Transcription factor Foxo1 represses T-bet-mediated effector functions and promotes memory CD8(+) T cell differentiation.

The evolutionary conserved Foxo transcription factors are important regulators of quiescence and longevity. Although, Foxo1 is known to be important in regulating CD8(+) T cell trafficking and homeostasis, its role in functional differentiation of antigen-stimulated CD8(+) T cells is unclear. Herein, we demonstrate that inactivation of Foxo1 was essential for instructing T-bet transcription factor-mediated effector differentiation of CD8(+) T cells. The Foxo1 inactivation was dependent on mTORC1 kinase, given that blockade of mTORC1 abrogated mTORC2-mediated Akt (Ser473) kinase phosphorylation, resulting in Foxo1-dependent switch from T-bet to Eomesodermin transcription factor activation and increase in memory precursors. Silencing Foxo1 ablated interleukin-12- and rapamycin-enhanced CD8(+) T cell memory responses and restored T-bet-mediated effector functions. These results demonstrate an essential role of Foxo1 in actively repressing effector or terminal differentiation processes to promote memory CD8(+) T cell development and identify the functionally diverse mechanisms utilized by Foxo1 to promote quiescence and longevity.

A central role for mTOR kinase in homeostatic proliferation induced CD8+ T cell memory and tumor immunity.

The cell-intrinsic mechanisms guiding naive CD8+ T cells for clonal expansion and memory generation via homeostatic proliferation (HP) are unclear. Here, we have shown that HP of naive CD8+ T cells requires IL-7-, but not IL-15-induced mTOR kinase activation. HP-induced mTOR enhances transcription factor T-bet for functional maturation and CD122 expression, which sensitizes for an IL-15-dependent memory transition by favoring transcription factor Eomesodermin over T-bet. Inhibition of mTOR blocks T-bet and CD122 expression but preserves memory in an IL-15-independent manner by promoting Eomesodermin expression. The ability of rapamycin to augment HP-induced memory was cell-intrinsic given that silencing mTOR in CD8+ T cells generated identical outcomes. Strikingly, HP-induced CD8+ T cell memory generated by IL-15-dependent or -independent mechanisms demonstrated identical tumor efficacy. These results indicate a central role for mTOR in HP-induced CD8+ T cell responses and demonstrate the importance for CD8+ memory in HP-induced tumor efficacy.

The mTOR kinase determines effector versus memory CD8+ T cell fate by regulating the expression of transcription factors T-bet and Eomesodermin.

The mechanisms underpinning integration of instructions that program naive CD8+ T cells for effector and/or memory differentiation are not well understood. Herein, we demonstrate that interleukin-12 (IL-12) enhanced and sustained antigen and costimulatory molecule (B7.1)-induced mTOR kinase activity in naive CD8+ (OT-I) T cells via phosphoinositide 3-kinase and STAT4 transcription factor pathways. Blocking mTOR activity by rapamycin reversed IL-12-induced effector functions because of loss of persistent expression of the transcription factor T-bet. Rapamycin treatment of IL-12-conditioned OT-I cells promoted persistent Eomesodermin expression and produced memory cell precursors that demonstrated enhanced sustenance and antigen-recall responses upon adoptive transfer. The memory cell precursors showed greater tumor efficacy than IL-12-conditioned effector OT-I cells. These results identify mTOR as the central regulator of transcriptional programs that determine effector and/or memory cell fates in CD8+ T cells. Targeting mTOR activity offers new opportunities to regulate CD8+ T cell-mediated immunity.

ß-Catenin in dendritic cells exerts opposite functions in cross-priming and maintenance of CD8+ T cells through regulation of IL-10.

Recent studies have demonstrated that ß-catenin in DCs serves as a key mediator in promoting both CD4(+) and CD8(+) T-cell tolerance, although how ß-catenin exerts its functions remains incompletely understood. Here we report that activation of ß-catenin in DCs inhibits cross-priming of CD8(+) T cells by up-regulating mTOR-dependent IL-10, suggesting blocking ß-catenin/mTOR/IL-10 signaling as a viable approach to augment CD8(+) T-cell immunity. However, vaccination of DC-ß-catenin(-/-) (CD11c-specific deletion of ß-catenin) mice surprisingly failed to protect them against tumor challenge. Further studies revealed that DC-ß-catenin(-/-) mice were deficient in generating CD8(+) T-cell immunity despite normal clonal expansion, likely due to impaired IL-10 production by ß-catenin(-/-) DCs. Deletion of ß-catenin in DCs or blocking IL-10 after clonal expansion similarly led to reduced CD8(+) T cells, suggesting that ß-catenin in DCs plays a positive role in CD8(+) T-cell maintenance postclonal expansion through IL-10. Thus, our study has not only identified mTOR/IL-10 as a previously unidentified mechanism for ß-catenin-dependent inhibition of cross-priming, but also uncovered an unexpected positive role that ß-catenin plays in maintenance of CD8(+) T cells. Despite ß-catenin's opposite functions in regulating CD8(+) T-cell responses, selectively blocking ß-catenin with a pharmacological inhibitor during priming phase augmented DC vaccine-induced CD8(+) T-cell immunity and improved antitumor efficacy, suggesting manipulating ß-catenin signaling as a feasible therapeutic strategy to improve DC vaccine efficacy.

Uncoupling protein 2 regulates metabolic reprogramming and fate of antigen-stimulated CD8+ T cells.

Adoptive cell therapy (ACT) employing ex vivo-generated tumor antigen-specific CD8+ T cells shows tumor efficacy when the transferred cells possess both effector and memory functions. New strategies based on understanding of mechanisms that balance CD8+ T cell differentiation toward effector and memory responses are highly desirable. Emerging information confirms a central role for antigen-induced metabolic reprogramming in CD8+ T cell differentiation and clonal expansion. The mitochondrial protein uncoupling protein 2 (UCP2) is induced by antigen stimulation of CD8+ T cells; however, its role in metabolic reprogramming underlying differentiation and clonal expansion has not been reported. Employing genetic (siRNA) and pharmacologic (Genipin) approaches, we note that antigen-induced UCP2 expression reduces glycolysis, fatty acid synthesis and production of reactive oxygen species to balance differentiation with survival of effector CD8+ T cells. Inhibition of UCP2 promotes CD8+ T cell terminal differentiation into short-lived effector cells (CD62L(lo)KLRG1(Hi)IFNγ(Hi)) that undergo clonal contraction. These findings are the first to reveal a role for antigen-induced UCP2 expression in balancing CD8+ T cell differentiation and survival. Targeting UCP2 to regulate metabolic reprogramming of CD8+ T cells is an attractive new approach to augment efficacy of tumor therapy by ACT.

Regulating mammalian target of rapamycin to tune vaccination-induced CD8(+) T cell responses for tumor immunity.

Vaccine strategies aimed at generating CD8(+) T cell memory responses are likely to show augmented efficacy against chronic challenges like tumor. The abundance in variety of memory CD8(+) T cells behooves development of vaccine strategies that generate distinct memory responses and evaluate them for tumor efficacy. In this study, we demonstrate the ability of a variety of rapamycin treatment regimens to regulate virus vaccination-induced CD8(+) T cell memory responses and tumor efficacy. Strikingly, a short course of high-dose, but not low-dose, rapamycin treatment transiently blocks viral vaccination-induced mammalian target of rapamycin activity in CD8(+) T cells favoring persistence and Ag-recall responses over type 1 effector maturation; however, prolonged high-dose rapamycin administration abrogated memory responses. Furthermore, a short course of high-dose rapamycin treatment generated CD8(+) T cell memory responses that were independent of IL-15 and IL-7 and were programmed early for sustenance and greater tumor efficacy. These results demonstrate the impact a regimen of rapamycin treatment has on vaccine-induced CD8(+) T cell responses and indicates that judicious application of rapamycin can augment vaccine efficacy for chronic challenges.

NY-ESO-1 protein glycosylated by yeast induces enhanced immune responses.

Vaccine strategies that target dendritic cells to elicit potent cellular immunity are the subject of intense research. Here we report that the genetically engineered yeast Saccharomyces cerevisiae, expressing the full-length tumour-associated antigen NY-ESO-1, is a versatile host for protein production. Exposing dendritic cells (DCs) to soluble NY-ESO-1 protein linked to the yeast a-agglutinin 2 protein (Aga2p) protein resulted in protein uptake, processing and MHC class I cross-presentation of NY-ESO-1-derived peptides. The process of antigen uptake and cross-presentation was dependent on the glycosylation pattern of NY-ESO-1-Aga2p protein and the presence of accessible mannose receptors. In addition, NY-ESO-1-Aga2p protein uptake by dendritic cells resulted in recognition by HLA-DP4 NY-ESO-1-specific CD4(+) T cells, indicating MHC class II presentation. Finally, vaccination of mice with yeast-derived NY-ESO-1-Aga2p protein led to an enhanced humoral and cellular immune response, when compared to the bacterially expressed NY-ESO-1 protein. Together, these data demonstrate that yeast-derived full-length NY-ESO-1-Aga2p protein is processed and presented efficiently by MHC class I and II complexes and warrants clinical trials to determine the potential value of S. cerevisiae as a host for cancer vaccine development.

Angiostatic activity of the antitumor cytokine interleukin-21.

Interleukin-21 (IL-21) is a recently described immunoregulatory cytokine. It has been identified as a very potent immunotherapeutic agent in several cancer types in animal models, and clinical studies are ongoing. IL-21 belongs to the type I cytokine family of which other members, ie, IL-2, IL-15, and IL-4, have been shown to exert activities on vascular endothelial cells (ECs). We hypothesized that IL-21, in addition to inducing the antitumor immune response, also inhibits tumor angiogenesis. In vitro experiments showed a decrease of proliferation and sprouting of activated ECs after IL-21 treatment. We found that the IL-21 receptor is expressed on vascular ECs. Furthermore, in vivo studies in the chorioallantoic membrane of the chick embryo and in mouse tumors demonstrated that IL-21 treatment disturbs vessel architecture and negatively affects vessel outgrowth. Our results also confirm the earlier suggested angiostatic potential of IL-2 in vitro and in vivo. The angiostatic effect of IL-21 is confirmed by the decrease in expression of angiogenesis-related genes. Interestingly, IL-21 treatment of ECs leads to a decrease of Stat3 phosphorylation. Our research shows that IL-21 is a very powerful antitumor compound that combines the induction of an effective antitumor immune response with inhibition of tumor angiogenesis.

The acute phase protein haptoglobin regulates host immunity.

The contribution of acute phase plasma proteins to host immune responses remains poorly characterized. To better understand the role of the acute phase reactant and major hemoglobin-binding protein haptoglobin (Hp) on the function of immune cells, we generated Hp-deficient C57BL/6J mice. These mice exhibit stunted development of lymphoid organs associated with lower counts of mature T and B cells in the blood and secondary lymphoid compartments. Moreover, these mice show markedly reduced adaptive immune responses as represented by reduced accumulation of IgG antibody after immunization with adjuvant and nominal antigen, abrogation of Th1-dominated delayed-type hypersensitivity reaction, loss of mitogenic responses mounted by T cells, and reduced T cell responses conveyed by APCs. Collectively, these defects are in agreement with the observations that Hp-deficient mice are not capable of generating a recall response or deterring a Salmonella infection as well as failing to generate tumor antigen-specific responses. The administration of Hp to lymphocytes in tissue culture partially ameliorates these functional defects, lending further support to our contention that the acute phase response protein Hp has the ability to regulate immune cell responses and host immunity. The phenotype of Hp-deficient mice suggests a major regulatory activity for Hp in supporting proliferation and functional differentiation of B and T cells as part of homeostasis and in response to antigen stimulation.

Aspergillus fumigatus extract differentially regulates antigen-specific CD4+ and CD8+ T cell responses to promote host immunity.

Invasive aspergillosis is a major cause of morbidity and mortality in the severely immunocompromised. The paucity of information about the mechanisms by which Aspergillus-derived factors regulate antigen-specific T cell responses in vivo poses a significant hurdle for devising effective immunization strategies to treat or prevent aspergillosis. By monitoring adoptively transferred T cell receptor transgenic, naive CD4+ (OT-II) and CD8+ (OT-I) T cells specific for distinct peptides of a nominal antigen, chicken ovalbumin (OVA), we demonstrate that sensitization with Aspergillus fumigatus (Af) extract plus OVA protein considerably enhances OT-I and OT-II T cell activation, which results in clonal expansion, primarily as a result of increased proliferation. The sensitization provided by Af extract promotes OT-I expansion accompanied by differentiation into interferon-gamma-producing cytotoxic cells. It is surprising that no effector differentiation of the induced OT-II response was observed. Moreover, the Af extract-induced OT-I and OT-II T cell expansion was transient, as considerable contraction in the numbers of detectable OT-I and OT-II T cells was evidenced by Day 10. In agreement with these observations, sensitization with Af extract plus OVA marginally promoted host immunity against an OVA-expressing thymoma (E.G7) challenge, and the protection was enhanced by resensitization with Af extract and OVA. Our results demonstrate the ability of Af extract to differentially regulate antigen-specific CD4+ and CD8+ T cell responses, resulting in limited augmentation of host immunity. This information suggests that strategies to target CD4+ T cell effector maturation may promote host immunity to Aspergillus and unexpectedly demonstrates the use for Af extract as a CD8+ T cell adjuvant.