The main purpose of this study is to see if IgPro20 can prevent infection in people with multiple myeloma (MM) who have hypogammaglobulinemia from receiving bispecific monoclonal antibodies (BsAbs).

Inclusion Criteria:

• Diagnosis of RRMM receiving a commercially available bispecific antibody
• Received at least 1 but no more than 4 cycles of BsAb
• Males or females greater than or equal to 18 years old at the time of consent
• ECOG ≤ 3
• Life expectancy > 12 months

Exclusion Criteria:

• HSCT within 3 months before enrollment
• Planned CAR-T therapy in the next 6 months
• >1 major (deep-seated) infection within the preceding 3 months
• HIV infection, Active HCV, or Active HBV infection
• Pregnancy
• Neutrophils < 500 x 10^9 per mL, Platelets < 30 x 10^9 per mL
• History of cancer other than MM in the last 3 years requiring active chemotherapy or radiation
• Known reaction/allergy to IgG products
• Intracranial hemorrhage or embolic CVA in the last 6 months
• Hyperproteinemia
• Protein-losing enteropathy
• Creatinine Cl <30 ml/min
• Documented progression on BsAb
• Known history of Hyperprolinemia
• On current or previous IVIG (in the last 3 months)

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.