MRD-Guided BCMA/CD3 Bispecific Antibody Treatment After Stem Cell Transplant for Newly Diagnosed Multiple Myeloma

Inclusion Criteria: 1. Be able to understand and voluntarily signs the informed consent form (ICF). 2. Age ≥ 18 years. 3. Newly diagnosed multiple myeloma according to the International Myeloma Working Group (IMWG) criteria. 4. MRD positivity (≥10-⁵) detected by EuroFlow. 5. Previous therapy limited to first-line treatment only, including: (1) Induction therapy with a 3- or 4-drug regimen containing a proteasome inhibitor and/or an immunomodulatory drug and/or an anti-CD38 monoclonal antibody; (2) Single or tandem autologous stem cell transplantation (ASCT); (3) Up to 2-4 cycles of consolidation therapy post-ASCT are permitted, with the total number of induction plus consolidation cycles not exceeding 8. 6. Completion of ASCT within ≤12 months from the start of induction therapy; and ≤6 months from the most recent ASCT at enrollment (≤7 months if consolidation therapy was administered). 7. No prior maintenance therapy. 8. Achieved at least a partial response (≥PR) according to the IMWG 2016 response criteria. 9. Presence of measurable disease at diagnosis. Exclusion Criteria: 1. Prior treatment with genetically modified adoptive cellular therapy. 2. History of allogeneic stem cell transplantation or solid organ transplantation. 3. Disease progression prior to enrollment (per IMWG 2016 response criteria), or presence of plasma cell leukemia, Waldenström macroglobulinemia, POEMS syndrome, or light-chain amyloidosis not attributable to symptomatic multiple myeloma. 4. Central nervous system involvement.