A First-in-human Study of KT501 Administered Subcutaneously to Patients With Rheumatoid Arthritis (RA).

This is a Phase 1, open-label, first-in-human study to investigate the safety, tolerability, pharmacokinetics and pharmacodynamics of KT501 administered subcutaneously to participants with Rheumatoid Arthritis (RA).

This is a Phase 1, open-label, first-in-human dose escalation study to investigate the safety, tolerability, pharmacokinetic and pharmacodynamic of KT501 by a single subcutaneous administration in participants with Rheumatoid Arthritis (RA). Up to a total of 5 cohorts with up to approximately 24 participants in total with RA will be enrolled. All participants will receive a single dose of KT501 on Day 1 and followed up until Week 12. For any participants with B cells lower than baseline level or lower limit quantification, whichever is lower, additional B cell follow up is required up to Week 48 after the study treatment.

Inclusion Criteria: 1. 18 to 75 years old 2. Diagnosis of adult-onset RA for at least 6 months 3. Moderately to severely active RA 4. Inadequate treatment response as defined in the protocol 5. RF + or ACPA+ 6. Stable use of traditional DMARDs is permitted 7. Willing and able to comply with all study assessments and adhere to the protocol schedule and restrictions. Exclusion Criteria: 1. Functional class IV as defined by the ACR Classification of Functional Status in RA 2. Presence of any concomitant autoimmune disease other than RA 3. Active infection, history of serious recurrent or chronic infection 4. History of progressive multifocal leukoencephalopathy 5. Have a diagnosis or history of malignant disease within 5 years or breast cancer diagnosed within the previous 10 years. 6. History of or planned organ transplant and/or autologous or allogeneic hematopoietic stem cell transplantation 7. Receipt of live vaccine within 4 weeks 8. Major surgery (including joint surgery) within 8 weeks prior to screening or planned major surgery within 6 months after study 9. Women who are pregnant or breastfeeding 10. Significant or uncontrolled medical disease that would preclude participant participation