This is a Phase 1, open-label, first-in-human study to investigate the safety, tolerability, pharmacokinetics and pharmacodynamics of KT502 administered subcutaneously to participants with Rheumatoid Arthritis (RA). The study will have 2 parts: Part A is a single ascending dose finding (SAD) and Part B is dose escalation by fractionated dosing.

Inclusion:

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:

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

This is a Phase 1 trial.