with rituximab, belimumab or any other biologic agent in the 6 months prior to screening. 2. Current treatment with methotrexate, azathioprine, mycophenolate mofetil, cyclosporine, tacrolimus, or other less common immunomodulatory drugs such as those falling into the class of disease-modifying antirheumatic drugs (DMARDs), not otherwise specified herein. Participants previously on methotrexate, azathioprine, mycophenolate mofetil, cyclosporine or tacrolimus, or other DMARDs should have withdrawn drug for at least 8 weeks (56 days) at the time of screening. 3. Treatment with cyclophosphamide, pulse methylprednisolone or IVIG within 6 months prior to screening. 4. Current treatment with potent inhibitors of Cytochrome P450 3A4 (CYP3A4) (e.g., ketoconazole) or receiving one or more concomitant medications that result in both moderate inhibition of CYP3A4 and potent inhibition of CYP2C19 (e.g., fluconazole) that would increase serum availability of Tofacitinib. Past treatment with the aforementioned agent is allowed if it was more than a week prior to the administration of the first dose of study medication. 5. History of chronic liver disease, not including well-controlled Sjogren's-related chronic liver disease or elevated liver function tests (LFT): * Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \>= 2x upper limit of normal at screening * Serum unconjugated bilirubin \> 2mg/dL at screening 6. Serum creatinine \>1.5mg/dL. 7. Protein to creatinine ratio of more than 1mg/dL at screening (repeated and confirmed three times or confirmed with 24 hours urine protein of more than 1000mg). 8. Active urinary sediment (WBC, red blood cell (RBC) or mixed cellular casts 1+ or more /hpf)). 9. Hypercholesterolemia: Values after 8-12 hour fasting blood specimen: total cholesterol \>250 mg/dL or LDL \>180 mg/dL or hypertriglyceridemia (triglyceride \>300 mg/dL) within-45 days of screening visit. 10. WBC \<2500/microliter or absolute neutrophil count (ANC) \<1,000/microliter, Hgb \<9.0 g/dL or platelets \<70,000/microliter or absolute lymphocyte count \< 500/microliter. 11. Pregnant or lactating women. Women of childbearing potential are required to have a negative pregnancy test at screening. 12. A history of drug or alcohol abuse within the 6 months prior to screening. 13. Currently receiving hemodialysis, peritoneal dialysis, or intestinal dialysis. 14. Active infection that requires the use of oral or intravenous antibiotics unresolved at least 14 days prior to the administration of the first dose of study medication. 15. Active chronic infections including but not limited to HIV, Hepatitis B, Hepatitis C, and BK viremia at screening visit. 16. Current or previous diagnosis of malignant disease, except for basal cell or squamous cell carcinoma of the skin with complete excision and clear borders or adequately treated in situ carcinoma of the cervix. 17. Known active tuberculosis. Participants with treated latent tuberculosis (LTB) will be eligible to participate. Participants with untreated LTB will not be excluded but will be evaluated by an infectious disease (I.D.) consultant and may become eligible for trial based on infectious disease consultant recommendations. 18. History of severe or systemic infection caused by common pathogens, or history of infection with pathogens that normally do not cause human disease. 19. Participants with active renal or central nervous system disease or a high activity level in any organ system (except articular) in ESSDAI. 20. Participants with known increased risk factors for major adverse cardiac event (MACE) including a history of: * Ischemic heart disease (e.g., history of acute myocardial infarction) * Heart failure * Cardiomyopathy * Severe valvular heart disease * Significant arrhythmias * Chronic renal failure * Cerebrovascular accident or transient ischemic attack * Uncontrolled diabetes mellitus * Uncontrolled hypertension * Current smokers or former smokers with less than 3 years since complete cessation and/or \>20 pack-years of smoking history. 21. Significant impairment of major organ function (lung, heart, liver, kidney) or any condition that, in the opinion of the Investigator, would jeopardize the participant's safety following exposure to the study drug. 22. Known history of arterial or venous thrombosis or at high risk for clotting disorder 23. Psychiatric illness or history of medical non-compliance that the study team feels will make the patient unlikely to complete the study 24. Uncontrolled thyroid disease as per PI or medically responsible investigator. 25. Known allergic reactions to Tofacitinib or its components 26. Treatment with another investigational drug/intervention within six months except for COVID-19 vaccines or therapies that have been granted an FDA emergency authorization.