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Aplastic Anemia

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  1. Aplastic Anemia Tissue Conference 1/19/00 Brad Kahl, MD

  2. Pancytopenia • Reduction of counts in all three cell lines • Differential Diagnosis • aplastic anemia • myelodysplasia • marrow replacement • leukemia, lymphoma, carcinoma, myelofibrosis • B12, folate • chemotherapy induced

  3. Pancytopenia • Differential Diagnosis continued • splenomegaly (any cause) • PNH • SLE • Congenital • Fanconi’s, Schwamann-Diamond, Folate uptake def

  4. Pancytopenia • Presentation varies with degree of cytopenia • anemia fatigue • thrombocytopenia bruising/bleeding • neutropenia infection • Approach • history • constitutional symptoms, pain, early satiety, etc... • diet, EtOH, exposures, occupation

  5. Pancytopenia • Approach • PE • nodes, spleen, sensory, portal htn • Labs • B12, folate, LFT’s, PNH, ANA • view smear (macrocytosis, megaloblastosis, tear drops, nuc RBC’s, malignant cells) • abdominal imaging • bone marrow evaluation


  6. Aplastic Anemia • Bone Marrow Failure • WHY?????????? • Stem cell defect (seed) • Stromal cell defect (soil) • Growth Factor defect (fertilizer) • Evidence suggests that majority of cases of idiopathic AA are due to immune suppression of the hematopoietic stem cell

  7. Aplastic Anemia Classification • Direct Toxicity • Iatrogenic (radiation, chemotherapy) • Benzene • Drug metabolites • Immune Mediated • Drug metabolites • transfusion associated • hepatitis associated • idiopathic

  8. Aplastic Anemia Pathophysiology • Evidence for an immunological basis arose from observations after BMT • unexpected improvement of pancytopenia in some patients after allogeneic graft failure • successful BMT of identical twins generally requires some sort of immunosuppressive conditioning regimen

  9. Aplastic Anemia Pathophysiology • Evidence for stem cells (seed) as targets • in vitro colony forming assays are used to define the stem cell compartment • two papers in 1996 showed profound deficits in the stem cell population in patients with AA • at the time of clinical presentation the absolute number of stem cells is < 1% of normal

  10. Aplastic Anemia Pathophysiology • What about the stroma (soil) and growth factors (fertilizer)? • successful BMT implies intact stroma since it is not replaced in the transplant • laboratory studies have shown the stroma of AA patients is able to support normal stem cell growth • stromal cells of AA patients tend to make increased levels of several growth factors (EPO, TPO, G-CSF) • clinical studies using factor replacement haven’t worked

  11. Aplastic Anemia Pathophysiology • Laboratory Evidence for Immune Destruction of Hematopoietic Stem Cells • mononuclear cells from blood and marrow of AA patients suppress hematopoietic colony formation by normal marrow stem cells • if selectively remove T cells from the sample, generally improve in vitro colony formation

  12. Aplastic Anemia Pathophysiology • What are the T cells doing? • Direct cellular cytotoxicity • blood and marrow of AA patients contain increased numbers of activated cytotoxic lymphocytes • the number and activity of these cells decreases after successful treatment with ATG

  13. Aplastic Anemia Pathophysiology • Cytokines • T cells of AA patients overproduce both IFN-gamma and TNF-alpha • both of these cytokines inhibit colony formation in vitro • IFN-gamma induces nitric oxide synthase (NOS) and production of nitric oxide (NO) • both induce expression of Fas receptor on CD34+ cells and activation of this receptor by its ligand induces apoptosis • both appear to inhibit mitosis • IFN-gamma increases IFN regulatory factor 1 which inhibits transcription of cellular genes and entry into the cell cycle

  14. Aplastic Anemia Pathophysiology

  15. Aplastic Anemia Pathophysiology • Inciting Events • much less clear, most cases--no clue • a few cases clearly associated with a non-A, non-B, non-C, non-G hepatitis • severe pancytopenia 1-2 months after an apparent viral hepatitis • patients tend to have a marked activation of cytotoxic lymphocytes and tend to respond favorably to immunosuppressive therapy

  16. Aplastic Anemia Pathophysiology • Drugs • implicated in 15-25% cases (difficult to study) • no animal model • some cases may be a direct toxic effect • some cases appear immune mediated • in general patients have similar characteristics as idiopathic AA and respond similarly to immunosuppression

  17. Aplastic Anemia Treatment • Options • BMT from donor vs. immunosuppression with ATG, CSA, or ATG/CSA combination • steroids, androgens generally ineffective • Trend towards separating severe AA and non-severe AA in current clinical trials

  18. Aplastic Anemia Treatment • Severe Aplastic Anemia Criteria • blood: • neutrophils < 500/mm3 • platelets < 20k • retics < 1% (corrected) • marrow • severe hypocellularity • moderate hypocellularity with hematopoietic cells representing < 30% of residual cells • need 2/3 blood and one marrow criteria

  19. Aplastic Anemia Treatment • Non-severe AA (Blood, April 99) • patients randomized to CSA vs. ATG/CSA • Overall Response Rate at 6 months • CSA 46% ATG/CSA 74% P=.02 • Similar early toxicity/infections

  20. Aplastic Anemia Treatment • Severe AA (Ann Int Med 1997) • Allo BMT vs. ImmunosuppressionORR15 Yr OS allogeneic BMT 89% 69% Immunosuppression 44% 38% • 40% BMT patients clinically extensive chronic GVHD • 1/227 receiving immunosuppression got ATG/CSA • 50/227 received ATG + mismatched bone marrow

  21. Aplastic Anemia Treatment • Severe Aplastic Anemia • NEJM 1991ORR ATG/Pred 31% ATG/Pred/CSA 65% • Blood 1992 ATG/LDM/oxymethalone 36% ATG/HDM/oxymetholone 48% • Blood 1995 ATG/CSA 78%

  22. Aplastic Anemia Treatment • Future • High Dose Cyclophosphamide vs. ATG • Addition of MMF to ATG/CSA combinations • ? allo BMT vs optimal immunosuppression?

  23. Aplastic Anemia Summary • idiopathic AA appears to be an AI disorder directed against hematopoietic stem cells • mediated by cytotoxic T cells and cytokines • allo BMT is the gold standard treatment • intensive immunosuppressive therapy has improved the outlook for patients ineligible for BMT due to age or lack of a suitable donor • expect further refinements in therapy as the pathophysiology is further elucidated