-  INCLUSION CRITERIA:

          -  Evidence of HCL by flow cytometry of blood or a solid (lymph node) mass, confirmed by
             the Laboratory of Pathology, NCI, including positivity for CD19, CD22, CD20, and
             CD11c. Patients with flow cytometry consistent with HCL variant (HCLv) are eligible,
             including those with CD25 and/or CD103 negative disease.

          -  BMBx or BMA consistent with HCL, confirmed by NIH Laboratory of Pathology, NCI, or the
             Department of Laboratory Medicine, Clinical Center, NIH, unless the diagnosis can be
             confirmed from a solid (lymph node) mass..

          -  Treatment indicated based on demonstration of at least one of the following no more
             than 4 weeks from the time of enrollment, and no less than 6 months after prior
             cladribine and no less than 4 weeks after other prior treatment, if applicable.

               -  Neutropenia (ANC less than 1000 cells/microl).

               -  Anemia (Hgb less than 10g/dL).

               -  Thrombocytopenia (Plt less than 100,000/microl).

               -  Absolute lymphocyte count (ALC) of greater than 5,000 cells/microL

               -  Symptomatic splenomegaly.

               -  Enlarging lymph nodes greater than 2cm.

               -  Repeated infections requiring oral or i.v. antibiotics.

               -  Increasing lytic bone lesions

        Patients who have eligible blood counts within 4 weeks from enrollment will not be
        considered ineligible if subsequent blood counts prior to enrollment fluctuate and become
        ineligible up until the time of enrollment.

          -  One of the following:

               -  At least 2 prior courses of purine analog

               -  1 prior course of purine analog plus greater than or equal to1 course of
                  rituximab if the response to the course of purine analog lasted less than 1 year.

               -  Diagnosis of HCL variant (HCLv)

               -  Unmutated (>98% homology to germline) IGHV4-34+expressing HCL/HCLv

          -  ECOG performance status (100) of 0-3

          -  Patients must be able to understand and give informed consent.

          -  Creatinine less than or equal to 1.5 or creatinine clearance greater than or equal to
             60 ml/min.

          -  Bilirubin less than or equal to 2 unless consistent with Gilbert s (total/direct
             greater than 5), ALT and AST less than or equal to 3 x upper limits of normal.

          -  No other therapy (i.e. chemotherapy, interferon) for 4 weeks prior to study entry, or
             cladribine for 6 months prior to study entry, unless progressive disease more than 2
             months after cladribine is documented.

          -  Age at least 18

          -  Men and women of reproductive potential must agree to use an acceptable method of
             birth control during treatment and for twelve months after completion of treatment.

          -  Patients must be willing to co-enroll in the investigator s companion protocol
             10-C-0066 titled Collection of Human Samples to Study Hairy Cell and other Leukemias,
             and to Develop Recombinant Immunotoxins for Cancer Treatment .

        EXCLUSION CRITERIA:

          -  Presence of active untreated infection

          -  Uncontrolled coronary disease or NYHA class III-IV heart disease.

          -  Known infection with HIV, hepatitis B or C.

          -  Pregnant or lactating women.

          -  Presence of active 2nd malignancy requiring treatment. 2nd malignancies with low
             activity which do not require treatment (i.e. low grade prostate cancer, basal cell or
             squamous cell skin cancer) do not constitute exclusions.

          -  Inability to comply with study and/or follow-up procedures.

          -  Presence of CNS disease

          -  Patients with history of non-response to both pentostatin plus rituximab and to
             bendamustine plus rituximab.

          -  Receipt of a live vaccine within 4 weeks prior to randomization. Efficacy and/or
             safety of immunization during periods of B-cell depletion have not been adequately
             studied. It is recommended that a patient s vaccination record and possible
             requirements be reviewed. The patient may have any required vaccination/booster
             administered at least 4 weeks prior to the initiation of study treatment. Review of
             the patient s immunization status for the following vaccinations is recommended:
             tetanus; diphtheria; influenza; Pneumococcal polysaccharide; Varicella; measles, mumps
             and rubella (MMR); and hepatitis B. Patients who are considered to be at high risk for
             hepatitis B virus (HBV) infection and for whom the investigator has determined that
             immunization is indicated should complete the entire HBV vaccine series at least 4
             weeks prior to participation in the study.