Discarded leukoreduction filters: a new source of stem cells for research, cell engineering and therapy?

New adult stem cell sources, devoid of the technical/ethical/economical barriers of those presently available, would favor the ongoing development of in vitro cell engineering and transplantation. Hematopoietic transplantation opened the way to and remains the most successful cell transplantation procedure. CD34+ cells that include hematopoietic stem cells (HSCs) and hematopoietic progenitors (HPs) are presently harvested from bone marrow (BM), cord blood or peripheral blood (after being mobilized from BM). The panel of potential donors, the quantities of collected cells and some other technical/medical problems still represent limiting factors to their transplantation in some patients. Steady state peripheral blood (SSPB) contains very low frequencies of CD34+ cells. They are trapped in leukoreduction filters (LRFs), which are discarded after the preparation of therapeutic red blood cell concentrates from individual blood donations. We recently developed a procedure allowing the easy and rapid elution of CD34+ cells from LRFs and we showed that they are functionally similar to those harvested from other sources. After providing an overview of the sources, interests and limitations of therapeutic HSCs presently available, we will provide arguments based on our and others' results suggesting that SSPB could become an attractive source of HSCs for hematopoietic transplantation and of other cell types for various research/development procedures.