That’s not actually how it works. Rejection of a transplanted organ means the body is developing antibodies against the organ.
Successful dosing and continued use of immunosuppressants inhibit the body from “rejecting” the transplanted organ(s).
I suspect you’re operating off a commonly held idea that transplanted organs have a “shelf life” but that’s not really true.
It’s important to keep in mind that transplanting organs is still comparatively new medical science (only about 70 years old) and that transplants are often for older patients or patients with other underlying conditions that caused the original organ failure to begin with.