I'd want to see a little more of the record before answering definitively. Can you tell what is the reason for the immunosuppression in this patient?
If that isn't specified in the record, then I think you I could use D89.89 first with the arthritis secondary, but I probably wouldn't use R06.9 since that is unspecified - I think a code from the M06.8- section would be more appropriate since it's specified what's causing the arthritis.
On the other hand, if the immunosuppression if due to a drug I wouldn't code it that way - you'd want to use a code for an adverse effect of the drug - e.g. T45.1X5A - as your primary code and then the rheumatoid arthritis as the secondary/manifestation code. You may want to consider querying the physician for clarification if you can't tell which is the case.