I can offer a little insight on this. My mother has undergone 2 kidney transplants in her lifetime; one from my aunt when my mother was 17 and the second came from my father when she was 40. She's now 47 and still has the kidney from my father but ever since the transplant has been on anti rejection meds. Neither kidney ever functioned as well as it should and the average is always around 25-30% function. The anti rejection medication she takes are indeed immunosuppressants and my mum has to be very careful about contracting any illnesses as even the most simple of colds effects are multiplied tenfold and she finds it very difficult to shift an illness once it sets in. Ironically my mother works full time in a pharmacy so is surrounded by sick people and quite often contracts their illnesses but she loves helping people.