Inclusion Criteria:

          -  Subjects with Relapsed/Refractory Multiple Myeloma.

          -  Subject has received three or more prior lines of therapy with exposure to a
             proteasome inhibitor (PI), an immunomodulatory imide (IMiD) and an anti-CD38
             monoclonal antibody (e.g., daratumumab).

          -  Subject has Measurable Disease, defined as at least 1 of the following:

               -  Serum M-protein ≥ 0.5 g/dL (≥ 5 g/L)

               -  Urine M-protein ≥ 200 mg / 24h

               -  Serum free light chain (FLC) assay: Involved FLC level ≥ 10 mg/dl (≥ 100 mg/L)
                  and an abnormal serum FLC ratio (< 0.26 or > 1.65).

          -  Subject has an Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 2.

          -  Prior bone marrow transplant is acceptable if subject is > 12 weeks (autologous) or >
             1 year (allogeneic) status-post transplantation

          -  Subject must have adequate bone marrow function, defined as:

               -  absolute neutrophil count (ANC) ≥ 1000/mm3;

               -  platelets ≥ 50,000/mm3;

               -  hemoglobin ≥ 8.0 g/dL.

          -  Subject must have an eGFR ≥ 30 mL/min as estimated by the MDRD formula.

          -  Subject must have total bilirubin ≤ 1.5 × upper limit of normal (ULN; except if the
             subject has a known diagnosis of Gilbert's syndrome, in which case bilirubin must be <
             3 x ULN).

          -  Serum calcium (corrected for albumin) at or below the ULN range.

        Exclusion Criteria:

          -  Subject has ever received BCMA-targeted therapy. Subjects who have received targeted
             therapy against non-BCMA targets will not be excluded

          -  Subject has a history of central nervous system involvement by their myeloma.

          -  Subject has a history of ≥ Grade 3 peripheral neuropathy.

          -  Subject has a history of plasma cell leukemia, POEMS syndrome, or amyloidosis.

          -  Subject has received any therapy to treat cancer or undergone a major surgical
             procedure within 21 days, or within 5 half-lives of an anticancer drug, prior to the
             first dose of study treatment, whichever is shorter.

          -  Subject has a history of major cardiac abnormalities.

          -  Subject has a known active infection requiring parenteral anti-infective treatment