Check rooms in monastery for controversial sources of therapy (4,5)
I believe the answer is:
stem cells
'controversial sources of therapy' is the definition.
(the use of stem cells is controversial)
'check rooms in monastery' is the wordplay.
'check' becomes 'stem' (both can mean to control or stop).
'rooms in monastery' becomes 'cells' (a monk's room is called a cell).
'stem'+'cells'='STEM CELLS'
'for' acts as a link.
(Other definitions for stem cells that I've seen before include "biological material for research?" , "Opportunities for development" , "Basic units of organism, not yet specialised" , "Organic units having the ability to regenerate tissue" .)