A recombinant T-cell activating bispecific antibody directed against the B-cell-specific membrane protein CD19 and the CD3 antigen found on T-lymphocytes, with potential immunostimulating and antineoplastic activities. Upon administration, CD3-activating CD19 bi-specific antibody A-319 targets and binds to both the CD3 antigen on cytotoxic T-lymphocytes (CTLs) and the CD19 antigen expressed on malignant B-cells. This activates and redirects CTLs, bringing CD19-expressing tumor cells and CTLs together, and results in a CTL-mediated immune response against CD19-expressing tumor cells. CD19 is a membrane antigen that is widely expressed during B-cell development, from pro-B-cell to early plasma cell stages.