CD34+ Cell Selection Reduces Tumor Cell Contamination in Myeloma Stem Cell Transplants

TORONTO—CD34+ selection of peripheral blood stem cells (PBSCs) significantly reduces tumor cell contamination while providing safe and rapid hematologic recovery for multiple myeloma patients receiving myeloablative therapy, Dr. A.K. Stewart, of Toronto Hospital, reported at ASH.

This multicenter phase III study randomized 190 patients with intermediate- and advanced-stage multiple myeloma to receive CD34+ selected or unselected autologous PBSCs after conditioning with busulfan (Myleran) and cyclophosphamide. All patients received GM-CSF starting 1 day post-transplant and continuing until neutrophil recovery.

CD34+ selection resulted in a median reduction of 3.1 logs of contaminating myeloma cells in the stem cell infusate, with the majority of CD34-enriched products having no detectable tumor.

Equivalent Engraftment

Neutrophil engraftment, the primary endpoint of the current analysis, was equivalent in both arms (median, 12 days). Platelet engraftment was also equivalent.

Multivariate analysis showed that time to platelet engraftment and the number of platelet transfusion events were influenced by the CD34+ cell dose. Rapid platelet engraftment occurred when patients received more than 2 × 10⁶ CD34+ cells/kg. Neutrophil and platelet engraftments were durable in all patients.

No differences were seen between the arms in any of the secondary endpoints: incidence of platelet or red blood cell transfusion, infections or bleeding events, general adverse events, hospitalization days, or overall survival.

Between day 0 and the 1-year visit 10 patients in each arm died. The percentage of patients who had progressed or died at 1 year was 25% (34) in the unselected arm and 26% (24) in the CD34-selected arm. “Any further analysis of these endpoints is premature at this time since so few events have occurred,” he said.