A Study of Gammagard Liquid (Immune Globulin Infusion, 10%) to Prevent Infections in Adults With Multiple Myeloma

Multiple myeloma is a cancer of the plasma cells in the bone marrow. The main aim of this study is to learn how well the Immune Globulin Infusion (human), 10 percentage (%) (IGI, 10%) can help prevent infections in participants with multiple myeloma receiving B-cell maturation antigen (BCMA) x cluster of differentiation 3 (CD3) directed bispecific antibody therapy. Participants will be randomly assigned to one of two groups: 1. Primary infection prevention group: They will receive IGI, 10% for 12 months. 2. Secondary infection prevention group: They will only receive IGI, 10% if they develop a serious infection during the 12 months study period. During the study, participants will visit their study clinic 15 times (for 4-week dosing interval) or 19 times (for 3-week dosing interval) and their total participation duration will be up to 14 months (including screening period approximately 8 weeks).