I think you might still run into rejection with that since its like not in sync with their immune system. So it would probably be better to temporarily have them on a pacemaker or mechanical heart while you grow a heart inside of them to replace the old one. Or the equivalent for other organs.
What does it mean to be "in sync" with an immune system?
AFAIK the immune systems works through antigen detection, the antigens that your immune system recognise as your own are innate to your own cells and are expressed automatically
