Special Feature: New Therapies for Aplastic Anemia

Special Feature: New Therapies for Aplastic Anemia BY SANFORD B. KRANTZ, MD

This morning I have chosen to refrain from any discourse on the politics of medicine. Instead I want to describe recent clinical investigations on the treatment of aplastic anemia that have greatly altered the outcome of this disease and that, once again, reaffirm the value of investigation to clinical medicine. Aplastic anemia is a disorder characterized by marrow hypoplasia or aplasia associated with peripheral blood pancytopenia of variable severity.l.2 Just a short time ago, most patients with severe aplastic anemia died of infection or hemorrhage within 6-12 months. 1•2 Now it is possible to treat aplastic anemia so that most patients survive without the need for transfusions. This change has come about, first, through a greater understanding of normal hematopoiesis; second, through an understanding of the pathogenesis of selective aplasias, and finally, through the application of this knowledge to aplastic anemia. It is now known that the hematopoietic pluripotential stem cell gives rise to selective progenitor cells that are committed to one line of hematopoiesis, erythrocytic, granulocytic, or megakaryocytic, and that the development of these progenitor cells into terminal red cells, white cells, or platelets is controlled by a specific hormone, such as erythropoietin in the case of the red cells. In rare cases, aplasia occurs that involves only a single progenitor cell line. These cases are described as pure red cell aplasia, white cell (granulocyte) aplasia, or megakaryocyte aplasia. Although the pathogenesis of aplastic anemia is still unclear, because of an inability to culture the pluripotential stem cell, substantial evidence exists that many cases of the selective single From the Department of Medicine, Division of Hematology, Veterans Administration Medical Center and Vanderbilt University, Nashville, Tennessee. Supported by VA Medical Research funds and Grants AM15555, T32 AM-07186, andRR-95 from the NationaLInstitutes of Health. Based on the Presidental Address delivered at the Annual Meeting of the Southern Society for Clinical Investigation, New Orleans, Louisiana, February 7, 1986. Reprint requests: Sanford B. Krantz, MD, Department of Medicine, Hematology Division, Vanderbilt Medical Center North C3101, Nashville, TN 37232. THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES

cell line aplasias are due to autoimmunity and that they repond to immunosuppressive therapy. The treatment of these isolated single cell line aplasias will be described first in order to understand better the evolution of the treatment for aplastic anemia. Pure Red Cell AplasIa (PRCA)

PRCA is a condition in which patients suddenly stop making erythroblasts in the bone marrow, but have normal white cell and platelet production. 3 The bone marrow has a normal cellularity because of normal granulopoiesis and a slight increase in small lymphocytes, but there are less than 0.5% mature erythroblasts. The blood generally has a normal leukocyte and platelet count, but less than 1% reticulocytes despite a severe anemia. These patients have a very high incidence of thymomas, so that, in addition to a bone marrow aspiration and biopsy, aCT scan of the chest should be performed. Of patients with a thymoma, 29% will have a remission of the anemia after the tumor is resected. In addition, PRCA may be produced by a wide variety of drugs, including chlorpropamide, diphenylhydantoin, gold, halothane, isoniazid, penicillin, phenobarbital, phenylbutazone, salicylazosulfapyridine, sulfathiazol, and tolbutamide. Any drug the patient is receiving when the PRCA is first noted should be discontinued. If the PRCA has arisen from the use ofa drug, it most often will disappear when the drug is discontinued. Erythropoietin levels are very high in most cases, indicating that the problem is a lack of marrow response to the hormone. Recent investigation has shown that some PRCA patients have an IgG antibody that acts on the marrow cells to inhibit erythropoiesis.3-6 When the marrow cells of these patients are removed from the body and incubated in vitro with a normal culture medium, they' often respond to erythropoietin with a large increase in hemoglobin synthesis and the manufacture of mature erythroblasts. 4,6 The erythroid progenitor cells are present and capable of developing into erythroblasts in vitro even when they cannot do this in vivo. When these cells are incubated with the patient's own plasma, or IgG, the rate of hemoglobin synthesis and erythroblast formation is markedly depressed,4-9 Some of these patients have an antibody that specifically injures the marrow 371

Aplastic Anemia

erythroblasts while not attacking the erythrocytes or lymphocytes,5 while others have an IgG that prevents the erythroid progenitor cells from developing into erythroblasts. 3.6 The discovery of an antibody to the marrow cells has led to the successful treatment ofPRCA patients with cytotoxic immunosuppressive drugs such as cyclophosphamide or azathioprine, in addition to corticosteroids.3-8 After the diagnosis is first made, it is wise to discontinue drugs and observe the patient for 3-4 weeks, since some patients will have a spontaneous remission. However, if the PRCA persists, treatment should be initiated with either high-dose prednisone (60 mg/day orally) or prednisone (30 mg/day orally) combined with cyclophosphamide, depending on the patient. Young patients probably should be treated with prednisone alone, since cyclophosphamide produces sterility and is leukemogenic. Highdose prednisone should be continued for 4 weeks, and if a remission has not occurred by then, it should be discontinued to be followed by combined prednisone and cyclophosphamide. High-dose prednisone has a 37-45% remission rate (Table 1), and remissions generally occur within 4 weeks. 7 Cyclophosphamide is begun at 50 mg/day by mouth for the first week in addition to prednisone (30 mg/day). Blood counts are then checked to be sure that no untoward leukocyte or platelet toxicity has been produced. These counts are usually stable over this period, and in the second week the cyclophosphamide is increased to 100 mg/day. Blood counts are checked after another 7 days, and if they are stable, the cyclophosphamide is increased to 150 mg/day. Blood counts are then checked every 1-2 weeks. As the cyclophosphamide is continued, one of two events may be noted: (1) reticulocytes may increase, and the patient may gradually begin to sustain his own hematocrit (Figure 1), or (2) the leukocyte count may begin to decline without an increase in reticulocytes.

In the first event, the cyclophosphamide and prednisone are slowly tapered and discontinued after the patients have normal hematocrits. In the second case, the cyclophosphamide is continued and even increased after 8 weeks until the leukocyte count declines to 2,000/ul. At this point the cyclophosphamide is discontinued, and when the marrow regenerates in 3-5 weeks, increased reticulocytes may appear. Prednisone is then slowly tapered and discontinued. Fifty-six percent ofPRCA patients, many of whom have been prednisone failures have a remission with this therapy.7 If the disease recurs, similar treatment should be reinitiated. After a second remission with the drugs, the patient should continue to take cyclophosphamide or azathioprine alone for a period of 2 years to sustain the remission. The drug can then be stopped to determine ifits continued administration is necessary. Many PRCA patients respond to this treatment even when an IgG antibody to their marrow cells cannot be identified, so a morphologic diagnosis of unremitting PRCA is sufficient to justify immunosuppressive therapy. If this treatment fails, alternative modes of treatment include splenectomy (Table 1), administration of antithymocyte globulin,9 intense plasmapheresis,lO cyclosporine,11.12 or highdose intravenous gammaglobulin. 13 Each of these latter alternative modes of treatment have been reported to produce remission in isolated cases, but the frequency of remission is not known. Figure 2 shows the response of a patient to horse anti-human thymocyte gamma globulin (HAHTGG) infused as recommended by Champlin et al. 14 This patient failed to respond to azathioprine or cyclophosphamide, in combination with prednisone, but had a rather dramatic response to 8 days of HAHTGG intravenous infusion at 20 mglkg day and has remained in remission for more than 2 years. We would use HAHTGG after a failure of cyclophospha-

TABLE 1 Remission Rate by Treatment Program* Primary . PRCA (No.lNo. Treated) Prednisone alone Cytotoxic drugs With prednisone Without prednisone Splenectomy

Secondary PRCA (No.lNo. Treated)

Total (No.lNo. Treated)

10/22

(45%)

0/5

(0%)

10/27

(37%)

13/23 0/7 2115

(56%) (0%) (13%)

5/9 0/4

(56%) .(0%)

116

(17%)

18/32 0/11 3/21

(56%) (0%) (14%)

• Modified from Reference 7.

372

June 1986 Volume 291 Number 6

Krantz

Packed cells transfused (units) Cyclophosphamide (mg) Prednisone (mg)

Leukocytes (ceII st,.,.I)

:3

o

0

DO

o

D

~l 30J

0

~l

Reticulocytes (%)

Packed cell

volume

~l

:j

i

0

10

20

30

40

50

iii

,

60 70 Days

80

90

100

110

,

i

120

130

Figure 1. Response of 43-year-old man with PRCA to prednisone and cyclophosphamide. Patient needed repeated blood transfusions during first 2 months of treatment. After he started prednisone and cyclophosphamide, retlculocytes gradually Increased to 5%, and patient maintained a normal packed cell volume without further transfusions. Both drugs were subsequently dlscontlnued.a

mide and prednisone and would then proceed to one of the other modes of treatment, depending on the condition of the patient. Pure White Cell Aplasia

Severe marrow granulocytic hypoplasia (pure white cell aplasia), like red cell aplasia, has been shown to be due, in some cases, to an IgG that inhibits the in vitro growth of the patient's granulocyte-macrophage progenitor cells. 15 Levitt et aP5 demonstrated that the marrow cells of their patient generated granulocyte macrophage colonies in vitro and that the serum IgG selectively inhibited the growth of these colonies while not affecting erythroid or mixed colony growth (Table 2). This disease has been successfully treated with high-dose intravenous immunoglobin. 16 HAHTGG would also seem to be an appropriate mode of therapy, but no reports of its use in white cell aplasia have appeared. Megakaryocyte Aplasia

Acquired megakaryocyte aplasia is an uncommon condition in which an isolated absence of bone marrow megakaryocytes occurs with severe thrombocytopenia. 17.18 Recent studies indicate that some of these cases have an autoimmune pathogenesis with antibodies that are selective for the megakaryocyte THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES

progenitor cells. 18.19 Some cases evolve out of autoimmune thrombocytopenic purpura,19 while others appear to originate as bone marrow failures without the latter condition. 17.18 Patients with megakaryocyte aplasia have responded to treatment with vinblastine-loaded platelets and intense plasmapheresis,19 vinblastine infusions,19 anti-thymocyte globulin,20 and cyclosporine. 21 Figure 3 shows the course of an 80-year-old woman with megakaryocyte aplasia and thrombocytopenic purpura who did not respond to fluorocortalone 80 mg/day and methenolone 25 mg/day given over 6 weeks. 21 The patient was allergic to horse and rabbit anti-thymocyte globulin and was started on cyclosporine 15 mg/kg/day by mouth over 14 days. One week after cessation of therapy, the platelet count began to rise and remained normal over 20 months. 21 Aplastic Anemia

Aplastic anemia most likely results from an injury to the marrow pluripotential hematopoietic stem cells, which impairs their ability to undergo normal proliferation and differentiation. The disease has been associated with various congenital and acquired disorders. However, in more that half of the cases, no association can be established with any preceding or co-existing illness or exposure to my373

Aplastic Anemia

RED CELL TRANSFUSIONS ,~--,~~,--~,--~,----~,--~,----~,

DRUG (mg)

200 100

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AZATHIOPRINE

o

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3~[

2.0 RETICS 10' ('>to)

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~o---o~~o~o~o~o~------~o~----~~~oo--~o>-~o

8,000 WBC 6,000 4,000 2,000

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i

(mg)

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374

June 1986 Volume 291 Number 6

Krantz

TABLE 2 Effect of Patient's Serum with or without Complement on Autologous Growth of Bone-Marrow Pluripotential (CFU-GEMM), Erythroid (BFU-E), and Granulocyte-Macrophage (CFU-GM) Hematopoietic Progenitors. * + Colonles/2 x 105 Marrow Cells Incubation Control marrow· Patient's marrowt Patient's marrow + AB serum + complementt Patient's marrow + patient's serumt Patient's marrow + patient's serum + complementt

CFU-GM

BFU-E

CFU-GEMM

55±8 66±10 60±8 57 ±6 6±4

155 ± 22 136 ± 14 127 ± 18 123 ± 12 114 ± 8

6.5 ± 2.0 5.5± 1.0 5.0 ± 1.5 4.5 ± 1.0 5.1 ±0.9

CFU-GM Inhibition

9 14

91

• Mean ± SD from 25 unrelated human marrow specimens. each plated In triplicate In methylcellulose cultures.

t Mean ± SD from two separate experiments. each plated In triplicate in methylcellulose cultures. +

From Reference 12.

elotoxic physical or chemical agents. In a number of cases of idiopathic aplastic anemia, there is indirect evidence that the injury to the marrow stem cells may be immunologically mediated: 1. Preparation of patients with aplastic anemia for a marrow transplant with irradiation, cyclophosphamide, and/or antilymphocyte globulin occasionally was followed by a failure of the graft, but normal hematopoiesis by the patient's own marrow cells occurred. 22 In addition, some physicians administered cytotoxic immunosuppressive drugs to patients with aplastic anemia and noted a remission. 23 2. The marrow cells from an identical twin sometimes failed to graft, but normal hematopoiesis commenced after the recipient identical twin was pretreated with cytotoxic immunosuppressive drugs before receiving a second marrow cell infusion from the identical twin. This indicated that some factor in the environment was suppressing normal marrow cell function. 24 3. In some cases removal of the T-Iymphocytes from the marrow cells led to increased hematopoiesis invitro.26 4. Studies on the treatment of patients with antilymphocyte globulin provided favorable therapeutic results. An investigation by Speck et aF6 was begun in which 15 patients received antilymphocyte globulin. The survial was 55% in 1 year.

The course and prognosis of aplastic anemia depend on the severity of marrow hypoplasia and the resulting pancytopenia. Patients with less than 25% cellularity on a bone marrow biopsy and two of three of the following peripheral blood cell concentrations, a corrected reticulocyte count of less than 1%, an absolute granulocyte count ofless than 500/flol and a platelet count less than 20,000/ flol are considered to have severe aplastic anemia. 2 Their median survival is 4-6 months. 2 Patients with higher granulocyte and platelet counts have a less severe from of aplastic anemia and a better short-term median survival, ranging from 6 to 12 months. Treatment Bone Marrow Transplantallon. Patients with se-

vere aplastic anemia who are less than 30 years of age are considered candidates for bone marrow transplantation,27.28 although some groups will accept patients up to 40 years old. 27 .28 With candidates for marrow transplantation, HLA typing of the patient and family members should be initiated as soon as possible after the diagnosis of severe aplastic anemia is made. If the patient is found to have an HLA-identical sibling, arrangements should be made for referral to a bone marrow transplantation center as soon as possible. It is estimated, however, that only 30% of patients with aplastic anemia have an HLA-identical re-

Figure 2. Response of a 50-year·old woman with PRCA to horse anll·human thymocyte gamma globulin (HAHTGG), 20 mg/kg/day, Intravenously, for 8 days, after failure to respond to azathlaprlne or cyclophosphamide, and prednisone. The patient has remained In remission for 2 years. THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES

375

Aplastic Anemia

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~;r~i~$Q~BO):L·_ _ _ _ _ _ _ _ _ _::::..®_~~10:.!:======w=ee=kS I =platelet concentrate

2' months

Figure 3. Blood cell values In a pallent with amegakaryocytlc thrombocytopenic purpura treated with cyclosporlne. WBC denotes white blood cells.21

lated donor, and bone marrow transplantation between unrelated, but HLA-matched individuals, is still experimental. The major complications seen in transplanted patients are marrow graft rejection, acute and chronic graft versus host disease (GVHD), and severe immunodeficiency in the early postgrafting period, resulting in a wide variety of viral, bacterial, and fungal infections as well as interstitial pneumonitis.27 Increasing patient age, development of acute GVHD, history of multiple transfusions, and refractoriness to random donor platelet transfusions at the time of transplantation are the major prognostic factors influencing survival of bone marror recipients. An average of 70% of transplanted patients are expected to be long-term survivors. The major problem in this group of patients is chronic GVHD which is greatly increased in patients over 30 years old. 27 Anti-human Thymocyte Gamma Globulin (AHTGG).

What can be done for patients with aplastic anemia who do not have a marrow donor? Because of the suspicion that aplastic anemia might be immunologically mediated, AHTGG was experimentally tried in severe aplastic anemia and was found to have a beneficial effect on its course. Today it is considered the treatment of choice for patients older than 30 376

years of age and for patients without a related suitable bone marrow donor.14.22.2~O AHTGG is prepared by immunizing horses or rabbits with human thymocytes commonly obtained by cannulating the thoracic duct. The optimal daily dose and the optimal duration of treatment with this agent have not yet been established. In many centers, AHTGG is given by slow intravenous infusion at a dose of 20 mg/kg/day for 8 days,14 along with prednisone given orally at a dose of 30-80 mg daily starting 24 hours before the first infusion and tapered over a 1-2-week period after completion. Forty-five to 70% of patients with severe aplastic anemia respond with an increase of their red cell, granulocyte, and platelet counts to levels that allow cessation of all transfusions. 14 ,22.29,30 Improvement of peripheral blood counts is usually seen within the first 2-3 months following treatment and approximately 30-40% of treated patients develop normal peripheral blood counts. Even these fine results may not represent optimum treatment. A recent report indicates that patients who received a second course of AHTGG had a 90% 6-month survival rate. 29 We have had a similar experience here at Vanderbilt. Using a rabbit antilymphocyte serum that was developed by Dr. Gary Niblack of the renal June 1986 Volume 291 Number 6

RED CELL TRANSFUSIONS

, 'II'

II

l

PLATELET TRANSFUSIONS

, ,m n,nn DRUG

[

120~

DRUG 80 (mg) 40

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II nun,

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I

I

I

5

10

15

I 20

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Y I

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~:~~~ 6,000 5,000 4,000

---- ~r

..... 10 1 0

180'OOO

150,000 90,000 60,000

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50

I 75

30 20 I 10 100

WEEKS

Figure 4. Thlrfy-four-year-old WOman with severe aplastic anemia who became resistant to platelet transfusions and had a marked hemorrhagic tendency. She was treated with rabbit antilymphocyte serUm (ALS), and her platelets rose to 50,000/111, but soon dropped again. A second course of horse anti-human thymocyte gamma gtobulln (HAHTGG) was administered, and once again her platelet count rose to 50,OOO/fLl. This time she went Into a complete remission, which has been sustained for more than 2years.

transplantation service or horse AHTGG, we have treated 16 patients with severe aplastic anemia and have observed six complete remissions (normal blood counts) and four partial remissions (significant increase in blood counts and absence of transfusion requirement). The last six patients that we treated have received a second course of AHTGG (horse) if they did not have a remission, or if their blood cell counts began to drop, and 5/6 of these patients have had a remission. Figure 4 shows the course of such a patient. Side effects of treatment with AHTGG include fever, chills, skin rash, arthralgias, anaphylactic reactions, serum sickness, and exacerbation of preexisting thrombocytopenia. AHTGG should be infused under close medical supervision, and the physician must be appropriately prepared to treat any signs of acute anaphylaxis promptly. Other allergic reactions can be managed by increasing the daily dose of concurrently administered corticosteroids. A history of allergy to horse or rabbit serum, or a positive skin test, are considered relative contraindications to the administration of AHTGG. In these. THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES

patients it is preferable to use a preparation of different animal origin, or attempt desensitization. The mechanism of action of AHTGG remains unknown. No evidence is yet available to document that the beneficial effect on hematopoiesis is mediated solely through immunosuppression. If it is mediated through immunosuppression, the precise immune system that may produce the aplasia is still not known. Cyclosporlne. If AHTGG treatment fails, cyclosporine is available. This drug has been reported to produce a remission of aplastic anemia in some patients with severe aplastic anemia,31.32 but has failed in others.33 Figure 5 shows the course of a 60-yearold woman with severe aplastic anemia who failed to respond to low- and high-dose prednisone, or AHTGG. 31 She had a severe hemorrhagic diathesis and an intracerebral hematoma before cyclosporin was administered orally at 12 mg/kg/day divided into two daily doses. After 6-7 days, the patient's bleeding tendency improved, and the platelet concentration began to increase. The granulocyte and reticulocyte concentrations also improved, but with 377

Aplastic Anemia

... - Treatment 1 (cot1icosteroids, 2 mglkgld)

t. - Treatment 2 (corticosteroids, 20,10, 5, 2.5 mg.'\
o - Treatment 4 (cyclosporine) 80.000

"8o

60.000

:c

References

'0

...

~

eo

pressive drugs. The precise pathogenesis of severe aplastic anemia is still not clear, but similar treatment has been applied with very encouraging results to those patients for whom bone marrow transplantation is not available. This treatment consists predominantly of repeated courses of AHTGG and has resulted in remission rates of 45-90%. Clinical investigation, proceeding from increased knowledge of basic hematopoiesis, has thus led to a marked improvement in the outcome of this very severe disease.

40,000

~Q)

m n;

a:

\I,()

160

Figure 5. Blood platelet counts during four successive therapeutic periods, each one Indicated from day 1 of therapy, In 60-year-old woman. The type and duration of each therapy are In~lcated,3'

the onset of renal and hepatic toxicity, the dose of cyclosporin was decreased to 7 mg/kg/day. Acyclovir. This drug has been administered to three patients with severe aplastic anemia and 2/3 have had a remission of the disease. 32 ,34 The dose was 15 mg/kg/day intravenously for 10 days. Corticosteroids. In conventional doses corticosteroids have been frequently used without success in severe aplastic anemia. Administration of high doses of 6-methylprednisolone (20 mg per kg daily, intravenously, tapered over 6 weeks) to these patients has been reported to result in recovery of hematopoiesis in 33% of cases. 35 Although these results are promising, such treatment still should be considered experimental. In our experience, we have had 2/2 fatal infections during this therapy and no longer use it. A recent report indicates that 1 gm per day intravenously for 3 days may be effective with less toxicity.3s Conclusion

Selective aplasias of the erythroid, granulocytic and megakaryocytic cell lines are now recognized, and many of these cases have an autoimmune pathogenesis as well as a good response to immunosup-

318

1. Camitta BM, Storb R, Thomas ED: Aplastic anemia. Pathogenesis, diagnosis, treatment, and prognosis. N Engl J Med 306:645-652, 1982. 2. Camitta BM, Storb R, Thomas ED: Aplastic anemia: Pathogenesis, diagnosis, treatment, and prognosis. N Engl J Med 306:712-718, 1982. 3. Krantz SB, Dessypris EN: Pure red cell aplasia, in Golde DW, Takaku F (eds): Hematopoietic Stem Cells. New York, Marcel Dekker, Inc, 1985, pp 229-251. 4. Krantz SB, Kao V: Studies on red cell aplasia, I. Demonstration of a plasma inhibitor to heme synthesis and an antibody to erythroblast nuclei. Proc Natl Acad Sci, USA, 58:493-500, 1967. 5. Krantz SB, Moore WH, Zaentz SD: Studies on red cell aplasia. V. Presence of erythroblast cytotoxity in "IG-globulin fraction of plasma. J Clin Invest 52:324-335, 1973. 6. Dessypris EN, Krantz SB, Roloff JS, Lukens IN: Mode of action of the IgG inhibitor of erythropoiesis in transient erythroblastopenia of childhood. Blood 59:114-123, 1982. 7. Clark DA, Dessypris EN, Krantz SB: Studies on pure red cell aplasia. XI. Results of immunosuppressive treatment of 37 patients. Blood 63:277-286, 1984. 8. Krantz SB, Hartmann RC: Paroxysmal nocturnal hemoglobinuria and pure red cell aplasia. Two rare anemias with immunologic implications. Postgrad Med 55:141-147, 1974. 9. Mangan KG, Shadduck RK: Successful treatment of chronic refractory pure red cell aplasia with anti thymocyte globulin: correlation with in vitro erythroid culture studies. Am J HematoI17:417-426, 1984. 10. Messner HA, Fauser AA, Curtis JE, Dotton D: Control of antibody-mediated pure red-cell aplasia by plasmapheresis. N Engl J Med 304:1334-1338, 1981. 11. Debusscher L, Paridaens R, Stryckmans P, Delwiche F: Cy_ · closporine for pure red cell aplasia. Blood 65:249, 1985. 12. Totterman TH, Nisell J, Killander A, Gahrton G, Lonnquist B: Successful treatment of pure red-cell aplasia with cyclosporin. Lancet 2:693, 1984. 13. Clauvell JP, Vainchenker W, Herrera A, Dellagi K, Vinci G, Tabilio A, Lacombe C: Treatment of pure red cell aplasia by high dose intravenous immunoglobulins. Br J Hematol 55: 380-381, 1983. 14. Champlin R, Ho R, Gale RP: Antithymocyte globulin treatment in patients with aplastic anemia. N Engl J Med 308: 113-118, 1983. 15. Levitt LJ, Ries CA, Greenberg PL: Pure white-cell aplasia: Antibody mediated autoimmune inhibition of granulopoiesis. N Engl J Med 308:1141-1146, 1983. 16. Barbui T, Bassan R, Viero R, Minetti B, Comotti B, Buelli M: Pure white cell aplasia treated by high-dose intravenous immunoglobulin. Br J Hematol 58:554-555, 1984. 17. Stoll DB, Blum S, Pasquale D, Murphy S: Thrombocytopenia with decreased megakaryocytes. Evaluation and prognosis. Ann Intern Med 94:170-175, 1981. 18. Hoffman R, Bruno E, Elwell J, Mazur E, Gewirtz AM, Dekker P, Denes AE: Acquired amegakaryocytic thrombocytopenic June 1986 Volume 291 Number 6

Krantz

purpura: A syndrome of diverse etiologies. Blood 60:11731178,1982. 19. Hoffman R, Zaknoen S, Yang HH, Bruno E, LoBuglio AF, Arrowsmith JB, Prchal JT: An antibody cytotoxic to megakaryocyte progenitor cells in a patient with immune thrombocytopenic purpura. N Engl J Med 312:1170-1174,1985. 20. Khelif A, French M, Follea G, Coiffier B, Dechavanne M, Viala J-J: Amegakaryocytic thrombocytopenic purpura treated with antithymocyte globulin. Ann Intern Med 102: 720,1985. 21. Hill W, LandgrafR: Successful treatment of amegakaryocytic thrombocytopenic purpura with cyclosporine. N Engl J Med 312:1060-1061, 1985. 22. Speck B, Cornu P, Jeannet M, Nissen C, Burri HP, Groff P, Nagel GA, Buchner CD: Autologous marrow recovery following allogeneic marrow transplantation in a patient with severe aplastic anemia. Exp Hematol4:131-137, 1976. 23. Baran DT, Griner PV, Klemperer MR: Recovery from aplastic anemia after treatment with cyclophosphamide. N Engl J Med 295:1522-1523, 1976. 24. The Royal Marsdon Hospital Bone-Marrow Transplantation Team: Failure of syngeneic bone-marrow graft without preconditioning in posthepatitis marrow aplasia. Lancet 2:742744,1977. 25. AscensaoJ, Kagen W, Moore M, Pahwa R, HansenJ, Good R: Aplastic anemia: evidence for an immunological mechanism. Lancet 1:669-671, 1976. 26. Speck B, Gluckman E, Haak HL, Van Rood JJ: Treatment of aplastic anemia by antilymphocyte globulin with and without allogeneic bone marrow infusions. Lancet 2:1145-1148, 1977. 27. Storb R, Thomas ED, Buckner CD, Appelbaum FR, Clift RA, Deeg HJ, Doney K, Hansen JA, Prentice RL, Sanders JE,

THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES

Stewart P, Sullivan KM, Witherspoon RP: Marrow transplantation for aplastic anemia. Sern in Hematol 21:27-35, 1984. 28. Thomas ED, Storb R: Acquired severe aplastic anemia: Progress and perplexity. Blood 64:325-328, 1984. 29. Gluckman E, Marmont A, Speck B, Gordon-Smith EC, for the Working Party on Severe Aplastic Anemia of European Group for Bone Marrow Transplantation: Immunosuppressive treatment of aplastic anemia as an alternative treatment for bone marrow transplantation. Sern in Hematol 21:11-19, 1984. 30. Speck B, Gratwohl A, Nissin C, Osterwalder B, Signer E, Jeannet M: Bone marrow graft versus ALG in patients with aplastic anemia. BiornedPharmacother 37:139-143,1983. 31. Stryckmans PA, Dumont JP, Velu TH, Debusscher L: Cyclosporine in refractory severe aplastic anemia. N Engl J Med 310:655-656, 1984. 32. Wisloff F, Godal HC: Cyclosporine in refractory severe aplastic anemia. N Engl J Med 312:1193, 1985. 33. Jacobs P, Wood L, Martell RW: Cyclosporin A in the treatment of severe acute aplastic anemia. BrJ Haematol61:267272,1985. 34. Bacigalupo A, Frassoni R, Van Lint MT: Acyclovir for the treatment of severe aplastic anemia. N Engl J Med 310: 1606-1607,1984. 35. Bacigalupo A, Podesta M, Van Lint MT, Vimercati R, Cerri R, Rossi E, Risso M, Carella A, Santini G, Damasio E, Giordano D, Marmont AM: Severe aplastic anemia: Correlation of in vitro tests with clinical response to immunosuppression in 20 patients. Br J Haematol47:423-433, 1981. 36. Issaragrisil S, Painkijagum A: Methylprednisolone and aplastic anemia. Ann Intern Med 103:964, 1985.

379