Frequency Of Circulating Tregs Research Articles

Abstract 3605: Phase II study of pembrolizumab in conjunction with lymphodepletion, TIL ACT, and high- or low-dose IL-2 in patients with metastatic melanoma

Abstract Background: In metastatic melanoma (MM) patients (pts), adoptive cell transfer (ACT) using tumor-infiltrating lymphocytes (TIL) can yield lasting responses. However, TIL ACT with high-dose IL-2 has notable toxicities. Anti-PD1 (pembrolizumab) is FDA approved for MM treatment. Our study aimed to merge TIL infusion with anti-PD1 in two arms, comparing high (HD, arm 1) and low (LD, arm 2) IL-2 doses. Methods: After tumor harvest and TIL expansion, pts were lymphodepleted with cyclophosphamide and fludarabine, followed by infusion with their ex-vivo expanded TIL combined with IL-2 (arm 1: 720,000 IU/kg IV q 8 hrs up to 15 doses; arm 2: 2 million IU SC for 14 days). Pts were given 200 mg of IV anti-PD1 starting 21 days post-TIL infusion, followed by doses every 3 weeks for up to 2 years. Blood was taken before lymphodepletion and before the first two anti-PD1 doses for flow cytometry and cytokine analysis The primary endpoint of the study was determination of overall response rate by RECISTS 1.1 criteria. Enrollment aimed for 18 pts per arm, monitoring the primary ORR endpoint using a Bayesian rule. Enrollment would halt in any arm if the ORR dropped below 40%. Results: The median age was 50 years (n=14: 6 F and 8 M). Of these 14 pts, 8, 2, 2, and 2 had cutaneous, uveal, mucosal, or unknown primary melanoma. Pts had a median of 3 lines of prior therapies (range 1-6), including anti-PD-1 (n=13). In arm 1, one pt had a partial response (PR) for 10 months, 2 had stable disease (SD), 3 had progressive disease (PD), and 1 was not evaluable (NE). In arm 2, one pt had an ongoing PR for over 76 months, 1 had SD, and 5 had PD. Due to ORR <40% in each arm, enrollment was stopped after treatment of 14 pts. There was no significant different in progression-free survival or overall survival between the two arms (p=0.99 and p=0.71, respectively). In general, toxicity levels were comparable in both arms; however, pts in arm 2 had slightly lower grade 3 febrile neutropenia (57% vs. 71%) and shorter hospitalization (median 16 days vs. 18 days) than pts in Arm 1. While no correlation was observed between the phenotype of the TIL product and clinical response, both PR pts received high numbers of TIL (38.6 × 10^9 and 93.7 × 10^9; mean: 32.6 × 10^9 cells), with a high CD8+/CD4+ T cell ratio (284.7 and 2.7; median: 2.7). IL-2 dose did not affect circulating Treg frequency, phenotype, or proliferation by flow cytometry 3 weeks post TIL infusion. IL-2 dose was not associated with CD4+ non-Treg and CD8+ T cell phenotype or proliferation. Addition of anti-PD1 reduced expression of checkpoints but did not boost T cell proliferation. Conclusion: Our treatment strategy did not yield any distinct difference between low and high dose IL-2, suggesting the potential of low-dose IL-2 as an alternative. Anti-PD1 did not have any appreciable effect on immune states potentially due to the cohorts being comprised of a heavily pre-treated heterogenous pt population. Citation Format: Merve Hasanov, Simin Kiany, Marie-Andrée Forget, Roland L. Bassett, Michael A. Davies, Adi Diab, Jeffrey E. Gershenwald, Isabella C. Glitza, Jeffrey E. Lee, Anthony Lucci, Jennifer L. McQuade, Sapna P. Patel, Merrick I. Ross, Hussein A. Tawbi, Jennifer Wargo, Michael K. Wong, Chantale Bernatchez, Patrick Hwu, Cara Haymaker, Rodabe N. Amaria. Phase II study of pembrolizumab in conjunction with lymphodepletion, TIL ACT, and high- or low-dose IL-2 in patients with metastatic melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3605.

Translational Studies Using the MALT1 Inhibitor (S)-Mepazine to Induce Treg Fragility and Potentiate Immune Checkpoint Therapy in Cancer.

Regulatory T cells (Tregs) play a critical role in the maintenance of immune homeostasis but also protect tumors from immune-mediated growth control or rejection and pose a significant barrier to effective immunotherapy. Inhibition of MALT1 paracaspase activity can selectively reprogram immune-suppressive Tregs in the tumor microenvironment to adopt a proinflammatory fragile state, which offers an opportunity to impede tumor growth and enhance the efficacy of immune checkpoint therapy (ICT). We performed preclinical studies with the orally available allosteric MALT1 inhibitor (S)-mepazine as a single-agent and in combination with anti-programmed cell death protein 1 (PD-1) ICT to investigate its pharmacokinetic properties and antitumor effects in several murine tumor models as well as patient-derived organotypic tumor spheroids (PDOTS). (S)-mepazine demonstrated significant antitumor effects and was synergistic with anti-PD-1 therapy in vivo and ex vivo but did not affect circulating Treg frequencies in healthy rats at effective doses. Pharmacokinetic profiling revealed favorable drug accumulation in tumors to concentrations that effectively blocked MALT1 activity, potentially explaining preferential effects on tumor-infiltrating over systemic Tregs. The MALT1 inhibitor (S)-mepazine showed single-agent anticancer activity and presents a promising opportunity for combination with PD-1 pathway-targeted ICT. Activity in syngeneic tumor models and human PDOTS was likely mediated by induction of tumor-associated Treg fragility. This translational study supports ongoing clinical investigations (ClinicalTrials.gov Identifier: NCT04859777) of MPT-0118, (S)-mepazine succinate, in patients with advanced or metastatic treatment-refractory solid tumors.

The effect of fingolimod on regulatory T cells in a mouse model of brain ischaemia

BackgroundThe role of the immune system in stroke is well-recognised. Fingolimod, an immunomodulatory agent licensed for the management of relapsing-remitting multiple sclerosis, has been shown to provide benefit in rodent models of stroke. Its mechanism of action, however, remains unclear. We hypothesised fingolimod increases the number and/or function of regulatory T cells (Treg), a lymphocyte population which promotes stroke recovery. The primary aim of this study was to rigorously investigate the effect of fingolimod on Tregs in a mouse model of brain ischaemia. The effect of fingolimod in mice with common stroke-related comorbidities (ageing and hypercholesteremia) was also investigated.MethodsYoung (15–17 weeks), aged C57BL/6 mice (72–73 weeks), and ApoE−/− mice fed a high-fat diet (20–21 weeks) underwent permanent electrocoagulation of the left middle cerebral artery. Mice received either saline or fingolimod (0.5 mg/kg or 1 mg/kg) at 2, 24, and 48 h post-ischaemia via intraperitoneal injection. Another cohort of young mice (8–9, 17–19 weeks) received short-term (5 days) or long-term (10 days) fingolimod (0.5 mg/kg) treatment. Flow cytometry was used to quantify Tregs in blood, spleen, and lymph nodes. Immunohistochemistry was used to quantify FoxP3+ cell infiltration into the ischaemic brain.ResultsFingolimod significantly increased the frequency of Tregs within the CD4+ T cell population in blood and spleen post-ischaemia in all three mouse cohorts compared to untreated ischemic mice. The highest splenic Treg frequency in fingolimod-treated mice was observed in ApoE−/− mice (9.32 ± 1.73% vs. 7.8 ± 3.01% in young, 6.09 ± 1.64% in aged mice). The highest circulating Treg frequency was also noted in ApoE−/− mice (8.39 ± 3.26% vs. 5.43 ± 2.74% in young, 4.56 ± 1.60% in aged mice). Fingolimod significantly increased the number of FoxP3+ cells in the infarct core of all mice. The most pronounced effects were seen when mice were treated for 10 days post-ischaemia.ConclusionsFingolimod increases Treg frequency in spleen and blood post-ischaemia and enhances the number of FoxP3+ cells in the ischaemic brain. The effect of fingolimod on this regulatory cell population may underlie its neuroprotective activity and could be exploited as part of future stroke therapy.

IL-37 Plays a Beneficial Role in Patients with Acute Coronary Syndrome.

Background Interleukin-37 (IL-37) acts as an inhibitor of innate and adaptive immunity. However, the exact role of IL-37 in the patients with acute coronary syndrome (ACS) remains to be elucidated. Methods Patients were classified into 4 groups: normal coronary artery (NCA), stable angina (SA), unstable angina (UA), and acute myocardial infarction (AMI). The circulating Treg, Th1, and Th17 frequencies were measured. The effect of IL-37 on stimulated peripheral blood mononuclear cells (PBMCs) and the influence of IL-37 on DCs were explored. In addition, the role of IL-37-treated tDCs on Treg cell expansion and the stability of these tDCs were also tested. Results Our results showed that the circulating Treg frequencies were decreased, while Th1 and Th17 frequencies were increased in ACS patients, and that IL-37 expanded Tregs but suppressed Th1 and Th17 cells in activated PBMCs derived from ACS patients. Of note, IL-37-treated human DCs obtained a tolerogenic phenotype, and such tDCs promoted expansion of Tregs and decreased the Th1 and Th17 populations when cocultured with CD4+ T cells. Interestingly, IL-37-treated DCs from patients with ACS are phenotypically and functionally comparable to IL-37-treated DCs from NCA patients, and tolerogenic properties of IL-37-treated DCs were highly stable. Conclusion In conclusion, our results reveal a beneficial role of IL-37 in the patients with ACS and suggest that autologous IL-37-treated tDCs may be a novel therapeutic strategy for the patients with ACS.

Investigation of immune cell markers in feline oral squamous cell carcinoma

Squamous cell carcinoma is the most common oral cancer in the cat and presents as a locally aggressive lesion for which an effective therapeutic protocol remains elusive. Feline oral squamous cell carcinoma (OSCC) shares many clinical characteristics with human head and neck squamous cell carcinoma (HNSCC). Accordingly, present studies were conducted to determine similarities for immune markers shared by feline OSCC and human HNSCC. Biopsies harvested from a feline patient cohort-1 (n = 12) were analyzed for lymphoid cell infiltrates by immunohistochemistry (IHC). Results revealed unique patterns of T cell infiltration involving both neoplastic epithelium and stroma that were detected in most patient tumor biopsies (92%) examined by IHC staining for CD3. Intratumoral B cell infiltrates were detected within tumor stroma only, based on IHC staining for CD79a and CD20 for all patients within the same cohort-1. Infiltration of tumors by a regulatory CD4 T cell subset (Tregs) defined by expression of the forkhead transcription factor FoxP3, was also detected in biopsies from 57% of patients and involved infiltration of neoplastic epithelium and stroma. Patient biopsies were also examined for expression of immunomodulator cyclooxygenase (COX)-2 and revealed positive but weak staining of neoplastic epithelium in a significant proportion of cases (75%). Interestingly, COX-2 expression was detected in both neoplastic epithelium and stroma. Blood collected from a second cohort of feline OSCC patients (n = 9) revealed an increased frequency of circulating CD4+FoxP3+ T cells when compared to healthy adult controls (n = 7) (P = 0.045), although frequencies of CD4+CD25+FoxP3+ T cells were comparable between patients and healthy pet cat controls. Lastly, biopsies from feline OSCC patients were characterized for histologic subtype using a classification scheme previously described for human HNSCC. This analysis revealed the conventional subtype as the predominant variant (75%) with conventional subtypes split evenly between well differentiated and moderately differentiated carcinomas. Two cases were classified as papillary and one case as basaloid subtypes. Correlations between subtype, immune marker scores or circulating Treg frequencies and clinical characteristics or outcome were not detected, most likely due to small patient numbers within patient cohorts. However, findings from these studies provide a preliminary step in the characterization of immune and histologic markers that will be critical to defining prognostic immune markers for feline OSCC and potential targets for testing of immunotherapeutics also relevant to human HNSCC in future studies.

Combinatorial Effect of HDAC6i and Ibrutinib Therapy in CLL Murine Model

Ibrutinib, a Bruton tyrosine kinase (BTK) inhibitor is now FDA approved for front line and relapsed and refractory CLL. Although this drug has been shown to be successful in controlling the disease, most patients only reach partial responses (PR) likely secondary to activation of alternative and redundant BCR signaling pathways. In the past several years, epigenetic changes in CLL have gained special attention (Tong et al 2010) because of their intricate interplay with previously described genetic events and its active role in the regulation of pathogenesis and immune-related pathways (Stilgenbauer et al 2002). Recent publications have described the differential expression of specific HDACs in CLL, as well as the impact of global histone deacetylase activity and its relation with progression and overall survival (Van Damme et al 2014, Yang et al 2015).Previously, we had reported that expression of HDAC6 is increased in CLL patient samples and cell lines. We have also demonstrated that modulation of this HDAC, effects cell proliferation and viability in CLL cell lines. Additionally, treatment with HDAC6i (ACY-738 - a potent and selective HDAC6i) demonstrated increased overall survival in euTCL1 mice, a murine CLL model. Treatment of euTCL1 mice (both adoptive transfer and aging model) with ACY-738 as a single agent resulted in 1) overall survival advantage, 2) reduction of tumor burden, 3) reduction in PD-L1 expression in the malignant B cell population and 4) decreased circulating Treg numbers. Furthermore, we demonstrated that in an in vitrostudy, treatment of HDAC6i with ibrutinib in CLL cell lines render strong synergistic cell killing. In our current study of this combinatorial approach, using the adoptive transfer euTCL1 model receiving Ibrutinib in drinking water and ACY-738 in feed, we demonstrate a further decrease in tumor burden when compared to single agent treatment with either compound alone. This observed effect on tumor burden occurred in conjunction with decreases in co-inhibitory molecules and circulating Treg frequency. The combination was well tolerated and no significant toxicity was observed.Since aberrant over-expression of HDAC6 in CLL cell lines and patient's samples have already been demonstrated (Van Damme et al 2012, Sahakian et al 2012) we sought to understand its mechanistic role in BCR survival pathways of CLL. Our studiesin normal B cells isolated from C57BL/6 and HDAC6KO mice, demonstrated a reduction in phosphorylation of BTK, ERK, and AKT. Similar results were observed when we compared euTCL1 to euTCL1/HDAC6KO B cells. Additionally,we observed decreased phosphorylation of ERK and SYK in MEC2-HDAC6KD cells when compared to parental control CLL cells. Moreover, RNA-Seq studies of the eu-TCL1/HDAC6KO versus euTCL1 B cells showed several key BCR signaling proteins altered by the deletion of HDAC6.In conclusion, these results from our preclinical CLL models suggest that combinatorial therapy of Ibrutinib plus HDAC6i show synergistic inhibition of BCR signaling and therefore a better overall treatment outcome. DisclosuresQuayle:Acetylon Pharmaceuticals: Employment, Equity Ownership. Jones:Acetylon Pharmaceuticals, Inc.: Employment, Equity Ownership. Pinilla-Ibarz:Gilead: Consultancy, Speakers Bureau; Pharmacyclics: Consultancy, Speakers Bureau; Novartis: Consultancy; Abbvie: Consultancy, Speakers Bureau; Novartis: Consultancy; Janssen: Consultancy, Honoraria; Gilead: Consultancy, Speakers Bureau.

Phenotypic and functional testing of circulating regulatory T cells in advanced melanoma patients treated with neoadjuvant ipilimumab

BackgroundWe have previously investigated neoadjuvant ipilimumab (ipi) for patients with locally/regionally advanced melanoma. That initial assessment of peripheral blood mononuclear cells (PBMC) showed a significant increase in shared tumor associated...

Foxp3(+) regulatory T cells are expanded in severe atopic dermatitis patients.

Regulatory T cells (Tregs) are known to play critical roles in homeostasis and immune responses in the skin. Whether Treg frequencies are altered in atopic dermatitis (AD) patients has been addressed by several studies, leading to conflicting results. The detection of Tregs by FOXP3 expression may lead to false-positive results as activated T cells without regulatory function may transiently upregulate this transcription factor. In contrast, measurement of the DNA methylation status of a region within the FOXP3 locus that is selectively demethylated only in bona fide Tregs (Treg-specific demethylated region, TSDR) represents a reliable method to quantify Tregs. Here, we measured circulating Treg frequencies of adult patients and detected a positive correlation with disease severity. Subsequent surface marker analysis revealed higher frequencies of CD45RA(+) CCR7(-) tissue-homing Tregs in the patient group with a tendency of reduced expression of CD39 compared with healthy donors, a marker for the highly suppressive TREM subtype.

Treatment with anti-OX40L or anti-TSLP does not alter the frequency of T regulatory cells in allergic asthmatics.

OX40-OX40L interactions and thymic stromal lymphopoietin (TSLP) are important in the induction and maintenance of Th2 responses in allergic disease, whereas T regulatory cells (Treg) have been shown to suppress pro-inflammatory Th2 responses. Both OX40L and TSLP have been implicated in the negative regulation of Treg. The effect of anti-asthma therapies on Treg is not well known. Our aim was to assess the effects of two monoclonal antibody therapies (anti-OX40L and anti-TSLP) on Treg frequency using a human model of allergic asthma. We hypothesized that the anti-inflammatory effects of these therapies would result in an increase in circulating Treg (CD4(+) CD25(+) CD127(low) Foxp3(+) cells) frequency. We measured Treg using flow cytometry, and our results showed that neither allergen challenge nor monoclonal antibody therapy altered circulating Treg frequency. These data highlight the need for assessment of airway Treg and for a more complete understanding of Treg biology so as to develop pharmacologics/biologics that modulate Treg for asthma therapy.

Regulatory T‐cell Subpopulations in Severe or Early‐onset Preeclampsia

A deficiency in regulatory T (Treg) cells causing reduced immune regulatory capacity has been proposed in preeclampsia. Utilizing recent advances in flow cytometry phenotyping, we aimed to assess whether a deficiency of Treg subpopulations occurs in preeclampsia. Six-color flow cytometry was used for Treg phenotyping in 18 preeclamptic women (one early-onset, one severe and 16 both), 20 women with normal pregnancy, and 20 non-pregnant controls. No differences were found in major Treg populations including CD127(low) CD25(+) /CD127(ow) FOXP3(+) , resting (FOXP3(dim) CD45RA(+) ), and activated (FOXP3(bright) CD45RA(-) ) Treg cells, whereas preeclamptic women showed increased CTLA-4(+) and CCR4(+) proportions within resting/activated Treg populations. Corticosteroid treatment prior to blood sampling (n = 10) affected the distribution of Treg populations. Although we found no major alterations in circulating Treg frequencies, differences in CTLA-4(+) and CCR4(+) frequencies suggest a migratory defect of Treg cells in preeclampsia. Corticosteroid treatment should be taken into account when evaluating Treg cells.

Ipilimumab treatment enhances CD4+ T cell activation while decreasing Treg and MDSC frequency in advanced melanoma patients

Ipilimumab is a fully human antibody that blocks CTLA-4 and has proven to extend overall survival in patients with unresectable stage III or stage IV melanoma. There is a need for well-documented pharmacodynamic markers together with potential predictive biomarkers that may allow for pretreatment selection of patients and screening for IRAE. Most of the recently published immune monitoring studies focus mainly on the effect that Ipilimumab has on T cell populations. To date, little information is available on the possible impact that Ipilimumab treatment may have on MDSC populations and their suppressive mechanisms. In order to evaluate these effects, we conducted an in-depth immune monitoring study centered on peripheral blood MDSC populations as well as T cells in advanced melanoma patients undergoing treatment with Ipilimumab. Six patients with advanced stage melanoma received Ipilimumab treatment at 3 or 10 mg/kg doses as part of an ongoing double blind randomized trial (BMS trial CA184-169). Twenty-two additional patients received 3 mg/kg doses. Blood samples were collected from each patient before treatment and at the time of the second and fourth Ipilimumab doses. ICOS+CD4+ T cell frequency was significantly increased after Ipilimumab treatment, suggesting an increase in the activation of this cellular population. Analysis of circulating Treg frequencies revealed an initial increase, significantly decreasing after the second Ipilimumab dose. The endpoint mean frequency of Tregs was significantly lower than the baseline. Changes in MDSC populations with granulocytic and monocytic phenotype (Lin-HLA-DR-/loCD15+ CD33+CD11b+ and Lin-HLA-DR-/loCD14+, respectively) were monitored and the results showed that after the first dose, the granulocytic MDSC population significantly decreased, remaining low at week 9. This decrease was accompanied by a significant decrease in the population of ARG1+ myeloid cells. Further analysis showed that the populations of granulocytic MDSCs and CD4+ICOS+ T cell populations presented a statistically significant correlation. These results provide a first look at the early responses of peripheral blood myeloid cell populations to Ipilimumab treatment. CTLA-4 blockade may be acting upon the granulocytic MDSC population reducing its frequency and functionality as soon as three weeks after administration of the first Ipilimumab dose. The mechanisms by which these in trans effects are taking place should be further explored as well as their possible relations to clinical benefit.

Behavior of Circulating CD4+CD25+Foxp3+ Regulatory T Cells in Colon Cancer Patients Undergoing Surgery

CD4+CD25+Foxp3+ regulatory T cells (Treg) specialize in suppressing immune responses. In this study, 47 consecutive colon cancer patients were subjected to circulating Treg frequency assessment by flow cytometry before and after cancer resection. Thirty-two healthy subjects served as controls. Circulating Treg frequencies were significantly higher in colon cancer patients with respect to healthy controls. When patients were subgrouped according to Dukes stages, a linear relationship was observed between Dukes stages and Treg frequencies. In radically resected patients, Treg frequencies were shown to have significantly dropped down. Patients with advanced colon cancer were more likely to have significantly higher proportions of circulating Treg frequencies than Dukes A and B patients when compared to healthy subjects. Of note, nonradically resected patients were found to display reductions in-but not normalization of-Treg frequencies. These results suggest that cancer itself may be able to drive Treg recruitment as a strategy of immunoevasion.

Inhibitory Effects of Monocytes on CD4+Foxp3+ T Cell Expansion In Patients with Immune Thrombocytopenia (ITP)

AbstractAbstract 380Foxp3+ regulatory T cells (Tregs) are crucial for the maintenance of immunological self-tolerance. Indeed, defective Treg compartments have been described in several autoimmune diseases, including in patients with ITP. We recently reported that ITP patients on treatment with thrombopoietic receptor (TPO-R) agonists, known to improve platelet counts, have increased Treg suppressive activity. We now find in a cohort of 31 ITP patients (median platelet count 66 ×109/L, range 5–326 ×109/L) who were tested at least at 2 different time points either before, during and after their treatment with TPO-R agents, a positive correlation between platelet counts and circulating Treg frequency (Foxp3+CD25hi, r=0.388, p=0.005) as well as in vitro suppressive activity (r=-0.556, p<0.0001), suggesting that patients with elevated platelet counts have an expanded Treg compartment, possibly due to generation of newly-formed (inducible) Tregs and/or proliferation of pre-existing Tregs. Interesting, patients' monocyte frequency were inversely correlated with platelet numbers (r=-0.467, p=0.006).and patients with platelet counts of >50×109/L had reduced frequency of CD14hiCD16neg classic monocytes compared to those with <50×109/L (5.3±0.5% versus 8± 1.2%, p=0.03) whereas both the Tregs frequency (3.4±0.1% versus 2.8±0.2%, p=0.04) and activity (p=0.003) were significantly elevated, raising the possibility that monocytes, which as mature antigen presenting state can affect Treg development, may be inhibiting Foxp3+ Treg frequency/activity in patients with ITP. As a first step to address the mechanisms of Treg expansion in patients with elevated platelet counts and to determine the role of moncytes, we investigated Foxp3 expression in ex vivo activated CD4+ cells from normal donors (n=7) and ITP patients (n=8) using flow cytometric methodology. Following 3 day stimulation of PBMCs with anti-CD3, a similar increase (p=0.9) in CD4+Foxp3+ T cell population was observed in cultures of normal (from 3.6±0.7% to 13.6±1.1%) and patients (from 2.9±1.4% to 12.6±2.1%), suggesting that mechanisms of Foxp3 upregulation after TCR triggering are intact in ITP patients. To determine whether the increase in CD4+Foxp3+ cell population was due to de novo expression of Foxp3 in non-Foxp3 CD4+ cells and/or selective outgrowth of pre-existing Foxp3+ cell population as has been reported for healthy controls, PBMCs were CFSE-labeled before stimulation with anti-CD3 and the proliferative responses and Foxp3 expression levels were analyzed after 3 days. Reports indicate that in stimulated PBMC cultures of normal volunteers, Foxp3high expression in dividing CFSElow CD4+ cells represent proliferation of pre-existing Foxp3+ cell populations whereas Foxp3 upregulation in non-dividing CFSEhigh CD4+ cells is representative of induced Foxp3+ cells and that both mechanisms account for Foxp3+Treg expansion in activated CD4+ cells. In controls and ITP patients, no significant differences were noted in the frequency of Foxp3+ cells in non-proliferating CFSEhigh (7.0±1.0% versus 9.2±1.7%, p=0.9) and dividing Foxp3highCFSElow (13.1±1.5% versus 10.5±1.2%, p=0.3) CD4+ cells, indicating that in ITP patients the proliferative responses of pre-existing Foxp3 cells as well as the ability to generate inducible Foxp3 cells are similar to those of healthy controls. To assess the role of monocytes in Foxp3 expansion, PBMCs were depleted of CD14+ fraction before stimulation with anti-CD3. Removal of CD14+ monocytes resulted in a 25% decrease in the frequency of proliferating CD4+ cells expressing Foxp3high in controls whereas it caused a 22% increase in patients (patients versus controls, p=0.02), but had a similar effect in the levels of Foxp3 expression in non-proliferating CD4+ cells in patients and controls (p=0.7), indicating that monocytes may have an inhibitory effect exclusively on expansion of pre-existing Tregs in patients with ITP. Altogether, our findings support the possibility that in ITP patients with low platelet counts, monocytes may inhibit Treg expansion and activity in response to T cell stimulation, but as platelet counts rise following treatment with TPO-R agonists, the inhibition is removed, enabling proliferation of preexisting CD4+Foxp3high T cells. Studies to characterize the “inhibitory” monocyte populations and the nature of the signals that drive Treg expansion in ITP patients are ongoing. Disclosures:Bussel:Portola: Consultancy; Amgen: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding; GlaxoSmithKline: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding; Ligand: Membership on an entity's Board of Directors or advisory committees, Research Funding; Shionogi: Membership on an entity's Board of Directors or advisory committees, Research Funding; Eisai, Inc.: Membership on an entity's Board of Directors or advisory committees; Cangene: Research Funding; Genzyme: Research Funding.

Results from a Phase I Clinical Study of the Novel Ii-Key/HER-2/neu(776–790) Hybrid Peptide Vaccine in Patients with Prostate Cancer

Active immunotherapy is emerging as a potential therapeutic approach for prostate cancer. We conducted the first phase I trial of an Ii-Key/HER-2/neu(776-790) hybrid peptide vaccine (AE37) with recombinant granulocyte macrophage colony-stimulating factor as adjuvant in patients with HER-2/neu(+) prostate cancer. The primary end points of the study were to evaluate toxicity and monitor patients' immune responses to the vaccine. Thirty-two HER-2/neu(+), castrate-sensitive, and castrate-resistant prostate cancer patients were enrolled. Of these, 29 patients completed all six vaccination cycles with AE37. Immunologic responses in the total patient population were monitored by delayed-type hypersensitivity and IFN-gamma ELISPOT and intracellular staining. Regulatory T-cell (Treg) frequency and plasma HER-2/neu and transforming growth factor-beta levels were also determined. Immunologic responses were also analyzed among groups of patients with different clinical characteristics. Local/systemic toxicities were monitored throughout the study. Toxicities beyond grade 2 were not observed. Seventy-five percent of patients developed augmented immunity to the AE37 vaccine and 65% to the unmodified AE36 peptide as detected in the IFN-gamma-based ELISPOT assay. Intracellular IFN-gamma analyses revealed that AE37 elicited both CD4(+) and CD8(+) T-cell responses. Eighty percent of the patients developed a positive delayed-type hypersensitivity reaction to AE36. Additionally, significant decreases could be detected in circulating Treg frequencies, plasma HER-2/neu, and serum transforming growth factor-beta levels. Patients with less extensive disease developed better immunologic responses on vaccination. AE37 vaccine is safe and can induce HER-2/neu-specific cellular immune responses in patients with castrate-sensitive and castrate-resistant prostate cancer, thus emphasizing the potential of AE37 to target HER-2/neu for the immunotherapy of prostate cancer.

S86 Results from the first phase I clinical study of the novel Ii-Key/HER-2(776–790) hybrid peptide vaccine in patients with prostate cancer

Purpose: Active immunotherapy is emerging as a potential therapeutic approach for prostate cancer. We conducted the first phase I trial of an Ii-Key/HER-2/neu(776–790) hybrid peptide vaccine (AE37) with recombinant granulocyte macrophage colony-stimulating factor as adjuvant in patients with HER-2/neu + prostate cancer. The primary end points of the study were to evaluate toxicity and monitor patients' immune responses to the vaccine. Experimental Design: Thirty-two HER-2/neu + , castrate-sensitive, and castrate-resistant prostate cancer patients were enrolled. Of these, 29 patients completed all six vaccination cycles with AE37. Immunologic responses in the total patient population were monitored by delayed-type hypersensitivity and IFN-γ ELISPOT and intracellular staining. Regulatory T-cell (Treg) frequency and plasma HER-2/neu and transforming growth factor-β levels were also determined. Immunologic responses were also analyzed among groups of patients with different clinical characteristics. Local/systemic toxicities were monitored throughout the study. Results: Toxicities beyond grade 2 were not observed. Seventy-five percent of patients developed augmented immunity to the AE37 vaccine and 65% to the unmodified AE36 peptide as detected in the IFN-γ–based ELISPOT assay. Intracellular IFN-γ analyses revealed that AE37 elicited both CD4 + and CD8 + T-cell responses. Eighty percent of the patients developed a positive delayed-type hypersensitivity reaction to AE36. Additionally, significant decreases could be detected in circulating Treg frequencies, plasma HER-2/neu, and serum transforming growth factor-β levels. Patients with less extensive disease developed better immunologic responses on vaccination. Conclusion: AE37 vaccine is safe and can induce HER-2/neu–specific cellular immune responses in patients with castrate-sensitive and castrate-resistant prostate cancer, thus emphasizing the potential of AE37 to target HER-2/neu for the immunotherapy of prostate cancer. Clin Cancer Res; 16(13); 3495–506. ©2010 AACR.

Systemic Reduction of Functionally Suppressive CD4dimCD25highFoxp3+ Tregs in Human Second Trimester Pregnancy Is Induced by Progesterone and 17β-Estradiol

CD4(+)CD25(high) regulatory T cells (Tregs) are implicated in the maintenance of murine pregnancy. However, reports regarding circulating Treg frequencies in human pregnancy are inconsistent, and the functionality and phenotype of these cells in pregnancy have not been clarified. The aim of this study was to determine the frequency, phenotype, and function of circulating Tregs in the second trimester of human pregnancy and the influence of progesterone and 17beta-estradiol on Treg phenotype and frequency. Based on expressions of Foxp3, CD127, and HLA-DR as determined by multicolor flow cytometry, we defined a proper CD4(dim)CD25(high) Treg population and showed, in contrast to most previous reports, that this population was reduced in second trimester of pregnancy. Unexpectedly, Foxp3 expression was decreased in the Treg, as well as in the CD4(+) population. These changes could be replicated in an in vitro system resembling the pregnancy hormonal milieu, where 17beta-estradiol, and in particular progesterone, induced, in line with the pregnancy situation, a reduction of CD4(dim)CD25(high)Foxp3(+) cells in PBMC from nonpregnant women. By coculturing FACS-sorted Tregs and autologous CD4(+)CD25(-) responder cells, we showed that Tregs from pregnant women still displayed the same suppressive capacity as nonpregnant women in terms of suppressing IL-2, TNF-alpha, and IFN-gamma secretion from responder cells while efficiently producing IL-4 and IL-10. Our findings support the view of hormones, particularly progesterone, as critical regulators of Tregs in pregnancy. Furthermore, we suggest that in the light of the results of this study, early data on circulating Treg frequencies in pregnancy need reevaluation.

Inhibition of phosphoantigen‐mediated γδ T‐cell proliferation by CD4+ CD25+ FoxP3+ regulatory T cells

Tumour growth promotes the expansion of CD4(+) CD25(+) FoxP3(+) regulatory T cells (Tregs) which suppress various arms of immune responses and might therefore contribute to tumour immunosurveillance. In this study, we found an inverse correlation between circulating Treg frequencies and phosphoantigen-induced gammadelta T-cell proliferation in cancer patients, which prompted us to address the role of Tregs in controlling the gammadelta T-cell arm of innate immune responses. In vitro, human Treg-peripheral blood mononuclear cell (PBMC) co-cultures strongly inhibited phosphoantigen-induced proliferation of gammadelta T cells and depletion of Tregs restored the impaired phosphoantigen-induced gammadelta T-cell proliferation of cancer patients. Tregs did not suppress other effector functions of gammadelta T cells such as cytokine production or cytotoxicity. Our experiments indicate that Tregs do not mediate their suppressive activity via a cell-cell contact-dependent mechanism, but rather secrete a soluble non-proteinaceous factor, which is independent of known soluble factors interacting with amino acid depletion (e.g. arginase-diminished arginine and indolamine 2,3-dioxygenase-diminished tryptophan) or nitric oxide (NO) production. However, the proliferative activity of alphabeta T cells was not affected by this cell-cell contact-independent suppressive activity induced by Tregs. In conclusion, these findings indicate a potential new mechanism by which Tregs can specifically suppress gammadelta T cells and highlight the strategy of combining Treg inhibition with subsequent gammadelta T-cell activation to enhance gammadelta T cell-mediated immunotherapy.

Frequency and absolute number of FoxP3+ regulatory T cells correlate with disease progression of chronic HIV-1 infection

CD4+CD25+ Regulatory T cells (Treg) have been found to down-regulate immune activation in HIV-1 infection. However, whether the depletion of Treg benefits to the disease status of HIV infection remains undefined. To address this issue, we enumerated the Treg absolute counts and frequency in 75 antiviral-naive HIV-1-infected individuals in this study. It was found that HIV-infected patients displayed a significant decline in Treg absolute counts but a significant increase in Treg frequency. In addition, with disease progression indicated by CD4 T-cell absolute counts, circulating Treg frequency gradually increased; while Treg absolute counts were gradually decreased, suggesting that the alteration of Treg number closely correlated with disease progression in HIV infection. Functional analysis further showed that Treg efficiently inhibit both CD4 and CD8 T cell proliferation in vitro. Thus, our findings indicates that Treg actively participate in pathogenesis of chronic HIV infection, influencing the disease progression.

CD4+CD25+ Regulatory T-Cell Frequency in HER-2/neu (HER)-Positive and HER-Negative Advanced-Stage Breast Cancer Patients

CD4(+)CD25(bright) regulatory T cells (Tregs) are increased in patients with several malignancies and correlate with disease stage and prognosis. Breast cancer patients represent a heterogeneous population with unpredictable disease progression even at advanced stages. Circulating Tregs in correlation with HER-2/neu (HER) status and treatment with chemotherapy, either alone or in combination with trastuzumab therapy, were monitored in advanced-stage breast cancer patients. Circulating Treg frequency and absolute counts of 46 HER(+) and 28 HER(-), stage III and IV, breast cancer patients before therapy and during trastuzumab therapy and/or chemotherapy have been compared with 24 healthy donors and correlated with plasma HER extracellular domain concentration and clinical outcome. Treg frequency in HER(+) patients was significantly increased compared with both HER(-) patients and healthy donors. Trastuzumab therapy, with or without combined chemotherapy, resulted in a progressive decrease of circulating Tregs. Percentage change in Tregs statistically correlated with percentage change in plasma HER extracellular domain. Furthermore, decrease in Tregs correlated with either objective clinical response or stable disease, whereas increased Treg frequency during trastuzumab therapy coincided with disease progression. No statistically significant change in Treg frequency following chemotherapy was observed in HER(-) patients. Treg cell frequency does not directly correlate with clinical stage in breast cancer, as stage III and IV HER(+) and HER(-) patients exhibit significantly different Treg profiles. Trastuzumab therapy, either alone or combined with chemotherapy, results in decreased Treg frequency in HER(+) advanced patients with an objective clinical response.