|Exclusion Criteria:||1) HIV or HHV-8 positive|
2) Skin lesions as sole measurable manifestation of MCD.
3) Previous lymphoma
4) Malignancies, except for adequately treated basal cell or squamous cell carcinoma of the skin, carcinoma in situ of the cervix, or cancer other than lymphoma, from which the subject has been disease-free for >/= 3 years.
5) Concurrent medical condition or disease (eg, autoimmune disease, active systemic infection, uncontrolled diabetes, acute diffuse infiltrative pulmonary disease) that is likely to interfere with study procedures or results, or that in the opinion of the investigator would constitute a hazard for participating in this study.
6) Prior exposure to agents targeting IL-6 or the IL-6 receptor.
7) Use of disallowed therapies: other concomitant anti-tumor therapies for Castleman's disease (eg, anti-CD20 antibodies, IL-6- or IL-6 receptor-targeted therapies, chemotherapy), biologic treatments such as anti-tumor necrosis factor alpha (TNF-alpha) antibodies, immunosuppressive agents (except stable doses of corticosteroids), and erythropoietin stimulating agents (ESAs).
8) Received an investigational drug (including vaccines), erythropoietin stimulating agents (ESAs), or any systemic treatment for Castleman's disease within 4 weeks (or in the case of rituximab, within 8 weeks) before the planned start of treatment.
9) Major surgery within 4 weeks of treatment.
10) History of uncontrolled heart disease such as unstable angina, congestive heart failure, myocardial infarction within preceding 12 months, hemodynamic instability or known left ventricular ejection fraction (LVEF) < 30%, or clinically significant rhythm or conduction abnormality.
11) Clinically significant infections, including known hepatitis C infection or known to be hepatitis B surface antigen (HBsAg) positive.
12) History of allogeneic transplant (except corneal transplants).
13) Known, unmanageable severe infusion related reactions to monoclonal antibodies or to murine, chimeric, or human proteins or their excipients.
14) Pregnant or nursing.
15) Vaccination with live, attenuated vaccines within 4 weeks of first administration of study agent.
16) Paraneoplastic pemphigus or bronchiolitis obliterans.
17) Any condition that, in the opinion of the investigator, would compromise the wellbeing of the subject or the study or prevent the subject from meeting or performing study requirements.