Autologous peripheral blood stem cells: collection and processing.

The rapid development in the area of collecting and processing autologous peripheral blood stem cells (PBSC) is reflected by the escalating number of patients treated with PBSC, and by the increasing amount of literature on the subject. Clinical experience suggests that among the variables with a negative influence on mobilization of PBSC, the most important may be the amount of previous stem cell toxic chemotherapy. In selecting patients suitable for autologous PBSC support, the requirement of an adequate anti-tumor therapy has to be weighed against the risk of chemotherapy related stem cell toxicity which will result in inability to collect a sufficient amount of PBSC. The general consensus is that a sufficient PBSC-autograft should contain 2-5 x 10(6) CD34+/kg body weight, but attempts to provide a recommended optimal or threshold level are hampered by the lack of standardized methods for CD34+ cell enumeration. In addition, the time to haematological recovery depends both on the dose of infused CD34+ cells and also on the amount of previous chemotherapy, which affects both the quality of the graft and the supportive microenvironment of the host. The quality of the autograft may also be contaminated by malignant cells, even if the biological significance of tumor cell detection in the PBSC graft has not yet been established. Recent development of methods for in vitro purging and selection of CD34+ cells for clinical use have provided the means to avoid or reduce reinfusion of malignant cells. Future directions of clinical research include the ability to define and enumerate the proportion of stem cells versus committed progenitor cells among the CD34+ cells in a PBSC collection, which will be important to ensure rapid engraftment as well as long term haematopoiesis.