The incidence and clinical significance of monoclonal and oligoclonal protein bands in multiple myeloma patients after BCMA–CAR‐T cell therapy: A retrospective study based on LEGEND‐2

Abstract The emergence of abnormal protein bands (APBs), also known as oligoclonal protein bands, has been documented in patients with multiple myeloma (MM) post hematopoietic stem cell transplantation. However, the incidence rate and clinical significance of APBs remain contentious. Few studies have explored the occurrence and prognostic implications of APBs in patients with MM treated with B‐cell maturation antigen (BCMA)–specific chimeric antigen receptor (CAR)‐T therapy. In this retrospective study, we examined the frequency, isotypes, and duration of APBs, as well as their correlation with MM disease characteristics, treatment response, clinical outcomes, and immune signature in patients with relapsed/refractory MM who had received LCAR‐B38M therapy at the Xi'an site of the phase 1 LEGEND‐2 trial. Among 47 patients assessed, 23 (48.9%) developed APBs following CAR‐T therapy, with IgG being the most common isotype. The median onset and duration of APBs post‐CAR‐T infusion were 3.6 and 5.8 months, respectively. Patients with APBs demonstrated significantly improved response to LCAR‐B38M therapy, along with longer overall and progression‐free survival. Furthermore, those with APBs exhibited enhanced recovery rates of immunoglobulins and higher absolute counts of white blood cells, neutrophils, and lymphocytes post‐CAR‐T treatment compared to those without APBs. However, no significant differences were observed between the two groups in the percentages of various T‐cell subsets and natural killer cells. Overall, the presence of APBs in patients with MM following CAR‐T treatment was associated with deeper remission and a more favorable prognosis, suggesting a robust humoral response and subsequent immune reconstitution.