Inclusion Criteria

Patients must have TTP with platelet count < 100,000/mL and microangiopathic hemolytic anemia which is defined as presence of at 3-10 fragmented red blood cells (schistocytes) per high power filed on the peripheral blood smear.

Patients will be included in the trial based on the following criteria:

• Either gender, age 17 or older
• Men and women of reproductive potential must agree to use an acceptable method of birth control during treatment and for six months after completion of treatment.
• TTP not related to underlying cancer, treatment of cancer or transplantation
• New onset TTP, or previously diagnosed TTP with an unmaintained remission for >12 months.
• LDH >2X upper limit of normal
• PT, PTT normal
• Direct antiglobulin test (DAT) negative
• Subject has provided written informed consent
• Patients who have received up to 3 plasmapheresis.

Exclusion Criteria

Patients will be excluded from the trial based on the following criteria:

• A diagnosis of AIDS. Patients with HIV infection with absolute CD4 counts >200/ul and no active, significant opportunistic infection are eligible
• Patients with a known hepatitis C infection (HCV) and/or with hepatitis B
• Patients receiving pheresis more than once a day
• Recent (within 1 year) bone marrow or hematopoietic stem cell transplant
• Patient is on calcineurin inhibitors, or is unable to come off them
• Acute or chronic disseminated intravascular coagulation (DIC), defined by D-dimers >8mg/ml and fibrinogen < 100 mg (0.1g)/dl
• A diagnosis of metastatic or non-metastatic malignancy other than basal cell carcinoma.
• Malignant hypertension (systolic BP>200 mm Hg or a diastolic BP>130 mm Hg
• Pregnancy (a negative serum pregnancy test should be performed for all women of childbearing potential within 7 days of treatment). Eligibility resumes 3 days after delivery
• Patients with family history of or a previous diagnosis of congenital TTP
• Patients with HUS
• Patients with sepsis