Trial: NCT05945524 (recruiting, France) in multiple myeloma. Intervention: bone marrow sampling at 12 weeks for single-cell immune/oncogenomic analyses in patients treated with teclistamab. Drug/mechanism: Teclistamab is a bispecific T‑cell–engaging antibody (IgG) that binds BCMA (TNFRSF17) on myeloma plasma cells and CD3 on T cells, redirecting and activating T cells to kill BCMA+ cells via TCR/CD3 signaling and cytotoxic effector functions. Targets/cells/pathways: BCMA-expressing malignant plasma cells, CD3+ T cells (TCR activation, cytotoxic pathways). The study seeks features distinguishing responders vs primary/secondary resistance under teclistamab therapy.