OKT3

Antibody Name: OKT3 (VH SGIIb or SGVa/JH2 | VL SGBI/Jk4)
References: Woodle, E.S., Thistlethwaite, J.R., Jolliffe, L.K., Zivin, R.A., Collins, A., Adair, J.R., Bodmer, M., Athwal, D., Alegre, M-L. and Bluestone, J.A. "Humanized OKT3 antibodies: successful transfer of immune modulating properties and idiotype expression" J. Immunol. (1992) 148:2756-2763.
Alegre, M.L., Collins, A.M., Pulito, V.L., Brosius, R.A., Olson, W.C., Zivin, R.A., Knowles, R., Thistlethwaite, J.R., Jolliffe, L.K. and Bluestone, J.A. "Effect of a single amino acid mutation on the activating and immunosuppressive properties of a 'humanized' OKT3 monoclonal antibody" J. Immunol. (1992) 148:3461-3468.
Adair, J.R., Athwal, D.S., Bodmer, M.W., Bright, S.M., Collins, A.M., Pulito, V.L., Rao, P.E., Reedman, R., Rothermel, A.L., Xu, D., Zivin, R.A. and Jolliffe, L.K. "Humanization of the murine anti-human CD3 monoclonal antibody OKT3" Hum. Antibod. Hybridomas (1994) 5:41-47.
Jolliffe, L.K., Zivin, R.A., Adair, J.R. and Athwal, D.S. "CD3 specific recombinant antibody" WO91/09968 (1991)
Donor Antibody: mouse
Acceptor Antibody: Human IgG4 | k (reduced affinity for FcR with IgG4)
Antigen: E-subunit on human CD3 on T cells
Laboratory: University of Chicago, IL; Ortho Pharmaceutical Corp., NJ; Celltech Ltd., UK; Ben May Institute, IL; R.W. Johnson, NJ
Design: Choice of KOL and REI because the structures were available. Backmutations following Campath-1H for resides 27-30:H, residues near CDRs, packing and intra/inter-domain packing residues. Eventually, reduced number of backmutations detailed in first paper.
Frameworks: VH KOL | VL REI
CDRs: All 6 VH and VL,Kabat Definition except CDR-H2 F63V (mouse->human).
Backmutations: Using Kabat CDR definition:
VH E6Q S23K S24A F27Y I28T S30T V48I A49G L78A
VL L46R L47W
Binding: Best binder gOKT3-7 (gLC/gHG) bound as well as mouse and chimaeric mAbs in competition binding assays. Functional assays (for T cell activation) of proliferation, induction of activation marker expression (CD25 and Leu23), lymphokine expression (TNF-α, IFN-γ).
Expression: transient cos-1 cell expression and larger scale preparation in roller bottles
Comment: Tested N-terminal residues 1 and 3 of VL, but no effect on binding. Contrast with C21.
Keystone meeting (1994) Lake Tahoe. Clinical studies showed transient anti-Idiotype response but no major immune responses to humanised mAbs.
NB: OKT3 was the first mAb product approved by the FDA for marketing as a therapeutic agent.
Suggest F(ab) or F(ab')2 fragments to avoid Fc effects and alter pharmacokinetics ("smaller" mAb). Alterations in hinge region may alter binding avidity, serum half-life or complement binding.
Clinical Indication: Modify immune response in cancer and organ transplant patients although further alterations to constant regions needed to minimise cross-linking of the bound mAb leading to proliferative signals.

explanation of symbols and abbreviations

José Saldanha © 1997-8. Birkbeck College, London WC1E 7HX.