The objective of this randomized, double-blind, placebo-controlled phase II clinical trial is to investigate the safety and efficacy of QLS12010 in subjects with moderate-to-severe rheumatoid arthritis.The main questions it aims to answer are:

• Efficacy and safety of QLS12010 in participants with rheumatoid arthritis.

Participants will be randomly allocated to four treatment groups at a 1:1:1:1 ratio to compare the efficacy and safety of different dosages of QLS12010 Capsules against the placebo.

Inclusion Criteria:

• 18-75 years old (inclusive).
• Diagnosed with rheumatoid arthritis as defined by the 2010 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria for at least 12 weeks prior to screening; ACR functional class I-III.
• Tender joint count (TJC) ≥ 4/68 and swollen joint count (SJC) ≥ 4/66.
• High Sensitivity C-Reactive Protein (hsCRP) > Upper Limit of Normal (ULN) or erythrocyte sedimentation rate (ESR) ≥ 28 mm/h at screening.
• Inadequate response to at least one conventional synthetic disease-modifying antirheumatic drug (csDMARD) and one biologic disease-modifying antirheumatic drug (bDMARD)/ targeted synthetic disease-modifying antirheumatic drug (tsDMARD).
• Glucocorticoid dose ≤ 10 mg/day prednisone-equivalent, stable for ≥ 2 weeks pre-screening and ≥ 4 weeks pre-baseline.
• Nonsteroidal Antiinflammatory Drugs (NSAIDs) or acetaminophen, stable for ≥ 1 week pre-screening and ≥ 2 weeks pre-baseline.

Exclusion Criteria:

• Participants with other inflammatory arthritis, systemic inflammatory diseases, or Felty syndrome.
• Participants with a history of malignancy within 5 years prior to screening.
• Concurrent conditions predisposing to QT interval prolongation; QTc interval (Fridericia-corrected) > 450 ms; or thyroid-stimulating hormone (TSH) > 5 mIU/L.
• Participants with untreated recurrent migraine.
• Participants with a history of opportunistic infection within 6 months prior to ICF signing; any infection requiring hospitalization or IV anti-infective therapy within 3 months; or any acute systemic infection within 2 weeks prior to baseline.
• Participants with HIV, HBV, HCV, Treponema pallidum, or active tuberculosis (TB).
• Participants with a history of major surgery performed within 2 months prior to baseline.
• Participants with a history of severe allergic reactions or known allergy to any component of the study drug.
• Prior receipt of cell therapy (e.g., CAR-T) or T-cell engager therapy.
• Participants with a history of strong CYP3A4 inhibitors/inducers, narrow therapeutic index CYP3A substrates, strong P-gp/BCRP inhibitors, P-gp/BCRP substrates, or any QT-prolonging drugs within 4 weeks or 5 half-lives prior to baseline.
• Participants with a history of addictive drug abuse within 1 year prior to ICF signing; or alcohol abuse within 6 months prior to ICF signing.
• Participants with blood pressure > 160/100 mmHg at baseline.
• Pregnant or lactating women.
• Participants with blood donation or total blood loss ≥ 400 mL within 3 months prior to ICF signing.
• Vaccination with or exposure to live/attenuated live vaccines within 4 weeks prior to screening.