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
This study is a Phase II study to determine the preliminary safety and efficacy of salvage radiation treatment after BCMA CAR-T therapy in subjects with RRMM.~The study population will consist of subjects with RRMM previously treated with SOC BCMA CAR-T cell therapy with active disease on the D30+ PET or other imaging scan after CAR-T infusion. Patients who are planned for salvage chemotherapy less than 14 days after completion of radiation treatment will be excluded.~Radiation treatment will be to bony or soft tissue plasmacytomas in up to five radiation treatment fields to 10-20Gy (or equivalent dose in 2Gy fractions of 10-21Gy). Final dose, target, and technique are per treating radiation physician discretion within these guidelines.~Thirty patients will be enrolled. The co-primary endpoints are objective response rate (ORR) at 6 months and duration of response (DOR) among responders.