Trispecific antibodies are also currently in preclinical investigation which, in addition to a T-cell binding domain and distinct myeloma antigen binding domain, includes a third domain that binds another distinct myeloma antigen or adds either T-cell costimulatory proteins to decrease T-cell anergy or cytokines to promote effector cell activation (e.g., IL-15 containing TriKEs) [170]. Here, PROS1 is linked to plasma cell myeloma.