DISEASE CHARACTERISTICS:

• Diagnosis of paroxysmal nocturnal hemoglobinuria

• Must have required ≥ 4 episodes of transfusions for anemia or anemia-related symptoms within the past year

  • Mean pre-transfusion hemoglobin ≤ 10. 5 g/dL over the past year
• Glycosylphosphatidylinositol (GPI)-deficient red blood cell clone (type III cells) of ≥ 10% by flow cytometry

• Must have received 1 packed red blood cell transfusion during the study observation period (within 48 hours of the hemoglobin level that precipitated the transfusion) and within 1.5 g/dL of the mean pre-transfusion hemoglobin level over the past year

  • Pre-transfusion hemoglobin ≤ 9 g/dL with symptoms
  • Pre-transfusion hemoglobin ≤ 7 g/dL without symptoms
• Received Neisseria meningitidis vaccination at least 2 weeks before initiation of study therapy

PATIENT CHARACTERISTICS:

Age

• 18 and over

Performance status

• Not specified

Life expectancy

• Not specified

Hematopoietic

• See Disease Characteristics
• Absolute neutrophil count > 500/mm^3
• Platelet count ≥ 100,000/mm^3

Hepatic

• Lactate dehydrogenase ≥ 1.5 times upper limit of normal

Renal

• Not specified

Immunologic

• No known or suspected active bacterial infection
• No recurrent bacterial infections
• No history of meningococcal disease

Other

• No known or suspected hereditary complement deficiency
• No other condition that would increase the patient's risk or confound the outcome of the study
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy

• See Disease Characteristics
• No prior bone marrow transplantation
• Concurrent epoetin alfa allowed*

Chemotherapy

• Not specified

Endocrine therapy

• Concurrent corticosteroids allowed**

Radiotherapy

• Not specified

Surgery

• Not specified

Other

• More than 30 days since prior participation in another investigational drug trial
• More than 30 days since prior investigational agents, devices, or procedures
• Concurrent immunosuppressants allowed*
• Concurrent warfarin allowed provided INR level is stable for the past 4 weeks and expected to remain stable during observation and study treatment
• Concurrent iron supplements or folic acid allowed**
• Concurrent low-molecular weight heparin allowed** NOTE: *Provided dose is stable for the past 26 weeks and during study observation and treatment

NOTE: **Provided dose is stable for the past 4 weeks and expected to remain stable (or decrease for corticosteroids) during study observation and treatment