Anti-thymocyte Globulin and Cyclosporine as First-Line Therapy in Treating Patients With Severe Aplastic Anemia

Inclusion Criteria: * All patients with sAA as defined by Camitta who are candidates for IS therapy; these criteria include bone marrow cellularity \< 25% or 25-50% with \< 30% of hematopoietic cells; it should also have two of the following three parameters: peripheral blood neutrophils \< 0.5 x 10\^9/L, platelets \< 20 x 10\^9/L and reticulocytes \< 60 x 10\^9/L in anemic patients * If cytogenetic testing has been done, it should show normal karyotype or be not informative * Patients should be either unwilling or otherwise ineligible (age, comorbidities, lack of donor) for bone marrow transplantation as a therapeutic modality * Not previously treated with ATG for sAA * Patients must have ECOG performance status of 0, 1, or 2 * Vitamin B12 and folic acid deficiency must be ruled out by measurement of serum levels * Patients must have had a bone marrow biopsy examination in the three months prior to enrolling in the study * Must be able to provide informed consent * Systemic and other hematologic causes of pancytopenia, based on clinical presentation, must have been ruled out Exclusion Criteria: * Patients with clinically evident congestive heart failure, serious cardiac arrhythmias; symptoms of coronary artery disease must be cleared by cardiology prior to therapy * Patients who have had chemotherapy, radiotherapy, or immunotherapy or other investigational drug use within 3 weeks prior to study entry * Pregnant women * All females of childbearing potential must have a blood test or urine study within two weeks prior to induction registration to rule out pregnancy * Women of childbearing potential are strongly advised to use an accepted and effective method of contraception * Patients who have medical, psychological, or social conditions that may interfere with the patient's participation in the study or evaluation of the study results