The present disclosure relates to methods for using BCMA-specific binding molecules (such as a BCMA-specific chimeric antigen receptor or antibody) in combination with ?-secretase inhibitors, which can be done concurrently or sequentially, to treat or prevent a B-cell related proliferative disease, such as a cancer or autoimmune disease, or the like. A BCMA-specific binding molecule in combination with ?-secretase inhibitor can be used in, for example, adoptive immunotherapy.