PURIFIED CD34(-) THY(+) STEM-CELLS DO NOT CONTAIN CLONAL MYELOMA CELLS() LIN()

High-dose therapy with autologous marrow or peripheral blood stem cell (PBSC) rescue has been extensively applied in the treatment of multip le myeloma (MM) patients during the past 10 years resulting in improve d event-free and overall survival when compared with standard chemothe rapy. However, relapses are common and cure is unlikely in the majorit y of patients. Because both bone marrow and PBSCs are contaminated wit h myeloma cells it is conceivable that relapse after autotransplantati on originates at least in part from autografted tumor cells. In this s tudy, mobilized PBSCs were examined for the presence of myeloma cells based on immunophenotyping and sensitive polymerase chain reaction (PC R)-based techniques. In addition, CD34(+) Lin(-) Thy(+) stem cells wer e purified from mobilized PBSC harvests of 10 MM patients by sequentia lly using counterflow elutriation centrifugation, treatment with pheny lalanine methylester, and flow sorting, using 5-parameter gating (prop idium iodide, forward scatter, side scatter, CD34(+) v Lin(-) and CD34 (+) v Thy(+)). Virtually all mobilized unsorted PBSC preparations cont ained myeloma cells in sufficient quantities (range, <0.01 to >10%) po tentially causing a disease relapse. Stem cell purification led to an overall enrichment by about 50-fold in all 10 patients; approximate to 90% of the final cell population expressed CD34(+) Lin(-) Thy(+) with no evidence of myeloma cell contamination based on flow cytometric an alysis of CD38(bright) cells (<0.1%). Quantitative PCR amplification o f patient-specific complementarity determining region III (CDRIII) DNA sequences showed depletion of clonal B cells by 2.7 to 7.3 logs, with the highest log reduction noted in the samples initially containing t he most tumor cells. Our results show that purification of CD34(+) Lin (-) Thy(+) cells depletes myeloma cells to undetectable levels from up to 10% present in unsorted PBSCs, thus offering a tool to investigate whether MM relapse after autotransplantation can be reduced markedly. (C) 1995 by The American Society of Hematology.