Hematopoietic cell transplantation (HCT) is the IV infusion of hematopoietic progenitor cells designed to establish marrow and immune function in patients with a variety of acquired and inherited malignant and nonmalignant disorders. They include hematologic malignancies (eg, leukemia, lymphoma, and myeloma), nonmalignant acquired bone marrow disorders (aplastic anemia), and genetic diseases associated with abnormal hematopoiesis and function (thalassemia, sickle cell anemia, and severe combined immunodeficiency). HCT also is used in the support of patients undergoing high-dose chemotherapy for the treatment of solid tumors for whom hematologic toxicity would otherwise limit drug administration (eg, breast, germ-cell, soft-tissue sarcomas, and neuroblastoma).

Types of transplantation

Since the advent of HCT in the 1960s, several different methods of transplantation have evolved. At present, the hematopoietic cells used for HCT are obtained from either bone marrow or peripheral blood. The decision to use a certain type of HCT is dictated by the patient’s disease and condition and the availability of a donor. In some cases, more than one approach is possible. Table 1 summarizes the advantages and disadvantages of each stem-cell source.

Allogeneic BMT, match related
This method involves procurement of bone marrow from a human leukocyte antigen (HLA)-identical sibling of the patient. In some cases, a partially matched sibling or family donor (one antigen mismatch) can be used for bone marrow transplantation (BMT).

Allogeneic BMT, match unrelated
Given that there are a limited number of alleles of the HLA system, typing of large numbers of individuals has led to the observation that full matches for patients exist in the general population. Tissue typing is performed on the patient’s blood, and a search of the computer files of various international registries is made to determine whether a patient has a match with an unrelated individual.

Haploidentical transplantation
This technique involves the transplantation of large numbers of T-cell–depleted stem cells from a donor, usually a sibling or a parent, who is half matched to the patient. Although these are the most difficult transplantations to perform successfully, there is great interest in this approach, because most patients will have a donor in their family who is at least a 50% HLA match. Most transplants will engraft, and few patients will have significant graft-versus-host disease (GVHD). However, the relapse rate is high, and the process of immune reconstitution is slow, with patients often having troublesome infections for a long time after transplantation.

Autologous BMT
This form of transplantation entails the use of the patient’s own bone marrow, which is harvested and then cryopreserved prior to administration of chemotherapy and/or high-dose radiation therapy. Following completion of therapy, the marrow cells are then thawed and reinfused into the patient to reestablish hematopoiesis.

Autologous peripheral blood stem-cell transplantation
With the recognition that the marrow stem cells circulate in the peripheral blood, methods have been devised to augment the number of these cells in the patient’s circulation. The blood is then collected on a cell separator and frozen in a manner similar to that of autologous marrow, to be used after high-dose chemotherapy and/or radiation therapy. This is now the most common source of stem cells used in the autologous setting.

Syngeneic transplantation
In this form of transplantation, marrow or peripheral blood stem cells are procured from an individual who is a genetic identical twin to the patient.