[Cryopreservation of circulating stem cells in large quantities]

We have collected peripheral blood mononuclear cells in large quantities by leukapheresis from children with malignant disorders. The cells were fractionated on discontinuous gradients of Percoll for enrichment of hematopoietic stem cells and reduction of sample volume. They were subsequently frozen in a programmed freezer and stored in liquid nitrogen. This procedure allows a reduced DMSO volume to be infused into patients and increases storage space. The recovery rates of progenitors evaluated by freeze-thaw analysis in small aliquots were 89% for granulocyte-macrophage colony-forming units (CFU-GM) and 106% for granulocyte, erythroid, macrophage, megakaryocyte colony-forming units (CFU-GEMM). Hence, we conclude that circulating stem cells can be collected and cryopreserved in large quantities without any loss of capacity. Further studies to evaluate the relevance of performing rescue surgery with these stem cells following marrow-ablative chemotherapy are underway.