Can spare transplanted organ (8)
I believe the answer is:
pancreas
'organ' is the definition.
(pancreas is a kind of organ)
'can spare transplanted' is the wordplay.
'transplanted' is an anagram indicator.
'can'+'spare'='canspare'
'canspare' is an anagram of 'PANCREAS'.
(Other definitions for pancreas that I've seen before include "Gland aiding digestion" , "secreting structure" , "insulin producer" , "Sweetbread" , "Part of body" .)