Inclusion Criteria:

          -  Multiple myeloma meeting the following criteria:

          -  Pathologically-documented diagnosis of multiple myeloma that has relapsed after at
             least two prior lines of therapy that must include a proteasome inhibitor (PI),
             immunomodulatory drug (IMiD), and, where approved and available, anti-CD38 therapy in
             any order OR that is refractory to PI, IMiD, and anti-CD38 therapy.

             ◾Subjects who could not tolerate a PI, IMiDs, or a CD38-directed therapeutic antibody
             due to unacceptable toxicities are eligible to enroll in the study.

          -  Measurable disease as per IMWG response criteria

          -  Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 2

        Exclusion Criteria:

          -  Known central nervous system involvement by multiple myeloma

          -  Previously received allogeneic stem cell transplant and one or more of the following:

               -  received the transplant < 6 months prior to study Day 1

               -  received immunosuppressive therapy < 3 months prior to study Day 1

               -  any active acute graft versus host disease (GvHD), grade 2- 4, according to the
                  Glucksberg criteria or active chronic GvHD requiring systemic treatment

               -  any systemic therapy against GvHD < 2 weeks prior to study Day 1

          -  Autologous stem cell transplantation less than 90 days prior to study day 1

          -  Multiple myeloma with IgM subtype

          -  POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and
             skin changes)

          -  Evidence of primary or secondary plasma cell leukemia at the time of screening

          -  Waldenstrom's macroglobulinemia

          -  Amyloidosis

          -  Dexamethasone at cumulative doses of greater than 160 mg or equivalent <3 weeks prior
             to study Day 1 is not allowed. Use of topical or inhaled steroids is acceptable

          -  Anticancer treatment (chemotherapy, IMiD, PI, molecular targeted therapy) < 2 weeks
             prior to study Day 1

          -  Treatment with a therapeutic antibody targeting CD38 < 12 weeks prior to study Day 1

          -  Systemic radiation therapy or major surgery < 28 days prior to study Day 1 as well as
             focal radiotherapy < 14 days prior to study Day 1.

          -  Major surgery within 28 days prior to study Day 1