Inclusion Criteria:

          -  A prior diagnosis of multiple myeloma with documented disease progression after last
             line of therapy

          -  Double refractory to an immunomodulatory drug (IMiD) and a Proteasome Inhibitor (PI)
             (regardless of the number of prior lines of therapy), or have received at least 3
             prior lines of therapy including an IMiD and a PI.

          -  Prior treatment with daratumumab or another anti-CD38 antibody may be allowed under
             certain circumstances

          -  Male and women of childbearing potential agrees to use contraception during the
             treatment period and during a specified time period after the last dose

        Exclusion criteria:

          -  Primary refractory disease (i.e. never responded with at least Minimal Response to any
             prior therapy for multiple myeloma)

          -  Prior treatment with CD38 CAR-T cell therapy or CD38/CD3 bispecific antibodies

          -  Any medical condition that may interfere with safety or participation in this study

          -  Other malignancy diagnosed or requiring treatment within the past 3 years with the
             exception of adequately treated basal cell carcinoma, squamous cell skin cancer,
             carcinoma in-situ of the cervix or breast or very low and low risk prostate cancer in
             active surveillance

          -  Known or suspected amyloidosis, plasma cell leukemia or POEMS syndrome (plasma cell
             dyscrasia with polyneuropathy, organomegaly, endocrinopathy, monoclonal protein and
             skin changes)

          -  Known central nervous system (CNS) or meningeal involvement of myeloma

          -  Prior stem cell transplant (autologous and/or allogenic) within 6 months of initiation
             of therapy or prior allogeneic stem cell transplantation with active
             graft-versus-host-disease

          -  Prior treatment with melflufen