GPRC5D

Talquetamab is a newly approved bispecific antibody targeting the CD3 receptor on T cells and a receptor, G protein-coupled receptor family C group 5 member D (GPRC5D), highly expressed on multiple myeloma (MM) cells. In addition to immune therapy-related adverse events (AEs) associated with bispecific antibody therapies, talquetamab is associated with unique skin/nail and oral GPRC5D-related side effects that require additional supportive care. This review provides clinical management strategies for talquetamab based on oncology nurses' experience during the MonumenTAL-1 (NCT03399799/NCT04634552) clinical trial. The objective of this review is to raise awareness among nurses and patients to better understand and manage the side effects associated with talquetamab treatment in order to optimize patient outcomes.

MonumenTAL-1 is a phase 1/2 clinical trial of talquetamab in patients with relapsed/refractory MM who are triple-class exposed. Details on overall response, safety, and AE incidence and occurrence were previously published. Management strategies for the T-cell-related and unique GPRC5D-related AEs were collected from oncology nurses from different study sites.

Talquetamab has shown overall response rates of >71% in patients with relapsed/refractory MM in the MonumenTAL-1 study. AEs were low grade and predictable; few led to study discontinuation.

Oncology nurses have specialized knowledge of treatment administration monitoring based on their participation in the MonumenTAL-1 trial. This review provides information for nurses in both the academic and community settings on how to monitor, counsel, and support patients, which will in turn improve patients' quality of life and overall survival.

Multiple myeloma (MM) is a complex hematological malignancy characterized by abnormal antibody production from plasma cells. Despite advances in the treatment, many patients experience disease relapse or become refractory to treatment. G-protein-coupled receptor class C group 5 member D (GPRC5D), an orphan GPCR predominantly expressed in MM cells, is emerging as a promising target for MM immunotherapy. Talquetamab, a Food and Drug Administration-approved T-cell-directing bispecific antibody developed for treatment of MM, targets GPRC5D. Here, we elucidate the structure of GPRC5D complexed with the Fab fragment of talquetamab, using cryo-electron microscopy, providing the basis for recognition of GPRC5D by the bispecific antibody. GPRC5D forms a symmetric homodimer with the interface between transmembrane helix (TM) 4 of one protomer and TM4/5 of the other protomer. A single talquetamab Fab interacts with the GPRC5D dimer with its orientation toward the dimer interface. All six complementarity-determining regions of talquetamab engage with extracellular loops and TM3/5/7. In particular, the side-chain of an arginine residue from the antibody penetrates into a shallow pocket on the extracellular surface of GPRC5D. The structure offers insights for optimizing antibody design against GPRC5D for relapsed or refractory MM therapy.

Off-the-shelf T-cell-redirecting bispecific antibodies targeting BCMA, GPRC5D, and FcRH5 have high activity in multiple myeloma with a manageable toxicity profile. However, not all patients respond to bispecific antibodies and patients can develop bispecific antibody resistance after an initial response. Mechanisms that contribute to bispecific antibody resistance are multifactorial and include tumour-related factors, such as high tumour burden, expression of T-cell inhibitory ligands, and antigen loss. Resistance due to antigen escape can be prevented by simultaneously targeting two tumour-associated antigens with a trispecific antibody or a combination of two bispecific antibodies. There is also increasing evidence that primary resistance to bispecific antibodies is associated with impaired baseline T-cell function. Long-term exposure to bispecific antibodies with chronic T-cell stimulation further aggravates T-cell dysfunction, which could contribute to failure of disease control. Therapeutic interference with T-cell exhaustion by targeting inhibitory or costimulatory pathways could improve bispecific antibody-mediated antitumour activity. The immunosuppressive microenvironment also contributes to bispecific antibody resistance. CD38-targeting antibodies hold promise as combination partners for bispecific antibodies because of their potential to eliminate CD38⁺ immune suppressor cells. In conclusion, a better understanding of the mechanisms underlying the absence of disease response has provided novel insights to optimise T-cell activity and bispecific antibody efficacy in multiple myeloma.