Submitted March 8, 2002
Accepted July 10, 2002
Human T-cells resistant to complement lysis by bivalent antibody can be efficiently lysed by dimers of monovalent antibody
Soren U Nielsen* and Edward G Routledge
Immunology and Microbiology, University of Newcastle, Newcastle upon Tyne, United Kingdom
* Corresponding author; email: s.u.nielsen{at}ncl.ac.uk.
It has been shown previously that bivalent human
1 CD3 mAb is ineffective at mediating lysis of human T cells with human complement (Routledge et al. 1991. Eur J. Immunol. 21: 2717-2725). In this paper we have used genetic engineering and sulphur chemistry to prepare two types of human 1 CD3 mAb dimer, with the aim of improving complement lysis activity. The IgG molecules forming the dimers were linked together at their C-termini by stable bismaleimide thioether bridges. The first dimer was composed of two bivalent mAb molecules. This dimer proved incapable of lysing human T cell blasts with human, rabbit or guinea pig complement. The second dimer consisted of two molecules of a monovalent derivative (possessing a single Fab domain) of the bivalent mAb. This dimer was highly lytic with human complement, with a lytic titre 64-fold greater than that of the non-dimerised monovalent mAb. The maximum level of lysis of human T-cell blasts achieved with this monovalent mAb dimer was equal to that obtained with the therapeutic anti-lymphocyte mAb Campath 1H, but its lytic titer was 4-fold greater. The monovalent mAb dimer was also found to be lytic in the presence of rabbit and guinea pig complement. Dimerisation of monovalent antibodies may provide a general strategy for improving the cytolytic activity of other mAbs that are normally unable to induce lysis with complement. The monovalent CD3 mAb dimer may have potential for development as an agent for immunotherapy of T-cell leukaemia.
