The medium may be used for serum free culture or supplemented with {TAIL ~ low levels} of {HEAD ~ serum} 
The medium may be used for serum free culture or supplemented with { TAIL ~ low levels } of { HEAD ~ serum }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD