Clinical Report: Bispecific Antibodies in Multiple Myeloma Management

Overview

Bispecific antibodies (BsAbs) represent a promising therapeutic advancement in multiple myeloma (MM), particularly for patients refractory to conventional treatments. Targeting antigens such as BCMA and GPRC5D, BsAbs engage T cells to induce myeloma cell apoptosis, demonstrating deep and sustained responses with manageable toxicity profiles.

Background

Multiple myeloma remains incurable despite advances with proteasome inhibitors, immunomodulators, and monoclonal antibodies, especially in patients with multiple relapses and treatment-resistant clones. BsAbs harness T-cell mediated cytotoxicity by simultaneously binding tumor antigens and CD3 on T cells, promoting immune synapse formation and MM cell apoptosis. Key targets include BCMA, GPRC5D, and FcRH5, with several BsAbs approved or in clinical development. These agents offer off-the-shelf availability and manageable side effects, including low-grade cytokine release syndrome and infections.

Data Highlights

FDA approvals include teclistamab and elranatamab targeting BCMA, and talquetamab targeting GPRC5D. Talquetamab received accelerated approval in August 2023 based on the MonumenTAL-1 study. Forimtamig, another GPRC5D × CD3 BsAb, was discontinued. BCMA expression correlates with disease progression and prognosis, while GPRC5D expression is independent of BCMA and remains stable post-BCMA therapy failure, enabling sequential or combination targeting strategies.

Key Findings

• BsAbs activate T cells by binding both MM cell antigens and CD3, inducing apoptosis via perforin and granzyme B.
• BCMA is a validated target with high expression on malignant plasma cells and is associated with poor prognosis; two anti-BCMA BsAbs are FDA approved.
• GPRC5D is a novel, highly specific MM target with minimal expression on healthy tissues, allowing targeting post-BCMA therapy failure.
• BsAbs demonstrate manageable toxicity profiles, including low-grade cytokine release syndrome and infections.
• Tri-specific antibodies add co-stimulatory signals or additional targets to enhance T cell activation and reduce anergy.
• Antigen shedding (e.g., soluble BCMA) may reduce efficacy, but GPRC5D’s structure limits shedding, potentially improving durability of response.

Clinical Implications

BsAbs provide a valuable treatment option for heavily pretreated and refractory MM patients, expanding therapeutic choices beyond conventional agents. Their manageable safety profile and off-the-shelf availability facilitate integration into clinical practice. Sequential or combination targeting of BCMA and GPRC5D may overcome resistance and improve outcomes, warranting consideration in treatment planning.

Conclusion

Bispecific antibodies targeting BCMA and GPRC5D have transformed the therapeutic landscape of multiple myeloma, offering deep, sustained responses in refractory disease with acceptable toxicity. Ongoing development and strategic use of these agents hold promise to further improve patient outcomes.

References

1. Chari et al. 2023 -- The Role of Bispecific Antibodies in Managing Multiple Myeloma