International Immunology, Vol. 12, No. 4, 505-516,
April 2000
© 2000 Japanese Society for Immunology
The CD45 tyrosine phosphatase regulates Campath-1H (CD52)-induced TCR-dependent signal transduction in human T cells
Laboratory of Lymphocyte Signalling and Development, Molecular Immunology Programme, The Babraham Institute, Cambridge CB2 4AT, UK
1 Department of Biophysics and Cell Biology, Debrecen University School of Medicine, H-4012 Debrecen, Hungary
2 Therapeutic Antibody Centre, Old Road, Headington, Oxford OX3 7JT, UK
Correspondence to: D. R. Alexander
Campath-1H, a humanized mAb undergoing clinical trials for treatment of leukemia, transplantation and autoimmune diseases, produces substantial lymphocyte depletion in vivo.The antibody binds to CD52, a highly glycosylated molecule attached to the membrane by a glycosylphosphatidylinositol anchor. Cross-linked Campath-1H is known to activate T cells in vitro. We have investigated the molecular basis for these effects by comparing the protein tyrosine phosphorylation signals induced by Campath-1H and the CD3 mAb OKT3 in primary T cells, and in CD45+TCR+, CD45TCR+ and CD45+TCR Jurkat subclones transfected with CD52. Our results show that Campath-1H triggers similar tyrosine phosphorylation events as OKT3 in both primary T cells and in the CD45+TCR+ Jurkat sub-clone, albeit at quantitatively lower levels. However, no phospholipase C
1 activation nor calcium signals were detected in response to CD52 ligation. The CD52-mediated induction of protein tyrosine phosphorylation was absolutely dependent upon the expression of both the TCR and the CD45 phosphotyrosine phosphatase at the cell surface. Cross-linking of Campath-1H was essential for signal transduction in all cells investigated. Fluorescence resonance energy transfer was used to demonstrate CD52 homo-association at the cell surface in Jurkat T cells in a TCR- and CD45-independent manner, and CD52TCR association in CD45+TCR+ cells. We propose a model to explain the activating effects of Campath-1H in which CD52 mAb cross-linking causes the trapping of TCR polypeptides within molecular complexes at the cell surface, thereby inducing signals via the TCR by a process which depends on the CD45-mediated regulation of the p56lck and p59fyn tyrosine kinases.
Keywords: Campath-1H, CD45, CD52, transduction
Transmitting editor: P. Beverley
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