Serum Immunoglobulin Changes in Multiple Myeloma Patients Treated with CAR T-Cell Therapy

Chimeric antigen receptor (CAR) T-cell therapy has emerged as a promising treatment for relapsed or refractory multiple myeloma (RRMM), with high response rates of 80-95%. Serum immunoglobulin changes have been observed throughout conventional multiple myeloma treatment, including after immunomodulatory drugs, proteasome inhibitors, and autologous stem cell transplantation. However, the clinical significance of new abnormal protein bands (APBs) following CAR T-cell therapy is largely unexplored. We retrospectively analyzed consecutive multiple myeloma (MM) patients who received CAR T-cell therapy at the University Hospital Bern between May 2021 and February 2024. Serum paraprotein (M-protein) patterns were assessed using immuno-fixation electrophoresis (IFE) before and after CAR T-cell treatment. Patients were grouped based on serum immunoglobulin changes. Among 46 patients, 9 (19.6%) developed new APBs following CAR T-cell therapy. No significant differences in overall survival (OS) or progression-free survival (PFS) were observed between patients with and without APBs. Immunoglobulin changes occurred in both relapsed and non-relapsed patients, suggesting that the appearance of new APBs does not indicate disease progression. This observation aligns with previous reports of paraprotein changes following conventional MM therapies. This report suggests that new APBs following CAR T-cell therapy are a relatively common finding but do not correlate with inferior clinical outcomes. Our results highlight the need for larger, multi-center studies to further investigate this phenomenon in MM patients undergoing CAR T-cell therapy.