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Department of Experimental Medicine, Institute of Human Anatomy, University of Genova, Genova, Italy;
National Institute for Cancer Research;
Advanced Biotechnology Center, Department of Immunology, S. Martino Hospital, Genova, Italy
Since the functional outcome of effector T lymphocytes depends on a
balance between activatory and inhibitory receptors, we studied the
ability of CTLA-4 (CD152) to inhibit the cytolytic function of CTL. In
22 TCR
ß+CD3+8+ CTL clones,
activation induced by anti-CD3, anti-CD28, or anti-CD2 mAb
was inhibited by anti-CD152 mAb in a redirected killing assay. In
eight clones inhibition was >40%, in 10 it ranged between 2040%,
and in four it was <20%. This suggests the existence of a clonal
heterogeneity as well as for the ability of CTLA-4 to inhibit
CD3/TCR-, CD28-, or CD2-mediated CTL activation. To support further
this contention, we used an experimental model based upon Ag-specific
CTL. Eight Ag-specific T cell clones that lyse autologous EBV-infected
B lymphocytes, but are unable to lyse allogeneic EBV-infected B
cell lines, were used in a cytolytic assay in which anti-CD152 mAb
or soluble recombinant receptor (i.e., CTLA-4 Ig) were included. In
this system, at variance from the redirected killing assay,
cross-linking of surface molecules by mAb does not occur. Thus,
addition of anti-CD152 mAb or of CTLA-4 Ig and anti-CD80/CD86
mAb to the assay should result in a blockade of receptor/ligand
interactions. As a consequence, inhibition of a negative signal, such
as that delivered via CD152, should enhance lysis. A >40% increment
of target cell lysis was achieved in three of eight clones studied.
Since it is not equally shared by all CTL clones, this feature also
appears to be clonally distributed.
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