This trial, sponsored by Amgen, Inc., which produces the recombinant methionyl human stem cell factor (r-metHuSCF), also involves two other institutions. The primary objective is determination of the safety of administering multiple doses of r-metHuSCF in the setting of acquired aplastic anemia and evaluation of the effect of r-metHuSCF on peripheral blood counts. Potential effects of r-metHuSCF on frequency of need for red cell or platelet transfusions and on bone marrow morphology/cellularity will also be evaluated.

This trial, sponsored by Amgen, Inc., which produces the recombinant methionyl human stem cell factor (r-metHuSCF), also involves two other institutions. The primary objective is determination of the safety of administering multiple doses of r-metHuSCF in the setting of acquired aplastic anemia and evaluation of the effect of r-metHuSCF on peripheral blood counts. Potential effects of r-metHuSCF on frequency of need for red cell or platelet transfusions and on bone marrow morphology/cellularity will also be evaluated.

Acquired moderate or severe aplastic anemia.

Intolerant to, or failure to durably respond to, ATG/ALG therapy with or without cyclosporin.

Patients may not have received ATG/ALG, therapy for 12 weeks prior to enrollment or cyclosporin for 4 weeks prior to enrollment.

Two years of age or older.

Karnofsky Performance Status greater than or equal to 60 percent.

Adequate organ function as defined by serum creatine less than 2.0 mg/dl and a bilirubin less than 2.0 mg/dl.

Patients (or their parent[s]/responsible guardian[s]) must be able to comprehend and be willing to sign an informed consent prior to starting r-metHuSCF therapy.

No current diagnosis or past history of myelodysplastic syndromes.

No diagnosis of Fanconi's anemia, dyskeratosis congenita, or other congenital forms of aplastic anemia.

No current diagnosis of clinically active paroxysmal nocturnal hemoglobinuria (PNH) defined as patients with clinically significant thrombosis or hemolysis.

No diagnosis of eosinophilic fasciitis.

No treatment with ATG, ALG, or other immunosuppresive agents within 12 weeks of enrollment or treatment with cyclosporine A or IL-3 within 4 weeks of enrollment.

No treatment with hematopoietic growth factors within 2 weeks of enrollment.

No evidence of active uncontrolled infection.

No known allergy to Ecoli-derived products.

No current or recent symptoms of asthma occurring within the past 10 years (including allergic asthma, or asthma induced by cold temperature, infection, or exercise).

No history of anaphylactic/anaphylactoid-type event manifested by disseminated urticaria, laryngeal edema, and/or bronchospasm (or for example: food, insect bites, etc). Patients with drug allergies, manifested solely by rash and/or urticaria, are not excluded. An isolated episode of urticaria occuring more than 3 years earlier is not a contraindication.

No significant nonmalignant disease including previously documented HIV infection, uncontrolled hypertension (diastolic blood pressure greater than 115 mmHg), unstable angina, congestive heart failure (greater than NY Class II), poorly controlled diabetes, coronary angioplasty within 6 months, or uncontrolled atrial or ventricular cardiac arrhythmias.

No pregnancy or breast feeding. Those of childbearing potential must observe adequate birth control measures.

No treatment with an investigational agent (other than hematopoietic growth factors) within 4 weeks of study entry.

No concurrent use of beta adrenergic blocking agents.

No concurrent use, or use within the past 2 weeks, of Monoamine Oxidase Inhibitors (MAO Inhibitors).

No psychiatric, addictive, or any disorder which compromises ability to give truly informed consent for participation in this study.