As in general shailah, The Gemorah in Sanhedrin (59b) reads:
?? ?? ??”? ?? ????? ??? ????? ?????? ???? ?? ??? ?????? ???? ?? ???? ????? ??? (????? ??, ??) ??????? ?????? ???? ????? ??? ???? ????? ??? ????? ???? ????? ?????? ???? ??? ????? ??? ??? ??? ??? ??? ?? ?? ??? ???? ?”? ??? ??? ??? ???? ?? ????? ??? ????? ?’ ???? ??’ ???? ???? ?? ???? ???? ??? ?”? ????? ???? ?? ???? ??? ??? ??? ??? ???? ?? ?????:
I would assume based on the above Gemorah that the reason it is mutar is entirely based on the fact that it is ??? ??? ??? ???? ?? ?????, meaning, that anything else even if it is unnatural it has the same status as natural regarding Tumah etc. As after all a donkey is still a donkey.
However Rashi says:
?? ???? ??? ??? ??? ??? ???? ?? ????? : ???? ????? ??? ??? ???? ???? ???:
From Rashi’s added words :
“- ???? ????? ??? – ??? ???? we can say that Rashi is implying that being that it was unnatural it has a status of “??? ????? ??? –
However, as Ubiq pointed out, the fact that it is taken and grown out of a natural’s cell might give it a diff status, although we might argue that is completely as ‘Panim Chadashos’ and is entirely a diff Min, or perhaps it has the status of ‘Yotzeih Min Hatomeh’ etc as well…
In any case, it is indeed a fascinating shailah with many angles to ponder…