Hematopoiesis

Clinical Aspects of Hematopoiesis Robert Wise, M.D.

I.

Overview of Hematopoietic Cell Growth and Differentiation Pluripotential stem cells • Progenitor cells committed to specific cell lineages • Precursor cells recognizable in the bone marrow • Circulating RBCs, WBCs, platelets

II.

The Important Hematopoietic Factors and Their Biologic Functions A.

General

Several growth factors act cooperatively at each of the different stages of hematopoietic cell development. Some growth factors (eg, stem cell factor (SCF) and IL-3), tend to act at earlier stages and on multiple cell lineages; others, like erythropoietin and thrombopoietin, act on later, more differentiated progenitor and precursor cells that are committed a single lineage. B.

Specific factors and their loci of action

Table 1.

Major Hematopoietic Growth Factors

Factor

Early/Late*

Major Target Cells*

Stem cell factor

Primarily very early

Early stem and progenitor cells

Interleukin-3

Primarily early

Progenitor cells of multiple lineages (RBCs, WBCs, platelets)

GM-CSF

Early and late

Progenitor cells of multiple lineages (granulocytes, monocytes, RBCs)

Interleukin-6

Early and late

B-lymphocytes, hematopoietic cells of multiple lineages

G-CSF

Primarily late

Neutrophil progenitor and precursor cells

G-CSF

Primarily late

Neutrophil progenitor and precursor cells

Primarily late

Monocyte-macrophage progenitor and precursor cells

Erythropoietin

Late

Erythroid progenitor and precursor cells

Thrombopoietin

Late

Platelet (megakaryocyte) progenitor and precursor cells

*

M-CSF

These are generalization since many of these factors act at different phases of hematopoiesis and on multiple cell lineages.

III. Diseases of Hematopoietic Stem Cells and Progenitor Cells

A.

Common Features:

Involvement of multiple cell lines (RBCs, neutrophils, platelets, sometimes lymphocytes) Associations/transformations among the several diseases Possible termination in myelodysplasia or acute myelogenous leukemia Potential cure by allogeneic bone marrow transplantation B.

Diseases: Aplastic anemia Acquired pure red cell aplasia (only erythroid line involved) Paroxysmal nocturnal hemoglobinuria Myeloproliferative disorders: polycythemia vera, CML, essential thrombocythemia, agnogenic myeloid metaplasia with myelofibrosis Myelodysplastic ("preleukemic") syndromes Acute myelogenous leukemia (AML) in its several forms

IV. Bone marrow transplantation (BMT): A.

Allogeneic BMT: replace abnormal marrow, stem cells (defective, as in aplastic anemia, or malignant, as in AML) with normal stem cells from a histocompatible donor. Also permits high dose therapy (which might otherwise be lethal) of the malignant disease before the marrow is transplanted.

B.

V.

Autologous BMT: permits use of very high doses of chemotherapy, often with total body irradiation, in treatment of malignant diseases, with reinfusion of the patient's own marrow stem cells to prevent aplastic anemia from ensuing. The marrow cells are harvested and cryopreserved before the high dose therapy is given, usually when the patient is in clinical remission. Stem cells from the peripheral blood instead of marrow cells are being used with increasing frequency. Problem: reinfusion of residual malignant cells in the marrow infusate could reseed the malignant process in the patient; various "purging" techniques using antibodies or cytotoxic drugs are used to try to eliminate residual malignant cells, but their value is not fully proven.

Clinical uses of hematopoietic growth factors (a field of rapid, ongoing clinical experimentation) A.

Erythropoietin - effective in anemia due to renal failure, chronic disease, malignancy, chemotherapy.

B.

G-CSF, GM-CSF

C.

D.

E.

1.

Hasten WBC recovering after chemotherapy

2.

Hasten WBC regeneration after BMT

3.

Increase harvest of stem/progenitor cells in peripheral blood for use of instead of marrow in BMT

4.

Increase WBC and combat infections in various congenital and acquired causes of neutropenia, including aplastic anemia, myelodysplasia, drug-induced agranulocytosis.

5.

Used in attempts to treat disorders of stem cell differentiation, eg, myelodysplasia.

IL-3, usually in combination with another growth factor such as C- or GM-CSF. Not in wide clinical use. Has been tried in several of the situations outlined for G-, GMCSF, hoping for multi-lineage (WBC, RBC, and platelet) response. Only partly successful to date. IL-6, IL-11. In trials to determine whether they will hasten platelet recovery after chemotherapy, BMT. Thrombopoietin. Recently identified. Good prospects of increasing platelet regeneration, perhaps if combined with IL-3, -6, or -11.

APLASTIC ANEMIA

Etiology: Idiopathic Drug-induced (chloramphenicol, benzene, etc) Radiation-induced Vital (hepatitis, EBV) Pathogenesis:

Treatment:

Autoimmune attack on hematopoietic stem cells

Transfusion, antibiotic support Allogeneic marrow transplantation Anti-thymocyte globulin, cyclosporine, combined therapy Androgens of limited value G-CSF to stimulate neutrophil response

Complications: Development of PNH defect, myelodysplasia, AML PURE RED CELL APLASIA Congenital (Blackfan-Diamond syndrome) vs. acquired Association with thymoma (may respond to tumor excision), lymphoproliferative disorders Autoimmune pathogenesis in many cases: antibodies to early erythroid cells; response to steroids, cyclophosphamide, cyclosporine Vital etiology (parvovirus-19) in rare cases of chronic PRCA (may respond to (globulin) Paroxysmal Nocturnal Hemoglobinuria Defect in Pig-a gene (phosphatidyl inositol glycan-anchor, type A defect). Lack of anchoring protein - decreased membrane proteins including delay accelerating factor (DAF), causing increased sensitivity to 1ysis by complement. Prototypic clinical manifestation consists of intravascular hemolysis (hemoglobinuria, hemosiderinuria), especially at night. May lead to iron deficiency. Frequently pancytopenia (Pig-a and DAF defect present in RBCs, neutrophils, platelets, lymphocytes, endothelial cells).

Thrombotic complications Renal abnormalities Diagnosis: sugar water (sucrose hemolysis) test, acid hemolysis (Ham) test, tests for deficiency of DAF and other anchored proteins Associations: PNH defect may be seen in other disorders with damaged stem cells (aplastic anemia, MPD, MDS, AML); PNH patients may develop AML Myelodysplastic Syndrome Defective differentiation of marrow cells (ineffective hematopoiesis) Peripheral blood cytopenias with usually hypercellular bone marrow "Dyspoietic" marrow cells, giving rise to "dysplastic" peripheral blood cells (ringed sideroblasts, Pelger cells, etc.) Often an "excess of blasts" in marrow, peripheral blood Chromosomal abnormalities, often involving chromosome 5 or 7 Clinical course: anemia, infection, bleeding, transformation to AML Treatment: EPO for anemia, G-CSF for neutropenia. Allogeneic bone marrow transplantation may be curative Acute Myelogenous Leukemia: Update Acute promyelocytic leukemia: All-trans retinoic acid leads to improved survival, causes promyelocytes to differentiate into mature neutrophils Adult AML: Consolidation therapy with high dose cytosine arabinoside, after remission induction, improves survival MPD vs. MDS vs. AML Myeloproliferative disorder: excessive proliferation of marrow cells with differentiation to mature cells virtually normal (increased peripheral blood counts) Myelodysplastic syndrome: defective differentiation of marrow cells (hypercellular marrow with decreased peripheral blood counts; marrow and peripheral blood cells may appear dysmorphic) Acute myelogenous leukemia: differentiation blocked at or near the level of the myeloblast

(marrow filled with blasts, with few normal precursor cells; normal peripheral blood cells decreased with variable numbers of blasts) Bone Marrow Transplantation (BMT) I.

Allogeneic: replace abnormal stem cells by normal stem cells from histocompatible marrow donor. Also permits high dose chemotherapy, XRT before marrow is transplanted. Aplastic anemia Acute leukemia and other marrow malignancies (e.g., multiple myeloma)

II.

Autologous: Permits high dose chemotherapy, XRT, before patient's own cryopreserved marrow cells are reinfused. Acute leukemia, other malignancies that are in remission or do not involve the marrow

III. Trend toward use of peripheral blood rather than BM stem cells References 1. Apperley JF et al: The effect of cytomegalovirus on hemopoiesis: in vitro evidence for selective infection of marrow stromal cells. Exp Hematol 17:38, 1989 2. Baranski Bet al: Epstein-Barr virus in the bone marrow of patients with aplastic anemia. Ann Intern Med 109:695, 1988 3. Bradley TR., and Metcalf D. The growth of mouse bone marrow cell in vitro. Aust J Exp Med Sci. 44:287, 1966 4. Brandt SJ et al. Effect of recombinant human ganulocyte-macrophage colony-stimulating factor on hematopoietic reconstitution after high-dose chemotherapy and autologous bone marrow transplantation. N Engl J Med. 318:869, 1988. 5. Erslev AJ: Erythropoietin. N Engl J Med 324:1339, 1991 6. Eschbach JW et al. Correction of the anemia of end-stage renal disease with recombinant human erythropoietin: Results of a combined Phase I and II clinical trial. N Engl J Med. 316:73, 1987. 7. Groopman, JEet al: Hematopoietic growth factors: biology and clinical applications. N Engl J Med 321:1449, 1989 8. Groopman JEet al. Effect of recombinant human granulocyte- macrophage colonystimulating factor on myelopoiesis in the acquired immunodeficiency syndrome. N Engl J

Med. 317:593, 1987. 9. Metcalf D: Control of granulocytes, and macrophages: molecular, cellular, and clinical aspects.. Science. 254:529, 1991. 10.

Storb R, Thomas ED, Buckner CD et al: Marrow transplantation for aplastic anemia. Sem Hematol 21:53, 1984.

11.

Till JE and McCulloch EA. A direct measurement of the radiation sensitivity of mouse bone marrow cells. Radiat Res. 14:213, 1961.

12.

Young NS, Alter BF: Aplastic anemia, Acquired and Inherited. WB Saunders. Philadelphia, 1994.

13.

Young N: Hematologic and hematopoietic consequences of B19 parvovirus infection. Semin Hematol 25:159, 1988