An anti-CD19/anti-CD3 bispecific tetravalent antibody with potential immunostimulatory and antineoplastic activities. Anti-CD19/CD3 tetravalent antibody AFM11 possesses two antigen-recognition and binding sites, one for the CD3 complex, a group of T-cell surface glycoproteins that complex with the T-cell receptor (TCR), and one for CD19, a tumor-associated antigen (TAA) overexpressed on the surface of B-cells. Upon bolus infusion of AFM11, this bispecific antibody binds to CD3-expressing T-cells and CD19-expressing cancer cells, thereby crosslinking CD19-expressing tumor B-cells and cytotoxic T-lymphocytes (CTLs). This may result in a potent CTL-mediated cell lysis of CD19-expressing B-lymphocytes. CD19, a B-cell specific membrane antigen, is expressed during both B-cell development and B-cell malignant growth.