The general objective of this study is to assess the efficacy and safety of Rituximab in the management of patients with refractory or relapsed thrombotic thrombocytopenic purpura-hemolytic uremic syndrome (TTP-HUS). There have been several case reports and case series describing the use of Rituximab in patients with TTP-HUS; however its use has not been studied in a large trial. It is hypothesized that Rituximab may ameliorate the severity of certain cases of TTP-HUS by decreasing the number of activity of B-cells which may result in decreased production of the ADAMTS13 protease inhibitor. Patients with TTP-HUS not responding to standard therapy or patients with relapsed disease may have particular benefit. Treatments that decrease the frequency of relapse or shorten the time to remission of TTP-HUS will be of benefit by decreasing the need for blood product support.

Inclusion Criteria:

• any patient 18 years or older diagnosed with relapsed or refractory TTP-HUS requiring therapy

Exclusion Criteria:

• alternate cause of hemolytic microangiopathy (evidence of DIC, malignant hypertension, vasculitis, anti-phospholipid antibody syndrome, post-partum acute renal failure)
• congenital or familial TTP
• TTP occuring post-stem cell, bone marrow, or solid organ transplant
• drug-induced TTP
• pregnancy or breast-feeding
• history of hepatitis B or C infection
• prior rituximab treatment
• active or metastatic cancer
• other causes of thrombocytopenia such as ITP, myelodysplastic syndrome, confirmed or suspected drug-induced thrombocytopenia
• refusal to receive blood products
• hypersensitivity to blood products, plasma products, murine proteins, or any component of the Rituximab formulation
• geographic inaccessibility
• co-morbid illness limiting life expectancy to less than 2 months independent of TTP
• failure to provide written informed consent