This is a randomized, double-blind, placebo-controlled, first-in-human phase I study. It consists of a single ascending dose part in healthy subjects (Part 1) and in patients with rheumatoid arthritis (Part 2) as well as a multiple dose part in healthy subjects (Part 3). The study will collect information on pharmacokinetics, safety and tolerability.

Inclusion Criteria:

1. Willing and able to give written informed consent for participation in the study and is willing and able to abide by the study restrictions.

2. Males and females aged between 18 and 65 years (inclusive) at Screening. For patients in the RA cohort, an age interval between 18 and 70 years (inclusive).

3. Normal clinically physical findings, apart from RA specific findings (including deviating laboratory values e.g., mild anaemia or swollen joints) for RA patients, including pulse rate, blood pressure, electrocardiogram (ECG), physical examination, and laboratory values (haematological/clinical chemistry) as judged by the Investigator. Healthy subjects must be negative for anti-CCP and have Rheumatoid Factor <1.5 ULN at Screening.

4. For Parts 1 and 3, body mass index (BMI) between 19.0 and 30.0 kg/m2 and body weight between 50 to 100 kg (inclusive) at Screening. For Part 2, body weight between 50 to 120 kg (inclusive) at Screening.

5. Sexually active male patients participating in the study must use a barrier method of contraception (condom) and refrain from sperm donation during the study and for at least 150 days after last dosing if their female sexual partner is of childbearing potential. Acceptable methods of birth control for female partners of male subjects are: hormonal contraceptives (oral contraceptives, implant or injection), intrauterine device (placed at least 1 month before the start of the study). Surgical sterilization of male patients can be accepted as a form of birth control if the sterilization procedure took place at least 6 months prior to the start of the study.

6. Females of childbearing potential must during the study and for at least 230 days after last dosing utilise a method of contraception that can achieve a failure rate of less than 1% per year when used consistently and correctly (defined in study protocol).

7. Females of non-childbearing potential must fulfil one of the following:

   • Irreversibly surgically sterile i.e., hysterectomy, bilateral salpingectomy, the fallopian tubes have been blocked or sealed (sterilization), and bilateral oophorectomy.
   • Spontaneous amenorrhoea during the last 12 months prior to enrolment, and having follicle stimulating hormone (FSH) levels in the postmenopausal range (i.e. ≥ 30 mIU/mL) at Screening.

   The following inclusion criterion is only applicable for RA patients:

8. Fulfilling the 2010 American College of Rheumatology (ACR)/European Union League Against Rheumatism (EULAR) classification criteria for RA [8].

   • Treatment with MTX for at least 12 weeks prior to treatment start and planned to continue with MTX during the study; if the MTX dose was changed during the 12-week period, such a patient may be included in the study based on Investigator judgement.
   • Patients naïve to biological disease modifying anti-rheumatic drug (bDMARD) or who are washed out (at least 5 half-lives) from such therapy before study drug dosing.
   • Patients naïve to conventional/targeted synthetic disease modifying anti-rheumatic drug (csDMARD/tsDMARD), except for MTX, or who are washed out since at least 12 weeks from such therapy before study drug dosing.
   • Use of oral glucocorticosteroids is allowed if equivalent to ≤5 mg/day of prednisolone on a stable dose for a least 4 weeks prior to dosing (Day 1) and expected to remain on that dose level for at least 4 weeks after dosing (Day 1).

Exclusion Criteria:

1. History of any clinically significant acute inflammatory joint disease (for the RA cohort; other than RA).

2. Any chronic or long-lasting disease which may interfere with the study objectives or jeopardise the safety of the subjects/patients as judged by the Investigator or responsible physician (for the RA cohort; other than RA).

3. Ongoing infection on Day-1.

4. Serious infection treated with antibiotics and evaluated by physician in the past 14 days prior to Day -1.

5. Current treatment with heparin products.

6. Use of any prescription or non-prescription drugs (excluding paracetamol, hormonal contraceptives), antacids, herbal, and dietary supplements (including St John's Wort) within 14 days (or 28 days if the drug is a potential hepatic enzyme inducer) or 5 half-lives (whichever is longer) prior to the first dose of study drug for healthy subjects and within 4 weeks prior to the first dose of study drug for RA patients, unless in the opinion of the Investigator the medication will not interfere with the study procedures or compromise subject/patient safety. In RA patients, MTX and folic acid use are exempted.

7. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≥ 2.0 times upper limit of normal (ULN); alkaline phosphatase and bilirubin ≥ 1.5 times the ULN at Screening or on Day -1. At screening, these assessments may be repeated once, at the discretion of the Investigator.

8. Serum creatinine > 1.5 times the ULN or eGFR <60 at Screening or on Day -1 (for Part 1 and Part 3). Estimated glomerular filtration rat (eGFR) <60 at Screening or on Day -1 (for Part 2). At Screening, these assessments may be repeated once, at the discretion of the Investigator.

9. Subjects/patients who have experienced surgery within 6 months of the screening visit that could negatively impact on the subject's/patient's participation in the opinion of a Principal Investigator or responsible physician.

10. High blood pressure at Screening or on Day -1, judged as clinically relevant by a Principal Investigator or responsible physician. A repeat test may be performed.

11. Positive test for human immunodeficiency virus (HIV), hepatitis B surface antigen (HBsAg), or hepatitis C virus antibody (anti-HCV) at Screening.

12. Having evidence of active TB or latent TB at Screening as assessed by chest X-ray (RA patients only) and/or by QuantiFERON®-test. Applicable for RA patients only: in case of rescreening within three months after Screening, negative results from the initial chest X-ray and/or QuantiFERON®-test performed during Screening do not need to be repeated.

13. Subjects/patients who are currently enrolled in or have recently participated in another interventional clinical study defined as having received the last intervention within 90 days or 5 half-lives of the study drug (whichever is longer) prior to dosing (Parts 1 and 2) vs. prior to first dosing (Part 3) of the study drug.

14. History or known hypersensitivity or allergy, or any form of allergic reactions to any excipients in the study drug or to humanized or murine monoclonal antibodies (or immunoglobulins).

15. Receipt of a vaccine within 4 weeks (COVID-19 vaccine within 6 weeks) prior to dosing and/or the intention to receive a vaccine during the study. Deviation from this should be judged by the Investigator and in dialogue with the Sponsor.

16. Recent confirmed COVID-19 infection, with less than 6 weeks between recovery and dosing of study drug.

17. Blood or plasma donation within 3 months of enrolment.

18. Positive urine drug screen or alcohol test at Screening or on Day -1.

19. History of drug or alcohol abuse, at the discretion of the Investigator, within past 12 months prior to Screening.

20. The subject currently smokes or uses nicotine-containing products. Former smokers will be eligible, provided they have not smoked for at least 1 month prior to Screening. Positive cotinine test results at Screening or on Day -1 are reason for exclusion. Such positive test results can be repeated once to exclude environmental influence on the subject.

21. A positive pregnancy test or lactation at Screening or on Day -1.

    The following exclusion criteria are only applicable for RA patients:

22. Intra-articular or systemic corticosteroid injection within 4 weeks prior to dosing.

23. Current or expected need of other immunosuppressant medication except MTX and/or intra-articular corticosteroid injections.

24. Known Gilbert's syndrome or Screening laboratory values indicating Gilbert's syndrome.

In Parts 1 and 2 (single dose, Cohorts 1-5 and 7) follow-up was 90 days. In Part 3 (multiple doses, i.e., four doses, Cohort 6) follow-up was 169 days after first dose.