The following criteria is provided for health care professionals.

Inclusion Criteria:

• ECOG (Eastern Cooperative Oncology Group) performance score of 1 or 0. Subjects in the Phase 2 portion: ECOG performance score of 2, 1, or 0.
• Diagnosis of multiple myeloma previously treated with at least one prior line of therapy. Induction therapy followed by stem cell transplant and maintenance therapy will be considered a single line of therapy. For Safety Expansion, subjects must have been previously treated with a proteasome inhibitor (e.g., bortezomib) and an immunomodulatory agent (e.g., thalidomide, lenalidomide). For Venetoclax-Dexamethasone Combination, subjects must have been been previously treated with a proteasome inhibitor (e.g., bortezomib) and an immunomodulatory agent (e.g., thalidomide, lenalidomide) AND have t(11;14)-positive multiple myeloma per the central lab testing. For Phase 2, subjects must have documented MM positive for t(11;14) translocation. If testing has been performed by non-central lab, retesting must be confirmed by central lab. Subjects must have evidence of disease progression on or within 60 days of last dose of most recent previous treatment based on IMWG criteria AND subjects must have previously received at least 2 lines of therapy, including an immunomodulatory drug, a proteasome inhibitor, daratumumab, and glucocorticosteroids. Daratumumab combination regimen must be one of the prior lines of therapy (for this study, daratumumab plus corticosteroids will not be considered a combination regimen) given alone or in combination, OR, subjects must be refractory to glucocorticosteroid and to the most recent immunomodulatory drug, proteasome inhibitor and daratumumab given alone or in combination.
• Measurable disease at Screening: Serum monoclonal protein of at least 1.0 g/dL (10g/L) by protein electrophoresis or at least 200 mg of monoclonal protein in the urine on 24-hr electrophoresis or serum immunoglobulin free light chain of at least 10 mg/dL and abnormal serum immunoglobulin kappa to lambda free light chain ratio.
• Subjects with a history of autologous or allogenic stem cell transplantation must have adequate peripheral blood counts independent of any growth factor support, and have recovered from any transplant related toxicity(s) and be at least 100 days post-autologous transplant prior to first dose of study drug or at least 6 months post-allogenic transplant prior to first dose of study drug and not have active graft-versus-host disease (GVHD), i.e., requiring treatment.
• Meet the following laboratory parameters, per the reference range, at least once during the screening period: ANC of at least 1000/μL (Subjects may use growth factor support to achieve ANC eligibility criteria), AST and ALT not higher than 3 x ULN, Calculated creatinine clearance of at least 30 mL/min using a modified Cockcroft-Gault calculation, platelet count of at least 30,000 mm³ (independent of transfusion for 2 weeks), hemoglobin of at least 8.0 g/dL (subjects may receive blood transfusion to achieve hemoglobin eligibility criteria), and total bilirubin not higher than 1.5 x ULN (subjects with Gilbert's Syndrome may have bilirubin higher 1.5 x ULN).

Exclusion Criteria:

• Exhibits evidence of other clinically significant uncontrolled condition(s), including, but not limited to: uncontrolled systemic infection (viral, bacterial, or fungal), diagnosis of fever and neutropenia within 1 week prior to first dose of study drug.
• Cardiovascular disability status of New York Heart Association Class greater than or equal to 3.
• Significant history of renal, neurologic, psychiatric, endocrinologic, metabolic, immunologic, cardiovascular or hepatic disease, within the last 6 months that, in the opinion of the investigator, would adversely affect his/her participation in the study.
• History of other active malignancies other than multiple myeloma within the past 3 years prior to study entry, with the following exceptions: adequately treated in situ carcinoma of the cervix uteri, basal cell carcinoma of the skin or localized squamous cell carcinoma of the skin, localized prostate cancer Gleason grade 6 or lower AND with stable prostate specific antigen (PSA) levels off treatment, previous malignancy confined and surgically resected (or treated with other modalities) with curative intent.
• Known HIV infection.
• Active hepatitis B or C infection