The disclosure features, inter alia, immunogenic XBP1-, CD138-, and CS1-derived peptides (and pharmaceutical compositions thereof). The peptides can be used in a variety of methods such as methods for inducing an immune response, methods for producing an antibody, and methods for treating a cancer (e.g., breast cancer, colon cancer, pancreatic cancer, a blood cancer, e.g., leukemia or a plasma cell disorder such as multiple myeloma or Waldenstrom's macroglobulinemia). The peptides (and pharmaceutical compositions comprising the peptides) can be used, e.g., in a method of treating a precancerous condition such as smoldering multiple myeloma. The peptides can also be included in MHC molecule multimer compositions and used in, e.g., methods for detecting a T cell in a population of cells.