Inclusion Criteria:

          -  Signed written informed consent obtained prior to study procedures

          -  Histologically- or cytologically-confirmed relapsed or refractory multiple myeloma
             (MM) with measurable disease

          -  Must have received at least 3 prior lines of therapy to include treatment with a
             proteasome inhibitor (eg, bortezomib, carfilzomib, or ixazomib) and an
             immunomodulatory agent (eg, lenalidomide, pomalidomide) unless double-refractory to
             both; and a hematopoietic stem cell transplant (HSCT), for those subjects considered
             HSCT-eligible.

          -  Quantitative serum IgG levels for subjects with IgG MM must not exceed the
             institutional upper limit of normal (ULN)

          -  ECOG 0 or 1

          -  Life expectancy of at least 6 months

          -  Absolute neutrophil (ANC) count greater than 1000/ µL

          -  Platelet count greater than 50,000/µL

          -  Estimated GFR >30mL/min/1.73m2

        Exclusion Criteria:

          -  Known active central nervous system (CNS) involvement by MM

          -  Systemic rheumatic or autoimmune diseases or acute or chronic infections

          -  Uncontrolled thromboembolic events or recent severe hemorrhage

          -  Subjects who are currently using more than 5mg/day of prednisone (or an equivalent
             glucocorticoid exceeding physiologic replacement levels)

          -  Prior treatment as follows:

               -  T cell-directed antibody therapy (eg. Alemtuzumab, anti-thymocyte globulin)
                  within 6 months of enrollment

               -  Any prior myeloma-directed therapy including cytotoxic chemotherapy, biologic
                  therapy, or radiotherapy within 2 weeks of enrollment

               -  Any mAb or other protein therapeutic containing Fc-domains within 4 weeks of
                  enrollment

               -  Experimental agents within 3 half-lives prior to enrollment, unless progression
                  is documented on therapy

               -  Prior BCMA-directed investigational agents at any time

               -  Prior cell or gene therapy, excluding transfers of genetically unmodified
                  autologous cells (eg. Hematopoietic stem cell transplantation), at any time; or
                  prior allogeneic HSCT at any time

          -  Pregnant or breastfeeding