as someone who doesn't know anything about the exact science behind it... I am aware of recipients requiring to take immuno suppressants to prevent organ rejection. But there has been a rare moment where the recipients blood type changed after receiving a new organ transplant. scienctific research is on the edge of a few breakthroughs that would make it possible to change blood type of organs so the patient never has to take immuno suppressing drugs. https://www.newscientist.com/article/2308568-lung-with-switched-blood-type-is-step-towards-universal-donor-organs/