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