Alemtuzumab in Treating Patients With B-Cell Chronic Lymphocytic Leukemia in Partial Remission or Complete Remission

DISEASE CHARACTERISTICS:

* Diagnosis of B-cell chronic lymphocytic leukemia (B-CLL) meeting the following criterion:

  * Confirmed by characteristic immunophenotype on peripheral blood flow cytometry
* In complete or partial remission after prior therapy for B-CLL

  * No treatment failure after receiving prior alemtuzumab therapy
* Minimal residual disease (MRD) status meeting 1 of the following criteria:

  * Detectable B-CLL MRD (i.e., MRD-positive) as shown by peripheral blood or bone marrow involvement
  * Undetectable B-CLL MRD (i.e., MRD-negative remission)
* Lymph nodes \< 2 cm in maximum diameter
* No persisting severe pancytopenia due to prior therapy rather than disease, as defined by the following criteria:

  * Neutrophil count \< 5,000/mm\^3
  * Platelet count \< 50,000/mm\^3
* No clinically progressive disease (i.e., peripheral blood B-cell count ≥ 5,000/mm³)
* No mantle cell lymphoma
* No CNS involvement with B-CLL

PATIENT CHARACTERISTICS:

* Not pregnant or nursing
* Negative pregnancy test
* Fertile patients must use effective contraception during and for 6 months after completion of study therapy
* Creatinine \< 2 times upper limit of normal (ULN)\*
* Bilirubin \< 2 times ULN\*
* No known HIV positivity
* No concurrent active infection
* No history of anaphylaxis after exposure to rat or mouse-derived, complementary-determining region-grafted humanized monoclonal antibodies
* No other concurrent severe diseases or mental disorders
* No concurrent active secondary malignancy NOTE: \*Unless secondary to direct infiltration of the liver by B-CLL or hemolysis

PRIOR CONCURRENT THERAPY:

* See Disease Characteristics
* No prior allogeneic stem cell transplantation

  * Any other prior therapy allowed
* At least 6 months since completion of last therapy for B-CLL
* More than 6 weeks since prior investigational agents
* No other concurrent cytotoxic agents