AN IN VITRO MODEL OF DELETIONAL TOLERANCE BY DNA VACCINATION.
Corrado Cancedda, Wei Huang, Nicole Suciu-Foca and Paul E. Harris. Division of Immunogenetics, College of Physicians and Surgeons of Columbia University, New York, New York.
The induction of tolerance to transplantation antigens, particularly those recognized via the indirect pathway, may provide a means to treat chronic rejection. Tolerance to such antigens may be achieved by several methods, including high doses of antigens, analog peptides and induction of regulatory T cells. Induction of programmed cell death in allopeptide specific T cells is also feasible. Mammalian expression vectors carrying the genes for human Fas ligand and chimeric invariant chain/tetanus toxoid residues 830-843 were constructed. Efficient transient expression of Fas L and chimeric invariant chain (in 20 % of the monocyte population) was accomplished using a poly lysine-human Ig complex to deliver plasmid DNA to monocyte Fc receptors for endocytosis. Simulteanous expression of Fas Ligand and presentation of antigen by autologous cultured human monocytes to antigen-specific T cell lines resulted in loss of Th proliferation on subsequent challange with antigen. When T cells lines with different specificity were mixed (anti-tetanus toxoid and anti-pertussis toxin) and cultured on monocytes loaded with tetanus antigen and transfected with Fas Ligand, bystander killing of pertussis specific T cells was limited, yet resulted in loss of anti tetanus reactivity in the T cell line mixture. Loss of T cell reactivity was due to apotosis of T cells as demonstrated in experiments using Fas L transfected monocyte effectors and jurkat target cells. The simulteanous delivery and presentation of allopeptide by HLA Class II molecules and the expression of Fas L on human monocytes may offer a means to achieve peripheral tolerance to allopeptides in transplant recipients with chronic rejection.