Abstract: A humanised antibody is provided in which the amino acid sequence of the CDRs is derived from the sequence of CDRs of a monoclonal antibody having the specificity of binding to resting and activated T-cells, inhibiting T-cell proliferation and lysing T-cells from mice transgenic for human CD2 and in which sufficient of the amino acid sequence of each CDR has been retained to provide the same specificity for the humanised antibody.

Abstract: A monoclonal antibody preparation having a single binding activity, which activity is in respect of a cell surface antigen, comprises IgG antibody molecules in which only one of the two light chains will bind to said antigen, the proportion of such antibody molecules being enhanced relative to IgG antibody molecules having two light chains which will bind to said antigen to thereby produce an enhancement of the binding activity of the preparation. Such preparations containing predominatly "monovalent antibodies" are of particular value in the areas of transplantation immunity, the treatment of neoplastic disease and cell sorting.