Negative selection of peripheral blood stem cells to support a tandem autologous transplantation programme in multiple myeloma

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Abstract
Summary.We recently described a two‐step negative selection procedure whereby peripheral blood stem cells (PBSCs) were efficiently purged of contaminating neoplastic cells by a combination of monoclonal antibodies. Here, we report 60 newly diagnosed multiple myeloma (MM) patients treated with a double transplant programme and randomized to receive either unmanipulated orin vitropurged PBSCs. We demonstrated that this technique is feasible and safe without significant loss of either CD34+ or CD3+ cells. Haematological engraftment and immunological reconstitution were rapid without treatment‐related mortality. Using polymerase chain reaction (PCR), we compared the level of minimal residual disease (MRD) in PBSC before and afterin vitropurging andin vivoafter transplant. A median of one tumour cell per 102normal cells (range 101−105) was seen in the unmanipulated aphereses with a 3–4 log reduction after manipulationin vitro. However, despite this tumour debulking, all patients remained PCR positivein vivo.At 3 years, the estimated event‐free survival was 40% in the control arm and 72% in the experimental arm (P = 0·05), whereas the estimated overall survival was 83% in both arms. This suggests that autologous transplantation using efficiently purged PBSCs can be performed safely, but confirms the need for innovative protocols for MRD eradicationin vivo.

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