Auto- and alloimmune reactivity to human islet allografts transplanted into type 1 diabetic patients

Allogeneic islet transplantation can restore an insulin-independent state in C-peptide-negative type 1 diabetic patients. We recently reported three cases of surviving islet allografts that were implanted in type 1 diabetic patients under maintenance immune suppression for a previous kidney graft. The present study compares islet graft-specific cellular auto- and alloreactivity in peripheral blood from those three recipients and from four patients with failing islet allografts measured over a period of 6 months after portal islet implantation. The three cases that remained C-peptide- positive for >1 year exhibited no signs of alloreactivity, and their autoreactivity to islet autoantigens was only marginally increased. In contrast, rapid failure (<3 weeks) in three other cases was accompanied by increases in precursor frequencies of graft-specific alloreactive T-cells; in one of them, the alloreactivity was preceded by a sharply increased autoreactivity to several islet autoantigens. One recipient had a delayed loss of islet graft function (33 weeks); he did not exhibit signs of graft- specific alloimmunity, but developed a delayed increase in autoreactivity. The parallel between metabolic outcome of human β-cell allografts and cellular auto- and alloreactivity in peripheral blood suggests a causal relationship. The present study therefore demonstrates that T-cell reactivities in peripheral blood can be used to monitor immune mechanisms, which influence survival of β-cell allografts in diabetic patients.