The purpose of the study is to evaluate the safety and efficacy of CND261 in patients with seropositive rheumatoid arthritis.

This is a Phase 1b, open-label, multicenter study evaluating the safety, tolerability, pharmacokinetics, pharmacodynamics, immunogenicity, and preliminary clinical activity of CND261 in patients with seropositive rheumatoid arthritis. The study consists of 2 parts: a dose-escalation part and an open-label expansion. Patients will be followed until Week 52.

Inclusion Criteria:

1. 18 to 75 years old
2. Diagnosis of adult-onset RA
3. Class I-III RA
4. Moderately to severely active RA
5. Inadequate treatment response as defined in the protocol
6. Stable use of any concomitant therapies

Exclusion Criteria:

1. Inadequate clinical laboratory parameters at Screening
2. Active infection
3. Receipt of or inability to discontinue any excluded therapies
4. Receipt of live vaccine within 4 weeks
5. Presence of any concomitant autoimmune disease
6. Active or known history of catastrophic anti-phospholipid syndrome
7. APS or thrombotic event not adequately controlled by anticoagulation therapy
8. History of progressive multifocal leukoencephalopathy
9. Central nervous system disease
10. Presence of 1 or more significant concurrent medical conditions
11. Have a diagnosis or history of malignant disease within 5 years
12. Serious mental illness, alcohol or drug abuse, dementia, or any other condition that would impair ability to receive planned treatment or to understand informed consent
13. History of or planned organ transplant and/or autologous or allogeneic hematopoietic stem cell transplantation
14. Major surgery requiring use of general anesthesia within 12 weeks or planned or expected major surgery during the study
15. Women who are pregnant or breastfeeding
16. Patients who do not agree to the use of highly effective contraception as defined by the protocol