Inclusion Criteria:

• Patients with relapsed or refractory multiple myeloma, with 1 to 3 therapies
• Must have received prior lenalidomide therapy and progressed on either a lenalidomide-containing regimen or lenalidomide maintenance (defined as a dose of 10-15 mg lenalidomide daily after induction regimen or maintenance)
• Must have measurable disease, as defined by International Myeloma Working Group criteria, having one or more of the following:
  • Serum M protein >= 1.0 g/dL
  • Urine M protein >= 200 mg/24 hours
  • Involved serum free light chain level >= 10 mg/dL with abnormal kappa/lambda ratio
  • Measurable biopsy-proven plasmacytomas (>= 1 lesion has a single diameter >= 2cm)
  • Bone marrow plasma cells >= 30%
• Age 18 years and older, and have the capacity to give informed consent
• Eastern Cooperative Oncology Group (ECOG) performance status of 0-2
• Subjects should have resolution of any toxicities from prior therapy to grade =< 1 or baseline prior to enrollment (with the exception of peripheral neuropathy)
• Subjects are required to have grade =< 2 peripheral neuropathy to enroll
• Prior autologous stem cell transplant is allowed; patients must be >= 6 months post- autologous stem cell transplantation to enroll
• Estimated glomerular filtration rate (eGFR) >= 20 ml/min
• Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) =< 3 x upper limit of normal (ULN)
• Total bilirubin =< 2 x ULN
• Absolute neutrophil count (ANC) >= 1,000/uL
• Platelets >= 50,000/uL
• Hemoglobin >= 8 g/dL
• Growth factor use or transfusions may be used to meet the eligibility requirement for ANC, platelets, and hemoglobin
• Female patients of childbearing potential and male patients must agree to use 2 effective forms of contraception or continuously abstain from heterosexual intercourse during the period of therapy, and for 6 months after discontinuation of study treatment for females and 3 months after discontinuation of study treatment for males

Exclusion Criteria:

• History of clinically significant cardiovascular disease, including congestive heart failure New York Heart Association (NYHA) class 3-4, symptomatic ischemia, left ventricular ejection fraction < 40%, uncontrolled conduction abnormalities, myocardial infarction in last 6 months
• Uncontrolled hypertension as determined by the principal investigator (PI) or designee
• Active plasma cell leukemia or systemic amyloid light-chain (AL) amyloidosis
• History of another primary malignancy that has not been in remission for at least 1 year
  • However, the following diagnoses are eligible for inclusion: non-melanoma skin cancer, localized prostate cancer, superficial bladder cancer, cervical carcinoma in situ, on biopsy or any prior malignancy with an estimated > 90% 1-year cure rate per sponsor-investigator
• Active hepatitis B, hepatitis C at time of screening
• Subjects with active uncontrolled infection
• Concurrent use of other anticancer agents or experimental treatments
• Treatment with anti-CD38 monoclonal antibody therapy in the last 6 months