Inclusion Criteria:

• Diagnosis of active multiple myeloma according to the International Myeloma Working Group diagnostic criteria
• Relapsed or relapsed/refractory multiple myeloma
• Previous treatment with both an immunomodulator and a proteosome inhibitor therapy
• Age ≥ 18 years
• Eastern Cooperative Oncology Group (ECOG) performance status (Zubrod) ≤ 2
• Ability to understand and willingness to sign a written informed consent document
• Ability to adhere with the study visit schedule and other protocol procedures
• Life expectancy of ≥ 12 weeks
• Normal organ and marrow function

Exclusion Criteria:

• Chemotherapy or radiotherapy within 3 weeks (6 weeks for nitrosoureas or mitomycin C) prior to day 1 or those who have not recovered from AEs due to agents administered more than 3 weeks earlier
• Treatment with another investigational agent during the study or within 4 weeks before day 1
• Major surgery within 4 weeks before day 1 (this does not include placement of vascular access device or tumor biopsies)
• Antineoplastic therapy with biological agents within 2 weeks before day 1
• Known HAHAs, HACAs, or HAMAs in response to previous MAb therapy
• Previous treatment with BT062
• Malignancy within 3 years before day 1, other than the trial indication multiple myeloma and excluding treated non-melanoma skin cancer, superficial bladder cancer and carcinoma in-situ of the cervix
• Severe diseases of skin, colon, esophagus, or eye within 1 year before day 1, as judged by the Investigator
• Severe infections necessitating use of antibiotics / antivirals during the screening period
• Clinically relevant active infection including active hepatitis B or C or human immunodeficiency virus (HBV, HCV, or HIV) or any other concurrent disease which, in the judgment of the investigator, would make the subject inappropriate for enrollment into this study
• Acute or relevant abnormalities in electrocardiogram (ECG), as judged by the Investigator. These abnormalities can be defined as recent myocardial infarction, uncontrolled cardiac arrhythmias and/or pronounced disturbances of the electrical conduction system of the heart.
• Significant cardiac disease such as recent myocardial infarction (≤ 6 months prior to day 1), unstable angina, uncontrolled congestive heart failure, uncontrolled hypertension (recurrent or persistent increases in systolic blood pressure ≥ 180 mm Hg or diastolic blood pressure ≥ 110 mm Hg), uncontrolled cardiac arrhythmias, grade 3 (Lown Criteria) or greater cardiac toxicity from prior chemotherapy
• History of clinically significant drug or alcohol abuse
• Unwillingness or inability to adhere to the requirements of the study
• Concomitant therapy with corticosteroids (except as indicated in low dose for other medical conditions such as inhaled steroid for asthma, topical use, or as premedication for administration of certain medications (including BT062) or blood products and for treatment of infusion reactions if needed)
• Concomitant antineoplastic therapies including chemotherapy, radiotherapy, or biological agents during the study
• Any condition, including laboratory abnormalities, that in the opinion of the Investigator places the subject at unacceptable risk if he or she are included in the study
• Breast-feeding
• Unwillingness to use an effective contraceptive method during the study and at least 3 months after administration of study drug - unless subject is naturally infertile. (Acceptable contraceptive methods include oral or injectable contraceptives, intrauterine devices (IUD), double-barrier method, contraceptive patch, surgical sterilization, or condoms).
• Positive serum or urine pregnancy test