Many strategies for tolerance induction have been developed, because this is the major goal of clinical transplantation. One of the most effective and best-studied approaches has been based on the injection of hematopoietic cells derived from the donor bone marrow, to establish a state of microchimerism in the recipient. A subset of hematopoietic stem cells might be responsible for the tolerogenic properties. These CD34+ bone marrow stem cells can be isolated and safely injected into kidney transplant recipients. In the authors' clinical trial, no adverse effects were observed, and the infusion of donor CD34+ cells was well tolerated.