Multiple myeloma treatment has undergone a significant transformation with the emergence of T-cell redirection therapies, including CAR T-cell therapies and bispecific antibodies. These novel approaches are providing new options for patients with relapsed/refractory disease who have exhausted conventional treatments.
The Current Landscape of T-Cell Redirection Therapies
The FDA has approved several groundbreaking therapies for patients with relapsed/refractory multiple myeloma who have received at least four prior lines of therapy and are triple-class exposed (to a proteasome inhibitor, an immunomodulatory agent, and an anti-CD38 monoclonal antibody). These include two CAR T-cell therapies—idecabtagene vicleucel (ide-cel; Abecma) and ciltacabtagene autoleucel (cilta-cel; Carvykti)—and three bispecific antibodies: the BCMA-targeted teclistamab-cqyv (Tecvayli) and elranatamab-bcmm (Elrexfio), and the GPRC5D-targeted talquetamab-tgvs (Talvey).
"For a relatively rare cancer, we already had a fair number of treatment choices in myeloma. However, they were limited by their duration of efficacy," explains Dr. Ajai Chari, director of clinical research in the Multiple Myeloma Program at the University of California, San Francisco (UCSF) Health. "Now, we have this huge explosion in interest in T-cell redirection, with multiple CAR T-cell therapies and bispecific antibodies. The question is: How do we use all these?"
Choosing Between CAR T-Cell Therapy and Bispecific Antibodies
The decision between CAR T-cell therapy and bispecific antibodies hinges primarily on the rate of disease progression. CAR T-cell therapy requires a significant "vein-to-vein" time for apheresis, manufacturing, and administration, whereas bispecific antibodies are available off-the-shelf.
"If you're in the clinic and a patient has disease that is rapidly progressing, I would steer that patient toward a bispecific," Dr. Chari advises. "Conversely, if a patient has relatively indolent disease, they live quite far away from an academic center where ongoing bispecific treatment may be a hassle, and they can tolerate high-grade cytokine release syndrome or neurotoxicity—maybe not the most frail patient, but a fit patient—I would prefer a CAR T-cell therapy for that patient, because they are going to have an amazing treatment-free interval that we can never provide with almost any other therapy."
Comparative Efficacy of Available Therapies
When comparing the two FDA-approved CAR T-cell therapies, cilta-cel has demonstrated superior efficacy in clinical trials. In the phase 1/2 CARTITUDE-1 trial, cilta-cel achieved an overall response rate (ORR) of 98% and a median progression-free survival (PFS) of 34.9 months in heavily pretreated patients.
In contrast, ide-cel showed a median PFS of 12.2 months in the phase 2 KarMMA trial. Phase 3 data further support cilta-cel's superiority, with a hazard ratio for PFS of 0.26 compared to 0.49 for ide-cel when each was compared to standard care in their respective trials.
"I would say to physicians, if you can, get cilta-cel," Dr. Chari recommends. "There still is a role for ide-cel where you may not have a cilta-cel manufacturing spot for a patient who is BCMA-naïve who lives far away."
Among bispecific antibodies, the BCMA-targeted agents teclistamab and elranatamab show similar efficacy and safety profiles. The choice between them may depend on convenience, schedule, and cost considerations. Talquetamab, targeting GPRC5D, offers a different safety profile with fewer infectious complications but introduces unique toxicities affecting the skin, nails, and oral cavity.
The Critical Importance of Strategic Sequencing
As the treatment landscape expands, thoughtful sequencing of therapies becomes increasingly important. Two key considerations have emerged: antigen loss and T-cell fitness.
"What happens after treatment with CAR T-cell therapy or bispecifics? Some of the issues to think about are antigen and genomic loss. Is the target still expressed at a protein level and at a genomic level?" Dr. Chari explains. Recent research suggests that monoallelic loss of BCMA or GPRC5D at baseline may lead to biallelic loss after targeted therapy, potentially necessitating a switch to a different target for subsequent treatments.
Perhaps even more crucial is the impact of prior therapies on T-cell fitness. Data from the CARTITUDE-2 trial revealed that patients who received a BCMA-targeted bispecific antibody before cilta-cel experienced a dramatic reduction in PFS—from 34.9 months to just 5.3 months.
"That's a big warning shot that if you have a patient that you're thinking about for cilta-cel, don't use a BCMA-targeted bispecific right before," Dr. Chari cautions. This finding underscores the importance of preserving T-cell quality, particularly before apheresis for CAR T-cell manufacturing.
Looking Ahead: Novel Targets and Combinations
The investigation of additional targets beyond BCMA and GPRC5D, such as FcRH5, could further expand the arsenal of T-cell redirection therapies. These developments may provide more options for sequential treatment strategies and potentially address resistance mechanisms.
As the field evolves, researchers are also exploring optimal combinations and sequences of these novel therapies with conventional treatments. Dr. Chari emphasizes the need for additional data to guide these decisions, particularly from randomized phase 3 trials of bispecific antibodies.
The rapid advancement of T-cell redirection therapies represents a significant step forward in multiple myeloma treatment. However, maximizing their benefit will require careful patient selection, strategic sequencing, and ongoing research to understand and manage resistance mechanisms. With thoughtful implementation, these innovative approaches offer hope for improved outcomes in patients with this challenging disease.
