there was a gal who had a cardiac arrest and became braindead
her family essentially 'donated' her body to science - as her body still functioned even though her cognition was severely and irreparably damaged....
as one could imagine, her kidneys were nonfunctional
scientists were able to genetically modify a pig kidney so that her body would not reject it - and would not need immune-suppressing drugs. IIRC, they actually had the thing linked up to her system - outside of her body in some sort of containment machine
truly macabre, but fascinating - from a scientistic point of view.
point being, we are almost there