The study will be conducted in phases, participants must start with phase 1 and follow through the phases in order. Phase 1, Screening to Determine Eligibility: evaluation to see if you are a good fit for the study. Phase 2, Treatment with Isatuximab, Lenalidomide and Dexamethasone: Treatment will be offered in cycles. Each treatment cycle is 28 days long. (REVLIMID®) is the brand name for lenalodomide Phase 3, Maintenance: After completing 24 treatment cycles, participants will move into the maintenance phase where they will take lenalidomide only. This is the standard treatment for their type of cancer, as approved by FDA. Participants will continue taking lenalidomide for as long as it is working to control their myeloma and are tolerating the medication. Phase 4, Long-Term Follow-Up: if the participant stops receiving treatment for any reason, they will enter the follow-up phase of the study. Prior to starting this phase, they will have a clinic visit to complete a series of lab tests and assessments. The study team will use these tests to evaluate how the participant's myeloma responded to the treatment received. This study will involve the following tests and procedures: a review of medical history, physical exam, performance status review, pregnancy test, bone survey, tumor assessment (CT, MRI, or PET-CT), bone marrow biopsy, blood tests, isatuximab infusion, dexamethasone dose, lenalidomide dose, concomitant medications review, pill diary review, and questionnaires.