This is a Phase 3 study. This means that the study drug has already been tested in healthy volunteers and people with RA (such as the contRAst-1, contRAst-2, contRAst-3 studies, and previously completed studies). It has also been tested in people with other conditions to see how safe it is and whether it might work. Before contRAst-1, contRAst-2, and contRAst-3, a total of 447 people had received otilimab.

Participants with rheumatoid arthritis who are aged 18 years or older at the time of signing informed consent, who have completed one of the qualifying GSK3196165 clinical studies, and who, in the opinion of the investigator, may benefit from treatment with GSK3196165. For participants on MTX: must be willing to continue treatment with oral folic acid (at least 5 mg/week) or equivalent while receiving MTX (mandatory co-medication for MTX treatment).

Study participants will be divided into 2 groups:

• Long-term treatment: otilimab 150 mg as an SC injection once a week.
• Long-term treatment: otilimab 90 mg as an SC injection once a week.

Although you will not know what investigational treatment you received in your previous study, this will be used by a computer to determine which of the 2 treatment groups you are assigned to in this study, as follows:

If you received 150 mg or 90 mg otilimab in your previous study, you will continue to receive the same dose of otilimab in this extension study.

If you received a comparator treatment in the previous study (for example, tofacitinib or sarilumab), the computer will assign you, by chance (like the flip of a coin), to receive either 150 mg or 90 mg otilimab in this study. This is called randomization.

You will have a 1-in-2 chance of receiving 150 mg otilimab and a 1-in-2 chance of receiving 90 mg otilimab.

The study doctor, study staff, and study participants will not know which dose study participants receive. This is to make sure the results of the two groups being studied are handled in the same way. Once the results of your initial contRAst study are known, you and the study doctor may be told what dose you are taking.

If during the extension study, one of the doses (150 mg or 90 mg) is found to be better in terms of benefits versus risks, participants may be switched to that dose.

In case of a medical emergency, the study staff will be able to find out what dose you are receiving.

When you join this study, you will continue taking the same csDMARD (conventional synthetic disease-modifying antirheumatic drug) treatment(s) (such as methotrexate, sulfasalazine, leflunomide and hydroxychloroquine) at the same dose and method as you were taking before the study.