• Written informed consent obtained to participate in the study and Health Insurance Portability and Accountability Act (HIPAA) authorization for release of personal health information (PHI). Consent must be obtained before performance of any study-related procedure not part of normal medical care, with the understanding that consent may be withdrawn by the subject at any time without prejudice to future medical care.

• Willing and able to adhere to the study visit schedule and other protocol requirements based on the judgement of the investigator or protocol designee.

• Predicted high risk for severe toxicity from intensive induction regimens, such as standard (full-dose) Bortezomib, cyclophosphamide, dexamethasone (VCD), lenalidomide, bortezomib, and dexamethasone (RVD), or lenalidomide and weekly dexamethasone (Rd) as each regimen was published. (Such regimens often use, for example, twice-weekly bortezomib or lenalidomide at 25 mg.) High-risk is defined as one of the following:

∙ Score ≥ 2 (indicating frail) on the International Myeloma Working Group instrument (IMWG; Palumbo et al. \[Blood 2015\]),

‣ Karnofsky Performance Status (KPS) ≤ 70,

‣ Felt not to be candidate for full-intensity induction by treating clinician due to comorbidities, performance status, or other factors not otherwise captured by the Palumbo system or performance status. The reason for the subject's non-candidacy for full-intensity therapy should be described in the clinical documentation.

• Subjects qualifying for enrollment by criterion C should be discussed with the Medical Monitor before enrollment, to ensure uniform application of this criterion across participating sites.

• Measurable MM diagnosed according to the following standard criteria. Criteria A and B must be met, in addition to C and/or D:

∙ Monoclonal plasma cells in bone marrow ≥ 10% and/or presence of biopsy-proven plasmacytoma

‣ Monoclonal protein (M-protein) present in serum and/or urine, defined as serum M-protein of ≥ 1 g/dL (0.5 g/dL for Immunoglobulin A (IgA) MM) OR urine M-protein of ≥ 200 mg/24 hours. Subjects lacking an M-protein meeting those criteria must have a serum free light chain assay with an involved light chain ≥ 10 mg/dL (100 mg/L) and an abnormal serum free light chain ratio.

‣ One or more MM-related organ dysfunction findings such as hypercalcemia, renal insufficiency, anemia, and bone lesions (CRAB) criteria listed below:

⁃ Calcium elevation in blood (serum calcium 1 mg/dL ≥ upper limit of normal or \> 11 mg/dL)

• Renal insufficiency (creatinine clearance \< 40 ml/min or serum creatinine \> 2 mg/dL)

• Anemia (hemoglobin \< 10 g/dL or ≥ 2 g/dL below normal)

• Bone lesions (lytic bone lesions) on x-rays, computerized tomography (CT), Magnetic resonance imaging (MRI) or Positron emission tomography (PET)

‣ Myeloma-related biomarker of malignancy (1 or more should be fulfilled):

⁃ ≥ 60% bone marrow plasmacytosis

• Serum involved / uninvolved free light chain ratio of ≥ 100, provided absolute level of involved light chain is at least 100 mg/L (10 mg/dL)

• More than one focal lesion on MRI ≥ 5 mm in size

• No prior systemic anti-myeloma therapy lasting more than 28 days (generally one cycle). Any prior therapy must be completed a minimum of 14 days before starting study drugs.

• Subjects who require radiotherapy (which must be localized in its field size) may be treated during screening but initiating study therapy should be deferred until the radiotherapy is completed and 14 days have elapsed since the last date of radiotherapy.

• Demonstrate adequate organ function and laboratory values as defined in below.

• Hematological

⁃ Hemoglobin (Hgb) ≥ 8 g/dL Transfusion of packed red blood cells or use of erythropoietin or analogs is permitted, if clinically appropriate, to achieve this threshold.

⁃ Absolute Neutrophil Count (ANC) ≥ 1.0 x 109/L Use of growth factors is permitted to fulfill this criterion, particularly if low ANC is felt to be due to MM by treating clinician. If low ANC is felt to be due to non-MM causes, such as myelodysplasia or other bone marrow disorders unrelated to MM, then subject should not be enrolled on the study.

⁃ Platelets ≥ 50 × 109/L if \< 50% of bone marrow nucleated cells are plasma cells, and

⁃ ≥ 30 × 109/L if ≥ 50% of BM (Bone Marrow) nucleated cells are plasma cells.

⁃ Platelet transfusions are permitted to reach entry criteria. If low platelets are felt to be due to non-MM causes, such as myelodysplasia or other bone marrow disorders unrelated to MM, then subject should not be enrolled on the study.

• Renal

• • Calculated or measured glomerular filtration rate (GFR):Any GFR as long as not currently dialysis-dependent

• Females of childbearing potential (FCBP)\* must have a negative serum or urine pregnancy test with a sensitivity of at least 25 mIU/mL within 10 - 14 days prior to and again within 24 hours of starting lenalidomide and must either commit to continued abstinence from heterosexual intercourse or begin TWO acceptable methods of birth control, one highly effective method and one additional effective method AT THE SAME TIME (Section 5.5), at least 28 days before she starts taking lenalidomide through 30 days after the last dose of lenalidomide and 5 months after the last dose of isatuximab. FCBP must also agree to ongoing pregnancy testing during the entire duration of treatment and monthly for 5 months after the last dose of isatuximab. Men must agree to use a latex or synthetic condom during sexual contact with a FCBP even if they have had a vasectomy from the time of signing the informed consent form through 30 days after the last dose of lenalidomide and 5 months after the last dose of isatuximab. These same subjects must not donate sperm. All subjects must be counseled at a minimum of every 28 days about pregnancy precautions and risks of fetal exposure. All subjects enrolled into this trial, must be registered in and must comply with all requirements of the REVLIMID REMS program \*A female of childbearing potential (FCBP) is a sexually mature female who: 1) has not undergone a hysterectomy or bilateral oophorectomy; or 2) has not been naturally postmenopausal for at least 24 consecutive months (i.e., has had menses at any time in the preceding 24 consecutive months).