XBP1 and plasma cell myeloma: Several epitopes, such as syndecan-1 (CD138), X-box–binding protein 1 (XBP1)-unspliced, XBP1-spliced, CS1, have been identified as potential targets in multiple myeloma (MM) and smoldering multiple myeloma (SMM), and their applications against MM and SMM were also very effective (348–350).