mRNA platforms, particularly for CAR-T and T-cell engagers, are leading the field with multiple ongoing trials, such as Cartesian Therapeutics’ Descartes series (e.g., Descartes-08 and -11 targeting BCMA in phase 1/2 for RRMM and high-risk newly diagnosed MM) [277,278], which highlight transient expression benefits like reduced cytokine release syndrome (CRS) and outpatient administration without lymphodepletion, alongside Moderna’s mRNA-2808 (tri-specific T-cell engager targeting BCMA, GPRC5D, and FcRH5) in Phase 1/2 (NCT07116616) for RRMM [142,143]. This evidence concerns the gene GPRC5D and Miyoshi myopathy.