-  INCLUSION CRITERIA:

          -  Diagnosis of HCL or HCLv.

          -  Treatment required for either 1) Absolute neutrophil count (ANC) <1/nL, 2) Hemoglobin
             <10g/dL, 3) Platelets<100/nL, 4) symptomatic splenomegaly, or 5) enlarging HCL mass >
             2cm in short axis. Patients who have eligible blood counts within 4 weeks from the
             initiation of study will not be considered ineligible if subsequent blood counts prior
             to enrollment fluctuate and become ineligible up until the time of enrollment.

          -  Patients must be Pseudomonas-immunotoxin naive.

          -  HCL or HCLv with at least 1 prior purine analog, and, for HCL patients with >=2-years
             1 month response, at least 1 other therapy. Age greater than or equal to 18 years as
             the disease under study, HCL/HCLv, has not been reported in children < age 18.

          -  ECOG performance status less than or equal to2 (Karnofsky greater than or equal to
             60%)

          -  Patients must have adequate organ and marrow function as defined below:

               -  Total bilirubin less than or equal to 1.5 mg/dL, unless consistent with Gilbert s
                  (ratio between total and direct bilirubin > 5)

               -  AST and ALT less than or equal to 3x upper limit of normal (ULN)

               -  Alkaline phosphatase < 2.5 ULN

               -  Serum creatinine less than or equal to 1.5 mg/dL or creatinine clearance greater
                  than or equal to 60 mL/min by Cockcroft-Gault equation, where creatinine
                  clearance = (140-age)(Kg weight)/(72 x Creatinine)

               -  Serum albumin greater than or equal to 2 g/dL

               -  Partial thromboplastin time (PTT) or Prothrombin time (PT)/International
                  Normalized Ratio < 2.5x ULN (If on warfarin, PT/INR < 3.5x ULN; If on any other
                  anticoagulation, Prothrombin time (PT) < 2.5x baseline)

               -  Fibrinogen greater than or equal to 0.5 lower limit of normal

          -  The effects of moxetumomab pasudotox-tdfk and rituximab on the developing human fetus
             are unknown therefore participants must use effective methods of contraception as
             directed below.

               -  Females of childbearing potential (< 50 years) who are sexually active with a
                  non-sterilized male partner must use a highly effective method of contraception
                  prior to study entry and or the duration of study participation and must agree to
                  continue using such precautions for 3 months after completion of Rituximab
                  administration. Contraception after this point should be discussed with a
                  responsible physician. Periodic abstinence, the rhythm method, and the withdrawal
                  method are not acceptable methods of contraception. Females of childbearing
                  potential are defined as those who are not surgically sterile (i.e., bilateral
                  tubal ligation, bilateral oophorectomy, or complete hysterectomy) or those who
                  are premenarchal or postmenopausal (defined as 12 months with no menses without
                  an alternative medical cause). A highly effective method of contraception is
                  defined as one that results in a low failure rate (i.e., less than 1% per year)
                  when used consistently and correctly. Not all methods of contraception are highly
                  effective. Should a woman become pregnant or suspect she is pregnant while she or
                  her partner is participating in this study, she should inform her treating
                  physician immediately.

               -  Non-sterilized males who are sexually active with a female partner of
                  childbearing potential must use an effective method of contraception from Day 1
                  until 90 days after receipt of the final dose of investigational product. It is
                  required that a female partner of a male subject also use an effective method of
                  contraception throughout this period.

          -  Ability of subject to understand and the willingness to sign a written informed
             consent document.

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

        EXCLUSION CRITIERIA:

          -  Patients who have had chemotherapy, immunotherapy or radiotherapy within 4 weeks or
             treatment with rituximab within last 3 months prior to initiation of treatment.

          -  Patients who are receiving any other investigational agents.

          -  Is pregnant or breastfeeding or expecting to conceive within the projected duration of
             the study, starting with the screening visit through 4 months after the last dose of
             trial treatment. Pregnant women are excluded from this study because moxetumomab
             pasudotox-tdfk and rituximab are agents with the potential for teratogenic or
             abortifacient effects. Because there is an unknown but potential risk for adverse
             events in nursing infants secondary to treatment of the mother with moxetumomab
             pasudotox-tdfk and rituximab, breastfeeding should be discontinued if the mother is
             treated with moxetumomab pasudotox-tdfk and rituximab.

          -  Patients with known brain metastases should be excluded from this clinical trial
             because of their poor prognosis and because they often develop progressive neurologic
             dysfunction that would confound the evaluation of neurologic and other adverse events.

          -  Uncontrolled intercurrent illness including, but not limited to, ongoing or active
             infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac
             arrhythmia, uncontrolled hypertension, uncontrolled pulmonary infection, pulmonary
             edema or psychiatric illness/social situations that would limit compliance with study
             requirements.

          -  Patients with retinal or choroidal detachment.

          -  Positive for Hepatitis B core antibody or surface antigen unless the patient is on
             Tenofovir or Entecavir and Hepatitis B Viral deoxyribonucleic acid (DNA) load is <2000
             IU/mL

          -  Active second malignancy requiring treatment other than minor resection of indolent
             cancers like basal cell and squamous skin cancers.

          -  Human immunodeficiency virus (HIV)-positive patients unless taking appropriate
             anti-HIV medications with a CD4 count of > 200. Otherwise, there may be an increased
             risk of lethal infections when temporarily suppressing normal B-cells.

          -  History of an allogeneic bone marrow transplant.

          -  Patients with a history of both thromboembolism and known congenital hypercoagulable
             conditions.

          -  Radioimmunotherapy within 2 years prior to enrollment in the study.

          -  Patients with history of thrombotic microangiopathy or thrombotic microangiopathy
             /HUS.

          -  Patients with corrected QT interval (Frederica) elevation > 500 msec (manually
             over-read by medically qualified person) based on at least two separate 12-lead ECGs.

          -  Patients on high dose estrogen (defined as > 0.625 mg/day of an estrogen compound).

          -  Oxygen saturation at rest < 88% measured by pulse oximetry or PaO2 less than or equal
             to 55 mm Hg.

          -  Patients with life expectancy of less than 6 months.

          -  Patients with clinical evidence of disseminated intravascular coagulation (Grade 3-4).

          -  Patients with < 50% of predicted forced expiratory volume (FEV1) or < 50% of predicted
             diffusing capacity for carbon monoxide, corrected for hemoglobin concentration and
             alveolar volume (DLCO). Note: Patients with no prior history of pulmonary illness are
             not required to have pulmonary function testing (PFT). Forced expiratory volume will
             be assessed after bronchodilator therapy.