Donor-derived hematopoietic stem cells in organ transplantation: technical aspects and hurdles yet to be cleared.

The use of hematopoietic stem-cell (HSC) therapy in organ transplantation is a challenge to promote chimerism with the aim of enhancing organ tolerance. Several HSC sources are available, including bone marrow (most of the time), peripheral blood after stem-cell mobilization, and placental blood. HSC collection techniques from vertebral bodies or iliac crests require a number of complex manipulations. The best yield of HSC is obtained from vertebral bodies. HSC harvesting by cytapheresis after cell mobilization with a cytokine such as granulocyte colony-stimulating factor should be preferred with a live donor. The number of CD3+ T cells is more than 10-fold higher in peripheral blood than in bone marrow. Cell separation by the immunoselection technique (positive selection of the CD34+ cell population) eliminates erythrocytes, granulocytes, and T cells, thus preventing the possible occurrence of acute graft-versus-host disease. In the future, an accreditation will be required for HSC collection and processing. In Europe, the reference tool is the Joint Accreditation Committee of Ishage-Europe or the Foundation for the Accreditation of Haematopoietic Cell Therapy manual, which provides standards for every technical step of these procedures.