Background and Importance Multiple Myeloma (MM) is a plasma cell neoplasm. The reduction and dysfunctionality of normal plasma cells together with treatment with anti-BCMA CAR-T leads to a deficit in humoral immunity that manifests as hypogammaglobulinemia and an increase in infections risk, which lead to the need to administer replacement therapy with intravenous polyclonal immunoglobulins (IgRT).

Aim and Objectives The primary objective of this study is to describe the use of immunoglobulins in patients who have received anti-BCMA CAR-T therapy (ide-cel, cilta-cel, ARI0002) for the treatment of MM in a clinical trial or as compassionate use.

Material and Methods This is a single-centre, observational, descriptive and retrospective study to describe the use of immunoglobulins in patients who had hypogammaglobulinemia, defined as IgG levels < 400 mg/dL, or any IgG level along with infectious events that require treatment with immunoglobulins. An institutional review board (IRB) approved the study.

Results 47 patients received an anti-BCMA CAR-T, with Ide-Cel being the CART in 70.21% (n=33) of them. Plasma IgG levels decreased progressively over time (median nadir month 7= 208 mg/dL (range 100–465) presenting a recovery around the eighth month post-infusion. Of these 47 patients, 22 (58.64%) received, at least once, IgRT. In these 22 patients, the median time until the start of treatment with IgRT was 123 days (range: 69 to 799). The rate of infectious events and febrile neutropenia grade 3–4 was 68.18% (15/22) in patients who received IgRT and 56% (14/25) in patients who did not receive IgRT (p=0.391).

Conclusion and Relevance These results reveal a period of hypogammaglobulinemia after anti-BCMA CAR T-cell therapy. The role and when to begin IgRT needs further exploration, as in this study has not improved the rate of grade 3–4 infectious events in patients who received it.

Conflict of Interest No conflict of interest.