Islet allograft rejection in nonobese diabetic mice involves the common gamma-chain and CD28/CD154-dependent and -independent mechanisms

Once nonobese diabetic (NOD) mice become diabetic, they are highly resistant to islet transplantation. The precise mechanism of such resistance remains largely unknown. In the present study we tested the hypothesis that islet allograft survival in the diabetic NOD mouse is determined by the interplay of diverse islet-specific T cell subsets whose activation is regulated by CD28/CD154 costimulatory signals and the common gamma-chain (gammac; a shared signaling element by receptors for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21). We found that common gammac blockade is remarkably effective in blocking the onset and the ongoing autoimmune diabetes, whereas CD28/CD154 blockade has no effect in suppressing the ongoing diabetes. However, CD28/CD154 blockade completely blocks the alloimmune-mediated islet rejection. Also, a subset of memory-like T cells in the NOD mice is resistant to CD28/CD154 blockade, but is sensitive to the common gammac blockade. Nonetheless, neither common gammac blockade nor CD28/CD154 blockade can prevent islet allograft rejection in diabetic NOD mice. Treatment of diabetic NOD recipients with CD28/CD154 blockade plus gammac blockade markedly prolongs islet allograft survival compared with the controls. However, allograft tolerance is not achieved, and all CTLA-4Ig-, anti-CD154-, and anti-gammac-treated diabetic NOD mice eventually rejected the islet allografts. We concluded that the effector mechanisms in diabetic NOD hosts are inherently complex, and rejection in this model involves CD28/CD154/gammac-dependent and -independent mechanisms.