Intrathymic delivery of plasmid-encoding endoplasmic reticulum signal-sequence-deleted MHC class I alloantigen can induce long-term allograft survival

Intrathymic (IT) delivery of donor alloantigen is a potent strategy to induce operational tolerance. In this study we determined whether this effect was dependent on direct allorecognition of the tolerogen. Ten microgrammes of plasmid, encoding either the wild-type major histocompatibility complex (MHC) class I molecule K^b or a truncated form in which the signal sequence for translocation into the endoplasmic reticulum was deleted, preventing cell surface expression and direct allorecognition of the tolerogen, was administered intrathymically to CBA.Ca (H2^k) recipients. In addition, recipients were treated with anti-CD4 antibody (YTA3.1) at the time of IT injection and underwent transplantation 28 days later with a fully mismatched C57BL/10 (H2^b) cardiac allograft. Wildtype, as well as truncated K^b genes, were able to induce long-term survival of the cardiac allografts, in contrast to empty control plasmid. Reverse-transcriptase PCR showed expression of the K^b genes for up to 28 days in thymus and spleen of pretreated recipients. These data show that direct allorecognition of the tolerogen was not required for the induction of long-term allograft survival following the introduction of plasmid-encoded MHC alloantigen into the thymus.