Inclusion Criteria:

- Age 18 or older at the time screening

- Symptomatic, previously untreated (with exception of corticosteroids) secretory
myeloma

- Written informed consent obtained from the patient/legal representative prior to
performing any protocol-related procedures, including screening evaluations

- Patient must agree to take Lenalidomide with low dose dexamethasone as their initial
therapy.

- ECOG performance status of 0, 1, or 2.

- Life expectancy of >6 months

- Serum creatinine ≤ 2

- ANC≥1000

- Platelets ≥ 50,000

- Total bilirubin ≤ 2 x ULN

- AST (SGOT) and ALT (SGPT) ≤ 3 x ULN

- Able to take aspirin (81 or 325 mg) daily as prophylactic anticoagulation (patients
intolerant to ASA may use warfarin or low molecular weight heparin)

Exclusion Criteria:

- Any condition that, in the opinion of the investigator, would interfere with
evaluation of the investigational product or interpretation of patient safety or
study results.

- Concurrent enrollment in another clinical study, except for non-interventional,
observational studies.

- Any chemotherapy, immunotherapy, biologic, investigational, for treatment of multiple
myeloma other than Lenalidomide and dexamethasone.

- Previous monoclonal antibody (mAb) or other treatment specifically directed against
CD19.

- History of serious allergy or reaction to any component of the MEDI-551 formulation
that would prevent administration.

- Previous systemic cancer therapy for myeloma.

- Any active secondary malignancy.

- Human immunodeficiency virus (HIV) positive serology or acquired immune deficiency
syndrome.

- Active hepatitis B as defined by seropositivity for hepatitis B surface antigen. Or
patients with positive hepatitis B core antibody titers.

- Patients with hepatitis C antibody will be eligible provided that they do not have
elevated liver transaminases or other evidence of active hepatitis.

- Documented current central nervous system involvement by multiple myeloma.

- Previous medical history or evidence of an intercurrent illness that may, in the
opinion of the investigator, compromise the safety of the patient in the study.

- Diagnosis of plasma cell leukemia

- Diagnosis of POEMS syndrome

- Diagnosis of Amyloidosis

- Diagnosis of non-secretory myeloma