Alemtuzumab in Treating Patients With B-Cell Chronic Lymphocytic Leukemia

DISEASE CHARACTERISTICS: Inclusion criteria: * Diagnosis of B-cell chronic lymphocytic leukemia (B-CLL) * Disease in complete or partial remission after completion of 4-6 courses of second-line cytoreductive therapy no less than 90 days and no more than 150 days ago * Second-line cytoreductive therapy must comprise 1 of the following regimens: * Fludarabine phosphate alone (F) * Fludarabine phosphate and cyclophosphamide (FC) * Fludarabine phosphate, cyclophosphamide, and rituximab (FCR) * Bendamustine hydrochloride alone (B) * Bendamustine hydrochloride and rituximab chemotherapy (BR) * Complete minimal residual disease response defined by the following: * At least negativity of 4-color-cytometry and/or even PCR-amplifiable clonal CDR III rearrangement of the IgV\_H * For PCR analysis, blood sample need to be taken at beginning or during second-line cytoreductive therapy before achievement of a clinical complete remission * Disease not refractory to first-line F/FC/FCR/B/BR if received such therapy Exclusion criteria: * Presence of bulky lymph nodes (\> 5 cm) after second-line F/FC/FCR/B/BR * Clinically apparent autoimmune cytopenia (i.e., autoimmune hemolytic anemia, autoimmune thrombocytopenia, or pure red cell aplasia) * CNS involvement with B-CLL PATIENT CHARACTERISTICS: Inclusion criteria: * ECOG performance status 0-1 * ANC ≥ 1,500/µL * Platelets ≥ 50,000/µL * Creatinine ≤ 1.5 times the upper normal limit (ULN) * Conjugated bilirubin ≤ 2 times ULN * Thyroid function normal * Not pregnant or nursing * Fertile patients must use effective contraception Exclusion criteria: * Severe infection during second-line treatment with F/FC/FCR/B/BR, meeting any 1 of the following criteria: * Any episode of NCI grade 4 infection * More than 1 episode of NCI grade 3 infection * Medical condition requiring long-term use of oral corticosteroids for more than 1 month * Active bacterial, viral, or fungal infection * HIV, hepatitis B virus, and/or hepatitis C virus-positive serum status * Concurrent severe diseases that exclude the administration of protocol therapy, including any of the following: * NYHA class III-IV heart insufficiency * Severe chronic obstructive lung disease with hypoxemia * Severe ischemic cardiac disease * Active secondary malignancy other than B-CLL prior to the study * Known hypersensitivity or anaphylactic reaction against murine proteins or one of the drug components PRIOR CONCURRENT THERAPY: * See Disease Characteristics * No more than 2 prior chemotherapies, including F/FC/FCR/B/BR therapy * No more than 1 pretreatment (before second-line therapy) with chlorambucil or F/FC/FCR/B/BR * No chemotherapy or radiotherapy for any neoplastic disease other than B-CLL prior to the study