Autoimmunity as an Endogenous Source of Heterologous Alloreactivity.

Abstract

In autoimmune Type 1 diabetic (T1D) recipients, the disease can recur in pancreatic islet transplants. However, because autoimmune T cells recognize autoantigens in the context of self MHC antigens, it is not clear how autoreactive (islet-specific) T cells may recognize MHC-unrelated islet allografts. In this study, determined the specificity of T cells infiltrating islet allografts in the non-obese diabetic (NOD) mouse model of T1D. We grafted 400-500 syngeneic (NOD, H-2g7) or allogeneic (C3H, H-2k) islets beneath the kidney capsule of spontaneously diabetic female NOD mice. Curiously, although the autoimmune repertoire is self (H-2g7) MHC-restricted, C3H allografts were more rapidly rejected in NOD mice (n = 6; MST 7days) than were syngeneic (NOD) islet grafts (n = 19; MST 11 days), p < .001. We tested the hypothesis that within the activated autoimmune T cell repertoire was a sub-population of T cell receptors (TCR) that cross-reacted with allogeneic MHC. To determine whether islet-autoreactive T cells infiltrate C3H islet allografts, we used 454 high-throughput TCR sequencing to compare the TCR repertoires expressed in the NOD recipient's residual endogenous pancreatic islets to those expressed by islet allograft-infiltrating T cells. A portion of TCRs were shared between the endogenous pancreatic islets and the C3H allograft. We next determined the specificity of TCRs used in high frequency in rejected C3H islet allografts. To this end, TCRs expressed in high frequency in the allograft (>1%) were cloned and tested for islet autoreactivity and/or alloreactivity following TCR cDNA transfection into IL-2 producing hybridoma cells. Of note, three TCRs studied that were the most frequent in the graft were also detected in the endogenous pancreas. As expected, all three TCRs were islet reactive. Surprisingly, all three of these TCR also were directly alloreactive to C3H spleen cells in the absence of either islet antigens or NOD APCs. Two of the three TCRs were MHC class I reactive (anti-H-2Dk), and the other was MHC class II-reactive (anti-I-Ak). These results suggest that dual auto/allo-reactive T cells are selectively expanded in islet allografts. As such, we propose that autoimmunity is an unusual source of endogenous heterologous alloreactivity that may target an allograft via simultaneous auto- and allo-reactive specificities.