Autologous peripheral blood progenitor cell (PBPC)
transplantation is increasingly being used for treatment of indolent
lymphomas. Since involvement of bone marrow and peripheral blood is frequent and methods to reduce the
lymphoma cell load of PBPC grafts are thus highly desirable, we have studied purging of PBPC comparing two immunomagnetic CD34+ selection systems (VarioMACS, Miltenyi Biotech; Bergisch Gladbach, Germany, and Isolex50 System, Baxter; Irvine, CA). Samples of freshly collected mobilized PBPCs were contaminated with BALM-3 or KARPAS422
lymphoma cells that had been labeled with the fluorescent
DNA stain Hoechst 33342. The mixture was subjected to separation with the two devices and the resulting "CD34+" fractions were screened for
lymphoma cells by limiting dilution using fluorescence microscopy and by polymerase chain reaction amplification of t(14;18) or CDRIII-rearrangements. Both devices yielded comparable purities (MACS 97% [87%-99%]; Isolex 97% [84%-99%]) and recoveries of CD34+ cells (MACS 56% [30%-81%]; Isolex 45% [24%-63%]). The overall depletion of
lymphoma cells was 3.9 log (2.6-5.9), however, residual contaminating cells were seen in every single experiment. The purging efficacy was dependent on the type of contaminating
lymphoma cell (BALM-3: 4.4 log [3.7-4.8]; KARPAS422: 3.2 log [2.6-4.2]; p = 0.018), whereas the type of selection system used or the percentage of CD34+ cells in the starting material had no influence. We conclude that excellent purification of CD34+ cells leading to a vigorous depletion of
lymphoma cells can be achieved with both CD34+ selection systems investigated. However, the efficacy of purging may greatly differ between individual
lymphomas, and complete eradication of contaminating cells from PBPC grafts may rarely be achieved with CD34+ selection alone.