An aglycosylated IgG1 antibody is provided having a human lambda constant region and having a binding affinity for the CD3 antigen complex in which in the heavy chain has a specified humanised variable region framework together with CDRs and the light chain has a specified rodent variable region framework together with CDRs CDR1: Thr Leu Ser Ser Gly Asn Ile Glu Asn Asn Tyr Val His CDR2: Asp Asp Asp Lys Arg Pro Asp CDR3: His Ser Tyr Val Ser Ser Phe Asn Val or a rodent sequence consisting of sufficient of that rodent framework region sequence optionally substituted with some but not all of the human amino acids selected from Asp-1, Phe-2, Met-3, Leu-4, Pro-7, His-8, Glu-12, Pro-14, Lys-15, Ile-19, Ile-20, Gln-39, Arg-40, Pro-41, Ala-44, Val-48, Phe-50, Ser-75, Ser-79, Gly-80, Leu-81, Gln-82, Thr-83, Asp-88 and Tyr-90. such as to allow stable light-heavy chain interaction for treatment by immunosuppression.
