Preclinical Analysis of Ciltacabtagene Autoleucel Combination Strategies with T Cell Bispecifics and Daratumumab to Support Optimization of Clinical Benefit in Myeloma Patients

Introduction Ciltacabtagene autoleucel (Cilta-cel) is a multiple myeloma (MM) specific CAR-T cell therapy targeting BCMA. Teclistamab (Tec), and talquetamab (Tal) are MM directed T cell bispecifics (BsAbs) targeting BCMA and GPRC5D, respectively. All three therapies are designed to harness the anti-tumor activity of T cells. Yet, little is known about their use in concert and/or their preferred sequencing to ensure maximal therapeutic benefit. Likewise, little data exist exploring the impact of daratumumab (Dara), a monoclonal antibody targeting CD38, on the efficacy of Cilta-cel. Our reverse translation work aims to characterize the underlying mechanistic interactions between these therapies to potentially inform on their optimal clinical utilization and help accelerate the development of regimens with curative intent in MM. Results Using an in vitro model in which healthy donor T cells were exposed to MM tumor cells and either Tec or Tal, we showed that exposure to BsAbs induced downregulation of CD28 on T cells and up-regulation of markers associated with T cell exhaustion. Downstream assays using these BsAb pre-exposed T cells revealed diminished expansion and reduced transduction efficiency during the generation of research grade Cilta-cel, and a reduced capacity of the derived CAR-T products to kill MM cells in a serial cytotoxicity assay. Tec and Tal produced similar results, suggesting this effect is BMCA and GPRC5D target agnostic. These data may have revealed an underlying mechanism to previously published studies in which MM patients who had been administered BCMA BsAbs prior to apheresis exhibited a lower response rate and a shorter duration of response to BCMA CAR-T as compared to patients who had not been administered BsAbs prior to apheresis. Interestingly, when BsAbs were concurrently added with research-grade Cilta-cel to MM cells, enhanced cytotoxicity was observed in a synergistic manner. These observations were associated with increased levels of activation and proliferation of the CAR negative T cells present in the co-culture along with increased expression of FAS and ICAM-1 on the tumor cells. Such characteristics are also aligned with CAR-T mediated increases in bystander killing, which in turn could help lower the threshold for response to BsAbs. The effect was most striking in models containing suboptimal CAR-T effector cells to tumor cells (E:T) ratio, which may be more representative of compromised T cell fitness and/or high tumor burden. Additionally, even a small percentage of CAR-T cells synergized with BsAbs, suggesting that introduction of BsAbs away from CAR-T peak expansion may still enhance clinical benefit. Finally, the addition of Dara, with or without BsAbs, also synergistically enhanced the in vitro cytotoxicity of research-grade Cilta-cel against MM cells. In contrast to BsAbs, Dara was shown to limit the overall expansion of research grade Cilta-cel. However, immunophenotyping data showed that the remaining CAR-T cells exhibited a reduction in the frequency of exhausted T cells and CD38+ Tregs, potentially indicating improved T cell fitness. Conclusion These preliminary data support careful consideration of the timing of apheresis with respect to treatment with BsAbs, to preserve T cell fitness. They also suggest that Tec, Tal and Dara, alone or in combination, may have an important role in bridging and maintenance strategies to enhance the cytotoxic activity of Cilta-cel, if labeling indications permit. Furthermore, these agents may potentially optimize reduced Cilta-cel cytotoxicity resulting from BsAb exposure prior to apheresis. Ultimately, mechanisms unraveled by this study may help guide trial designs and the development of novel therapeutic regimens, although more investigation will be required.