Hematopoietic Stem Cell Transplantation
Hematopoietic stem cell (HSC) transplantation is a rapidly evolving technique that offers a potential cure for hematologic cancers (leukemias, lymphomas, myeloma) and other hematologic disorders (eg, primary immunodeficiency, aplastic anemia, myelodysplasia). HSC transplantation is also sometimes used for solid tumors (eg, some germ cell tumors) that respond to chemotherapy. (See also Overview of Transplantation.)
HSC transplantation contributes to a cure by
HSC transplantation may be autologous (using the patient's own cells) or allogeneic (using cells from a donor). Stem cells may be harvested from
Peripheral blood has largely replaced bone marrow as a source of stem cells, especially in autologous HSC transplantation, because stem cell harvest is easier and neutrophil and platelet counts recover faster. Umbilical cord HSC transplantation has been restricted mainly to children because there are too few stem cells in umbilical cord blood for an adult. A potential future source of stem cells is induced pluripotent stem cells (certain cells taken from adults and reprogrammed to act like stem cells).
There are no contraindications to autologous HSC transplantation.
Contraindications to allogeneic HSC transplantation are relative and include age > 50, previous HSC transplantation, and significant comorbidities.
Allogeneic HSC transplantation is limited mainly by lack of histocompatible donors. A human leukocyte antigen (HLA)-identical sibling donor is ideal, followed by an HLA-matched sibling donor. Because only one fourth of patients have such a sibling donor, mismatched related or matched unrelated donors (identified through international registries) are often used. However, long-term disease-free survival rates may be lower than those with HLA-identical sibling donors.
The technique for umbilical cord HSC transplantation is still in its infancy, but it is gaining interest. About 20,000 cord blood transplantations have been done since the procedure was introduced in 1989. Because cord blood contains immature stem cells, HLA matching appears less crucial than for the other types of hematopoietic stem cell transplantation. One concern about the procedure is the antigen-inexperienced nature of immune cells in cord blood, leading to a higher percentage of naive T cells, which increases risk of reactivating infections with cytomegalovirus or Ebstein-Barr virus.
For bone marrow stem cell harvest, 700 to 1500 mL (maximum 15 mL/kg) of marrow is aspirated from the donor’s posterior iliac crests; a local or general anesthetic is used.
For peripheral blood harvest, the donor is treated with recombinant growth factors (granulocyte colony-stimulating factor or granulocyte-macrophage colony-stimulating factor) to stimulate proliferation and mobilization of stem cells; standard apheresis is done 4 to 6 days afterward. Fluorescence-activated cell sorting is used to identify and separate stem cells from other cells.
Stem cells are then infused over 1 to 2 hours through a large-bore central venous catheter.
Before allogeneic hematopoietic stem cell transplantation for cancer, the recipient first is given a conditioning regimen (eg, a myeloablative regimen such as cyclophosphamide 60 mg/kg IV once a day for 2 days with full-dose total body irradiation or busulfan 1 mg/kg orally 4 times a day for 4 days plus cyclophosphamide without total body irradiation) to induce remission and suppress the immune system so that the graft can be accepted.
Similar conditioning regimens are used before allogeneic HSC transplantation, even when cancer is not the indication, to reduce incidence of rejection and relapse.
Such conditioning regimens are not used before autologous HSC transplantation for cancer; cancer-specific drugs are used instead.
Nonmyeloablative conditioning regimens (eg, with cyclophosphamide, thymic irradiation, antithymocyte globulin [ATG], and/or cyclosporine) may reduce morbidity and mortality risks and may be useful for older patients, patients with comorbidities, and patients susceptible to a graft-vs-tumor effect (eg, those with multiple myeloma).
Reduced intensity regimens (eg, fludarabine with melphalan, oral busulfan, or cyclophosphamide) have intensity and toxicity between myeloablative and nonmyeloablative regimens. Resulting cytopenias may be prolonged and result in significant morbidity and mortality, and require stem cell support.
After hematopoietic stem cell transplantation, recipients are given colony-stimulating factors to shorten duration of posttransplantation leukopenia, prophylactic anti-infective drugs, and, after allogeneic HSC transplantation, up to 6 months of prophylactic immunosuppressants (typically methotrexate and cyclosporine) to prevent donor T cells from reacting against recipient HLA molecules (graft-vs-host disease). Broad-spectrum antibiotics are usually withheld unless fever develops.
Engraftment typically occurs 10 to 20 days after HSC transplantation (earlier with peripheral blood stem cells) and is defined by an absolute neutrophil count > 500/mcL (> 0.5 × 109/L).
(See also Posttransplantation Complications.)
Complications of stem cell transplantation can occur early (< 100 days after transplantation) or later. After allogeneic HSC transplantation, risk of infections is increased.
Major early complications include
Failure to engraft and rejection affect < 5% of patients and manifest as persistent pancytopenia or irreversible decline in blood counts. Treatment is corticosteroids for several weeks.
Acute GVHD occurs in recipients of allogeneic hematopoietic stem cell transplants (in 40% of HLA-matched sibling graft recipients and 80% of unrelated donor graft recipients). It causes fever, rash, hepatitis with hyperbilirubinemia, vomiting, diarrhea, abdominal pain (which may progress to ileus), and weight loss.
Risk factors for acute GVHD include
Diagnosis of acute GVHD is obvious based on history, physical examination, and liver test results. Treatment is methylprednisolone 2 mg/kg IV once a day, increased to 10 mg/kg if there is no response within 5 days.
Major later complications include
Chronic GVHD may occur by itself, develop from acute GVHD, or occur after resolution of acute GVHD. It typically occurs 4 to 7 months after HSC transplantation (range 2 months to 2 years). Chronic GVHD occurs in recipients of allogeneic HSC transplants (in about 35 to 50% of HLA-matched sibling graft recipients and 60 to 70% of unrelated donor graft recipients).
Chronic GVHD affects primarily the skin (eg, lichenoid rash, sclerotic skin changes) and mucous membranes (eg, keratoconjunctivitis sicca, periodontitis, orogenital lichenoid reactions), but it also affects the gastrointestinal tract and liver. Immunodeficiency is a primary feature; bronchiolitis obliterans similar to that after lung transplantation can also develop. Ultimately, GVHD causes death in 20 to 40% of patients who have it.
Treatment may not be necessary for GVHD that affects the skin and mucous membranes; treatment of more extensive disease is similar to that of acute GVHD. T-cell depletion of allogeneic donor grafts using monoclonal antibodies or mechanical separation reduces incidence and severity of GVHD but also eliminates the graft-vs-tumor effect that may enhance stem cell proliferation and engraftment and reduce disease relapse rates. Relapse rates with autologous HSC transplantation are higher because there is no graft-vs-tumor effect and because circulating tumor cells may be inadvertently collected with stem cells and transplanted. Ex vivo tumor cell purging before autologous transplantation is under study.
In patients without chronic GVHD, all immunosuppression can be stopped 6 months after hematopoietic stem cell transplantation; thus, late complications are rare in these patients.
Prognosis after hematopoietic stem cell transplantation varies by indication and procedure.
Overall, disease relapse occurs in
Overall, success (cancer-free bone marrow) rates are
Compared with chemotherapy alone, HSC transplantation improves survival of patients with multiple myeloma. Success rates are low for patients with more advanced disease or with responsive solid cancers (eg, germ cell tumors). Relapse rates are reduced in patients with graft-vs-host disease (GVHD), but overall mortality rates are increased if GVHD is severe.
Intensive conditioning regimens, effective GVHD prophylaxis, cyclosporine-based regimens, and improved supportive care (eg, antibiotics as needed, herpesvirus and cytomegalovirus prophylaxis) have increased long-term disease-free survival after HSC transplantation.