{HEAD ~ The primary cells} are cultivated in a serum free medium comprising {TAIL ~ a factor} selected from the group consisting of growth factors and attachment factors 
{ HEAD ~ The primary cells } are cultivated in a serum free medium comprising { TAIL ~ a factor } selected from the group consisting of growth factors and attachment factors
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH