GR1803 Injection in Patients With Relapsed/Refractory Multiple Myeloma

D1 given at a dose of 30ug/kg, D4 given at a dose of 90ug/kg, D8 given at a dose of 180ug/kg, followed by weekly dosing up to cycle 9, and cycle 10 and onwards, every 2 weeks, with a dosing cycle of every 4 weeks