irradiating {TAIL ~ the mixture} of leukocytes in {HEAD ~ the presence} of a psoralen at a temperature between about 20° C. and about 28° C.; followed by 
irradiating { TAIL ~ the mixture } of leukocytes in { HEAD ~ the presence } of a psoralen at a temperature between about 20 ° C. and about 28 ° C. ; followed by
OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH 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