This study is the first time REGN5458 will be combined with other cancer therapies. The main goal is to understand if REGN5458 can be given safely with other cancer study treatments, and if so, what dose of REGN5458 should be used for each combination. The investigational drug, REGN5458, is not approved by the Food and Drug Administration (FDA). Are you Eligible? (Inclusion Criteria) Are you at least 18 years of age? - Are you likely to live for at least six more months? -Do you have measurable disease as defined in the protocol according to International Myeloma Working Group (IMWG)...