USE OF ANTI-CTLA-4
HUMAN MONOCLONAL ANTIBODIES FOR DEPLETION OF ACTIVATED T CELLS IN TRANSPLANTATION.
Pistillo M.P.,
*Tazzari P.L., °Stirpe F., °Bolognesi A., °Polito L., Capanni
P., §Pioli C., §Doria G.,*Conte
R., Ferrara G.B. Immunogenetics Lab., National Cancer Institute c/o CBA,
Genova; *Transfusion Medicine Service, Policlinico S.Orsola-Malpighi and
°Experimental Pathology Department, Bologna; §Biology Department,
Tor Vergata, University, Roma, Italy.
CTLA-4
is a T cell costimulatory receptor which behaves as a negative regulator
of T cell activation by interferring with the CD28 costimulation pathway.
The signal transduced by CTLA-4 blocks IL-2 production, IL-2 receptor expression
and cell cycle progression, thus making CTLA-4 a good candidate for targeted
immunotherapy. In our study we generated human recombinant anti-CTLA-4
scFv antibodies in order to obtain either immunotoxins to be used
for depletion ofactivated T cells,
or modulating ligands for stimulation or blocking of CTLA-4 negative signal.
Both these approaches could result in the suppression of the immune response
and prevent bone marrow and allograft rejection. The anti-CTLA-4 scFvs
have been produced by the phage display technology and recognize different
CTLA-4 epitopes expressed on activated T cells and dendritic cells but
not on resting T cells, B cells and stem cells. Since the epitopes recognized
by the scFvs are different from the epitopes with which CTLA-4 binds its
ligands CD80/CD86 we though to use them as a delivery system for toxins
from plants. An immunotoxin was prepared by chemically linking scFv#83
to the ribosome inactivating protein saporin. The immunotoxin was shown
to induce apoptosis of CD3/CD28 stimulated human T cells and to decrease
the MLR in a dose-dependent fashion.We also evaluated its toxicity in
vitro on different cell lines and in vivo in experimental models.
As to the second approach, the scFvs increase IL-2 and IFN-g
secretion by activated human and murine T lymphocytes suggesting their
possible use for blocking the interaction of CTLA-4 with its ligands. Thus,
both the approaches described may be successfully used in the induction
of transplantation tolerance.