Multiple Myeloma — Disease Background

Multiple myeloma (MM) is the second most common hematologic malignancy, characterized by clonal expansion of malignant plasma cells in bone marrow, monoclonal protein production, and end-organ damage (hypercalcemia, renal insufficiency, anemia, bone lesions). Genomic heterogeneity including translocations, hyperdiploidy, and del(17p) drives prognosis stratification.

Treatment has been revolutionized by proteasome inhibitors, immunomodulatory drugs, anti-CD38 antibodies (daratumumab), and most recently BCMA-targeted therapies including CAR-T cells (idecabtagene vicleucel, ciltacabtagene autoleucel) and bispecific antibodies (teclistamab). GPRC5D and FcRH5 represent next-generation immunotherapy targets.

Research Use Only (RUO)

Fig. 1 Major pathogenic pathways in Multiple Myeloma

Key Research Targets

BCMA (TNFRSF17, CD269) — BCMA is a plasma cell-specific surface receptor for BAFF/APRIL and the primary target for myeloma CAR-T cell therapy and bispecific antibodies (teclistamab). Anti-BCMA antibodies enable flow cytometric quantification, CAR-T target density studies, soluble BCMA serum measurement, and ADC internalization assays.

CD38 — CD38 is a transmembrane glycoprotein highly expressed on myeloma cells, serving as the target for daratumumab and isatuximab. Anti-CD38 antibodies support IHC and flow cytometric identification, CDC/ADCC mechanism studies, and research into CD38 expression loss as a resistance mechanism.

CD138 (Syndecan-1, SDC1) — CD138 is the canonical plasma cell marker used for myeloma diagnosis and minimal residual disease (MRD) monitoring by multiparameter flow cytometry. Anti-CD138 antibodies are essential for bone marrow plasma cell enumeration, IHC-based plasmacytoma diagnosis, and cell sorting for downstream genomic analysis.

GPRC5D — GPRC5D is an orphan G protein-coupled receptor selectively expressed on plasma cells, serving as the target for talquetamab (bispecific antibody). Anti-GPRC5D antibodies enable expression profiling, flow cytometric quantification, and research into GPRC5D as an alternative immunotherapy target when BCMA is lost.

References

1. Munshi NC, Anderson LD Jr, Shah N, et al. Idecabtagene vicleucel in relapsed and refractory multiple myeloma. N Engl J Med. 2021;384(8):705-716. DOI

2. Moreau P, Garfall AL, van de Donk NWCJ, et al. Teclistamab in relapsed or refractory multiple myeloma. N Engl J Med. 2022;387(6):495-505. DOI

3. Facon T, Kumar S, Plesner T, et al. Daratumumab plus lenalidomide and dexamethasone for untreated myeloma. N Engl J Med. 2019;380(22):2104-2115. DOI

4. Chari A, Minnema MC, Berdeja JG, et al. Talquetamab, a T-cell–redirecting GPRC5D bispecific antibody for multiple myeloma. N Engl J Med. 2022;387(24):2232-2244. DOI

5. Manier S, Salem KZ, Park J, et al. Genomic complexity of multiple myeloma and its clinical implications. Nat Rev Clin Oncol. 2017;14(2):100-113. DOI