"The task of immune cells is to recognize foreignness. And fight with it. An implanted foreign organ, or its fragment, is undoubtedly a foreign body. The immune system therefore begins to fight it. However, now immunopressives – and therefore immunosuppressants – are so effective that the rejection of transplants is inhibited."
January 1, 1970
https://en.wikiquote.org/wiki/W%C5%82odzimierz_Ptak