Participants will be assigned to a combination of anti-CD38 monocloncal antibody plus GR1803 injection.

Participants will receive GR1803 injection.

The dose limiting toxicities are defined as any of the following events: drug related hematological or non-hematological toxicity of grade 3 or higher.

Adverse event is any untoward medical occurrence in a clinical trial participants administered a pharmaceutical product, regardless of causal relationship to the study treatment. This includes any unfavorable or unintended sign, symptom, or disease temporally associated with the use of the product.

Serious adverse event is an adverse event that results in any of the following outcomes: death, life-threatening, inpatient hospitalization or prolongation of existing hospitalization, persistent or significant disability/incapacity, congenital anomaly/birth defect, other medically important events.

The percentage of participants who have a partial response or better according to the International Myeloma Working Group criteria

Time from initial partial response or better to progressive disease or death due to any cause

Time from first administration of GR1803 injection to tumor progerssion or death from any cause