Phase II Study of Salvage Radiation Treatment After B-cell Maturation Antigen Chimeric Antigen Receptor T-cell Therapy for Relapsed Refractory Multiple Myeloma

Objectives Primary Objective: • The primary objective of the study is to evaluate the preliminary efficacy of salvage radiation therapy after BCMA CAR-T cell therapy in subjects with RRMM. Secondary Objectives: • Evaluate the safety of and other efficacy parameters of radiation treatment after BCMA CAR-T cell therapy in subjects with RRMM Exploratory Objectives: * Evaluate the immunophenotype and/or expression profile, and perform functional bulk and single cell analysis of CAR T cells, endogenous T cells as well as other immune cells in the blood, bone marrow and/or tumor tissue with BCMA CAR-T therapy and RT * Evaluate changes in the levels of cytokines, chemokines, and soluble factors in the blood with BCMA CAR-T therapy and RT * Evaluate changes in T cell receptor repertoire with BCMA CAR-T therapy and RT * Evaluate gut microbiome of patients treated with BCMA CAR-T therapy and RT