• ≥18 years of age at the time of signing informed consent.

• Voluntarily signed informed consent form.

• Diagnosis of relapsed/refractory multiple myeloma (Parts 1a and 1b), with measurable disease at screening visit as follows:

• Multiple Myeloma (at least one of the criteria below):

‣ Serum M-protein greater or equal to 0.5 g/dL.

‣ Urine M-protein greater or equal to 200 mg/24 h.

‣ Serum free light chain (FLC) assay: involved FLC level greater or equal to 3 mg/dL (30 mg/L) provided serum FLC ratio is abnormal.

‣ A biopsy-proven evaluable plasmacytoma\*.

‣ Bone marrow plasma cells \> 10% of total bone marrow cells\*.

‣ Non secretory patient will be allowed provided they have measurable disease by PET-CT or bone marrow aspiration, as designated\*.

• Results pre-dating the Screening visit by up to 28 days may be used to establish eligibility.

• R/R MM subjects must have been exposed to at least three prior lines of therapy including the following agents:

∙ proteasome inhibitor

‣ immunomodulatory (IMiDs) agent

‣ anti-CD38 antibody

• For part 1a: At least one of the following risk factors: a. Extra-medullary disease (EMD) - defined as a MM lesion that is not connected to a bone. b. previous exposure to an anti-BCMA therapy.

• Eastern Cooperative Oncology Group (ECOG) performance status 0 - 2.

• Women of child-bearing potential (WCBP), defined as a sexually mature woman who has not undergone a hysterectomy or tubal ligation or who has not been naturally postmenopausal for at least 24 consecutive months, must have a negative serum pregnancy test prior to treatment. All sexually active WCBP and all sexually active male subjects must agree to use effective methods of birth control throughout the study.

• Recovery to ≤ Grade 2 or baseline of any non-hematologic toxicities due to prior treatments, excluding alopecia and Grade 3 neuropathy, and toxicities that are irreversible and not expected to interfere with study treatment or pose safety concerns, per investigator judgement.

• Ability and willingness to adhere to the study visit schedule and all protocol requirements.

⁃ For subjects with relapsed multiple myeloma who have previously undergone allogenic stem cell transplantation: no evidence of graft versus host disease after cessation of any immunosuppressive therapy for at least one month before recruitment to the study.