This trial is conducted in Europe. The aim of the trial is to investigate the safety, tolerability, pharmacokinetics (exposure of the trial drug in the body) and pharmacodynamics (the effect of the investigated drug on the body) of NNC0215-0384 administered to subjects with moderate to severe rheumatoid arthritis (RA) concomitantly treated with methotrexate (MTX).

Inclusion Criteria:

• Male or female, age between 18 and 75 years (both years inclusive), for Russia only: Age between 18-65 years (both years inclusive)
• Moderate to severe RA, confirmed by a Disease Activity Score based on 28 joints and C-reactive protein (DAS28 (CRP)) equal to or above 4.5 and a minimum of five tender and five swollen joints based on a 28 joint count (a joint can score as both tender and swollen)
• MTX (10-25 mg/week both inclusive) for at least 16 weeks, with an unchanged dose for at least 6 weeks prior to screening and until randomisation
• Females who are not of child-bearing potential must have been post-menopausal for at least 1 year confirmed by follicle-stimulating hormone (FSH) equal to or above 26.7 U/L or be surgically sterile

Exclusion Criteria:

• Past or current inflammatory joint disease other than RA (e.g. gout [crystal proven], psoriatic arthritis, juvenile idiopathic arthritis, reactive arthritis or Lyme disease
• Any active or ongoing chronic infectious disease (e.g. chronic osteomyelitis, chronic pyelonephritis) within 4 weeks prior to randomisation
• Clinically significant cardiac or cardiovascular disease
• Past or current malignancy
• Evaluation of tuberculosis screening indicative of latent or active tuberculosis (TB)