Immune modulation of CD4+CD25+ regulatory T cells by zoledronic acid

Mechanism exploration of Zoledronic acid combined with PD-1 in the treatment of hepatocellular carcinoma

How to increase the response of immune checkpoint inhibitors (ICIs) is a challenge. In clinical, we found that Zoledronic acid (ZA) may increase the anti-tumor effect of immunotherapy for hepatocellular carcinoma (HCC). To explore the underlying mechanism, we established a mouse model of HCC by subcutaneously injecting Hepa1-6 cell line. The result showed that the tumor volume in the ZA plus anti-PD-1 monocloning antibody (anti-PD-1 mAb) treatment groups was significantly smaller than that of control group, and the onset time of tumor inhibition was even shorter than that of the anti-PD-1 mAb group. Using flow cytometry (FC) to detect the proportion of major immune cell subsets in tumor tissues of each group of mice, we found that the synergistic anti-tumor effect of ZA and anti-PD-1 mAb may be related to ZA-induced polarization of macrophages toward the M1 phenotype. Next, we performed bulk RNA sequencing on tumor samples from different groups to obtain differentially expressed genes (DEGs), which were then input DEGs into pathway enrichment analysis. Data indicated that ZA participated in the M1-type polarization via ferroptosis-related pathways. Our results revealed how ZA involves in the anti-tumor effect of PD-1 monoclonal antibody and provided a potential therapeutic candidate for patients with HCC.

Association between bisphosphonate use and COVID-19 related outcomes

Background

Although there are several efficacious vaccines against COVID-19, vaccination rates in many regions around the world remain insufficient to prevent continued high disease burden and emergence of viral variants. Repurposing of existing therapeutics that prevent or mitigate severe COVID-19 could help to address these challenges. The objective of this study was to determine whether prior use of bisphosphonates is associated with reduced incidence and/or severity of COVID-19.

Methods

A retrospective cohort study utilizing payer-complete health insurance claims data from 8,239,790 patients with continuous medical and prescription insurance January 1, 2019 to June 30, 2020 was performed. The primary exposure of interest was use of any bisphosphonate from January 1, 2019 to February 29, 2020. Bisphosphonate users were identified as patients having at least one bisphosphonate claim during this period, who were then 1:1 propensity score-matched to bisphosphonate non-users by age, gender, insurance type, primary-care-provider visit in 2019, and comorbidity burden. Main outcomes of interest included: (a) any testing for SARS-CoV-2 infection; (b) COVID-19 diagnosis; and (c) hospitalization with a COVID-19 diagnosis between March 1, 2020 and June 30, 2020. Multiple sensitivity analyses were also performed to assess core study outcomes amongst more restrictive matches between BP users/non-users, as well as assessing the relationship between BP-use and other respiratory infections (pneumonia, acute bronchitis) both during the same study period as well as before the COVID outbreak.

Results

A total of 7,906,603 patients for whom continuous medical and prescription insurance information was available were selected. A total of 450,366 bisphosphonate users were identified and 1:1 propensity score-matched to bisphosphonate non-users. Bisphosphonate users had lower odds ratios (OR) of testing for SARS-CoV-2 infection (OR = 0.22; 95%CI:0.21-0.23; p<0.001), COVID-19 diagnosis (OR = 0.23; 95%CI:0.22-0.24; p<0.001), and COVID-19-related hospitalization (OR = 0.26; 95%CI:0.24-0.29; p<0.001). Sensitivity analyses yielded results consistent with the primary analysis. Bisphosphonate-use was also associated with decreased odds of acute bronchitis (OR = 0.23; 95%CI:0.22-0.23; p<0.001) or pneumonia (OR = 0.32; 95%CI:0.31-0.34; p<0.001) in 2019, suggesting that bisphosphonates may protect against respiratory infections by a variety of pathogens, including but not limited to SARS-CoV-2.

Conclusions

Prior bisphosphonate-use was associated with dramatically reduced odds of SARS-CoV-2 testing, COVID-19 diagnosis, and COVID-19-related hospitalizations. Prospective clinical trials will be required to establish a causal role for bisphosphonate-use in COVID-19-related outcomes.

Funding

This study was supported by NIH grants, AR068383 and AI155865, a grant from MassCPR (to UHvA) and a CRI Irvington postdoctoral fellowship, CRI2453 (to PH).

Structural insights into the binding of zoledronic acid with RANKL via computational simulations

Zoledronic acid (ZOL) inhibits receptor activator of nuclear factor-κB ligand (RANKL) and reduces bone turnover. This plays an important role in the development of bisphosphonate-related osteonecrosis of the jaw (BRONJ). Previous reports have shown that ZOL binds to the enzyme farnesyl pyrophosphate synthase (FPPS) to block its activity. However, the mechanism of action of ZOL and its interaction with RANKL is still unclear. In this study, we confirmed that ZOL significantly suppressed the bone remodeling in ZOL-treated rats, investigated whether ZOL could bind to RANKL and examined the interactions between these molecules at the atomic level. Surface plasmon resonance (SPR) assay was performed to validate that ZOL could directly bind to RANKL in a dose dependent manner, and the equilibrium constant was calculated (K_D = 2.28 × 10⁻⁴ M). Then, we used molecular docking simulation to predict the binding site and analyze the binding characteristics of ZOL and RANKL. Through molecular dynamics simulation, we confirmed the stable binding between ZOL and RANKL and observed their dynamic interactions over time. Binding free energy calculations and its decomposition were conducted to obtain the binding free energy −70.67 ± 2.62 kJ/mol for the RANKL–ZOL complex. We identified the key residues of RANKL in the binding region, and these included Tyr217(A), Val277(A), Gly278(A), Val277(B), Gly278(B), and Tyr215(C). Taken together, our results demonstrated the direct interaction between ZOL and RANKL, indicating that the pharmacological action of ZOL might be closely related to RANKL. The design of novel small molecules targeting RANKL might reduce the occurrence of BRONJ.

Immunotherapy of Cancer by Targeting Regulatory T cells

Regulatory T (Treg) cells maintain immune homeostasis by inhibiting abnormal/overactive immune responses to both autogenic and nonautogenic antigens. Treg cells play an important role in immune tolerance, autoimmune diseases, infectious diseases, organ transplantation, and tumor diseases. Treg cells have two functional characteristics: T cell anergy and immunosuppression. Treg cells remain immune unresponsive to high concentrations of interleukin-2 and anti-CD3 monoclonal antibodies. In addition, the activation of Treg cells after TCR-mediated signal stimulation inhibits the activation and proliferation of effector T cells. In the process of tumor development, Treg cells accumulate locally in the tumor and lead to tumor escape by inducing anergy and immunosuppression. It is believed that targeted elimination of Treg cells can activate tumor-specific effector T cells and improve the efficiency of cancer immunotherapy. Therefore, inhibition/clearance of Treg cells is a promising strategy for enhancing antitumor immunity. Here, we review studies of cancer immunotherapies targeting Treg cells.

Disruption of FDPS/Rac1 axis radiosensitizes pancreatic ductal adenocarcinoma by attenuating DNA damage response and immunosuppressive signalling

Background

Radiation therapy (RT) has a suboptimal effect in patients with pancreatic ductal adenocarcinoma (PDAC) due to intrinsic and acquired radioresistance (RR). Comprehensive bioinformatics and microarray analysis revealed that cholesterol biosynthesis (CBS) is involved in the RR of PDAC. We now tested the inhibition of the CBS pathway enzyme, farnesyl diphosphate synthase (FDPS), by zoledronic acid (Zol) to enhance radiation and activate immune cells.

Methods

We investigated the role of FDPS in PDAC RR using the following methods: in vitro cell-based assay, immunohistochemistry, immunofluorescence, immunoblot, cell-based cholesterol assay, RNA sequencing, tumouroids (KPC-murine and PDAC patient-derived), orthotopic models, and PDAC patient's clinical study.

Findings

FDPS overexpression in PDAC tissues and cells (P < 0.01 and P < 0.05) is associated with poor RT response and survival (P = 0.024). CRISPR/Cas9 and pharmacological inhibition (Zol) of FDPS in human and mouse syngeneic PDAC cells in conjunction with RT conferred higher PDAC radiosensitivity in vitro (P < 0.05, P < 0.01, and P < 0.001) and in vivo (P < 0.05). Interestingly, murine (P = 0.01) and human (P = 0.0159) tumouroids treated with Zol+RT showed a significant growth reduction. Mechanistically, RNA-Seq analysis of the PDAC xenografts and patients-PBMCs revealed that Zol exerts radiosensitization by affecting Rac1 and Rho prenylation, thereby modulating DNA damage and radiation response signalling along with improved systemic immune cells activation. An ongoing phase I/II trial (NCT03073785) showed improved failure-free survival (FFS), enhanced immune cell activation, and decreased microenvironment-related genes upon Zol+RT treatment.

Interpretation

Our findings suggest that FDPS is a novel radiosensitization target for PDAC therapy. This study also provides a rationale to utilize Zol as a potential radiosensitizer and as an immunomodulator in PDAC and other cancers.

Funding

National Institutes of Health (P50, P01, and R01).

Osteoimmuno-Oncology: Therapeutic Opportunities for Targeting Immune Cells in Bone Metastasis

Immunotherapies provide a potential treatment option for currently incurable bone metastases. Bone marrow is an important secondary lymphoid organ with a unique immune contexture. Even at non-disease state immune cells and bone cells interact with each other, bone cells supporting the development of immune cells and immune cells regulating bone turnover. In cancer, tumor cells interfere with this homeostatic process starting from formation of pre-metastatic niche and later supporting growth of bone metastases. In this review, we introduce a novel concept osteoimmuno-oncology (OIO), which refers to interactions between bone, immune and tumor cells in bone metastatic microenvironment. We also discuss therapeutic opportunities of targeting immune cells in bone metastases, and associated efficacy and safety concerns.

Investigation of Intravenous Zoledronic Acid Therapy on Circulating Lymphocyte Subpopulation in Patients with Primary Osteoporosis: A Pilot Study

BACKGROUND

Several studies have investigated the immunomodulating properties of zoledronic acid on T lymphocytes, but the causal relationship between the function of T cells and the efficacy of zoledronic acid has not been elucidated.

OBJECTIVE

To investigate the causal relationship between the function of zoledronic acid and T cells.

METHODS

We conducted an observational perspective study to observe the effect of intravenous zoledronic acid once yearly for 2 years on lymphocyte subsets in patients with primary osteoporosis through observing the blood cells analysis and the level of lymphocyte subpopulations before and on day 1, 2, and 3 after first and second administration of intravenous zoledronic acid and bone mineral destiny 1 year after a single administration of zoledronic acid.

RESULTS

White blood cell count and neutrophils increased, whereas lymphocytes and eosinophils decreased after the first and second zoledronic acid infusion. The count of CD3+T cells, CD3+CD4+T cells, and CD16+CD56+ natural killer lymphocytes decreased from day 1 to day 3 after the first and second zoledronic acid infusion, but the results of second infusion showed no significance.

CONCLUSIONS

Further, larger size, more in-depth studies are indicated to examine whether the short-term changes in white blood cells and lymphocyte subtypes noted after 2 once-yearly zoledronic acid injections in this small population of adult patients is associated with the stimulation of immune mechanisms. (Curr Ther Res Clin Exp. 2021; 82:XXX-XXX).

Effect of Gemcitabine based chemotherapy on the immunogenicity of pancreatic tumour cells and T-cells

PURPOSE

Chemotherapy for advanced pancreatic cancer has limited efficacy due to the difficultly of treating established tumours and the evolution of tumour resistance. Chemotherapies for pancreatic cancer are typically studied for their cytotoxic properties rather than for their ability to increase the immunogenicity of pancreatic tumour cells. In this study Gemcitabine in combination with immune modulatory chemotherapies Oxaliplatin, zoledronic acid and pomalidomide was studied to determine how combination therapy alters the immunogenicity of pancreatic tumour cell lines and subsequent T-cell responses.

METHODS

Pancreatic tumour cell lines were stimulated with the chemotherapeutic agents and markers of immune recognition were assessed. The effect of chemotherapeutic agents on DC function was measured using uptake of CFSE-stained PANC-1 cells, changes in markers of maturation and their ability to activate CD8+ T-cells. The effect of chemotherapeutic agents on T-cell priming prior to activation using anti-CD3 and anti-CD28 antibodies was determined by measuring IFN-γ expression and Annexin V staining using flow cytometry.

RESULTS

These agents demonstrate both additive and inhibitory properties on a range of markers of immunogenicity. Gemcitabine was notable for its ability to induce the upregulation of human leukocyte antigen and checkpoints on pancreatic tumour cell lines whilst inhibiting T-cell activation. Pomalidomide demonstrated immune modulatory properties on dendritic cells and T-cells, even in the presence of gemcitabine.

DISCUSSION

These data highlight the complex interactions of different agents in the modulation of tumour immunogenicity and immune cell activation and emphasise the complexity in rationally designing chemo immunogenic combinations for use with immunotherapy.

Comparative Immunology and Immunotherapy of Canine Osteosarcoma

Approximately 800 people are diagnosed with osteosarcoma (OSA) per year in the USA. Although 70% of patients with localized OSA are cured with multiagent chemotherapy and surgical resection, the prognosis for patients with metastatic or relapsed disease is guarded. The small number of patients diagnosed annually contributes to an incomplete understanding of disease pathogenesis, and challenges in performing appropriately powered clinical trials and detecting correlative biomarkers of response. While mouse models of OSA are becoming increasingly sophisticated, they generally fail to accurately recapitulate tumor heterogeneity, tumor microenvironment (TME), systemic immune dysfunction, and the clinical features of tumor recurrence, metastases, and chemoresistance, which influence outcome. Pet dogs spontaneously develop OSA with an incidence that is 30-50 times higher than humans. Canine OSA parallels the human disease in its clinical presentation, biological behavior, genetic complexity, and therapeutic management. However, despite therapy, most dogs die from metastatic disease within 1 year of diagnosis. Since OSA occurs in immune-competent dogs, immune factors that sculpt tumor immunogenicity and influence responses to immune modulation are in effect. In both species, immune modulation has shown beneficial effects on patient outcome and work is now underway to identify the most effective immunotherapies, combination of immunotherapies, and correlative biomarkers that will further improve clinical response. In this chapter, the immune landscape of canine OSA and the immunotherapeutic strategies used to modulate antitumor immunity in dogs with the disease will be reviewed. From this immunological viewpoint, the value of employing dogs with spontaneous OSA to accelerate and inform the translation of immunotherapies into the human clinic will be underscored.

Oestrogen and zoledronic acid driven changes to the bone and immune environments: Potential mechanisms underlying the differential anti-tumour effects of zoledronic acid in pre- and post-menopausal conditions

Late stage breast cancer commonly metastasises to bone and patient survival averages 2-3 years following diagnosis of bone involvement. One of the most successful treatments for bone metastases is the bisphosphonate, zoledronic acid (ZOL). ZOL has been used in the advanced setting for many years where it has been shown to reduce skeletal complications associated with bone metastasis. More recently, several large adjuvant clinical trials have demonstrated that administration of ZOL can prevent recurrence and improve survival when given in early breast cancer. However, these promising effects were only observed in post-menopausal women with confirmed low concentrations of circulating ovarian hormones. In this review we focus on potential interactions between the ovarian hormone, oestrogen, and ZOL to establish credible hypotheses that could explain why anti-tumour effects are specific to post-menopausal women. Specifically, we discuss the molecular and immune cell driven mechanisms by which ZOL and oestrogen affect the tumour microenvironment to inhibit/induce tumour growth and how oestrogen can interact with zoledronic acid to inhibit its anti-tumour actions.

Zoledronate decreases CTLA-4 in vivo and in vitro independently of its action on bone resorption

Acute phase response (APR) following intravenous zoledronate (ZOL) administration is related to activation and increased proliferation of γδ T cells, attributed to the molecular mechanism of action of nitrogen-containing bisphosphonates (N-BPs). ZOL, however, has also been reported to inhibit the proliferation of regulatory T cells in vitro and to reduce the expression of Cytotoxic T-Lymphocyte Antigen-4 (CTLA-4), a negative regulator of T cell activation that is increased in patients with autoimmune diseases. There are, however, no data on the relationship between ZOL treatment and soluble(s)CTLA-4 either in vivo in relevant patient populations or in vitro with the use of assays relevant to the mechanism of action of N-BPs. The objectives of the present study were firstly, to characterize the ZOL-induced APR in patients with inflammatory rheumatic diseases (IRDs) and its relationship with changes in circulating sCTLA-4 and secondly, to investigate the effects of ZOL on CTLA-4 production and expression by peripheral blood mononuclear cells (PBMCs). We studied 10 postmenopausal women with IRDs treated with intravenous ZOL 5 mg. Five women experienced APR (APR+) associated with significant decreases in blood lymphocytes and increases in granulocytes and serum CRP. Serum sCTLA-4 values were increased in all patients before ZOL administration and decreased significantly 72 h after the ZOL infusion (from 30.0 ± 2.9 to 6.3 ± 1.8 ng/ml; p < 0.001) with no differences between APR+ and APR- patients. Consistent with the results of the in vivo study, ZOL (1 μM) decreased the production of sCTLA-4 by 87% and 57% after 3 and 5 days in cultures of peripheral blood mononuclear cells (PBMCs) in vitro, respectively, and inhibited the expression of both cytoplasmic and membrane-bound CTLA-4. Our results reveal a novel immunoregulatory action of ZOL that is not related to its action on bone resorption but might be associated with reported clinically significant extraskeletal outcomes of ZOL treatment.

The critical role of calcineurin/NFAT (C/N) pathways and effective antitumor prospect for colorectal cancers

Transcription factors (TFs) like a nuclear factor of activated T-cells (NFAT) and its controller calcineurin are highly expressed in primary intestinal epithelial cells (IECs) due to delamination, damage by tumor-associated flora and selective activation in the intestinal tract tumor are crucial in the progression and growth of colorectal cancer (CRC). This study sought to summarize the current findings concerning the dysregulated calcineurin/NFAT (C/N) signaling involved in CRC initiation and progression. These signalings include proliferation, T-cell functions, and glycolysis with high lactate production that remodels the acidosis, which genes in tumor cells provide an evolutionary advantage, or even increased their attack phenotype. Moreover, the relationship between C/N and gut microbiome in CRC, especially role of NFAT and toll-like receptor signaling in regulating intestinal microbiota are also discussed. Furthermore, this review will discuss the proteins and genes relating to C/N induced acidosis in CRC, which includes ASIC2 regulated C/N1 and TFs associated with the glycolytic by-product that affect T-cell functions and CRC cell growth. It is revealed that calcineurin or NFAT targeting to antitumor, selective calcineurin inhibition or targets in NFAT signaling may be useful for clinical treatment of CRC. This can further aid in the identification of specific targets via cancer patient-personalized approach. Future studies should be focused on targeting to C/N or TLR signaling by the combination of therapeutic agents to regulate T-cell functions and gut microbiome for activating potent anticancer property with the prospect of potentiating the antitumor therapy for CRC.

Zoledronic acid blocks the interaction between breast cancer cells and regulatory T-cells

BACKGROUND

Zoledronic acid (ZA), a nitrogen-containing bisphosphonate, inhibits osteoclastogenesis. Emerging evidence suggests that ZA has anti-tumor and anti-metastatic properties for breast cancer cells. In a mouse model of ZA-related osteonecrosis of the jaw, ZA administration was found to suppress regulatory T-cells (Tregs) function. Our previous reports also demonstrated ZA acted as an immune modulator to block Tregs. Manipulation of Tregs represents a new strategy for cancer treatment. However, the relationship among ZA, Tregs, and cancer cells remains unclear. In this study, we investigated the effects of ZA on the interaction of breast cancer cells and Tregs.

METHODS

The anti-tumor effect of ZA on triple negative breast cancer cell lines were validated by XTT, wound healing and apoptosis analysis. A flow cytometry-based assay was used to analyze the immunosuppressive effect of Tregs treated with media conditioned by breast cancer cells, and a transwell assay was used to evaluate the chemotactic migration of Tregs. Differential gene expression profile on MDA-MB-231 treated with ZA (25 μM) was analyzed by. microarrays to describe the molecular basis of actions of ZA for possible direct anti-tumor effects. Enzyme-linked immunosorbent assays and quantitative real-time PCR were used to investigate the effect of ZA on the expression of cytokines/factors by breast cancer cells.

RESULTS

ZA was found to inhibit the proliferation and migration of breast cancer cells. Media conditioned by the MDA-MB-231 cells promoted the expansion, chemotactic migration, and immunosuppressive activity of Tregs, and these effects were attenuated in a dose-dependent manner by ZA treatment, and the attenuation was due to reduced expression of selected breast cancer cell factors (CCL2, CCL5, and IDO).

CONCLUSIONS

ZA can significantly affect the interaction between breast cancer cells and Tregs. Our findings indicate that ZA is a potential therapeutic agent that can be used to reduce cancer aggressiveness by abolishing the supportive role of Tregs.

Effect of surgery and radiotherapy on complete blood count, lymphocyte subsets and inflammatory response in patients with advanced oral cancer

Background

The immune system has a known role in the aetiology, progression and final treatment outcome of oral squamous cell cancers. The aim of this study was to evaluate the influence of radical surgery and radiotherapy on advanced oral squamous cell carcinoma blood counts, lymphocyte subsets and levels of acute inflammatory response markers.

Methods

Blood samples were obtained from 56 patients 5 days before and 10 days after surgery, 30 days and 1 year after radiotherapy. The whole blood count, lymphocyte subsets and inflammatory response markers (C-reactive protein, erythrocyte sedimentation rate, leukocyte count, expression of index CD64 and index CD163 on neutrophils and monocytes) were measured, statistically analysed and correlated with clinical treatment outcomes.

Results

The post-operative period was characterised by the onset of anaemia, thrombocytosis, lymphopenia with reduced B lymphocyte, T helper cell and NK cell counts, and a rise in acute phase reactants. Immediately after radiotherapy, the anaemia improved, the lymphopenia worsened, and thrombocyte levels returned to pre-treatment values. There was a drop in counts across the T and B cell lines, including a reduction in B lymphocytes, naïve and memory T cells with reduced CD4+ and CD8+ counts and a decreased CD4/CD8 ratio. One year after radiotherapy all the lymphocyte subsets remained depressed, the only exception being NK cells, whose levels returned to pre-treatment values.

Conclusions

We concluded that surgery resulted in a stronger acute phase response than radiotherapy, while radiotherapy caused a long-lasting reduction in lymphocyte counts. There was no correlation between any of the pre-treatment parameters and the clinical outcome.

Triple negative breast cancer: Key role of Tumor-Associated Macrophages in regulating the activity of anti-PD-1/PD-L1 agents

Triple-negative breast cancer (TNBC) is associated with a poor prognosis, due to its aggressive behaviour and lack of effective targeted therapies. Immunocheckpoint inhibitors, such as anti-programmed cell death 1 (PD-1) and anti-PD-ligand(L)1 agents, are in course of investigation in TNBC, used alone or in combination with other systemic or local approaches. However, the high cost of these drugs and the lack of validated predictive biomarkers support the development of strategies aimed to overcome resistance and optimize the efficacy of these approaches. Tumor-Associated Macrophages (TAMs) derive from peripheral blood monocytes recruited into the TNBC microenvironment and, in response to several stimuli, undergo M1 (classical) or M2 (alternative) activation. In TNBC, TAMs promote tumor growth and progression by several mechanisms that include the secretion of inhibitory cytokines, the reduction of effector functions of Tumor Infiltrating Lymphocytes (TILs) and the promotion of Regulatory T cell (Treg). Interestingly, TAMs have been shown to directly and indirectly modulate PD-1/PD-L1 expression in tumor environment. On this scenario, several TAM-centered strategies have been proposed, such as the suppression of TAM recruitment, the depletion of their number, the switch of M2 TAMs into antitumor M1 phenotype and the inhibition of TAM-associated molecules. In this review, we will illustrate the activity of TAMs and associated molecules in TNBC, focusing on their role in modulating the expression of PD-1/PD-L1 and on the emerging TAM-tailored strategies for TNBC patients.

Zoledronic acid inhibits NFAT and IL-2 signaling pathways in regulatory T cells and diminishes their suppressive function in patients with metastatic cancer

Regulatory T cells (Treg) suppress anti-tumor immune responses and their infiltration in the tumor microenvironment is associated with inferior prognosis in cancer patients. Thus, in order to enhance anti-tumor immune responses, selective depletion of Treg is highly desired. We found that treatment with zoledronic acid (ZA) resulted in a selective decrease in the frequency of Treg that was associated with a significant increase in proliferation of T cells and natural killer (NK) cells in peripheral blood of patients with metastatic cancer. In vitro, genome-wide transcriptomic analysis revealed alterations in calcium signaling pathways in Treg following treatment with ZA. Furthermore, co-localization of the nuclear factor of activated T cells (NFAT) and forkhead box P3 (FOXP3) was significantly reduced in Treg upon ZA-treatment. Consequently, reduced expression levels of CD25, STAT5 and TGFβ were observed. Functionally, ZA-treated Treg had reduced capacity to suppress T and NK cell proliferation and anti-tumor responses compared with untreated Treg in vitro. Treatment with ZA to selectively inhibit essential signaling pathways in Treg resulting in reduced capacity to suppress effector T and NK cell responses represents a novel approach to inhibit Treg activity in patients with cancer.