Peripheral blood progenitor cells for HPC transplants involving unrelated donors

Volume 40, June 2000 TRANSFUSION 731 For the past 30 years, marrow transplantation has been used successfully to treat an ever-increasing number of diseases. Over the past 10 years, peripheral blood progenitor cell (PBPC) concentrates have replaced marrow as the source for autologous progenitor cell transplants. Since 1995, some centers have been using PBPC concentrates in place of marrow for transplants involving HLA-compatible siblings,1-4 and trials using PBPC concentrates for transplants involving HLA-compatible unrelated donors for second transplants were begun by the National Marrow Donor Program (NMDP) in early 1997. Experience with transplants involving HLA-compatible sibling donors has shown that PBPC concentrates can be collected safely and that these transplants are effective. From the donor’s point of view, the collection of PBPC concentrates has several advantages over that of marrow: avoiding the potential risk of anesthesia, the painful aspiration procedure, and the prolonged postcollection recovery period. PBPC concentrates may also be advantageous for transplant recipients, in that they contain more hematopoietic precursors than marrow does.5 Preliminary studies on transplants involving HLA-compatible sibling donors have found that, when PBPC concentrates are used in place of marrow, both neutrophil and platelet engraftment times and acute transplant-associated morbidity are reduced, while the incidence of acute GVHD is similar.5 Recipients of PBPC concentrates also have a more rapid reconstitution of Tand B-cell proliferation responses to phytohemagglutinin, pokeweed mitogen, tetanus toxoid, and Candida sp.6 Although results are promising, some studies have suggested that the incidence of chronic GVHD in recipients of PBPC concentrate transplants is high,7 and some centers are reducing the number of T cells in PBPC concentrates by antibody-mediated selection of CD34+ cells.8 Preliminary results of allogeneic transplants using PBPC concentrates enriched with CD34+ cells have been encouraging, in that engraftment has remained rapid, while the incidence of acute and chronic GVHD has been low.8 Transplants using marrow from HLA-compatible unrelated donors have been used to successfully treat acute myelogenous leukemia, acute lymphocytic leukemia, chronic myelogenous leukemia, aplastic anemia, congenital immunodeficiencies, metabolic storage diseases, and many other diseases. The success rates of unrelated-donor marrow transplants are as high as 74 percent for patients with chronic myelogenous leukemia.9 When compared with transplants involving HLA-compatible siblings, however, transplants from unrelated donors are complicated by higher rates of GVHD and transplantrelated mortality. It is possible that the use of PBPC concentrates rather than marrow for unrelated-donor transplants could result in higher rates of engraftment and less transplant-associated morbidity and hence better disease-free survival. Trials of PBPC concentrates for unrelated-donor transplants are therefore now warranted. In this review, the procedures used to collect marrow from unrelated donors and to mobilize and collect PBPC concentrates from sibling donors are compared and contrasted. PBPC mobilization and collection issues unique to unrelated donors and precautions that should be taken to ensure the well-being of the unrelated donor in this setting are discussed.