Anti-CD19 antibodies

A method of treating a B cell leukemia comprising administering a humanized antibody or antigen-binding fragment thereof that binds CD19 to a subject with a B cell leukemia, wherein the B cells associated with the B cell leukemia express CD19 antigen, wherein the humanized anti-CD19 antibody comprises the light chain complementarity determining region (CDR) sequences CDR1 KASQSVDYDGDSYLN (SEQ ID NO:

• 16);
• CDR2 DASNLVS (SEQ ID NO:
• 17);
• and CDR3 QQSTEDPWT (SEQ ID NO:
• 18) and the heavy chain CDR sequences CDR1 SYWMN (SEQ ID NO:
• 19);
• CDR2 QIWPGDGDTNYNGKFKG (SEQ ID NO:
• 20) and CDR3 RETTTVGRYYYAMDY (SEQ ID NO:
• 21), wherein said humanized anti-CD 19 antibody or fragment thereof comprises human antibody framework (FR) and constant region sequences with one or more framework region amino acid residues substituted from the corresponding framework region sequences of the parent murine antibody, and wherein said substituted FR residues comprise the substitution of phenylalanine for serine at Kabat residue 91 of the heavy chain variable region.