Local Autoantigen Expression as Essential Gatekeeper of Memory T-CeIl Recruitment to Islet Grafts in Diabetic Hosts

It is generally believed that inflammatory cues can attract noncognate, "bystander" T-cell specificities to sites of inflammation. We have shown that recruitment of naive and in vitro activated autoreactive CD8 T cells into endogenous islets requires local autoantigen expression. Here, we demonstrate that absence of an autoantigen in syngeneic extrapancreatic islet grafts in diabetic hosts renders the grafts "invisible" to cognate memory (and naive) T cells. We monitored the recruitment of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-reactive CD8 T cells into IGRP-competent and IGRP-deficient islet grafts in diabetic wild-type or IGRP(-/-) nonobese diabetic hosts (harboring either naive and memory T cells or only naive IGRP-specific T-cells, respectively). All four host-donor combinations had development of recurrent diabetes within 2 weeks. Wild-type hosts recruited IGRP-specific T cells into IGRP(+/+) but not IGRP(-/-) grafts. In IGRP(-/-) hosts, there was no recruitment of IGRP-specific T cells, regardless of donor type. Graft-derived IGRP activated naive IGRP-specific T cells, but graft destruction invariably predated their recruitment. These results indicate that recurrent diabetes is exclusively driven by autoreactive T cells primed during the primary autoimmune response, and demonstrate that local antigen expression is a sine qua non requirement for accumulation of memory T cells into islet grafts. These findings underscore the importance of tackling autoreactive T-cell memory after [beta]-cell replacement therapy.