Pig lung transplanted into a human

They were kind of developed, and then abandoned due to governments saving on research (not because they didn't work). Or at least one kind was: "organoids" (which is a play on that they could be grown in any form, so some student decided to print a kind of alien-shaped almost-kidney, which then led to an article ... plus when used people want a flat relatively thin shape)

They are extensively used in pharmacological research because they match real organs very well on the cellular level. But there is further research necessary to implement the large scale parts. E.g. in kidneys the actual kidney and the connection to the gall bladder forms separately and is then combined into an organ. That doesn't work, yet.

And in some cases nobody has the courage to actually use it. The list of reasons why a liver organoid couldn't be implanted into a live patient is growing very thin. Well, aside from funding (which is massive if it fails, at least the equivalent of a year's pay. 3 or 4 times a year's pay for a doctoral student).

I would like to point out that this research isn't especially badly treated. It has fared better than most programs. But it probably can't even be saved. The actual defunding happened 5 years ago and last year even the PI has moved on, and every doctoral student involved also has. I'm sure they'll answer questions on the subject if you ask, but you'll have to rebuild things from papers and email questions. There is a spinoff selling organoids to pharma, but tiny ones (think clusters of x0000 cells). If the research in scaling organoids to full sizes is restarted now, you can't really expect results the first year, maybe two at least.

It isn't just the US that is defunding science.