Abstract: A murine anti-CD20 monoclonal antibody having cell growth inhibitory activities is disclosed. Cell growth inhibitory activities include apoptosis against human CD20 antigen expressing cells in culture of the CD20 antigen expressing cells without effector cells. The anti-CD20 monoclonal antibody is incorporated into chimeric anti-CD20 monoclonal antibodies in which the amino acid sequences of the variable regions of the anti-CD20 monoclonal antibody and the amino acid sequences of the constant regions of human immunoglobulin are fused. Also a humanized anti-CD20 monoclonal antibody is described which includes all of the variable region CDRs of the H chain of the anti-CD20 monoclonal antibody and all of the variable region CDRs of the L chain of the anti-CD20 monoclonal antibody and an amino acid sequence of human immunoglobulin. A nucleotide sequence encoding the amino acid sequence of the chimeric or humanized anti-CD20 monoclonal antibody can be expressed in mammalian cells.

Abstract: Disclosed is a monoclonal antibody capable of inducing a specific biological reaction through the binding of the monoclonal antibody to a CD20 antigen on the surface of a cell. A monoclonal antibody having a high binding affinity to an extracellular epitope of a CD20 antigen and also having biological activities including a cell growth inhibitory activity is cloned. The monoclonal antibody is chimerized or humanized to develop a therapeutic agent for a disease in which B cells are involved.