A first-in-human, open label, phase I/II study to evaluate the safety, anti-tumor activity, pharmacokinetics, and pharmacodynamics of SAR446523 monotherapy, an anti-GPRC5D ADCC-enhanced monoclonal antibody in dose escalation and dose optimization, and to evaluate the efficacy of SAR446523 in dose expansion, in participants with relapsed and refractory multiple myeloma.