Disclosed are humanized RFB4 antibodies or antigen-binding fragments thereof. therapy of B-cell associated diseases, such as B-cell malignancies, autoimmune disease and immune dysfunction disease. Preferably, hRFB4 comprises the light and heavy chain RFB4 CDR sequences with human antibody FR and constant region sequences, along with heavy chain framework region (FR) amino acid residues Q1, F27, V48, A49, F68, R98, T117 and light chain residues L4, S22, K39, G100, V104, and K107. More preferably, the heavy and light chain variable region sequences of hRFB4 comprise SEQ ID NO:7 and SEQ ID NO:8, respectively. In certain embodiments, trogocytosis (antigen shaving) induced by hRFB4 plays a significant role in determining antibody efficacy and disease responsiveness for treatment of B-cell diseases, such as hematopoietic cancers, immune system dysfunction and/or autoimmune disease.