Aplastic anaemia: pathogenetic mechanisms and treatment with special reference to immunomodulation

Current status of allogeneic bone marrow transplantation in acquired aplastic anemia

Bone marrow transplantation is an effective therapy for aplastic anemia. Infusion of allogeneic hematopoietic stem cells after high-dose immune suppression restores normal hematopoiesis in most patients and long-term follow-up has confirmed the durability of donor hematopoiesis. However, success of this approach is limited by transplant-related complications, such as graft failure, graft-versus-host disease, and various organ toxicities. Long-term survival rates range from less than 40% to more than 90% in reported series. These rates have improved over the past 20 years due to significant reductions in graft-versus-host disease, interstitial pneumonitis, and early transplant-related mortality. Most long-term survivors have excellent performance status. Late effects such as cataracts, thyroid disorders, joint problems, and therapy-related cancers are observed, especially in patients who received radiation for pretransplant conditioning. Results are best in young patients transplanted with bone marrow from a human leukocyte antigen (HLA)-identical sibling; early transplantation is appropriate in this group. For older patients or those without an HLA-identical related donor, transplants are better reserved for those who fail to respond to immunosuppressive therapy.

Antithymocyte immunoglobulin in severe aplastic anemia and bone marrow transplantation

OBJECTIVE

To review antithymocyte immunoglobulin (ATG) and its current role in the treatment of severe aplastic anemia (SAA), focusing on ATG in immunosuppressive therapy compared with bone marrow transplantation (BMT).

DATA SOURCES

A MEDLINE search (1966 to 1996) of English-language literature and human subjects pertaining to ATG and BMT therapy in SAA was performed. Additional literature was obtained from reference lists of pertinent articles identified through the search.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for possible inclusion in the review. Pertinent information, as judged by the authors, was selected for discussion.

DATA SYNTHESIS

The hallmark of SAA is pancytopenia and bone marrow hypoplasia. Although the etiology in a majority of cases remains unknown, current data implicate an immune-mediated destruction of stem cells. ATG is a potent immunosuppressive agent and has emerged as an important therapy for patients with SAA. The exact mechanism of immunosuppressive action is not fully understood, although ATG appears to disrupt cell-mediated immune responses resulting in inhibition or altered T-cell function. Numerous trials have evaluated the use of ATG both as monotherapy and in combination with other immunosuppressive agents. Treatment with ATG in SAA has demonstrated a 40-70% response rate. Data suggest that intensive immunosuppressive therapy with ATG in combination with cyclosporine may provide the optimal immunosuppressive treatment. Questions still remain concerning complications and long-term survival of the patients. Although more than a 2-year follow-up shows a decline in mortality, a plateau in the survival curve was not achieved. BMT is a potential treatment for SAA. Although there is a high initial mortality due to treatment-related toxicities, successful marrow engraftment provides a cure for SAA. Many patients (75-90%) experience long-term survival after allogenic BMT. Age, donor availability, and severity of disease limit the number of eligible patients.

CONCLUSIONS

Due to excellent results with BMT, it has become the therapy of choice for selected patients with SAA. For patients who are not eligible for BMT, intensive immunosuppressive therapy with ATG and cyclosporine is recommended. Further study to better understand the pathogenesis of SAA and prevent treatment-related complications is essential to provide the best care to all patients.

First report of a B cell lymphoproliferative disorder arising in a patient treated with immune suppressants for severe aplastic anemia

Aplastic anemia is a disorder characterized by pancytopenia and bone marrow hypocellularity. There is some evidence that aplastic anemia may be due to suppression of hematopoiesis by activated T-suppressor cells. Thus, immunosuppressive agents have been used as an alternative to bone marrow transplantation for treatment. We report on a unique case of a patient with aplastic anemia who was treated with a course of immunosuppression including cyclosporine (CSA), anti-thymocyte globulin (ATG), and prednisone. Five months after this treatment, the patient developed a B cell lymphoproliferative disorder which was successfully treated with radiation therapy. Prior reports of CSA-associated lymphoproliferative disorders have appeared in the literature as potential side effects of immunosuppression following transplantation. This is the first report of a lymphoproliferative disorder associated with immunosuppressive treatment of aplastic anemia in a nontransplant setting. Thus, when presenting options for treatment of aplastic anemia, lymphoproliferative disorders should be included as a rare complication of immunosuppressive therapy.

Severe aplastic anemia associated with seronegative community-acquired hepatitis C virus infection

Aplastic anemia (AA) is a rare complication of viral hepatitis affecting mainly children or young adults. Most reported cases have been associated with community-acquired non-A, non-B hepatitis, but hepatitis A and B have also been implicated in a few patients. We report on a 43-year-old woman with severe AA, in association with acute hepatitis C virus (HCV) infection, diagnosed by detection of HCV RNA by the polymerase chain reaction technique. Her AA was successfully treated with anti-thymocyte globulin and cyclosporin A. The hepatitis C progressed to chronic disease but, despite a follow-up time of 2 years, the patient still has no detectable anti-HCV antibodies, as evaluated with a second-generation anti-HCV assay.

The colony stimulating factors

Hematopoiesis is a dynamic process, which generate in the range of 10(9) cells/kg each day of erythroid and myeloid cells respectively. In vitro assays that were developed 20 years ago, have been used to define factors that can stimulate growth and differentiation of bone marrow (BM) derived progenitor cells. These growth factors for hematopoiesis were termed Colony Stimulating Factors (CSFs) since the assay system was to induce colonies. With the application of molecular biologic approaches, the genes encoding for these CSFs have been localized and cloned. Production of CSFs and other soluble signal substances (cytokines) as pure proteins have led to important insights into how hematopoiesis is regulated by a complex network made up by interactions between cells and cytokines. The availability of CSFs in clinically useful amounts has also led to clinical trials with new strategies for treating hematopoietic dysfunctions, congenital or acquired. Because others have recently reviewed clinical applications or basic science studies on the colony stimulating factors, we will summarize the two with focus on common features between the different CSFs.