A Study of AMG 557 in Adults With Systemic Lupus Erythematosus

Inclusion Criteria: * Before any study-specific procedure, the appropriate written informed consent must be obtained; * Men and women, between the ages of 18 and 70 years old, inclusive, at the time of randomization; * Diagnosis of SLE as defined by the most recent ACR criteria, including a positive ANA at screening or documented positive ANA (the titer should be at least 1:80) in the past. * SLE duration of at least six months, as diagnosed by a physician; * Stable disease, defined as no change in SLE therapy within the previous 30 days; and, in the opinion of the investigator, no anticipated need for a change in SLE therapy will be required while the subject is enrolled in the study; * Normal or clinically acceptable ECG (12-lead reporting ventricular rate and PR, QRS, QT, QTc) at screening and Day -1 based on the opinion of the investigator; * Body mass index from 18 to 40 kg/m2 at screening; * Able and willing to complete entire study according to study schedule. * Immunizations up to date, with a minimum of tetanus, diphtheria, pertussis (td/Tdap), pneumococcal (polysaccharide) and influenza (during flu season) vaccinations, as determined by the Principal Investigator. Exclusion Criteria: * Positive serology for HIV antibodies, hepatitis B surface antigen or hepatitis C antibodies (confirmed by PCR or RIBA); * Have had signs or symptoms of a viral, bacterial or fungal infection within 30 days of study randomization; * Evidence of active or latent tuberculosis as assessed by PPD or Quantiferon testing at screening; * Have donated blood or experienced a loss of blood \>500mL within 4 weeks of randomization; * History of ethanol or drug abuse within the last one year prior to randomization; * Evidence of significant renal insufficiency, defined by: The glomerular fitration rate \< 50 mL/min using the Cockroft and Gault equation; * Evidence of liver disease (eg, serum ALT or AST \> 2x upper limit of normal); * Total WBC \<3000 x 106/L; * Neutrophil count \< 1500 x106/L * Platelet count \<75,000 x 106/L * Hemoglobin \<10g/dL * Any disorder (including psychiatric), condition or clinically significant disease (other than a diagnosis of SLE) that would, by it progressive nature and/or severity, interfere with the study evaluation, completion and/or procedures in the medical judgment of the investigator. This includes any age related co-morbidites such as presence of congestive heart failure, angina, chronic obstructive pulmonary disease, asthma, and malignancies (other than resected squamous and basal cell carcinoma of the skin). * Presence or history of vasculitis (comprising internal organs or extremities or leading to peripheral neuropathy) within the last 3 years, presence or history of active CNS lupus (defined as seizure disorder, cerebral vascular accident, psychosis ascribed to SLE , encephalitis, meningitis, and myelitis) requiring therapy within the last 3 years; * Uncontrolled hypertension (Blood pressure \> 150/95); * Poorly controlled diabetes (HbA1c \> 8%); * Any history of granulomatous disease including autoimmune granulomatous vasculitis and sarcoidosis; * Underlying condition that predisposes the subject to infections (eg, history of splenectomy); * Any disorder or condition that prevents the subject from providing truly informed consent; * Prior administration of any other biologic that primarily targets the immune system (eg, Lymphostat-B, TACI-Ig, or CTLA4-Ig) in the past 9 months. This includes prior administration of AMG 557; * Presence of AMG 557 anti-bodies; * Prior administration of rituximab \> 9 months with CD19+ B cells \<5/µL; * Administration of cyclophosphamide (or any other alkylating agent), cyclosporine, tacrolimus, or sirolimus, or \> 100 mg/day prednisone or equivalent in the 6 months prior to randomization; * Participated in an investigational drug trial involving a monoclonal antibody (not targeting the immune system) within 3 months or 5 half-lives, whichever time period is longer, prior to randomization; * Participated in any another investigational drug or device trial within the previous 30 days or 5 half-lives, whichever time period is longer, prior to randomization; * Administration of \>10 mg/day prednisone (or equivalent) in the 30 days prior to randomization; * Known sensitivity to mammalian derived products; * Unwilling to practice an effective method of double-barrier contraception as determined by the investigator for the duration of the study; * Positive serum hCG at screening or positive urine hCG on D-1; or females who are currently lactating; * Known allergies to shellfish or any excipients found in KLH; * Previous immunization with KLH.