A recombinant antibody derivative composed of tri-specific T-cell activating construct (TriTAC) directed against the human tumor-associated antigen (TAA) B-cell maturation antigen (BCMA; TNFRSF17), the epsilon domain of CD3 antigen (CD3e) found on T-lymphocytes, and albumin, with potential immunostimulating and antineoplastic activities. Upon administration, BCMA/CD3e TriTAC HPN217 targets and binds to BCMA on tumor cells and CD3e on cytotoxic T-lymphocytes (CTLs), thereby bringing BCMA-expressing tumor cells and CTLs together, which results in the CTL-mediated cell death of BCMA-expressing tumor cells. The albumin-binding domain targets and binds to serum albumin, thereby extending the serum half-life of HPN217. BCMA, a member of the tumor necrosis factor receptor superfamily (TNFRSF), is overexpressed on malignant plasma cells and plays a key role in plasma cell survival.