Tumor-associated immune suppression can lead to defective T cell-mediated antitumor immunity. Here, we identified a unique phenotype of exhausted T cells in mice with advanced acute myelogenous leukemia (AML). This phenotype is characterized by the coexpression of Tim-3 and PD-1 on CD8 ؉ T cells in the liver, the major first site of AML metastases. PD-1 and Tim-3 coexpression increased during AML progression. PD-1 ؉ Tim-3 ؉ CD8 ؉ T cells were deficient in their ability to produce IFN-␥, TNF-␣, and IL-2 in response to PD-1 ligand (PDL1) and Tim-3 ligand (galectin-9) expressing AML cells. PD-1 knockout (KO), which were partially resistant to AML challenge, up-regulated Tim-3 during AML progression and such Tim-3 ؉ PD-1-KO CD8 ؉ T cells had reduced cytokine production. Galectin-9 KO mice were more resistant to AML, which was associated with reduced T-regulatory cell accumulation and a modest induction of PD-1 and Tim-3 expression on CD8 ؉ T cells. Whereas blocking the PD-1/ PDL1 or Tim-3/galectin-9 pathway alone was insufficient to rescue mice from AML lethality, an additive effect was seen in reducing-albeit not eliminating-both tumor burden and lethality when both pathways were blocked. Therefore, combined PD-1/PDL1 and Tim-3/galectin-9 blockade may be beneficial in preventing CD8 ؉ T-cell exhaustion in patients with hematologic malignancies such as advanced AML. (Blood. 2011;117(17):4501-4510) Introduction T-cell exhaustion, a state of T-cell dysfunction characterized by diminished cytokine production, impaired killing, and hypoproliferation, was first characterized in the settings of chronic lymphocytic choriomeningitis virus (LCMV) infection. 1,2-5 Since its discovery, the process of T-cell exhaustion has been of intense interest and has been the subject of study in viral infections such as hepatitis C virus 2,6 and HIV, 3,7 as well as in tumor models. 8,9,10,11 Cell-surface antigen determinants such as program death-1 (PD-1), CTLA-4, and, in some instances, CD28 (eg, hepatitis C viral infection) can be used to identify antigen-specific T cells that are at an exhaustion stage. 4 T-cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) is a type I membrane glycoprotein and its expression can be found on terminally differentiated Th1 cells and innate immune cells. [12][13][14] is its only confirmed Tim-3 ligand to date, 15,16 although it is known that Tim-3 can also bind to certain carbohydrate moieties. 17 Ligation of Tim-3 on T cells and gal-9 inhibits Th1 responses and plays an important role in infection, autoimmunity, peripheral tolerance, and inflammation. 14,[18][19][20][21] In addition to its negative regulatory role in dampening the immune system, a recent report showed a synergistic effect of Tim-3 signaling and lipopolysaccharide in producing proinflammatory cytokines by naive dendritic cells (DCs) and monocytes, 22 indicating a dual role of the Tim-3 signaling pathway at a different phase of immune responses.Studies have demonstrated a strong correlation between PD-1 and Tim-3 coexpressi...

Tumor-induced immune defects can weaken host immune response and permit tumor cell growth. In a systemic model of murine acute myeloid leukemia (AML), tumor progression resulted in increased regulatory T cells (Treg) and elevation of program death-1 (PD-1) expression on CD8 cytotoxic T cells (CTLs) at the tumor site. PD-1 knockout mice were more resistant to AML despite the presence of similar percentage of Tregs compared with wild type. In vitro, intact Treg suppression of CD8 T-cell responses was dependent on PD-1 expression by T cells and Tregs and PD-L1 expression by anti-gen-presenting cells. In vivo, the function of adoptively transferred AML-reactive CTLs was reduced by AML-associated Tregs. Anti-PD-L1 monoclonal antibody treatment increased the proliferation and function of CTLs at tumor sites, reduced AML tumor burden, and resulted in long-term survivors. Treg depletion followed by PD-1/PD-L1 blockade showed superior efficacy for eradication of established AML. These data demonstrated that interaction between PD-1 and PD-L1 can facilitate Treg-induced suppression of T-effector cells and dampen the antitumor immune response. PD-1/PD-L1 blockade coupled with Treg depletion represents an important new approach that can be readily translated into the clinic to improve the therapeutic efficacy of adoptive AML-reactive CTLs in advanced AML disease. (Blood. 2010;116(14):2484-2493)

IntroductionGraft-versus-host disease (GVHD) remains an important complication after allogeneic bone marrow transplantation (BMT). Despite broadly reactive pharmacologic agents, GVHD is not uniformly avoided and immunosuppression may cause malignancy recurrence or immunodeficiency. Selective GVHD preventive approaches retaining a graft-versus-leukemia (GVL) effect are needed.Interleukin-21 (IL-21) is produced by CD4 ϩ T cells (especially T helper 17 [Th17]-producing cells) and natural killer T (NKT) cells 1 and signals through the IL-2␥c and IL-21R complex. IL-21R is expressed on hematopoietic and epithelial cells and promotes the activation, differentiation, maturation, or expansion of NK cells, B cells, CD8 ϩ and CD4 ϩ T cells, dendritic cells, and macrophages, resulting in anticancer activity. 2-5 IL-21 facilitates autoimmunity in some [6][7][8] but not all 9,10 experimental models by supporting immunoglobulin production and Th17 cell-mediated pathogenesis.Because IL-21 augments Th17 cell differentiation, indirect evidence for the role of IL-21 in GVHD pathogenesis may be derived from such GVHD studies. Whereas IL-17 and Th17 cells reduce GVHD mediated by CD4 ϩ and CD8 ϩ donor T cells, 11 Th17 cells accelerated GVHD mediated exclusively by CD4 ϩ T cells. 12 Naive CD4 ϩ T cells skewed toward a Th17 phenotype in vitro have been used to demonstrate that Th17 cells contribute to GVHD pathogenesis, especially involving the skin and lung. 13 IL-21 has been described variably as an inhibitor 14 or enhancer 15 of Th1 differentiation. IL-21 supports Th17 cell survival at the expense of regulatory T cells (Tregs), which are reciprocally controlled by Th17 cells. 16 By inhibiting naive T-cell conversion into CD4 ϩ 25 ϩ FoxP3 ϩ regulatory T cells (termed inducible Tregs, iTregs), 17,18 limiting the suppression of T-effectors (Teffs) by Tregs, and augmenting Th17 responses, 19,20 IL-21 may increase GVHD lethality.The present studies were conducted to delineate the influence of IL-21 on GVHD and GVL and to elucidate the mechanisms associated with the observed biologic effects. We show that blocking or abrogating the IL-21 signaling pathway reduced acute GVHD mortality and tissue damage in the small intestine and the colon associated with decreased frequencies of interferon ␥ (IFN␥)-producing tissue-resident donor T cells in the colonic lamina propria (LP). At the same time FoxP3-expressing Tregs, which were virtually absent in the presence of IL-21, were found at relatively high frequencies at the site of inflammation in the colon and the small intestine in the absence of IL-21. These data, which are the first to demonstrate an in vivo role for IL-21 in iTreg generation, suggested a causative role of iTregs in GVHD attenuation. This was confirmed using Teffs incapable of generating iTregs. Despite acute GVHD attenuation, we show that GVL can occur in the absence of IL-21. Lastly, we show that the perforin and IL-21 pathways are nonredundant in the context of both the GVHD and GVL settings. Methods MiceC57BL/6 (H-2 b , term...

IntroductionAcute myeloid leukemia (AML) with unfavorable cytogenetics has a poor outcome, even when treated with aggressive chemotherapy. 1,2 With chemoradiotherapy and hematopoietic stem cell transplantation, a graft-versus-leukemia effect can be observed even in patients with unfavorable cytogenetics. 3 Although donor lymphocyte infusion (DLI) given as adoptive immunotherapy after hematopoietic stem cell transplantation has improved the outcomes of certain types of leukemia, 4-6 for patients with AML, DLI has been less effective likely due at least in part to its rapid tumor progression. 7,8 As a result of the anti-AML effects of DLI and with the observation that antitumor-specific cytotoxic T cells (CTLs) can be generated in vitro from cancer patients, adoptive CTL therapy has been proposed for decades as cancer treatment. [9][10][11][12][13][14] However, the adoptive transfer of anti-AML-reactive CTLs alone has not solved the problem of AML disease recurrence. 15 In patients with chronic myelogenous leukemia, a complete remission was achieved in a patient with accelerated-phase disease after adoptive treatment with leukemia-reactive CTLs. 16 In rodents with minimal disease, CTL adoptive transfer also has not been uniformly curative despite the early transfer of large numbers of anti-AML-reactive CTLs. 17,18 Enhancing CTL function in vivo via the administration of supportive cytokine therapy such as interleukin-2 (IL-2), 20 and interferons 21 can improve antitumor efficacy but has been associated with substantial side effects. Therefore, recent studies have focused on eliminating the suppressive factors in the tumor environment to circumvent CTLs from inhibition. 22,23 T-regulatory cells (Tregs) are important regulators of immune responses in transplantation, 24,25 allergy, 26,27 and autoimmune disease. 28,29 In AML patients, the frequency of Tregs was noted to be significantly higher compared with healthy persons, likely due to increased proliferation. 30 Human AML cells have been noted to favor the conversion of CD4 ϩ 25 Ϫ T cells into Tregs via modulation of tryptophan catabolism. 31 Tregs that have been recruited to, or converted either before migration into or within the tumor environment, can have a profound inhibition on T cell-mediated immune response. 32 Multiple mechanisms have been defined to be responsible for the suppression, including secretion of transforming growth factor-␤ 33,34 and IL-10, 33,34 as well as inhibition of dendritic cell (DC) maturation. 33,35 Despite the great potential for Treg depletion in cancer therapies, the efficacy has been limited to prophylactic settings where depletion of Tregs is given before the establishment of tumor. 36,37 The present studies were undertaken to determine whether endogenous Tregs present at the site of AML dissemination constrained the antileukemia efficacy of anti-AML CTL adoptive transfer in a rodent model as a prelude to future clinical trials. We observed that AML progression correlated with increased Tregs at the sites of AML disease. Incr...