A Study to Learn About the Effects of Felzartamab Infusions in Adults With Kidney Transplants Who Have Late Isolated Microvascular Inflammation

This study is looking for adults aged 18 to 74 who have had a kidney transplant at least six months ago. Before joining, doctors will need to confirm you have 'isolated microvascular inflammation' (MVI) based on a recent kidney biopsy. This means the inflammation must be in the tiny blood vessels, and your doctors must have checked that you don't have certain types of immune proteins called 'donor-specific antibodies' in your blood that usually cause rejection.

You would not be able to join if you had a blood type mismatch for your transplant or a history of multiple organ transplants. If you've recently had other strong treatments for problems with your transplanted kidney, you might need to wait a few months before being considered. Also, if your kidney function is rapidly getting worse and you might need dialysis very soon, this study would not be suitable.

If you join this study, you will be in it for about one year. In the first part, you'll be randomly assigned to receive either felzartamab or a dummy medicine called a placebo. Neither you nor the study team will know which you are getting during this time. Both are given as an infusion (drip) into your vein at the study clinic every few weeks for 24 weeks.

After 24 weeks, if you were on the placebo, you will switch to felzartamab, and everyone will know you are receiving the active drug. This second part lasts for another 28 weeks. You'll have kidney biopsies at the very start, at 24 weeks, and at 52 weeks to check your kidney health. You'll also have regular blood tests and check-ups at the clinic throughout the year to monitor your progress and safety.