A Study to Investigate Safety, Tolerability, and PK of Oral Doses of TCK-276 in Patients With Rheumatoid Arthritis

Inclusion Criteria: * Diagnosis of RA and meeting the 2010 American College of Rheumatology/European League Against Rheumatism classification criteria for RA. * Patients between the ages of 18 and 64 years, inclusive, at the Screening Visit. * Female patient must be not pregnant, not breast feeding and one of the following conditions need to apply: 1. Of non-childbearing potential based on documented surgical treatment or post-menopausal, meaning patient had spontaneous amenorrhea for at least 12 months without alternate medical cause prior to Screening Visit and follicle stimulating hormone (FSH) \> 40 U/mL at the Screening Visit. 2. Of childbearing potential and using a highly effective method of contraception and agrees to remain on a highly effective method from the time of signing the informed consent form (ICF) until 21 days after the last dose. * Male patient must agree to stay abstinent or must use together with his female partner(s) a form of highly effective contraceptive (failure rate of \< 1% per year) from the time of signing the ICF until up to 3 months after the last dose of the study drug. * Nonsmokers (or other nicotine use) as determined by history and by negative urine cotinine concentration at the Screening Visit and at Admission. * Body mass index (BMI) between 18.5 and 32.0 kg/m2, inclusive, at the Screening Visit. * Patient is required to have completed a COVID-19 vaccine regimen within no more than 5 months prior to screening to be eligible for the study. * Permitted concomitant medications for any reason, must be on a stable dose. * Permitted medications include: anti-malarials; nonsteroidal anti-inflammatory drugs including selective cyclooxygenase-2 inhibitors at approved dosage, and low dose oral corticosteroids; methotrexate concomitantly with folic acid or folinic acid. Exclusion Criteria: * Female patients who are breastfeeding or have a positive urine pregnancy test. * Patients who are unable to eat the prescribed meals during the stay at the site; vegetarian or vegan. * Patient has a history of significant drug allergy. * Patient has used a study drug, any prohibited medication(s), over-the-counter (OTC) medications, vitamins, dietary and herbal supplements. * Patient has a history of active suicidal ideation, or any psychiatric disorders that will affect the patient's ability to participate in the study. * Patient has a current or recent history of uncontrolled, clinically significant infectious, hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, neurologic, or allergic disease. * Patient with any of the laboratory abnormalities as per reference. * Patient has a history of alcohol and/or drug abuse within 24 weeks. * Patient has positive results for drug testing and breath alcohol test. * Regular consumption of alcohol within 6 months prior to the Screening Visit. * Patient has positive test for hepatitis B surface antigen (HBsAg), anti-hepatitis B core (HBc) antibodies, hepatitis C virus (HCV) antibody, and/or human immunodeficiency virus (HIV) antibody at Screening Visit. * Patient has QT interval corrected for heart rate (QTc) using Fridericia's correction (QTcF) \> 450 ms for males or QTcF \> 470 ms for females either at the Screening Visit or Admission, based on safety 12-lead electrocardiogram (ECG). Patient has Screening or Admission ECG with second- or third-degree atrioventricular block, bundle branch block, arrhythmia (but not sinus arrhythmia or supraventricular premature beats), or illegible QT interval. * Patient has history or evidence of cardiopathy, acute coronary syndrome, hypertrophic cardiomyopathy, myocarditis or QT prolongation syndrome. * Patient is unwilling to abstain from drinks and foods containing alcohol, grapefruit, or caffeine * Patient has donated blood or experienced acute blood loss (including plasmapheresis) of greater than 500 mL within 90 days prior to the first dose of study drug. * Patients with a known immunodeficiency disorder. Have a history of a major organ transplant or hematopoietic stem cell/marrow transplant. * Patients with infections requiring treatment or hospitalization within 14 days prior to the Screening Visit, parenteral antimicrobial therapy within 60 days prior to the Screening Visit, infected joint prosthesis; history of herpes zoster, active herpes simplex, or herpes simplex on suppressive therapy. * Patient has a chronic hepatic disease or hepatic impairment. * Patient has a history of Mycobacterium tuberculosis or positive interferon gamma release assay for tuberculosis (IGRA-TB) or abnormal chest X-ray (for positive IGRA-TB patients). * Patient has a history of any lymphoproliferative disorder. * Patient has a history of COVID-19 unless fully recovered with no sequelae for 14 days. * Patient who had a severe course of COVID-19 (extracorporeal membrane oxygenation, mechanically ventilated). * Patient who has recent exposure to someone who has COVID-19 symptoms or positive test result. * Patient who has a positive reverse transcription polymerase chain reaction (RT-PCR) test for Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2). * Patient who has clinical signs and symptoms consistent with SARS-CoV-2 infection. * Patients may not receive any live/attenuated vaccine from 30 days prior to the Screening Visit until Day 14 Follow-up Visit. * COVID-19 vaccine should not be given 1 week prior to the Screening Visit. * Patients with malignancy or history of malignancy except adequately treated or excised non-metastatic basal cell or squamous cell cancer of the skin or cervical carcinoma in situ. Previous treatment with total lymphoid irradiation. * History of recurrent inflammatory joint disease other than RA or history of any other autoimmune rheumatic diseases other than Sjogren's syndrome. * Major surgery within 30 days prior to the Screening Visit or patients with planned surgery. * Patients who have an abnormal chest X-ray for interstitial lung disease (ILD) and/or patients with history of ILD. * History of fainting or family history of sudden death. * Patient has any disorder that would interfere with the absorption, distribution, metabolism or excretion of study drug. * Patient has a history of deep vein thrombosis and/or pulmonary embolism. * Patient has poor venous access.