Inclusion Criteria:

- Diagnosed with multiple myeloma that is refractory or has relapsed after treatment

- Measurable serum and/or urine M-protein

- Failed 1 or 2 prior therapies for multiple myeloma

- 18 years of age or older

Exclusion Criteria:

- Received more than 2 prior therapies for multiple myeloma.

- Previous cancer therapies (chemotherapy, biologic therapy, radiation therapy or
immunosuppressants) within the last 3 weeks

- Received monoclonal antibodies within the last 3 weeks (chimeric or murine) or 8
weeks (human or humanized)

- Received investigational (not yet approved by a regulatory authority) agent to treat
multiple myeloma within the last 4 weeks

- Subjects who received a stem cell transplant using cells from themselves in the past
16 weeks

- Subjects who received a stem cell transplant using cells from another individual

- Previously treated with bortezomib or mapatumumab

- Known HIV, hepatitis-B, hepatitis-C, or hepatitis A infection

- Infection requiring antibiotics or hospitalization within the last 2 weeks

- Major surgery within the last 4 weeks

- Diagnosis with POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy,
monoclonal gammopathy, and skin changes)

- History of other cancers within the past 5 years

- Pregnant or breast-feeding women