Natural killer T-cells participate in rejection of islet allografts in the liver of mice.

A role of natural killer T (NKT) cells in transplant rejection remains unknown. Here, we determined whether NKT cells participate in rejection of islet allografts, using NKT cell-deficient mice. Survival of islet allografts in streptozotocin-induced diabetic CD1d(-/-) mice or Valpha14 NKT cell(-/-) mice was significantly prolonged without immunosuppression when grafted into the liver, but not beneath the kidney capsule, compared with wild-type mice. Acceptance of intrahepatic islet allografts was achieved in CD1d(-/-) mice by a subtherapeutic dose of rapamycin, which was abrogated in conjunction with the transfer of hepatic mononuclear cells from wild-type, but not from CD1d(-/-), mice at islet transplantation. The second islet grafts from a donor-specific, but not from a third-party, strain in CD1d(-/-) mice bearing functional islet allografts were accepted without immunosuppression at 120 days after the initial transplantation. These findings demonstrate that NKT cells play a significant role in rejection of islet allografts in the liver of mice, but that NKT cells are not essential for induction of donor-specific unresponsiveness in this model. The current study indicates that NKT cells might be considered as a target for intervention to prevent islet allograft rejection when the liver is the site of transplantation.

Valpha14 NK T cell-triggered IFN-gamma production by Gr-1+CD11b+ cells mediates early graft loss of syngeneic transplanted islets.

Pancreatic islet transplantation is a highly promising approach for the treatment of insulin-dependent diabetes mellitus. However, the procedure remains experimental for several reasons, including its low efficiency caused by the early graft loss of transplanted islets. We demonstrate that Gr-1+CD11b+ cells generated by transplantation and their IFN-gamma production triggered by Valpha14 NKT cells are an essential component and a major cause of early graft loss of pancreatic islet transplants. Gr-1+CD11b+ cells from Valpha14 NKT cell-deficient (Jalpha281-/-) mice failed to produce IFN-gamma, resulting in efficient islet graft acceptance. Early graft loss was successfully prevented through the repeated administration of alpha-galactosylceramide, a specific ligand for Valpha14 NKT cells, resulting in dramatically reduced IFN-gamma production by Gr-1+CD11b+ cells, as well as Valpha14 NKT cells. Our study elucidates, for the first time, the crucial role of Gr-1+CD11b+ cells and the IFN-gamma they produce in islet graft rejection and suggests a novel approach to improving transplantation efficiency through the modulation of Valpha14 NKT cell function.

Beneficial effects of costimulatory blockade with anti-inducible costimulator antibody in conjunction with CTLA4Ig on prevention of islet xenograft rejection from rat to mouse.

BACKGROUND: Costimulatory signals have been reported to play an important role in islet-xenograft rejection, although the precise mechanisms remain unknown. The aim of the present study was to determine a role of a novel costimulatory molecule, inducible costimulator (ICOS), in rat islet-xenograft rejection in conjunction with CTLA4Ig with respect to cellular as well as humoral immune responses. METHODS: Isolated rat islets were transplanted into the liver of streptozotocin (180 mg/kg) induced diabetic mice. Cellular immune responses to islet xenografts, and productions of anti-rat antibody in mice were examined by flow cytometry (FACS) after transplantation. RESULTS: Intrahepatic rat islet xenografts were rejected in mice within 8 days after transplantation. FACS analysis revealed an expansion of CD8(+) T cells in the liver as well as a production of anti-rat antibody in recipient mice in association with rejection. The treatment with anti-ICOS antibody in conjunction with CTLA4Ig produced a marked prolongation of islet-xenograft survival with neither expansion of CD8(+) T cells nor production of anti-rat antibody, whereas, in contrast, those treated with anti-ICOS antibody or CTLA4Ig alone did not have prolonged survival, and CD8(+) T cells were expanded. CONCLUSION: These findings demonstrate that cellular rather than humoral immune responses are considered responsible for islet-xenograft rejection from rat to mouse and that the blockade of costimulatory signals with anti-ICOS antibody in conjunction with CTLA4Ig has a favorable effect on prevention of islet xenograft rejection.