-  INCLUSION CRITERIA:

        Evidence of HCL by flow cytometry, reviewed by the Laboratory of Pathology, NCI, including
        positivity for CD19, CD22, CD20, and CD11c.

        BMBx consistent with HCL, reviewed by Laboratory of Pathology, NCI. BMBx may be negative in
        HCLv in patients with increasing peripheral blood HCLv cells and spleen size.

        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 purine analog 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.

          -  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.

        No prior purine analog therapy except up to 1 prior course of cladribine.

        No prior rituximab unless HCLv patient.

        ECOG performance status (78) of 0-3.

        Patients must be able to understand and give informed consent.

        Women of child-bearing age and all men must use birth control of any type until at least 12
        months after the last dose of therapy.

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

        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 2.5 times 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.

        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.

        Subject has provided written informed consent

        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 is allowed only if viral load is undetectable andif
        on anti-hepatitis B therapy like Entecavir. Hepatitis C is allowed only if viral load is
        undetectable, and if the patient has received curative therapy.

        Patients with documented history of no response to cladribine, and without 50% improvement
        in platelets, hemoglobin or granulocytes. This exclusion does not apply to HCLv. These
        patients are eligible regardless of prior response to CDA.

        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, which is symptomatic.

        At the Investigator s discretion, 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. Per the investigator s discretion, 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.