CD34(+)-selected peripheral blood progenitor cell transplantation in patients with multiple myeloma: tumour cell contamination and outcome

Thirty-six patients with multiple myeloma (23 PR1, nine PR2, four stable di sease) were entered into a pilot study evaluating the use of CD34(+)-select ed peripheral blood progenitor cell transplantation (PBPCT) following high- dose melphalan alone or high-dose melphalan and total body irradiation. Per ipheral blood progenitor cells (PBPCs) were mobilized with cyclophosphamide and granulocyte colony stimulating factor (G-CSF). CD34(+) selection using the Cellpro Ceprate-SC system was performed in 22 cases with an adequate y ield in 20. 10 patients failed to mobilize sufficient cells to permit selec tion and in four cases selection was not performed for other reasons. 16 pa tients therefore received unselected PBPC. Tumour cell contamination was ev aluated by IgH gene fingerprinting (fpPCR). Harvested PBPC were fpPCR posit ive in 13/20 CD34(+)-selected cases and remained positive after selection i n seven. Harvested PBPC were studied in 9/16 patients receiving unselected cells; fpPCR was positive in five and negative in four. There was no differ ence in event-free survival (EFS) between the CD34(+)-selected group and th e unselected group (median 21 and 26 months, respectively, P=ns). The CD34( +)-selection process therefore reduced contamination but did not eliminate it completely, and in this small non-randomized study there was no apparent clinical benefit of CD34(+)-selection.