The CD45 tyrosine phosphatase regulates Campath-1H (CD52)-induced TCR-dependent signal transduction in human T cells.
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(+), CD45(-)TCR(+) 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 gamma 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 CD52-TCR 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 p56(lck) and p59(fyn) tyrosine kinases.
Hederer
R A
RA
Laboratory of Lymphocyte Signalling and Development, Molecular Immunology Programme, The Babraham Institute, Cambridge CB2 4AT, UK.
Guntermann
C
C
Miller
N
N
Nagy
P
P
Szollosi
J
J
Damjanovich
S
S
Hale
G
G
Alexander
D R
DR
D000074323:Alemtuzumab; D000911:Antibodies, Monoclonal / Q000502:physiology*; D061067:Antibodies, Monoclonal, Humanized; D000912:Antibodies, Neoplasm / Q000502:physiology*; D015703:Antigens, CD / Q000378:metabolism / Q000502:physiology*; D000951:Antigens, Neoplasm; D000074301:CD52 Antigen; D002118:Calcium / Q000502:physiology; D020013:Calcium Signaling / Q000276:immunology; D002478:Cells, Cultured; D006023:Glycoproteins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000276:immunology; D007527:Isoenzymes / Q000276:immunology; D019169:Jurkat Cells; D017493:Leukocyte Common Antigens / Q000502:physiology*; D051966:Phospholipase C gamma; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D013601:T-Lymphocytes / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D014162:Transfection; D010738:Type C Phospholipases / Q000276:immunology
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000912:Antibodies, Neoplasm; D015703:Antigens, CD; D000951:Antigens, Neoplasm; D000074301:CD52 Antigen; C000613862:CD52 protein, human; D006023:Glycoproteins; D007527:Isoenzymes; D011948:Receptors, Antigen, T-Cell; D000074323:Alemtuzumab; D015544:Inositol 1,4,5-Trisphosphate; D017493:Leukocyte Common Antigens; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002118:Calcium