Selective elimination of antigen-specific T cells by antigen-targeted drug-labeled antigen-presenting cell membranes

grantor: University of TorontoSince antigen-specific auto-aggressive T cells have been found in association with many autoimmune diseases, a treatment to eliminate such antigen-specific T cell clones was developed. The complex of peptide antigen and class II MHC protein is used to target a cytotoxic drug to antigen-specific T cells. The drug is bound covalently to antigen-presenting cells (APC) and protein antigens (Ag) are added to the cells for processing and presentation of peptides. The APC contain class II MHC (Ia) protein to present the peptide Ag to the T cell receptor and adhesion proteins for optimal interaction with the T cell. Either the Ag-bearing intact APC, or Ia$\sp+$-membranes shed spontaneously from them, were used as drug carriers to target drug to the T cells. The drugs being used are phototoxic fluorescent compounds. When irradiated with light of an appropriate wavelength, they give off toxic free radicals and singlet oxygen. These toxic by products are short-lived and damage cells only in their immediate vicinity, cutting down on non-specific side effects. APC from B hybridoma cells or their shed membranes bearing Ag peptides were able to target the drug selectively to Ag-specific T hybridoma cells. Both spontaneous T cell proliferation and antigen-induced IL-2 production of target T cells were inhibited. The specific effect could be blocked by anti-TCR mAb and anti-Ia mAb. A similar Ag-targeted cytotoxic effect was demonstrated on Ag-specific T cell lines and ex vivo Ag specific lymph node cells by using APC from thymus cells, or their shed membranes, bearing Ag peptides and drug. The Ag-specific effect was inhibited by anti-Ia antibody and by drug-free membranes carrying the Ag-Ia complex. This indicated that the antigen-specific phototoxic effect was mediated by interaction of the Ag-Ia complex with the T cell receptor. These "immunotoxins" may be useful as the basis for further development of a method to eliminate antigen-specific T cell clones in vivo in autoimmune diseases such as Multiple Sclerosis.Ph.D