Phase I Trial of GR1803 Injection in Patients With RRMM

All subjects will receive GR1803 injection until intolerable toxicity or investigator-assessed disease progression occurs (except in cases of disease progression due to discontinuation of the drug as a result of an adverse event) or until the subject has been administered the drug for 52 weeks or until the subject withdraws consent or until the investigator determines that the subject needs to be discontinued.