IL-2 immunotoxin therapy modulates tumor-associated regulatory T cells and leads to lasting immune-mediated rejection of breast cancers in neu-transgenic mice

Studies in cancer patients have suggested that breast tumors recruit regulatory T cells (Tregs) into the tumor microenvironment. The extent to which local Tregs suppress antitumor immunity in breast cancer is unknown. We questioned whether inhibiting systemic Tregs with an IL-2 immunotoxin in a model of neu-mediated breast cancer, the neu-transgenic mouse, could impact disease progression and survival. As in human breast cancer, cancers that develop in these mice attract Tregs into the tumor microenvironment to levels of approximately 10-25% of the total CD4+ T cells. To examine the role of Tregs in blocking immune-mediated rejection of tumor, we depleted CD4+CD25+ T cells with an IL-2 immunotoxin. The treatment depleted Tregs without concomitant lymphopenia and markedly inhibited tumor growth. Depletion of Tregs resulted in a persistent antitumor response that was maintained over a month after the last treatment. The clinical response was immune-mediated because adoptive transfer of Tregs led to a complete abrogation of the therapeutic effects of immunotoxin treatment. Further, Treg down-modulation was accompanied by increased Ag-specific immunity against the neu protein, a self Ag. These results suggest that Tregs play a major role in preventing an effective endogenous immune response against breast cancer and that depletion of Tregs, without any additional immunotherapy, may mediate a significant antitumor response.     

Regulatory T cells prevent CD8 T cell maturation by inhibiting CD4 Th cells at tumor sites

Natural regulatory T cells (Tregs) are present in high frequencies among tumor-infiltrating lymphocytes and in draining lymph nodes, supposedly facilitating tumor development. To investigate their role in controlling local immune responses, we analyzed intratumoral T cell accumulation and function in the presence or absence of Tregs. Tumors that grew in normal BALB/c mice injected with the 4T1 tumor cell line were highly infiltrated by Tregs, CD4 and CD8 cells, all having unique characteristics. Most infiltrating Tregs expressed low levels of CD25Rs and Foxp3. They did not proliferate even in the presence of IL-2 but maintained a strong suppressor activity. CD4 T cells were profoundly anergic and CD8 T cell proliferation and cytotoxicity were severely impaired. Depletion of Tregs modified the characteristics of tumor infiltrates. Tumors were initially invaded by activated CD4(+)CD25(-) T cells, which produced IL-2 and IFN-gamma. This was followed by the recruitment of highly cytotoxic CD8(+) T cells at tumor sites leading to tumor rejection. The beneficial effect of Treg depletion in tumor regression was abrogated when CD4 helper cells were also depleted. These findings indicate that the massive infiltration of tumors by Tregs prevents the development of a successful helper response. The Tregs in our model prevent Th cell activation and subsequent development of efficient CD8 T cell activity required for the control of tumor growth.     

Tumor-secreted miR-214 induces regulatory T cells: a major link between immune evasion and tumor growth

An increased population of CD4⁺CD25^highFoxp3⁺ regulatory T cells (Tregs) in the tumor-associated microenvironment plays an important role in cancer immune evasion. However, the underlying mechanism remains unclear. Here we observed an increased secretion of miR-214 in various types of human cancers and mouse tumor models. Tumor-secreted miR-214 was sufficiently delivered into recipient T cells by microvesicles (MVs). In targeted mouse peripheral CD4⁺ T cells, tumor-derived miR-214 efficiently downregulated phosphatase and tensin homolog (PTEN) and promoted Treg expansion. The miR-214-induced Tregs secreted higher levels of IL-10 and promoted tumor growth in nude mice. Furthermore, in vivo studies indicated that Treg expansion mediated by cancer cell-secreted miR-214 resulted in enhanced immune suppression and tumor implantation/growth in mice. The MV delivery of anti-miR-214 antisense oligonucleotides (ASOs) into mice implanted with tumors blocked Treg expansion and tumor growth. Our study reveals a novel mechanism through which cancer cell actively manipulates immune response via promoting Treg expansion.     

Depletion of regulatory T cells in HIV infection is associated with immune activation

Immune activation during chronic HIV infection is a strong clinical predictor of death and may mediate CD4(+) T cell depletion. Regulatory T cells (Tregs) are CD4(+)CD25(bright)CD62L(high) cells that actively down-regulate immune responses. We asked whether loss of Tregs during HIV infection mediates immune activation in a cross-sectional study of 81 HIV-positive Ugandan volunteers. We found that Treg number is strongly correlated with both CD4(+) and CD8(+) T cell activation. In multivariate modeling, this relationship between Treg depletion and CD4(+) T cell activation was stronger than any other clinical factor examined, including viral load and absolute CD4 count. Tregs appear to decline at different rates compared with other CD4(+) T cells, resulting in an increased regulator to helper ratio in many patients with advanced disease. We hypothesize that this skewing may contribute to T cell effector dysfunction. Our findings suggest Tregs are a major contributor to the immune activation observed during chronic HIV infection.     

CTLA4 expression is an indicator and regulator of steady-state CD4+ FoxP3+ T cell homeostasis

The presence of FoxP3(+) regulatory T cells (Tregs) is necessary for control of deleterious immune responses in the steady state; however, mechanisms for maintaining the frequency and quality of endogenous Tregs are not well defined. In this study, we used in vivo modulators of the CD28 and CTLA4 pathways administered to intact mice to reveal mechanisms controlling the homeostasis and phenotype of endogenous Tregs. We demonstrate that expression of the negative costimulatory regulator CTLA4 on FoxP3(+) Tregs in vivo is a direct consequence of their rapid, perpetual homeostasis. Up-regulation of CTLA4 expression occurs only on FoxP3(+) Tregs undergoing extensive proliferation and can be abrogated by inhibiting the CD28 pathway, coinciding with a reduction in FoxP3(+) Treg proliferation and frequency. We further demonstrate that CTLA4 negatively regulates steady-state Treg homeostasis, given that inhibiting CTLA4 signaling with an anti-CTLA4 blocking Ab greatly enhances Treg proliferation and overall Treg frequency. Our findings provide new insight into the origin and role of CTLA4 expression on natural FoxP3(+) Tregs and reveal opposing effects of costimulation modulators on the steady-state level and quality of Tregs, with implications regarding their effects on endogenous Tregs in patients receiving immunotherapy.     

Myeloid-derived suppressor cells prevent type 1 diabetes in murine models

Effective immunotherapy for type 1 diabetes (T1D) relies on active induction of peripheral tolerance. Myeloid-derived suppressor cells (MDSCs) play a critical role in suppressing immune responses in various pathologic settings via multiple mechanisms, including expansion of regulatory T cells (Tregs). In this study, we investigated whether MDSCs could act as APCs to induce expansion of Ag-specific Tregs, suppress T cell proliferation, and prevent autoimmune T1D development. We found that MDSC-mediated expansion of Tregs and T cell suppression required MHC-dependent Ag presentation. A murine T1D model was established in INS-HA/RAG(-/-) mice in which animals received CD4-HA-TCR transgenic T cells via adoptive transfer. We found a significant reduction in the incidence of diabetes in recipients receiving MDSC plus HA, but not OVA peptide, leading to 75% diabetes-free mice among the treated animals. To test further whether MDSCs could prevent diabetes onset in NOD mice, nondiabetic NOD/SCID mice were injected with inflammatory T cells from diabetic NOD mice. MDSCs significantly prevented diabetes onset, and 60% of MDSC-treated mice remained diabetes free. The pancreata of treated mice showed significantly lower levels of lymphocyte infiltration in islet and less insulitis compared with that of the control groups. The protective effects of MDSCs might be mediated by inducing anergy in autoreactive T cells and the development of CD4(+)CD25(+)Foxp3(+) Tregs. Thist study demonstrates a remarkable capacity of transferred MDSCs to downregulate Ag-specific autoimmune responses and prevent diabetes onset, suggesting that MDSCs possess great potential as a novel cell-based tolerogenic therapy in the control of T1D and other autoimmune diseases.     

Identification and in vitro expansion of functional antigen-specific CD25+ FoxP3+ regulatory T cells in hepatitis C virus infection

CD4(+)CD25(+) regulatory T cells (CD25(+) Tregs) play a key role in immune regulation. Since hepatitis C virus (HCV) persists with increased circulating CD4(+)CD25(+) T cells and virus-specific effector T-cell dysfunction, we asked if CD4(+)CD25(+) T cells in HCV-infected individuals are similar to natural Tregs in uninfected individuals and if they include HCV-specific Tregs using the specific Treg marker FoxP3 at the single-cell level. We report that HCV-infected patients display increased circulating FoxP3(+) Tregs that are phenotypically and functionally indistinguishable from FoxP3(+) Tregs in uninfected subjects. Furthermore, HCV-specific FoxP3(+) Tregs were detected in HCV-seropositive persons with antigen-specific expansion, major histocompatibility complex class II/peptide tetramer binding affinity, and preferential suppression of HCV-specific CD8 T cells. Transforming growth factor beta contributed to antigen-specific Treg expansion in vitro, suggesting that it may contribute to antigen-specific Treg expansion in vivo. Interestingly, FoxP3 expression was also detected in influenza virus-specific CD4 T cells. In conclusion, functionally active and virus-specific FoxP3(+) Tregs are induced in HCV infection, thus providing targeted immune regulation in vivo. Detection of FoxP3 expression in non-HCV-specific CD4 T cells suggests that immune regulation through antigen-specific Treg induction extends beyond HCV.     

Regulatory T cells selectively preserve immune privilege of self-antigens during viral central nervous system infection

Regulatory T cells (Tregs) are important for the attenuation of immune reactions. During viral CNS infections, however, an indiscriminate maintenance of CNS immune privilege through Treg-mediated negative regulation could prevent autoimmune sequelae but impair the control of viral replication. We analyzed in this study the impact of Tregs on the development of acute viral encephalomyelitis, T cell-mediated antiviral protection, and prevention of CNS autoimmunity following intranasal infection with the gliatropic mouse hepatitis virus strain A59. To assess the contribution of Tregs in vivo, we specifically depleted CD4(+)Foxp3(+) T cells in a diphtheria toxin-dependent manner. We found that depletion of Tregs had no impact on viral distribution and clearance and did not significantly alter virus-specific CD4(+) and CD8(+) T cell responses. However, Treg depletion led to a more severe CNS inflammation associated with neuronal damage. Dissection of the underlying immunopathological mechanisms revealed the elaborate Treg-dependent regulation of self-reactive CD4(+) T cell proliferation within the CNS-draining lymph node and downtuning of CXCR3 expression on T cells. Taken together, these results suggest that Tregs preserve CNS immune privilege through selective control of CNS-specific Th cells while keeping protective antiviral immunity fully operative.     

Regulatory T cells in CNS injury: the simple, the complex and the confused

Regulatory CD4(+)CD25(+)Foxp3(+) T cells (Tregs) have been the focus of significant attention for their role in controlling immune responses. Although knowledge of Treg biology has burgeoned, wide gaps remain in our understanding of Treg function under both normal and pathological conditions. Pioneering studies demonstrated roles for Tregs in cancer and autoimmune diseases, including experimental autoimmune encephalitis, and this knowledge is often applied to other pathologies including neurodegenerative conditions. However, differences between immunity in neurodegeneration and in malignancy or autoimmunity are often neglected. Thus, Treg manipulations in central nervous system (CNS) neurodegenerative conditions often yield unexpected outcomes. In this piece, we explore how the immunology of neurodegeneration differs from that of cancer and autoimmunity and how these differences create confusion about the role of Tregs in neurodegenerative conditions.     

Endogenous regulatory T cells adhere in inflamed dermal vessels via ICAM-1: association with regulation of effector leukocyte adhesion

Regulatory T cells (Tregs) must express appropriate skin-homing adhesion molecules to exert suppressive effects on dermal inflammation. However, the mechanisms whereby they control local inflammation remain unclear. In this study we used confocal intravital microscopy in wild-type and Foxp3-GFP mice to examine adhesion of effector T cells and Tregs in dermal venules. These experiments examined a two-challenge model of contact sensitivity (CS) in which Treg abundance in the skin progressively increases during the course of the response. Adhesion of CD4(+) T cells increased during CS, peaking 8-24 h after an initial hapten challenge, and within 4 h of a second challenge. At these time points, 40% of adherent CD4(+) T cells were Foxp3(+) Tregs. CD4(+) T cell adhesion was highly dependent on ICAM-1, and consistent with this finding, anti-ICAM-1 prevented Treg adhesion. Skin TGF-β levels were elevated in skin during both challenges, in parallel with Treg adhesion. In the two-challenge CS model, inhibition of ICAM-1 eliminated Treg adhesion, an effect associated with a significant increase in neutrophil adhesion. Similarly, total CD4(+) T cell depletion caused an increase in adhesion of CD8(+) T cells. Because Treg adhesion was restricted by both of these treatments, these experiments suggest that adherent Tregs can control adhesion of proinflammatory leukocytes in vivo. Moreover, the critical role of ICAM-1 in Treg adhesion provides a potential explanation for the exacerbation of inflammation reported in some studies of ICAM-1-deficient mice.     

Regulatory T-cell depletion synergizes with gp96-mediated cellular responses and antitumor activity

Despite its potent immunostimulatory properties, vaccination with autologous tumor-derived gp96 has relatively modest antitumor effect in a range of clinical trials. Based on our previous study showing a gp96-mediated immune balance between CTL and Tregs, here we investigated possible synergy between gp96 vaccine and systemic Treg depletion on induction of antitumor T-cell immunity and the mechanisms accounting for synergistic efficacy. In gp96-peptide complex immunized BALB/c mice, anti-CD25 mAb treatment significantly increased IFN-γ-producing CD8(+) and CD4(+) T cells by about 1-2-fold in spleen and 40-50% in lymph node. A significantly higher number of peptide-specific CTL were observed under anti-CD25 mAb treatment compared with no treatment. Moreover, Treg depletion synergistically improved the anticancer activity of tumor-derived gp96 vaccine in the poorly immunogenic and highly tumorigenic B16 melanoma model in C57BL/6?J mice. While gp96 immunization alone led to the modest enhancement of CTL activities in spleen, the combination with Treg depletion dramatically increased tumor-specific CTL responses. In addition, the combination resulted in a significant increase of CD8(+) T-cell infiltration in tumor, which correlated with an enhanced inhibition of tumor growth. Our results provide evidence that targeting Tregs may provide a more efficient strategy to potentiate gp96-mediated T-cell responses and enhance the antitumor efficiency of gp96-based therapeutic vaccine.     

Strongyloides ratti infection induces expansion of Foxp3+ regulatory T cells that interfere with immune response and parasite clearance in BALB/c mice

To escape expulsion by their host's immune system, pathogenic nematodes exploit regulatory pathways that are intrinsic parts of the mammalian immune system, such as regulatory T cells (Tregs). Using depletion of Treg mice, we showed that Foxp3(+) Treg numbers increased rapidly during infection with the nematode Strongyloides ratti. Transient depletion of Tregs during the first days of infection led to dramatically reduced worm burden and larval output, without aggravation of immune pathology. The transient absence of Tregs during primary infection did not interfere with the generation of protective memory. Depletion of Tregs at later time points of infection (i.e., day 4) did not improve resistance, suggesting that Tregs exert their counterregulatory function during the priming of S. ratti-specific immune responses. Improved resistance upon early Treg depletion was accompanied by accelerated and prolonged mast cell activation and increased production of types 1 and 2 cytokines. In contrast, the blockade of the regulatory receptor CTLA-4 specifically increased nematode-specific type 2 cytokine production. Despite this improved immune response, resistance to the infection was only marginally improved. Taken together, we provide evidence that Treg expansion during S. ratti infection suppresses the protective immune response to this pathogenic nematode and, thus, represents a mechanism of immune evasion.     

Surgical trauma-induced CCL18 promotes recruitment of regulatory T cells and colon cancer progression

Background: Surgical stress has been suggested to facilitate colon cancer growth and metastasis. However, the precise mechanisms by which surgical trauma promotes colon cancer progression remain poorly understood. Methods: To unravel the mechanisms underlying surgery-induced colon cancer progression, a syngenic transplantation tumor model was established with CT26 cells, and the effect of laparotomy on tumor progression was investigated. Especially, the expression of several chemokines was assessed, and their roles in recruiting CD4+ CD25+ regulatory T cells (Tregs) after surgery were analyzed. Results: Tregs population was significantly increased in the tumor tissue and peripheral blood of tumor-bearing mice after laparotomy. C-C motif chemokine ligand 18 (CCL18) expression was significantly upregulated after laparotomy in tumor tissue and the peritoneal cavity of tumor-bearing mice, and it was positively correlated with the recruitment of Tregs. Functionally, CCL18 knockdown significantly reduces tumor growth and angiogenesis compared with control. Through analysis of Tregs, we found an upregulated proportion of Tregs in tumor tissue, peritoneal cavity, and peripheral blood after laparotomy, but this enhancement was blocked after CCL18 knockdown. In patients with colon cancer, a higher Tregs proportion is positively correlated to more advanced clinical TNM stages and shorter survival. Furthermore, a positive correlation was found between the serum CCL18 level and the Treg proportion in clinical samples. Conclusion: Surgical trauma contributes to colon cancer progression by increasing CCL18 expression and hence promotes Treg recruitment, which leads to an immunosuppressive environment.     

CD4+CD25+ T regulatory cells dominate multiple immune evasion mechanisms in early but not late phases of tumor development in a B cell lymphoma model

Tumors use a complex set of direct and indirect mechanisms to evade the immune system. Naturally arising CD4(+)CD25(+)FoxP3(+) T regulatory (Treg) cells have been implicated recently in tumor immune escape mechanism, but the relative contribution of these cells to overall tumor progression compared with other immune evasion mechanisms remains to be elucidated. Using the A20 B cell lymphoma as a transplantable tumor model, we demonstrate that this tumor employs multiple direct (expression of immunoinhibitory molecule PD-L1, IDO, and IL-10, and lack of expression of CD80 costimulatory molecule) and indirect (down-regulation of APC function and induction of Treg cells) immune evasion mechanisms. Importantly, Treg cells served as the dominant immune escape mechanism early in tumor progression because the physical elimination of these cells before tumor challenge resulted in tumor-free survival in 70% of mice, whereas their depletion in animals with established tumors had no therapeutic effect. Therefore, our data suggest that Treg cells may serve as an important therapeutic target for patients with early stages of cancer and that more vigorous combinatorial approaches simultaneously targeting multiple immune evasion as well as immunosurveillance mechanisms for the generation of a productive immune response against tumor may be required for effective immunotherapy in patients with advanced disease.     

Treg depletion inhibits efficacy of cancer immunotherapy: implications for clinical trials

Background

Regulatory T lymphocytes (Treg) infiltrate human glioblastoma (GBM); are involved in tumor progression and correlate with tumor grade. Transient elimination of Tregs using CD25 depleting antibodies (PC61) has been found to mediate GBM regression in preclinical models of brain tumors. Clinical trials that combine Treg depletion with tumor vaccination are underway to determine whether transient Treg depletion can enhance anti-tumor immune responses and improve long term survival in cancer patients.

Findings

Using a syngeneic intracrabial glioblastoma (GBM) mouse model we show that systemic depletion of Tregs 15 days after tumor implantation using PC61 resulted in a decrease in Tregs present in tumors, draining lymph nodes and spleen and improved long-term survival (50% of mice survived >150 days). No improvement in survival was observed when Tregs were depleted 24 days after tumor implantation, suggesting that tumor burden is an important factor for determining efficacy of Treg depletion in clinical trials. In a T cell dependent model of brain tumor regression elicited by intratumoral delivery of adenoviral vectors (Ad) expressing Fms-like Tyrosine Kinase 3 ligand (Flt3L) and Herpes Simplex Type 1-Thymidine Kinase (TK) with ganciclovir (GCV), we demonstrate that administration of PC61 24 days after tumor implantation (7 days after treatment) inhibited T cell dependent tumor regression and long term survival. Further, depletion with PC61 completely inhibited clonal expansion of tumor antigen-specific T lymphocytes in response to the treatment.

Conclusions

Our data demonstrate for the first time, that although Treg depletion inhibits the progression/eliminates GBM tumors, its efficacy is dependent on tumor burden. We conclude that this approach will be useful in a setting of minimal residual disease. Further, we also demonstrate that Treg depletion, using PC61 in combination with immunotherapy, inhibits clonal expansion of tumor antigen-specific T cells, suggesting that new, more specific targets to block Tregs will be necessary when used in combination with therapies that activate anti-tumor immunity.     

T regulatory cells contribute to the attenuated primary CD8+ and CD4+ T cell responses to herpes simplex virus type 2 in neonatal mice

The first weeks of life are characterized by immune tolerance and increased susceptibility to intracellular pathogens. The neonatal adaptive response to HSV is attenuated compared with adult control models in humans and mice. T Regulatory cells (Tregs) control autoimmunity and excessive immune responses to infection. We therefore compared Treg responses in the draining lymph nodes (LN) of HSV-infected neonatal and adult C57BL/6 mice with the effect of Treg depletion/inactivation by anti-CD25 (PC61) treatment before infection on Ag-specific T cell effector responses at this site. There was a small, but significant increase in the frequency of CD4(+)Foxp3(+) Tregs at day 3 postinfection (p.i.) in the LN of neonatal and adult mice, compared with age-matched mock-infected controls. Depletion of Tregs before HSV infection significantly enhanced HSV-specific CD8(+) T cell cytotoxicity in vivo, cell number, activation, and granzyme B expression 4 days p.i. only in neonatal mice, and significantly enhanced CD8(+) and CD4(+) T cell IFN-gamma responses in both infected adults and neonates. Treg depletion also reduced the titer of infectious virus in the draining LN and nervous system of infected neonates on days 2 and 3 p.i. Treg suppression of the neonatal CTL response p.i. with HSV was associated with increased expression of TGF-beta in the draining LN at day 4 p.i. compared with uninfected neonates, but IL-10 was increased in infected adults alone. These experiments support the notion that the newborn primary T cell effector responses to HSV are suppressed by Tregs.     

Comprehensive analysis of frequency and phenotype of T regulatory cells in HIV infection: CD39 expression of FoxP3+ T regulatory cells correlates with progressive disease

There are conflicting data about the frequency and role of regulatory T cells (Tregs) during the course of HIV infection. Peripheral blood of a large cohort of HIV-infected patients (n = 131) at different stages of disease, including 15 long-term nonprogressors and 21 elite controllers, was analyzed to determine the frequency and phenotype of Tregs, defined as CD4(+), CD25(high), CD127(low), FoxP3(high) cells. A significantly increased relative frequency of Tregs within the CD4(+) compartment of HIV(+) patients compared to that of healthy controls (P < 0.0001) was observed. Additionally, the relative frequency of Tregs directly correlated with HIV viral load and inversely with CD4(+) counts. However, the absolute Treg number was reduced in HIV-infected patients versus healthy controls (P < 0.0001), with the exception of elite controllers (P > 0.05). The loss of absolute Treg numbers coincided with rising markers of immune activation (P < 0.0006). The initiation of antiviral therapy significantly increased absolute Treg numbers (P < 0.0031). We find that the expression of CD39, a newly defined ectonucleotidase with immunomodulatory functions on Tregs, correlated with progressive HIV disease, HIV viral load, and immune activation. Of note, when tested in peripheral blood mononuclear cells of healthy volunteers, the in vitro capacity to suppress T-cell proliferation was limited to CD4(+), CD25(high), CD39(+) T cells. Interestingly, Tregs of elite controllers exhibited not only the highest expression of CCR5, CTLA-4, and ICOS but also the lowest level of CD39. The data presented here reconcile the seemingly contradictory results of previous studies looking at Tregs in HIV and highlight the complexity of Treg-mediated immunoregulation during human viral infections.     

Differential effects of denileukin diftitox IL-2 immunotoxin on NK and regulatory T cells in nonhuman primates

Denileukin diftitox (DD), a fusion protein comprising IL-2 and diphtheria toxin, was initially expected to enhance antitumor immunity by selectively eliminating regulatory T cells (Tregs) displaying the high-affinity IL-2R (α-β-γ trimers). Although DD was shown to deplete some Tregs in primates, its effects on NK cells (CD16(+)CD8(+)NKG2A(+)CD3(-)), which constitutively express the intermediate-affinity IL-2R (β-γ dimers) and play a critical role in antitumor immunity, are still unknown. To address this question, cynomolgus monkeys were injected i.v. with two doses of DD (8 or 18 μg/kg). This treatment resulted in a rapid, but short-term, reduction in detectable peripheral blood resting Tregs (CD4(+)CD45RA(+)Foxp3(+)) and a transient increase in the number of activated Tregs (CD4(+)CD45RA(-)Foxp3(high)), followed by their partial depletion (50-60%). In contrast, all NK cells were deleted immediately and durably after DD administration. This difference was not due to a higher binding or internalization of DD by NK cells compared with Tregs. Coadministration of DD with IL-15, which binds to IL-2Rβ-γ, abrogated DD-induced NK cell deletion in vitro and in vivo, whereas it did not affect Treg elimination. Taken together, these results show that DD exerts a potent cytotoxic effect on NK cells, a phenomenon that might impair its antitumoral properties. However, coadministration of IL-15 with DD could alleviate this problem by selectively protecting potentially oncolytic NK cells, while allowing the depletion of immunosuppressive Tregs in cancer patients.     

Aminoacyl-tRNA synthetase-interacting multifunctional protein 1 suppresses tumor growth in breast cancer-bearing mice by negatively regulating myeloid-derived suppressor cell functions

Myeloid-derived suppressor cells (MDSCs) are one of the most important cell types that contribute to negative regulation of immune responses in the tumor microenvironment. Recently, aminoacyl-tRNA synthetase-interacting multifunctional protein 1 (AIMP1), a novel pleiotropic cytokine, was identified as an antitumor protein that inhibits angiogenesis and induces antitumor responses. However, the effect of AIMP1 on MDSCs in the tumor environment remains unclear. In the present study, we demonstrated that AIMP1 significantly inhibited tumor growth in 4T1 breast cancer-bearing mice and reduced MDSCs population of tumor sites and spleens of tumor-bearing mice. AIMP1 reduced expansion of MDSCs from bone marrow-derived cells in the tumor-conditioned media. AIMP1 also negatively regulated suppressive activities of MDSCs by inhibiting IL-6 and NO production, and Arg-1 expression. Furthermore, treatment of breast cancer-bearing mice with AIMP1 decreased the capacity of MDSCs to suppress T cell proliferation and Treg cell induction. Western blot and inhibition experiments showed that downregulation of MDSCs functions by AIMP1 may result from attenuated activation of STATs, Akt, and ERK. These findings indicate that AIMP1 plays an essential role in negative regulation of suppressive functions of MDSCs. Therefore, it has a significant potential as a therapeutic agent for cancer treatment.