A quantitative study of peripheral blood stem cell contamination in diffuse large-cell non-Hodgkin's lymphoma: one-half of patients significantly mobilize malignant cells

Autologous transplantation using peripheral blood stem cells (PBSCs) collec ted after chemotherapy, followed by growth factor administration (ASCT), is increasingly used in the treatment of non-Hodgkin's lymphoma (NHL), Howeve r, quantitative data regarding contaminating malignant cells in the harvest s are still scarce. We prospectively investigated 37 diffuse large-cell lym phomas (DLCLs) in complete remission (CR) that were treated according to mu lticentric protocols at our centre. DNA was extracted from the diagnostic l ymph node. The complementarity-determining region (CDR) III was sequenced a nd a patient-specific oligomer synthesized. Contamination was evaluated sem iquantitatively by polymerase chain reaction (PCR) and was confirmed by a l imiting dilution analysis. PBSCs collected at regeneration after administra tion of granulocyte colony-stimulating factor (G-CSF), steady-state bone ma rrow (BM) and peripheral blood samples at CR were compared. DNA was availab le in 37 patients, from which 22 rearrangements could be sequenced. Patient s (n = 15) who had both the required follow-up samples and a suitable clona l marker were investigated. In two cases, the patient-specific PCR assay se t up at diagnosis later gave false-negative results in samples in which clo nal DNA was still detectable by other sets of primers. PBSC contamination w as highly variable: 7 out of 15 patients showed a PBSC/BM ratio of NHL cell s greater than 1 log, whereas 8 out of 15 patients showed no difference and could vary from one apheresis to another. Eight ASCTs were performed, five of which used highly contaminated PBSCs: four patients relapsed early, thr ee with disseminated lymphoma. Thus, 50% of DLCLs in CR seem to mobilize si gnificantly malignant cells at regeneration under G-CSF Considering the hig her numbers of cells reinfused, this translates into a much higher number o f lymphoma cells reinfused when compared with autologous bone marrow transp lantation (ABMT). However, their clonogenic potential remains unknown and, despite concerning observations in certain cases, it is still unclear wheth er this has an impact upon the outcome of ASCT.