Glucocorticoid-induced TNF receptor family related protein (GITR) is present on many different cell types. Previous studies have shown that in vivo administration of an anti-GITR agonist mAb (DTA-1) inhibits regulatory T cells (Treg)-dependent suppression and enhances T cell responses. In this study, we show that administration of DTA-1 induces >85% tumor rejection in mice challenged with B16 melanoma. Rejection requires CD4+, CD8+, and NK1.1+ cells and is dependent on IFN-γ and Fas ligand and independent of perforin. Depletion of Treg via anti-CD25 treatment does not induce B16 rejection, whereas 100% of the mice depleted of CD25+ cells and treated with DTA-1 reject tumors, indicating a predominant role of GITR on effector T cell costimulation rather than on Treg modulation. T cells isolated from DTA-1-treated mice challenged with B16 are specific against B16 and several melanoma differentiation Ags. These mice develop memory against B16, and a small proportion of them develop mild hypopigmentation. Consistent with previous studies showing that GITR stimulation increases Treg proliferation in vitro, we found in our model that GITR stimulation expanded the absolute number of FoxP3+ cells in vivo. Thus, we conclude that overall, GITR stimulation overcomes self-tolerance/ignorance and enhances T cell-mediated antitumor activity with minimal autoimmunity.

Glucocorticoid-induced tumor necrosis factor receptor family-related gene (GITR) is a member of the tumor necrosis factor receptor (TNFR) family that is expressed at low levels on unstimulated T cells, B cells, and macrophages. Upon activation, CD4+ and CD8+ T cells up-regulate GITR expression, whereas immunoregulatory T cells constitutively express high levels of GITR. Here, we show that GITR may regulate alloreactive responses during graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (BMT). Using a BMT model with major histocompatibility complex class I and class II disparity, we demonstrate that GITR stimulation in vitro and in vivo enhances alloreactive CD8+CD25− T cell proliferation, whereas it decreases alloreactive CD4+CD25− proliferation. Allo-stimulated CD4+CD25− cells show increased apoptosis upon GITR stimulation that is dependent on the Fas–FasL pathway. Recipients of an allograft containing CD8+CD25− donor T cells had increased GVHD morbidity and mortality in the presence of GITR-activating antibody (Ab). Conversely, recipients of an allograft with CD4+CD25− T cells showed a significant decrease in GVHD when treated with a GITR-activating Ab. Our findings indicate that GITR has opposite effects on the regulation of alloreactive CD4+ and CD8+ T cells.

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (HSCT).Migration of donor-derived T cells into GVHD target organs plays a critical role in the development of GVHD and chemokines and their receptors are important molecules involved in this process. Here, we demonstrate in murine bone marrow transplantation models that the expression of the inflammatory CC chemokine receptor 2 (CCR2) on donor-derived CD8 ؉ T cells is relevant for the control of CD8 ؉ T-cell migration and development of GVHD. Recipients of CCR2-deficient (CCR2 ؊/؊ ) CD8 ؉ T cells developed less damage of gut and liver than recipients of wild-type CD8 ؉ T cells, which correlated with a reduction in overall GVHD morbidity and mortality. Assessment of donor CD8 ؉ T-cell target organ infiltration revealed that CCR2 ؊/؊ CD8 ؉ T cells have an intrinsic migratory defect to the gut and liver. Other causes for the reduction in GVHD could be excluded, as alloreactive proliferation, activation, IFN-␥ production and cytotoxicity of CCR2 ؊/؊ CD8 ؉ T cells were intact. Interestingly, the graft-versustumor effect mediated by CCR2 ؊/؊ CD8 ؉ T cells was preserved, which suggests that interference with T-cell migration by blockade of CCR2 signaling can separate GVHD from GVT activity. ( IntroductionAllogeneic hematopoietic stem cell transplantation (HSCT) is a well-established therapy for a variety of malignant and nonmalignant disorders of the hematopoietic system and for certain solid tumors. 1 A major complication limiting the success and wider application of allogeneic HSCT is the occurrence of acute graft-versus-host disease (GVHD), which is a rapidly progressive illness with immunosuppression, cachexia and specific target organ damage of liver, intestines, skin, and lung. 2 Donor-derived alloreactive T cells play a major role in the pathogenesis of GVHD and depletion of T cells from the donor cell inoculum remains the most effective approach to prevent the development of disease. 3 However, alloreactive donor T cells also display graft-versus-tumor (GVT) activity, which is increasingly being recognized as an important component of the overall antitumor effect of an allogeneic HSCT. 4 Recent murine bone marrow transplantation studies suggest that specifically interfering with T-cell migration represents an attractive therapeutic approach toward the goal of amelioration of GVHD without reducing GVT activity. 5,6 It is known that 3 families of migration molecules (selectins, chemokines, integrins, and their respective ligands and receptors) control T-cell migration in homeostasis and inflammation 7 and members of all 3 families have been identified as important players during GVHD. 5 CC chemokine receptor 2 (CCR2) and its main ligand chemokine ligand 2 (CCL2) are among the chemokine receptor-ligand pairs that control leukocyte migration during inflammatory processes. 8,9 CCL2 (originally termed monocyte chemoattractant protein-1 [MCP-1]) belongs to the family of inflammatory CC chemokines and was one...