A humanized immunoglobulin IgG1 kappa monoclonal antibody directed against the B-cell-specific membrane protein CD-19 with potential immunostimulating and antineoplastic activities. Anti-CD19 monoclonal antibody MEDI-551 binds to CD19, which may result in a cytotoxic T-lymphocyte (CTL) response and antibody-dependent cellular cytotoxicity (ADCC) to CD19-expressing B-cells. The Fc portion of MEDI-551 does not contain a fucose sugar moiety, which may contribute to its enhanced ADCC activity. CD19 is a membrane antigen that is widely expressed during B-cell development, from pro-B-cell to early plasma cell stages.