Interferon-γ–triggered indoleamine 2,3-dioxygenase competence in human monocyte-derived dendritic cells induces regulatory activity in allogeneic T cells

Blood ◽  
2009 ◽  
Vol 114 (15) ◽  
pp. 3235-3243 ◽  
Author(s):  
Birgit Jürgens ◽  
Ursula Hainz ◽  
Dietmar Fuchs ◽  
Thomas Felzmann ◽  
Andreas Heitger
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Proinflammatory Cytokine ◽  
Human Monocyte ◽  
Third Party ◽  
Cytokine Release ◽  
Regulatory Activity ◽  
Indoleamine 2,3 Dioxygenase ◽  
Ifn Γ

Abstract The role of the tryptophan-metabolizing enzyme indoleamine 2,3-dioxygenase (IDO) in down-regulating human alloresponses has recently been controversially debated. We here demonstrate that human monocyte-derived dendritic cells (mDCs) can be endowed with sustained IDO competence in vitro by 48-hour activation with lipopolysaccharide (LPS) and interferon-gamma (IFN-γ). IFN-γ also amplified proinflammatory cytokine secretion during activation. Yet, on reculture after activation cytokine production ceased, whereas IDO enzymatic activity continued. Manipulation of tryptophan metabolism did not affect proinflammatory cytokine release, suggesting that IFN-γ triggers IDO activity and proinflammatory cytokine release as distinct cellular programs. IDO-competent DCs down-regulated allogeneic T-cell responses, but this IDO-mediated effect was overcome by slightly modifying cell culture conditions. Nevertheless, the CD4+CD25+ T-cell fraction stimulated by IDO-competent DCs displayed substantial suppressor activity. This suppressive activity (1) required allogeneic stimulation for its induction, (2) affected third-party T cells, and (3) was reduced by the IDO inhibitor methyl-thiohydantoin-tryptophan. It became also manifest when DC/T-cell cocultures were initiated with naive (CD4+CD25−CD45RA+) T cells, indicating the differentiation of adaptive regulatory T cells. Together, these findings suggest that IFN-γ triggered IDO competence in human mDCs constitutes a critical factor for endowing allogeneic T cells with regulatory activity.

Regulation of human auto- and alloreactive T cells by indoleamine 2,3-dioxygenase (IDO)–producing dendritic cells: too much ado about IDO?

Blood ◽  
2005 ◽  
Vol 105 (6) ◽  
pp. 2480-2486 ◽  
Author(s):  
Peter Terness ◽  
Jing-Jing Chuang ◽  
Thomas Bauer ◽  
Lucian Jiga ◽  
Gerhard Opelz
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Cell Response ◽  
Human Monocyte ◽  
T Cell Response ◽  
Regulatory Function ◽  
Blood Monocytes ◽  
Indoleamine 2,3 Dioxygenase ◽  
Ifn Γ

AbstractAlthough dendritic cells (DCs) strongly stimulate the immune response, they can also induce unresponsiveness. Recently, a human monocyte-derived DC subpopulation was described that constitutively expresses indoleamine 2,3-dioxygenase (IDO). These DCs were defined as nonadherent CD123+/CC chemokine receptor 6+ (CCR6+) cells that suppress the allogeneic T-cell response. In the present study, we generated nonadherent, mature DCs from human blood monocytes. As expected, in addition to the classic markers, these cells expressed CD123 and CCR6. Reverse transcription–polymerase chain reaction (RT-PCR), however, did not show IDO gene transcription, nor did we detect enzymatic IDO activity. Treating the cells with interferon-γ (IFN-γ) resulted in significant IDO production. Subsequently, we studied the regulatory properties of IDO-producing DCs on autologous and allogeneic T-cell responses. Neither OKT3-stimulated T cells of healthy donors nor myelin basic protein (MBP)–specific T cells of patients with multiple sclerosis (MS) were suppressed by autologous IDO DCs. However, whereas IDOneg DCs supported further stimulation of preactivated MBP-specific T cells of an MS patient, IDOpos DCs had lost this capacity. The allogeneic T-cell response was only marginally suppressed by IDO DCs. Our findings show that nonadherent CD123+/CCR6+ human DCs do not constitutively express IDO, and, even if they express the enzyme after IFN-γ treatment, they possess only limited T-cell regulatory function.

Potential Tolerizing Capacity of Human Dendritic Cells Featuring High Levels of Expression and Activity of the Tryptophan Metabolizing Enzyme Indoleamine 2,3 Dioxygenase.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 623-623
Author(s):  
Andreas Heitger ◽  
Birgit Juergens ◽  
Ursula Hainz ◽  
Dietmar Fuchs
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
T Cell Responses ◽  
Cell Fraction ◽  
Cell Responses ◽  
Indoleamine 2,3 Dioxygenase ◽  
Ifn Γ ◽  
Human Dendritic Cells ◽  
Expression And Activity

Abstract An enhanced tryptophan metabolism mediated by the enzymatic activity of indoleamine 2,3 dioxygenase (IDO) has recently been demonstrated to profoundly affect T cell responses. By the present study we explored whether human dendritic cells (DCs) displaying high IDO expression and activity, down-regulate allogeneic T cell responses. A comparison of lipopolysaccaride (LPS), interferon-γ (IFN-γ), and CD40L as DC maturation agents showed that most abundant IDO expression and activity in DCs was observed when immature DCs were exposed to a combination of LPS and IFN-γ for 48 hours. This time period of maturation was associated with the development of a mature DC phenotype. In contrast, semi-mature DCs, i.e. DCs matured for 4 hours only, were IDO negative. In co-cultures with allogeneic T cells both types of DCs began to metabolize tryptophan, as determined by decreasing concentrations of tryptophan and increasing concentrations of kynurenines in cell culture supernatants, but mature IDO positive DCs did so at a faster rate (complete consumption of tryptophan within 16 hours of co-culture) than semi-mature DCs. A comparison of the allo-stimulatory capacity of semi-mature IDO negative DCs and mature IDO positive DCs showed that at a high DC/T cell ratio (1:1) IDO positive DCs had a significantly reduced capacity to stimulate allogeneic T cells (median 63% reduction, n=5). The reduction of the allogeneic T cell response induced by IDO positive DCs was reversed upon the addition of the IDO inhibitor methylhydantoin-tryptophan to the co-cultures, suggesting an IDO dependent mechanism. Furthermore, allogeneic T cells exposed to IDO positive DCs had an increased rate of apoptosis in the activated cell fraction and after 8 days of co-culture contained a cell fraction (~30%) displaying a CD4+CD25+highFOXP3+ phenotype. These latter cells, when enriched by fluorescent activated cell sorting (FACS), were able to suppress the proliferative response of naive T cells to anti-CD3 mediated stimulation, which indicates the generation of a regulatory T cell population by IDO positive DCs. Together, these findings suggest that the amount of IDO expression and activity by DCs is one feature to govern the type of response of stimulated T cells. Human DCs can be induced to display high levels of IDO expression and activity and, thereby, acquire the ability to effectivley modulate allogeneic T cell responses towards tolerance by eliminating allo-reactive T cells through apoptosis and augmentation of their regulatory rather than their effector potential. Our current approaches address whether this property can be employed to use DCs for the generation of allo-antigen specific tolerance in the setting of hematopoietic cell transplantation.

Ifosfamide impairs the allostimulatory capacity of human dendritic cells by intracellular glutathione depletion

Blood ◽  
2003 ◽  
Vol 102 (10) ◽  
pp. 3668-3674 ◽  
Author(s):  
Maria C. Kuppner ◽  
Anabel Scharner ◽  
Valeria Milani ◽  
Christoph von Hesler ◽  
Katharina E. Tschöp ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Nk Cells ◽  
Cell Function ◽  
Nk Cell ◽  
Human Monocyte ◽  
Glutathione Depletion ◽  
Intracellular Glutathione ◽  
Ifn Γ

AbstractIfosfamide, a clinically potent chemotherapeutic agent, causes the depletion of intracellular glutathione (GSH) levels in various cell types. GSH is the major intracellular reductant against oxidative stress. 4-Hydroxyifosfamide (4-OH-IF), the activated form of ifosfamide, depletes GSH levels in T cells and natural killer (NK) cells; this is accompanied by a decrease in T-cell and NK-cell function. Here we demonstrate for the first time that human monocyte-derived dendritic cells (DCs) express higher constitutive levels of GSH and are less sensitive to 4-OH-IF-induced GSH depletion than T cells and NK cells. Treatment of DCs with 4-OH-IF significantly reduced their ability to stimulate allogeneic T-cell proliferation and interferon-γ (IFN-γ) production. Ifosfamide also decreased DC interleukin-12p70 (IL-12p70) production after stimulation with lipopolysaccharide (LPS) and IFN-γ. The decrease in allostimulatory capacity and in IFN-γ and IL-12 production correlated with a decrease in intracellular GSH in the DCs. The responses could be restored by reconstituting DC GSH levels with glutathione monoethyl ester (GSH-OEt). 4-OH-IF had no inhibitory effect on the ability of DCs to present exogenously added tyrosinase peptide to tyrosinase-specific cytotoxic T lymphocytes (CTLs). These studies suggest that in cancer patients treated with ifosfamide, protection strategies based on glutathione reconstitution may enhance DC function. (Blood. 2003;102: 3668-3674)

scholarly journals Batf3-Dependent Dendritic Cells Promote Optimal CD8 T Cell Responses against Respiratory Poxvirus Infection

2018 ◽  
Vol 92 (16) ◽  
Author(s):  
Pritesh Desai ◽  
Vikas Tahiliani ◽  
Georges Abboud ◽  
Jessica Stanfield ◽  
Shahram Salek-Ardakani
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Vaccinia Virus ◽  
Respiratory Infection ◽  
Host Resistance ◽  
T Cell Responses ◽  
Cell Responses ◽  
Ifn Γ ◽  
The Impact

ABSTRACTRespiratory infection with vaccinia virus (VacV) elicits robust CD8+T cell responses that play an important role in host resistance. In the lung, VacV encounters multiple tissue-resident antigen-presenting cell (APC) populations, but which cell plays a dominant role in priming of virus-specific CD8+effector T cell responses remains poorly defined. We used Batf3−/−mice to investigate the impact of CD103+and CD8α+dendritic cell (DC) deficiency on anti-VacV CD8+T cell responses. We found that Batf3−/−mice were more susceptible to VacV infection, exhibiting profound weight loss, which correlated with impaired accumulation of gamma interferon (IFN-γ)-producing CD8+T cells in the lungs. This was largely due to defective priming since early in the response, antigen-specific CD8+T cells in the draining lymph nodes of Batf3−/−mice expressed significantly reduced levels of Ki67, CD25, and T-bet. These results underscore a specific role for Batf3-dependent DCs in regulating priming and expansion of effector CD8+T cells necessary for host resistance against acute respiratory VacV infection.IMPORTANCEDuring respiratory infection with vaccinia virus (VacV), a member ofPoxviridaefamily, CD8+T cells play important role in resolving the primary infection. Effector CD8+T cells clear the virus by accumulating in the infected lungs in large numbers and secreting molecules such as IFN-γ that kill virally infected cells. However, precise cell types that regulate the generation of effector CD8+T cells in the lungs are not well defined. Dendritic cells (DCs) are a heterogeneous population of immune cells that are recognized as key initiators and regulators of T-cell-mediated immunity. In this study, we reveal that a specific subset of DCs that are dependent on the transcription factor Batf3 for their development regulate the magnitude of CD8+T cell effector responses in the lungs, thereby providing protection during pulmonary VacV infection.

CD56+ human blood dendritic cells effectively promote TH1-type γδ T-cell responses

Blood ◽  
2009 ◽  
Vol 114 (20) ◽  
pp. 4422-4431 ◽  
Author(s):  
Georg Gruenbacher ◽  
Hubert Gander ◽  
Andrea Rahm ◽  
Walter Nussbaumer ◽  
Nikolaus Romani ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Human Blood ◽  
Γδ T Cells ◽  
Rapid Expansion ◽  
Γδ T Cell ◽  
Hla Dr ◽  
Tnf Α ◽  
Ifn Γ

Abstract CD56+ human dendritic cells (DCs) have recently been shown to differentiate from monocytes in response to GM-CSF and type 1 interferon in vitro. We show here that CD56+ cells freshly isolated from human peripheral blood contain a substantial subset of CD14+CD86+HLA-DR+ cells, which have the appearance of intermediate-sized lymphocytes but spontaneously differentiate into enlarged DC-like cells with substantially increased HLA-DR and CD86 expression or into fully mature CD83+ DCs in response to appropriate cytokines. Stimulation of CD56+ cells containing both DCs and abundant γδ T cells with zoledronate and interleukin-2 (IL-2) resulted in the rapid expansion of γδ T cells as well as in IFN-γ, TNF-α, and IL-1β but not in IL-4, IL-10, or IL-17 production. IFN-γ, TNF-α, and IL-1β production were almost completely abolished by depleting CD14+ cells from the CD56+ subset before stimulation. Likewise, depletion of CD14+ cells dramatically impaired γδ T-cell expansion. IFN-γ production could also be blocked by neutralizing the effects of endogenous IL-1β and TNF-α. Conversely, addition of recombinant IL-1β, TNF-α, or both further enhanced IFN-γ production and strongly up-regulated IL-6 production. Our data indicate that CD56+ DCs from human blood are capable of stimulating CD56+ γδ T cells, which may be harnessed for immunotherapy.

scholarly journals Sunitinib Exerts In Vitro Immunomodulatory Activity on Sarcomas via Dendritic Cells and Synergizes With PD-1 Blockade

2021 ◽  
Vol 12 ◽  
Author(s):  
Darina Ocadlikova ◽  
Mariangela Lecciso ◽  
Javier Martin Broto ◽  
Katia Scotlandi ◽  
Michele Cavo ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Cell Lines ◽  
Effector T Cells ◽  
Sarcoma Cell ◽  
Ifn Γ ◽  
Sarcoma Cells

BackgroundHigh-grade sarcomas are a heterogeneous group of aggressive tumors arising in bone and soft tissues. After relapse, treatment options are limited. The multi-targeted receptor tyrosine kinase inhibitors (TKIs) sunitinib and inhibitor of PD-1 (anti-PD-1) nivolumab have shown antitumor activity in selected subtypes. In this study, we examine the role of TKIs and PD-1 based therapy in in vitro cocultures of sarcoma.MethodsThe human osteosarcoma (SaOS-2) and synovial sarcoma (SYO-1) cell lines were treated with sunitinib. After cell death and proliferation assessment, expression of PD-L1 was analyzed by flow cytometry. Sunitinib-treated sarcoma cells were cocultured with dendritic cells (DCs), and the phenotype of mature DCs was determined by flow cytometry. Mature DCs were cultured with autologous T cells. PD-1 expression on T cells, their proliferation, T regulatory cell (Tregs) induction and IFN-γ production, before and after nivolumab exposure, were analyzed.ResultsAlong with its anti-proliferative and direct pro-apoptotic effect on sarcoma cell lines, sunitinib prompted PD-L1 upregulation on sarcoma cells. Interestingly, sunitinib-treated sarcoma cells drive DCs to full maturation and increase their capacity to induce sarcoma-reactive T cells to produce IFN-γ. Conversely, no effect on T cell proliferation and T cell subpopulation composition was observed. Moreover, both bone and synovial sarcoma cell lines induced Tregs through DCs but sunitinib treatment completely abrogated Treg induction. Finally, sarcoma cell lines induced PD-1 upregulation on both effector T cells and Tregs when loaded into DCs, providing a rationale for using PD-1 blockade. Indeed, PD-1 blockade by nivolumab synergized with sunitinib in inducing IFN-γ-producing effector T cells.ConclusionsTaken together, our in vitro data indicate that the treatment of sarcoma cells with sunitinib can exert significant changes on immune cell subsets toward immune activation, leading to DC-based cross-priming of IFN-γ-producing effector T cells and reduced Treg induction. PD-1 blockade with nivolumab has a synergistic effect with sunitinib, supporting the use of TKI and anti-PD-1 approach in sarcomas, and perhaps in other cancers. DC-targeted drugs, including toll-like receptor 3 inhibitors and CD47 inhibitors, are under development and our preclinical model might help to better design their clinical application.

scholarly journals Generation of Human CD8 T Regulatory Cells by CD40 Ligand–activated Plasmacytoid Dendritic Cells

2002 ◽  
Vol 195 (6) ◽  
pp. 695-704 ◽  
Author(s):  
Michel Gilliet ◽  
Yong-Jun Liu
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Cd8 T Cells ◽  
Transforming Growth Factor ◽  
Cd8 T Cell ◽  
Cd40 Ligand ◽  
Plasmacytoid Dendritic Cells ◽  
Target Cells ◽  
Ifn Γ

Although CD8 T cell–mediated immunosuppression has been a well-known phenomenon during the last three decades, the nature of primary CD8 T suppressor cells and the mechanism underlying their generation remain enigmatic. We demonstrated that naive CD8 T cells primed with allogeneic CD40 ligand–activated plasmacytoid dendritic cells (DC)2 differentiated into CD8 T cells that displayed poor secondary proliferative and cytolytic responses. By contrast, naive CD8 T cells primed with allogeneic CD40 ligand–activated monocyte-derived DCs (DC1) differentiated into CD8 T cells, which proliferated to secondary stimulation and killed allogeneic target cells. Unlike DC1-primed CD8 T cells that produced large amounts of interferon (IFN)-γ upon restimulation, DC2-primed CD8 T cells produced significant amounts of interleukin (IL)-10, low IFN-γ, and no IL-4, IL-5, nor transforming growth factor (TGF)-β. The addition of anti–IL-10–neutralizing monoclonal antibodies during DC2 and CD8 T cell coculture, completely blocked the generation of IL-10–producing anergic CD8 T cells. IL-10–producing CD8 T cells strongly inhibit the allospecific proliferation of naive CD8 T cells to monocytes, and mature and immature DCs. This inhibition was mediated by IL-10, but not by TGF-β. IL-10–producing CD8 T cells could inhibit the bystander proliferation of naive CD8 T cells, provided that they were restimulated nearby to produce IL-10. IL-10–producing CD8 T cells could not inhibit the proliferation of DC1-preactivated effector T cells. This study demonstrates that IL-10–producing CD8 T cells are regulatory T cells, which provides a cellular basis for the phenomenon of CD8 T cell–mediated immunosuppression and suggests a role for plasmacytoid DC2 in immunological tolerance.

scholarly journals Polarization of Allogeneic T-Cell Responses by Influenza Virus-Infected Dendritic Cells

2000 ◽  
Vol 74 (17) ◽  
pp. 7738-7744 ◽  
Author(s):  
Sangkon Oh ◽  
Maryna C. Eichelberger
Keyword(s):  
Immune Response ◽  
T Cells ◽  
Dendritic Cells ◽  
Influenza Virus ◽  
T Cell ◽  
Interleukin 2 ◽  
Dependent Manner ◽  
Ifn Γ ◽  
High Doses ◽  
Type Response

ABSTRACT The developing immune response in the lymph nodes of mice infected with influenza virus has both Th1- and Th2-type characteristics. Modulation of the interactions between antigen-presenting cells and T cells is one mechanism that may alter the quality of the immune response. We have previously shown that the ability of dendritic cells (DC) to stimulate the proliferation of alloreactive T cells is changed by influenza virus due to viral neuraminidase (NA) activity. Here we show that DC infected with influenza virus A/PR/8/34 (PR8) stimulate T cells to produce different types of cytokines in a dose-dependent manner. Optimal amounts of the Th1-type cytokines interleukin-2 (IL-2) and gamma interferon (IFN-γ) were produced from T cells stimulated by DC infected with low doses of PR8, while the Th2-type cytokines IL-4 and IL-10 were produced only in response to DC infected with high doses of PR8. IL-2 and IFN-γ levels corresponded with T-cell proliferation and were dependent on the activity of viral NA on the DC surface. In contrast, IL-4 secretion required the treatment of T cells with NA. Since viral particles were released only from DC that are infected with high doses of PR8, our results suggest that viral NA on newly formed virus particles desialylates T-cell surface molecules to facilitate a Th2-type response. These results suggest that the activity of NA may contribute to the mixed Th-type response observed during influenza virus infection.

Interleukin-12 Gene Expression into Acute Myeloid Leukemia-Derived Dendritic Cells Overcomes T-Cell Functional Impairment Induced by Leukemic Microenvironment.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1816-1816
Author(s):  
Antonio Curti ◽  
Simona Pandolfi ◽  
Michela Aluigi ◽  
Alessandro Isidori ◽  
Isabella Alessandrini ◽  
...  
Keyword(s):  
Gene Expression ◽  
T Cells ◽  
Acute Myeloid Leukemia ◽  
Dendritic Cells ◽  
T Cell ◽  
Myeloid Leukemia ◽  
Interleukin 12 ◽  
Functional Features ◽  
Ifn Γ ◽  
Acute Myeloid

Abstract Acute myeloid leukemia (AML) cells are poorly immunogenic and release soluble factors inhibiting T-cell function. AML-derived dendritic cells (AML-DCs) have better antigen presentation capacity than leukemic blasts but share with AML cells some immunosuppressive features. In this study, we show that AML-DCs generated from CD14− AML samples (which represent 80% of total AML patients) are defective in IL-12 production. We, then, transfected CD14−-derived AML-DCs with IL-12 gene through the novel non-viral method nucleofection. IL-12 gene-nucleofected AML-DCs produce significant amount of IL-12 while maintain leukemia-specific karyotype, DC-like phenotype and function. In presence of the supernatant from the human leukemic cell line K562, allogeneic T-cell proliferation and interferon (IFN)-γ production induced by mock-transduced AML-DCs are significantly reduced. This effect is mainly directed on T cells, since AML-DC phenotype and cytokine production are not affected by leukemic supernatant. However, when stimulated by IL-12-producing AML-DCs, T cells produce higher concentrations of IFN-γ, thus maintaining a Th1 cytokine profile. In conclusion, IL-12 gene can be expressed into AML-DCs defective in endogenous IL-12 production by using a novel non-viral method which does not modify their phenotypical, cytogenetic and functional features. IL-12 gene expression into AML-DC counteracts the inhibitory effect of leukemic microenvironment on T lymphocytes

Regulatory T Cells Expanded by Autologous Mature Human Dendritic Cells Expressing Indoleamine 2,3-Dioxygenase Are Potent Suppressors of T Cell Proliferation.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1553-1553
Author(s):  
Davi d J. Chung ◽  
Marco Rossi ◽  
Emanuela Romano ◽  
Jennifer Pressley ◽  
Christophe Antczak ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Regulatory T Cells ◽  
De Novo ◽  
T Cell Proliferation ◽  
Indoleamine 2,3 Dioxygenase ◽  
Naturally Occurring ◽  
Dose Dependent

Abstract Best characterized as initiators of immunity, dendritic cells (DCs) also play an integral role in immune modulation. Immature DCs, for example, process self-antigens to induce and maintain tolerance. The immunoregulatory effects of DCs, however, are not limited to immature subtypes. Immunogenic mature DCs can also induce T regs to curb immune responses. We have found that human monocyte-derived DCs (moDCs) upregulate the immunomodulatory enzyme indoleamine 2,3-dioxygenase (IDO) with maturation and expand functionally active, naturally occurring as well as inducible regulatory T cells (T regs) in an IDO-dependent manner. Priming of resting bulk T cells with autologous, IDO-expressing, mature moDCs in the absence of exogenous cytokines results in up to 10-fold expansion of CD4+CD25hiFoxp3+CD127neg T cells that mediate significant dose-dependent suppression of both allogeneic and autologous T cells stimulated de novo by DCs. The expansion of T regs by IDO-expressing moDCs involves cell-to-cell contact, CD80/CD86 ligation, and IL-2. Autologous priming in the presence of a competitive inhibitor of IDO, 1-methyl-tryptophan, diminishes T reg expansion. Candidate T regs were further characterized after cytofluorographic sorting primed bulk T cells into CD4+CD25hi, CD4+CD25int, and CD4+CD25neg subpopulations. Post-sort analysis showed that >60% of the CD4+CD25hi cells coexpressed Foxp3, which was not present in the CD4+CD25neg cells. CD4+CD25hi T regs exerted dose-dependent inhibition of DC-stimulated allogeneic T cell proliferation, with >90% inhibition at a suppressor to responder T cell ratio of 1:1 and ~50% inhibition at a ratio of 1:25. CD4+CD25int cells produced intermediate suppression depending on dose, and CD4+CD25neg cells were not inhibitory. CD4+CD25hi T regs mediated similar suppression of autologous T cell responses to stimulation de novo by DCs. CD4+CD25hi T regs also inhibited the generation of cytotoxic T lymphocytes (CTLs) specific for the Wilms’ tumor gene product (WT-1). The addition of CD4+CD25hi T regs to CTL-priming cultures resulted in a >80% decrease in specific target cell lysis of a WT-1-expressing cell line. Separate studies showed that T reg-mediated suppression is contact dependent and also requires TGF-beta, suggesting inhibition by naturally occurring and inducible T regs, respectively. Depletion of CD4+CD25hi T cells from bulk T cells by negative immunoselection with anti-CD25 magnetic beads at the outset of autologous priming significantly blunts T reg expansion, indicating a requirement for pre-existing T regs in the bulk T cell population. T reg expansion also occurs in priming cultures using cytofluorographically-sorted CD4+CD25neg T cells, indicating de novo generation of T regs from CD4+CD25neg precursors. In summary, our results demonstrate a mechanism by which mature, IDO-expressing, human moDCs expand autologous, naturally occurring as well as inducible T regs that functionally suppress the proliferation of both autologous and allogeneic T cells. Inhibition of this counter-regulatory pathway should result in more sustained benefit from active DC-based immunotherapy.

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