First In Human (FIH) Study of REGN5459 in Adult Patients With Relapsed or Refractory Multiple Myeloma (MM)

In the phase 1 portion of the study, the primary objectives are to assess the safety, tolerability, and dose-limiting toxicities (DLTs) and to determine a recommended phase 2 dose regimen (RP2DR) of REGN5459 as monotherapy in patients with relapsed or refractory multiple myeloma (MM) who have exhausted all therapeutic options that are expected to provide meaningful clinical benefit. In the phase 2 portion of the study, the primary objective is to assess the preliminary anti-tumor activity of REGN5459 as measured by objective response rate (ORR). In the phase 1 and phase 2 portion, the secondary objectives of the study are: * To assess the preliminary anti-tumor activity of REGN5459 as measured by duration of response (DOR), progression-free survival (PFS), rate of minimal residual disease (MRD) negative status, and overall survival (OS) * To evaluate the pharmacokinetic (PK) properties of REGN5459 * To characterize the immunogenicity of REGN5459 * To evaluate the effects of REGN5459 on patient-reported quality of life (QoL), symptoms, functioning and general health status In the phase 1 portion of the study only, the secondary objective of the study is to assess the preliminary anti-tumor activity of REGN5459 as measured by ORR. In the phase 2 portion of the study only, the secondary objective of the study is to evaluate the safety and tolerability of REGN5459.