• Participant has given voluntary signed written informed consent before performance of any study related procedure that is not part of normal medical care, with the understanding that consent may be withdrawn by the participant at any time without prejudice to their future medical care.

• Eastern Cooperative Oncology Group (ECOG) performance status ≤ 1.

• Male or female participants age ≥ 18 years

• The effects of elranatamab on the developing human fetus are unknown. For this reason and because anti-BCMA bispecific antibodies are known to be teratogenic, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 4 months after completion of elranatamab administration.

• Prior diagnosis of MM as defined according to IMWG criteria.

• Measurable disease of multiple myeloma as defined by at least one of the following prior to idecabtagene vicleucel infusion:

‣ Serum monoclonal protein ≥ 0.5 g/dL. Patients with IgD disease and lower amounts of monoclonal protein may be permitted to enroll with PI approval

⁃ ≥ 200 mg of monoclonal protein in the urine on 24 hour electrophoresis

⁃ Serum free light chain ≥ 100 mg/L (10 mg/dL) and abnormal serum free kappa to serum free kappa light chain ratio (\<0.26 or \>1.65)

• Previously treated relapsed and refractory multiple myeloma following idecabtagene vicleucel as infusion as standard of care who have achieved at least a PR or better per IMWG criteria. Patients will have received idecabtagene per label including after at least 4 prior lines of therapy and relapsed after an immunomodulatory drug (IMiD), a proteasome inhibitor and an Anti-CD38 monoclonal antibody

• left ventricular ejection fraction (LVEF) ≥40% as determined by a multiple gated acquisition scan (MUGA) scan or echocardiogram (ECHO).

• Participants must meet the following organ and marrow function as defined below:

‣ Absolute neutrophil count ≥1000/microlitre (mcL). Use of granulocyte-colony stimulating factors is permitted if completed at least 7 days prior to planned start of dosing.

⁃ Platelet count ≥25,000/mcL. Platelet transfusion support is permitted if completed at least 7 days prior to planned start of dosing.

⁃ Hemoglobin ≥8 g/dL. Red blood cell transfusion support is permitted if completed at least 7 days prior to planned start of dosing.

⁃ Calculated creatinine clearance ≥30 mL/min by Cockcroft-Gault equation.

⁃ Patient has adequate hepatic function, as evidenced by each of the following:

• Serum total bilirubin \<2 mg/dL; and

∙ Serum aspartate transaminase (ALT) and/or aspartate transaminase (AST) values \< 2.5 × the upper limit of normal (ULN) of the institutional laboratory reference range. Patients with elevated bilirubin due to Gilbert's syndrome may be permitted with PI approval (e.g. total bilirubin \<3 mg/dL and normal direct bilirubin).

• Ability to understand and the willingness to sign a written informed consent document. (Providing consents in as many languages as possible is encouraged)