• Documented informed consent of the participant and/or legally authorized representative.

‣ Assent, when appropriate, will be obtained per institutional guidelines.

• Karnofsky Performance Status (KPS) of \>= 70%.

• Life expectancy \>= 16 weeks.

• Participant must have a confirmed diagnosis of active MM as defined by the International Myeloma Working Group (IMWG) criteria.

• Participant must have a confirmed CS1+ MM as evaluated by City of Hope (COH) Pathology Core.

• Participant must have measurable disease defined as meeting at least one of the criteria below:

‣ Serum M-protein \>= 0.5 g/dL.

⁃ Urine M-protein \>= 200 mg/24 hour.

⁃ Involved serum free light chain (sFLC) level \>= 10 mg/dL with abnormal kappa/lambda ratio.

⁃ Measurable biopsy-proven plasmacytomas (\>= 1 lesion that has a single diameter \>= 2 cm)

⁃ Bone marrow plasma cells \>= 30%.

• Participant must have relapsed or refractory disease after all 3 prior treatment regimens with the following requirements:

‣ Participant must have received prior treatment with an immunomodulatory agent.

⁃ Participant must have received prior treatment with a proteasome inhibitor.

⁃ Participant must have received prior treatment with an anti-CD38 antibody.

⁃ Participants must be refractory to last line of therapy prior to study enrollment (refractory myeloma is defined as disease that is nonresponsive, progression on treatment, or shows progression within 60 days after the last prior line of therapy).

⁃ Participants who were not candidates to receive one or more of the above treatments are eligible; however, the reason must be clearly documented in the case report form.

⁃ Note: induction chemotherapy, autologous stem-cell transplantation (ASCT), and maintenance therapy should be considered as 1 regimen.

• Additionally, if a participation underwent autologous transplant he/she be \>= 90 days from transplant at the time of enrollment.

• Total serum bilirubin =\< 2.0 mg/dL.

• Participants with Gilbert syndrome may be included if their total bilirubin is =\< 3.0.

• Aspartate aminotransferase (AST) \< 2.5 x upper limit of normal (ULN).

• Alanine aminotransferase (ALT) \< 2.5 x ULN.

• Serum creatinine =\< 2.5 x ULN or estimated creatinine clearance of \>= 40 mL/min per the Cockcroft-Gault formula, and the participant is not on hemodialysis.

• Absolute neutrophil count \>= 1000/uL. Transfusions and growth factors must not be used to meet these requirements at initial screening.

• Hemoglobin (Hb) \>= 8 g/dl. Transfusions and growth factors must not be used to meet these requirements at initial screening.

• Platelet count \>= 50,000/uL (\>= 30,000/uL if bone marrow plasma cells are \>= 50% of cellularity). Transfusions and growth factors must not be used to meet these requirements at initial screening.

• Left ventricular ejection fraction \>= 45% within 8 weeks before enrollment.

• Oxygen (O2) saturation \>= 92%.

• Women of childbearing potential (WOCBP): Negative urine or serum pregnancy test.

• If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required.

• Agreement by females and males of childbearing potential to use an effective method of birth control or abstain from heterosexual activity for the course of the study through at least 3 months after the last dose of protocol therapy.

‣ Childbearing potential defined as not being surgically sterilized (men and women) or have not been free from menses for \> 1 year (women only).