This trial is conducted in Europe. The aim of this trial is to describe the safety and tolerability of single intravenous (i.v.) and subcutaneous (s.c.) doses of NNC0215-0384 in subjects with active rheumatoid arthritis (RA) on background methotrexate (MTX) treatment.

Inclusion Criteria:

• Active RA, characterised by a DAS28 (CRP)(Disease Activity Score based on 28 joints and CRP) above 3.2 and a minimum of two swollen joints based on a 68/66 joint count at screening
• Concomitant treatment with MTX (7.5 - 25 mg/week both inclusive) for at least 16 weeks, with a stable dose for at least 6 weeks prior to dosing

Exclusion Criteria:

• Subjects with chronic inflammatory autoimmune disease other than RA
• History of or current inflammatory joint disease other than RA such as gout (crystal proven), psoriatic arthritis, juvenile idiopathic arthritis, current reactive arthritis or Lyme disease
• Any active or ongoing chronic infectious disease (e.g. chronic osteomyelitis, chronic pyelonephritis) requiring systemic anti-infectious treatment within 4 weeks prior to randomisation
• Clinically significant cardiac or cardiovascular disease
• Past or current malignancy
• Latent or active tuberculosis (TB) as documented by: A positive QuantiFeron® test (test can be performed up to 2 months prior to dosing). One retest is allowed in case of inconclusive results.- A history of active TB within the last 3 years even, if treated effectively. - A history of active TB more than 3 years ago, if there is no documentation that the prior anti-TB treatment was appropriate in duration and type