NOVEL METHOD FOR IN-VITRO DEPLETION OF T-CELLS BY MONOCLONAL ANTIBODY-TARGETED PHOTOSENSITIZATION

An immunotargeting method (called photo-immunotargeting) has been deve loped for selective in vitro cell destruction. The procedure combines the photosensitizing (toxic) effect of light-induced dye-molecules, e. g., hematoporphyrin (HP) and the selective binding ability of monoclon al antibodies (mAb) to cell surface molecules. The photosensitizer HP molecules were covalently attached to monoclonal antibodies (a-Thy-1) recognizing an antigen on the surface of T lymphocytes, and used for T cell destruction. To increase the selectivity of the conventional tar geting methods, a physical activation step (local light irradiation) a s a second degree of specificity was employed. The HP in conjugated fo rm was sufficient to induce T cell (thymocytes, EL-4 cell line) death after irradiation at 400 nm, at tenfold lower concentration compared t o the photosensitizing effect of unbound HP. The selective killing of T lymphocytes (bearing the Thy-1 antigen) in a mixed cell population w as demonstrated after a treatment with the phototoxic conjugate and li ght irradiation. This method can be useful for selective destruction o f one population (target cell) in an in vitro heterogeneous cell mixtu re, e.g., in bone marrow transplants for T cell depletion to avoid gra ft vs, host reaction. (C) 1998 Elsevier Science B.V.