FLUORESCENCE IN-SITU HYBRIDIZATION FOR THE BCR ABL REARRANGEMENT IS DEPENDENT ON THE PERCENTAGE OF NONLYMPHOCYTIC CELLS IN PERIPHERAL-BLOODSTEM-CELL HARVESTS/

Interphase fluorescence in situ hybridization (FISH) for the transloca tion t(9;22) is widely used for quantifying minimal residual disease ( MRD) in PBSC harvests from CML patients. We investigated the influence of cell composition on the percentage of positive FISH signals in 17 BCR/ABL-positive leukapheresis products from 12 CML patients. In these PBSC harvests, a significant correlation between the percentage of no nlymphocytic nucleated cells and BCR/ABL positivity was measured (k = 0.81). This correlation was not seen in patients who became BCR/ABL ne gative after mini-ICE chemotherapy, CD34 enrichment was performed by i mmunomagnetic separation in 7 patients. There was a statistically sign ificant increase in BCR/ABL positivity after CD34+ selection (p = 0.01 8). This may have been caused by passive depletion of BCR/ABL-negative lymphocytes. Our findings suggest that quantitative results of t(9;22 ) FISH have to be corrected for cell composition when comparing differ ent stem cell products. CD34+ selection before FISH analysis may be on e way to enrich for nonlymphocytic cells and to concentrate on the pro genitor compartment.