Autologous and allogeneic transplantation with peripheral blood CD34+ cells: a pediatric experience

Peripheral blood stem cells (PBSC) have replaced bone marrow (BM) as the primary form for autologous hematopoietic stem cell transplantation. Furthermore, the use of allogeneic PBSC transplantation is now rapidly expanding and several centers have adopted this procedure. A new strategy in the use of PBSC is positive selection of CD34+ hematopoietic progenitor (CD34+) cells, and indeed large-scale devices for the clinical exploitation of CD34+ cell selection are now commercially available. In the autologous setting, the primary advantage of using CD34+ selected PBSC is reduced tumor cell contamination during PBSC preparation. On the other hand, in the allogeneic setting, CD34+ selection methods are used to reduce the incidence and severity of GvHD. Initial trials of CD34+ selected PBSC transplants have mainly been performed in adult cancer patients, and experience with CD34+ selected PBSC transplantation in pediatric populations is still limited. The purpose of this review is to clarify the status of CD34+ selected PBSC transplantation in the pediatric population.

All authors of the present review work in the field of pediatric stem cell transplantation and in a stem cell processing laboratory, and have contributed to original papers published in peer-reviewed journals. The materials examined in the present review include articles and abstracts published in journals covered by the Science Citation Index and Medline. However, since there is still limited experience with CD34+ cell selection in pediatric populations, information on experience in adults will be discussed regarding the CD34+ cell-selection procedures and transplantation. Pediatric experience with transplants with CD34+ selected cells will be presented and discussed primarily based on our own experience. Specific problems related to PBSC mobilization and collection in children will also be discussed.

A review of the literature shows that with current CD34+ selection methods, purity of the CD34+ cell fraction can range from 30% to 90%, and two to three logs of T-cell depletion can be achieved. Tumor cell contamination has not yet been fully evaluated. The clonogenic activity of progenitor cells after CD34+ selection from PB remains high. Transplantation of autologous selected CD34+ cells from PBSC gives prompt and stable engraftment. The long-term therapeutic efficacy should be evaluated with regard to tumor recurrence. Allogeneic CD34+ selected cells successfully engraft immunomyeloablated recipients though a mega-cell dose effect between HLA-matched pairs. The results of allogeneic CD34+ selected cell transplantation from HLA-mismatched donors are, so far, not satisfactory because of the high rate of rejection, severe infectious complications and relapse of the disease. CD34+ selection may also be used as a target of gene therapy, as a source of dendritic cells for cancer immunotherapy and for the treatment of patients with autoimmune disease.