Blockade of GITR-GITRL interaction maintains Treg function to prolong allograft survival.

Involvement of Treg in transplant tolerance has been demonstrated in multiple models. During the active process of graft rejection, these regulatory cells are themselves regulated and inactivated, a process termed counter-regulation. We hypothesize that ligation of the costimulatory molecule glucocorticoid-induced TNF receptor-related protein (GITR) on Treg inhibits their ability to promote graft survival, and by blocking GITR ligation graft survival can be prolonged. To this aim, we have designed a soluble GITR fusion protein (GITR-Fc), which binds GITR ligand and inhibits activation of GITR. Here, we show that GITR-Fc prolonged mouse skin graft survival, and this prolongation is dependent on Treg. In a full MHC-mismatched skin graft setting, GITR-Fc significantly improved graft survival when used in combination with MR1, anti-CD40L, while GITR-Fc alone did not demonstrate graft prolongation. These results demonstrate that disruption of binding of GITR with GITR ligand may be an important strategy in prolonging allograft survival.

GITR Blockade Facilitates Treg Mediated Allograft Survival.

BACKGROUND: Many models of transplant tolerance have been found to depend on the induction of regulatory T cells (Tregs). Innate immune signals are known to suppress Tregs thereby augmenting immunity by abrogating Treg function. Such signals may also provide a barrier to transplantation tolerance mediated by Tregs. A number of cell surface molecules expressed by Tregs have been found to inhibit Treg activity, the best characterized of which is the glucocorticoid-induced tumor necrosis factor receptor-related (GITR) protein. METHODS: By using an adoptive transfer model of allograft rejection, we can study the effects of inflammation and antigen-specific Tregs on graft survival. Inflammation resulting from the transplant procedure counter-regulates the suppressor activity of Tregs. To assess whether Treg activity could be enhanced by blocking GITR signaling, we compared the capacity of Tregs to prolong the survival of grafts in the presence or absence of activation-inducible TNF receptor (AITRL)-Fc, a novel construct that binds GITR. RESULTS: We report that interruption of GITR-GITR ligand (GITRL) binding by AITRL-Fc resulted in long-term Treg-dependent acceptance of skin grafts in the setting of innate immune signals that otherwise interfere with Treg activity. CONCLUSIONS: Inflammation and other innate immune signals may activate antigen presenting cells to upregulate GITRL. GITR-GITRL interaction is one pathway by which antigen presenting cells may enhance the adaptive response to foreign antigen by counter-regulating Tregs and by costimulating effector T cells. By blocking this interaction with AITRL-Fc, one can sustain the benefit conferred by graft-protective Tregs.

Donor age and cold ischemia interact to produce inferior 90-day liver allograft survival.

BACKGROUND: Expanded regional sharing of liver allografts may increase cold ischemia and allograft failure, particularly with livers from older donors. The aim of this study was to examine whether older donor age and cold ischemic time interact to produce inferior allograft survival. METHODS: We undertook a retrospective cohort study of adult liver transplants in the United States performed between December 1, 1995 and December 31, 2005, using data from the Organ Procurement and Transplantation Network. The primary outcome was allograft failure within 90 days. RESULTS: Forty-four thousand seven hundred fifty-six liver transplant recipients were analyzed. Older age was defined as 45 years or more, and prolonged cold ischemia was defined as 12 hours or more. Using data from the pre-Model for End Stage Liver Disease (MELD), post-MELD and combined eras, three separate analyses of the interaction between older donor age and prolonged cold ischemia were performed. In multivariable logistic regression, the interaction of age 45 years or more and cold ischemia more than or equal to 12 hr reached statistical significance in the combined (OR 1.24, CI 1.08-1.42, P<0.01) and pre-MELD (OR 1.26, CI 1.08-1.46, P<0.01) datasets, but not in the smaller post-MELD dataset (OR 1.18, CI 0.81-1.72, P=0.38). In the combined dataset, recipients of livers from donors aged 45 years or more and cold ischemia more than or equal to 12 hr showed an adjusted absolute risk of allograft failure at 90 days of 17.3% (odds ratio 1.84), compared with 11.1% for recipients of livers from donors older than 45 years and cold ischemia less than 12 hr. CONCLUSIONS: These findings suggest that older donor age and prolonged cold ischemia interact to increase liver allograft failure at 90 days. Proposals to expand regional sharing of older livers should be regarded with caution.