A Study of Elranatamab Outpatient Administration in Patients With Relapsed/Refractory Multiple Myeloma

Inclusion Criteria: 1. Written informed consent, according to institutional guidelines, signed and dated by the participant or by a legal guardian prior to the performance of any study-specific procedures, sampling, or analyses 2. At least 18 years-of-age at the time of signature of the ICF 3. Has documented diagnosis of MM according to IMWG diagnostic criteria 4. Measurable disease at screening, as assessed by local laboratory, defined by any of the following: 1. Serum M-protein level ≥0.5 g/dL 2. Urine M-protein level ≥200 mg/24 hours 3. Light chain MM without measurable M-protein in the serum or the urine: serum free light chain (sFLC) ≥10 mg/dL and abnormal serum immunoglobulin kappa lambda FLC ratio 4. For participants without measurable disease in the serum, urine, or involved FLC, presence of plasmacytomas (≥2 cm x 1 cm) 5. Relapsed and/or refractory MM received ≥1 prior line of therapy and must have been exposed to both lenalidomide and an anti-CD38 monoclonal antibody (in the same or separate prior lines) 6. ECOG Performance Status score of 0 or 1 7. Human immunodeficiency virus (HIV)-positive participants are eligible if they meet all of the following: 1. No detectable viral load (i.e., \<50 copies/mL) at screening 2. CD4+ count \>300 cells/mm3 at screening 3. No acquired immunodeficiency syndrome (AIDS)-defining opportunistic infections within 6 months of screening 4. Receiving highly active antiretroviral therapy (HAART). Any changes in HAART due to resistance/progression should occur at least 3 months prior to enrollment. A change in HAART due to toxicity is allowed up to 4 weeks prior to enrollment. HAART that could interfere with study treatment is excluded (consult the Medical Monitor for a review of medications prior to enrollment, if needed). 8. Adequate organ function, defined as follows: 1. Hemoglobin (Hgb) ≥8 g/dL (≥5 mmol/L; without prior red blood cell \[RBC\] transfusion within 7 days before laboratory testing; recombinant human erythropoietin use is permitted) 2. Platelets \>50 x109/L 3. Absolute neutrophil count (ANC) ≥10.x109/L (prior growth factor support is permitted but must be without support for 7 days for G-CSF or GM-CSF and for 14 days for pegylated G-CSF) 4. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2.5xupper limit of normal (ULN) 5. Estimated glomerular filtration rate (eGFR) ≥30 mL/min based on Modified Diet in Renal Disease (MDRD) 4-variable formula calculation or creatinine clearance measured by 24-hour urine collection 6. Total bilirubin \<1.5xULN (isolated total bilirubin) ≥1.5xULN with conjugated \[direct\] bilirubin \<1.5xULN is allowed for those participants with known congenital nonhemolytic hyperbilirubinemias) 7. Corrected serum calcium ≤14 mg/dL (≤3.5 mmol/L) or free ionized calcium ≤6.5 mg/dL (≤1.6 mmol/L) 9. Participants must be able and willing to receive prophylaxis for Varicella zoster virus (VZV) and Pneumocystis jirovecii pneumonia (PJP) as follows: 1. VZV prophylaxis (e.g. acyclovir or valacyclovir) must be initiated prior to or on Day 1 of study treatment, continued throughout the treatment period, and maintained for at least 3 months after the final dose 2. PJP prophylaxis must likewise be initiated prior to or on Day 1 of study treatment, continued throughout the treatment period, and maintained for at least 3 months after the final dose 10. A woman of childbearing potential must have a negative highly sensitive serum pregnancy test at screening and again within 24 hours of the start of study treatment and must agree to further serum or urine pregnancy tests during the study. 11. A woman must be: a. Not of childbearing potential, or b. Of childbearing potential and practicing true abstinence; or i. Have a sole partner who is vasectomized; or ii. Practicing ≥1 highly-effective, user-independent method of contraception. R 12. A woman must agree not to donate eggs (ova, oocytes) or freeze for future use, for the purposes of assisted reproduction during the study and for 4 months after receiving the last dose of study treatment. 13. A man must wear a condom (with or without spermicidal foam/gel/film/cream/suppository when engaging in any activity that allows for passage of ejaculate to another person during the study and for a minimum of 90 days after receiving the last dose of study treatment. If a female partner is of childbearing potential, she must also be practicing a highly effective method of contraception. 14. A male participant must agree not to donate sperm for the purpose of reproduction during the study and for a minimum of 90 days after receiving the last dose of study treatment. Exclusion Criteria: 1. History of antitumor therapy as follows, before the first dose of study drug 1. Targeted therapy, epigenetic therapy, or treatment with an investigational drug or used an invasive investigational medical device within 21 days or at least 5 half-lives, whichever is shorter. 2. Monoclonal antibody treatment for MM within 21 days. 3. Cytotoxic therapy within 21 days. 4. PI therapy within 14 days. 5. Immunomodulatory agent therapy within 7 days. 6. Radiotherapy within 14 days or focal radiation within 7 days. 7. Prior gene modified adoptive cell therapy (e.g., chimeric antigen receptor modified \[CAR\]-T cells) ≤12 weeks before the first dose of study drug 2. Has received any of the following: 1. Packed red blood cells within the last 7 days prior to dosing 2. Platelet transfusions within the last 7 days prior to dosing 3. Live vaccine within 1 month prior to screening or plans to receive a live vaccine during the study 3. History of Grade ≥3 CRS or ICANS with prior therapies. 4. Current treatment with strong or moderate inducers of cytochrome P450 (CYP) 3A4 (CYP3A4) that cannot be discontinued at least 7 days prior to the start of elranatamab treatment and during the study. 5. Has myelodysplastic syndrome