An interleukin-2-IgG-Fas ligand fusion protein suppresses delayed-type hypersensitivity in mice by triggering apoptosis in activated T cells as a novel strategy for immunosuppression

Background. Cell-mediated immune responses can be down-regulated by inducti on of apoptosis of immunoreactive lymphocytes, In the present study, we hav e tested the feasibility of a strategy for immunosuppression by the selecti ve induction of apoptosis in activated, interleukin (IL)-2 receptor-positiv e lymphocytes, using a triple IL-2-IgG-FasL fusion protein. The IL-2-IgG-Fa sL fusion protein combines IL-2 for the selection of activated T cells, wit h the extracellular domain of the Fast molecule for inducing T-cell apoptos is, These components were separated by the Fc part of IgG1 serving as a spa cer as well as for half-life prolongation. Methods. The gene for the chimeric protein was created by fusing DNA sequen ces encoding for the three functional components: human IL-2, the Fc part o f human IgG1, and the extracellular domain of murine Fast. When the fusion gene was expressed in murine J558L cells, we obtained soluble dimeric immun oglobulin-like proteins in the supernatant. After analyzing the function of the IL-2 and Fast portions individually in vitro, a delayed-type hypersens itivity (DTH) reaction to sheep red blood cells as model for cell-mediated immune responses was investigated to evaluate the IL-2-IgG-FasL-mediated im munosuppression in vivo. Results. In vitro, the IL-2-IgG-FasL fusion protein supported IL-a-dependen t proliferation of Fas-resistant CTLL-2 cells, whereas concanavalin A-T bla sts were induced to undergo apoptosis by the Fast portion. in vivo, this fu sion protein potently inhibited a murine DTH. This was associated with an i ncreased rate of apoptosis in activated lymphocytes in the spleen, even at very low doses of the fusion protein. Furthermore, a second antigen challen ge 10 days after IL-2-IgG-FasL treatment still failed to elicit a DTH respo nse. Conclusion. The abrogation of a standard T cell-dependent immune response i n vivo demonstrates that IL-2-IgC-FasL can be successfully exploited to tri gger the death of deleterious T cells, presenting a potentially useful stra tegy in the management of autoimmune diseases and allotransplant rejections .