6-Month Phase I/II Open Label PRTX-100 in Previous Rheumatoid Arthritis Study Participants and Sera Collection

Part A Inclusion Criteria: 1. Has completed the written informed consent process 2. Received PRTX-100 or placebo in Study 104 3. Receiving methotrexate or leflunomide therapy for at least 12 weeks 4. Must be on a stable weekly dose of methotrexate (12.5 to 25 mg) or daily leflunomide (10-20 mg/day) by the same route of administration for at least 3 weeks prior to the start of study drug. 5. Agrees to notify the investigator when deviating from protocol requirements for concomitant medications 6. Agrees to stay in contact with the study site for the duration of the study, provide updated contact information as necessary, and has no current plans to move from the study area for the duration of the study 7. Agrees to avoid elective surgery for the full duration of the study 8. For female subjects: agrees to avoid pregnancy from 28 days prior to Study Day 0 and for the full duration of the study. Women physically capable of pregnancy (not sterilized and still menstruating or within 1 year of the last menses if menopausal) in sexual relationships with men must use an acceptable method of avoiding pregnancy during this period. Acceptable methods of avoiding pregnancy include a sterile sexual partner, sexual abstinence (not engaging in sexual intercourse), hormonal contraceptives (oral, injection, transdermal patch, or implant), vaginal ring, intrauterine device (IUD), or the combination of a condom or diaphragm with spermicide. Part A Exclusion Criteria: 1. Diagnosis of any other inflammatory arthritis (e.g. psoriatic arthritis, spondyloarthropathy, gout) 2. ACR Functional Classification IV 3. Systemic involvement secondary to rheumatoid arthritis (vasculitis, pulmonary fibrosis or Felty's syndrome. Secondary Sjogren's syndrome is permitted. 4. Any receipt of abatacept, adalimumab, certolizumab pegol, etanercept, golimumab, tocilizumab or tofacitinib within 3 weeks of Study Day 0 5. Any receipt of infliximab within 6 weeks of Study Day 0 6. Any receipt of rituximab or other anti-CD20 antibodies within 12 months of study day 0 7. Any receipt of another investigational product within 4 weeks or 4 half-lives whichever is longer prior to Study Day 0 8. Hepatitis B surface antigen positive, HIV positive, hepatitis C antibody positive 9. Uncontrolled Type 2 Diabetes or Type I diabetes 10. Positive urine pregnancy test 11. Diagnosis of hepatic cirrhosis 12. Urinalysis must reflect no evidence of systemic or local disease process 13. Severe anemia, defined as \< 10 g/dL or hematocrit \< 30% 14. Evidence of significant active infection 15. Shared a residence within the last year with an individual on anti-tuberculosis treatment or with culture or smear positive tuberculosis 16. Previous medical history that may compromise the safety of the subject in the study, including but not limited to: severe impairment of pulmonary function or other pulmonary disease; chronic illness with signs of cardiac or renal failure; suspected progressive neurological disease or poorly controlled epilepsy 17. Evidence of a new acute illness that may compromise the safety of the subject in the study 18. History or evidence on physical examination of any systemic disease or any acute or chronic illness that, in the opinion of the investigator, may interfere with the evaluation of the safety of the study drug 19. History or evidence (including chest X-ray) of active tuberculosis 20. Any current medical, psychiatric, occupational, or substance abuse problems that, in the opinion of the investigator, will make it unlikely that the subject will comply with the protocol. Part B Inclusion Criteria 1. Has completed the written informed consent process 2. Is in a state of good health 3. Agrees to stay in contact with the study site for the duration of the study, provide updated contact information as necessary, and has no current plans to move from the study area for the duration of the study 4. Agrees to avoid elective surgery for the full duration of the study 5. For female subjects: agrees to avoid pregnancy from 28 days prior to Study Day 0 and for the full duration of the study. Women physically capable of pregnancy (not sterilized and still menstruating or within 1 year of the last menses if menopausal) in sexual relationships with men must use an acceptable method of avoiding pregnancy during this period. Acceptable methods of avoiding pregnancy include a sterile sexual partner, sexual abstinence (not engaging in sexual intercourse), hormonal contraceptives (oral, injection, transdermal patch, or implant), vaginal ring, intrauterine device (IUD), or the combination of a condom or diaphragm with spermicide. Part B Exclusion Criteria 1. Diagnosis of cancer or autoimmune disease. 2. Any receipt of another investigational product within 4 weeks or 4 half-lives whichever is longer prior to Study Day 0 3. Hepatitis B surface antigen positive, HIV positive, hepatitis C antibody positive 4. Uncontrolled Type 2 Diabetes or Type I diabetes 5. Diagnosis of hepatic cirrhosis 6. Positive urine pregnancy test 7. Urinalysis must reflect no evidence of systemic or local disease process 8. Severe anemia, defined as \< 10 g/dL or hematocrit \< 30% 9. Previous medical history that may compromise the safety of the subject in the study, including but not limited to: severe impairment of pulmonary function or other pulmonary disease; chronic illness with signs of cardiac or renal failure; suspected progressive neurological disease or poorly controlled epilepsy 10. Evidence of a new acute illness that may compromise the safety of the subject in the study 11. History or evidence on physical examination of any systemic disease or any acute or chronic illness that, in the opinion of the investigator, may interfere with the evaluation of the safety of the study drug 12. Any current medical, psychiatric, occupational, or substance abuse problems that, in the opinion of the investigator, will make it unlikely that the subject will comply with the protocol.