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