Eltrombopag: More Than Just a Thrombopoietin Receptor Agonist (TPO-RA) in Immune Thrombocytopenia (ITP)

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a skewed proinflammatory T cell profile. Thrombopoietin-receptor agonists (TPO-RA) have largely replaced immunosuppressants in the management of this disorder, with some patients achieving remission after a period of treatment with TPO-RA. The potential immune modulatory role of TPO-RA has not been fully investigated. The two current TPO-RA licensed for use in ITP; Eltrombopag (Elt) and Romiplostim (Romi) act on different parts of the TPO-R and have similar response rates. However, patients can respond to one agent but not the other. Elt has been described to have a strong iron chelating effect, and hence we propose that it may have an additive immunomodulatory effect on the T cells, absent in Romi. We determined the immunomodulatory effect of Elt by assessing the proliferation and functionality of T-cell lines and primary T-cells. T cell proliferation was assessed using both CFSE proliferation assay and MTT cell viability assay. T cell phenotype and functionality were assessed by multicolor surface and intracellular flow cytometric staining. Cells were co-cultured with Elt and Romi in vitro and ex vivo with both Jurkat and DG75 cells lines as well as primary cells, respectively. Deferoxamine (DFX) was used as a positive control for iron-chelation, and human TPO was used as a positive control for TPO-RA. All treatment doses were based on their calculated therapeutic serum levels. Mann Whitney U and Kruskal-Wallis H statistical tests were applied where applicable, and a P value of less than 0.05 were considered significant. Elt significantly decreased Jurkat T cells proliferation in a dose-dependent manner compared to no treatment and Romi. DFX, an iron chelator, also decreased Jurkat T cell proliferation to comparable levels of Elt. Interestingly, this anti-proliferative effect of Elt was only observed on Jurkat T cells, but not DG75 B cell line. Ex vivo CFSE proliferation assay was performed on primary CD4 and CD8 T cells assessing the antiproliferative effect of Elt. Elt significantly reduced proliferation compared to no treatment. DFX exhibited a similar antiproliferative effect on primary T cells, however, less potent compared to Elt. Neither Romi nor TPO affected the proliferation of Jurkat cells, DG75 cells or primary T cells. The functionality of CD4 and CD8 T cells was assessed based on the capacity of T cells to produce intracellular TNFα, IFNγ and Granzyme B. Elt significantly reduced the percentages of TNFα+/IFNγ+ CD4+ and CD8+ T cells in a dose-dependent manner. This reduction was also observed, albeit to a lesser extent, when T cells were treated with DFX. Furthermore, Granzyme B expression in CD8+ T cells was significantly reduced when cells were treated Elt, compared to no treatment. Romi did not affect the frequency of CD8+ TNFα+/IFNγ+ populations nor the expression of Granzyme B in CD8+ T cells. CD4+ and CD8+ T cells did not express TPO-R on their surface. To confirm the immunomodulatory role of Elt in vivo, the terminally-differentiated effector (CD45RA+CD62L-) CD8+ T cells were assessed in 13 Elt-treated patients and 11 Romi-treated patients. Patients on Elt had significantly reduced frequency of effector CD8 T cells compared to Romi-treated patients (44% vs 76.8%; p<0.01). Taken together, these novel findings suggest an off target immunomodulatory nature of Elt besides its thrombopoietic effect. This dose-dependent immunomodulatory effect is not TPO-R dependent and targets T cells primarily. This study is the first to display such property of Elt and could explain why there is a differential response to Elt and Romi. We hypothesise that Elt may be more effective in patients with T cell mediated disease, whilst patients with predominantly antibody mediated disease are more likely respond to Romi. These findings can also offer an explanation for Elt effectiveness in other T cell-mediated autoimmune conditions such as Aplastic Anemia. Disclosures Cooper: Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Rigel: Consultancy, Membership on an entity's Board of Directors or advisory committees; Principia: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.

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A Novel Function of CD26-Mediated Costimulation in the Cytotoxic Activity of Human CD8+ T Cells in Xenogeneic Chronic Graft-Versus-Host Disease (cGVHD) and GVL Mice Model.

Blood ◽

10.1182/blood.v114.22.3548.3548 ◽

2009 ◽

Vol 114 (22) ◽

pp. 3548-3548

Author(s):

Ryo Hatano ◽

Kei Ohnuma ◽

Taketo Yamada ◽

Wataru Takasawa ◽

Yuko Endo ◽

...

Keyword(s):

T Cells ◽

Cytotoxic Activity ◽

Board Of Directors ◽

Cd8 T Cells ◽

Granzyme B ◽

Human Lymphocytes ◽

Dependent Manner ◽

Mice Model ◽

Advisory Committees

Abstract Abstract 3548 Poster Board III-485 CD26 is a 110-kDa cell surface glycoprotein with known dipeptidyl peptidase IV (DPPIV) activity in its extracellular domain, capable of cleaving amino-terminal dipeptides with either L-proline or L-alanine at the penultimate position. CD26 activity is dependent on cell type and the microenvironment, which influence its multiple biological roles. CD26 plays an important role in immunology, autoimmunity, diabetes and cancer. The role of CD26 in immune regulation has been extensively characterized, with our recent findings elucidating its linkage with signaling pathways and structures involved in T cells activation as well as antigen presenting cell (APC)-T-cell interaction. CD26 is preferentially expressed on human CD4+ memory T cells and CD4+CD45RO+CD26+ T cells exhibit response maximally to the recall antigen tetanus toxoid. Human T-helper 1 (Th1) cells display a higher expression of CD26 and are much more sensitive to CD26-mediated costimulation than human Th2 cells. In contrast, the role of CD26 in human CD8+ T cells still remains to be elucidated, while CD8+ T cells express CD26 as well as CD4+ T cells. In this study, we studied the effector function of CD26-mediated costimulation of CD8+ T cells. In comparison with CD28-medaited costimulation, which is one of representative T cell costimulatory pathway, CD26-mediated costimulation in CD8+ T cells showed delayed proliferation than that of CD28 stimuatlion, but finally expanded to a similar extent. The secretion of inflammatory cytokines, TNF-alpha and IFN-gamma, was strongly induced after CD26-mediated costimulation. In contrast, the secretion of IL-2 and IL-5 was significantly less as compared with CD28-mediated costimulation. Finally, we showed that the expression of Granzyme B, one of the major effector molecules in the cytotoxic activity of CD8+ T cells, was markedly enhanced by CD26-mediated costimulation in dose dependent manner of anti-CD26 monoclonal antibody stimulation. Moreover, with CD26-mediated costimulation, CD8+ T cells were observed to kill target cells in a Granzyme B-dependent manner. Next, we examined CD26-dependent organ injury by human T cells using xenogeneic chronic GVHD (x-cGVHD) mice model. About 6 weeks after transplantation of human peripheral blood mononuclear cells (PBMC) into NOG-Scid mice, mice develop loss pf hair, loss of weight, and human CD8+ lymphocytes infiltration into liver, lung, and salivary glands, which exhibit pathological changes of cGVHD. Administration of anti-human CD26 mAb decreased onset of x-cGVHD, while human lymphocytes were grafted successfully. Finally, we examined whether GVL effect is exerted via CD26-mediated costimulation, using x-cGVHD mice model in which P388 leukemic cells were grafted subcutaneously. In this tumor-graft model, P388 cells were not grafted in mice with onset of x-cGVHD, which indicated that GVL effect was exerted by human lymphocytes. On the other hand, P388 cells were also diminished in mice with decreased x-cGVHD by administration of anti-CD26 mAb. Taken together, our data strongly suggest that CD26-mediated costimulation in CD8+ T cells deeply involves in the pathology of cGVHD. The present study offers a novel notion that CD26 may become one of therapeutic targets of GVHD without impairment of GVL effect. Disclosures: Yamada: Y's Therapeutics: Membership on an entity's Board of Directors or advisory committees. Dang:Y's Therapeutics: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Morimoto:Y's Therapeutics: Patents & Royalties, a board member.

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Targeting CD38 is lethal to Breg-like chronic lymphocytic leukemia cells and Tregs, but restores CD8+ T-cell responses

Blood Advances ◽

10.1182/bloodadvances.2019001091 ◽

2020 ◽

Vol 4 (10) ◽

pp. 2143-2157 ◽

Cited By ~ 1

Author(s):

Alak Manna ◽

Timothy Kellett ◽

Sonikpreet Aulakh ◽

Laura J. Lewis-Tuffin ◽

Navnita Dutta ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Chronic Lymphocytic Leukemia ◽

Cd8 T Cells ◽

Mononuclear Cells ◽

Transforming Growth Factor ◽

Ex Vivo ◽

Xenograft Model ◽

Lymphocytic Leukemia ◽

Dependent Manner

Abstract Patients with chronic lymphocytic leukemia (CLL) are characterized by monoclonal expansion of CD5+CD23+CD27+CD19+κ/λ+ B lymphocytes and are clinically noted to have profound immune suppression. In these patients, it has been recently shown that a subset of B cells possesses regulatory functions and secretes high levels of interleukin 10 (IL-10). Our investigation identified that CLL cells with a CD19+CD24+CD38hi immunophenotype (B regulatory cell [Breg]–like CLL cells) produce high amounts of IL-10 and transforming growth factor β (TGF-β) and are capable of transforming naive T helper cells into CD4+CD25+FoxP3+ T regulatory cells (Tregs) in an IL-10/TGF-β-dependent manner. A strong correlation between the percentage of CD38+ CLL cells and Tregs was observed. CD38hi Tregs comprised more than 50% of Tregs in peripheral blood mononuclear cells (PBMCs) in patients with CLL. Anti-CD38 targeting agents resulted in lethality of both Breg-like CLL and Treg cells via apoptosis. Ex vivo, use of anti-CD38 monoclonal antibody (mAb) therapy was associated with a reduction in IL-10 and CLL patient-derived Tregs, but an increase in interferon-γ and proliferation of cytotoxic CD8+ T cells with an activated phenotype, which showed an improved ability to lyse patient-autologous CLL cells. Finally, effects of anti-CD38 mAb therapy were validated in a CLL–patient-derived xenograft model in vivo, which showed decreased percentage of Bregs, Tregs, and PD1+CD38hiCD8+ T cells, but increased Th17 and CD8+ T cells (vs vehicle). Altogether, our results demonstrate that targeting CD38 in CLL can modulate the tumor microenvironment; skewing T-cell populations from an immunosuppressive to immune-reactive milieu, thus promoting immune reconstitution for enhanced anti-CLL response.

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T Cell Immunity Toward Viral- and Tumor-Antigens Is Preserved in MDS Patients

Blood ◽

10.1182/blood-2019-126792 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 4225-4225

Author(s):

Hussein Hamad ◽

Wingchi K Leung ◽

Spyridoula Vasileiou ◽

Shivani Mukhi ◽

Quillan Huang ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Board Of Directors ◽

Healthy Donor ◽

Tumor Antigens ◽

Ex Vivo ◽

Advisory Committees ◽

Cell Immunity ◽

Healthy Donors ◽

T Cell Lines

Myelodysplastic syndromes (MDS) are a heterogeneous group of disorders characterized by bone marrow failure and a propensity to progress to acute myeloid leukemia (AML). A core component of the underlying pathogenesis in MDS is deregulation of inflammatory cytokines, such as tumor growth factor-β (TGFβ), which impact the function of immune cells and hence their capacity to mount anti-infective or anti-tumor responses. However, little is known about antigen-specific T cell function in patients with MDS. We hypothesized that virus-specific T cell (VST) function might be preserved in patients with MDS, and that the functional capacity of T cells reactive against tumor-associated antigens aberrantly overexpressed by clonal MDS cells such as Cyclin A1 (CCNA1) and Proteinase (PR3) might also be preserved and exploited for immunotherapeutic purposes. Following informed consent, we collected peripheral blood samples from 10 patients (pts) with MDS and 17 healthy donors. Most pts (9 out of 10) were transfusion dependent and 3 subsequently underwent an allogeneic HSCT. Table 1 summarizes the other clinical characteristics, karyotypic and mutational profile at the time of blood collection. Compared with T cells isolated from healthy donors, MDS patient-derived T cells had a similar CD4 to CD8 ratio (1.5-2.5:1 for healthy donors and 3:1 for MDS pts), but displayed a more exhausted profile at baseline (CD3+TIM3+: 1% in healthy donors and 5% in MDS pts) and produced higher levels of inflammatory cytokines [IFNγ (18±3pg/ml vs 36±16pg/ml, healthy donor vs MDS; p=0.12), and IL-8 (56±32 vs 704±446 pg/ml, p=0.01)]. Next, to assess the capacity of MDS pts to mount ex vivo functional virus-directed responses, we stimulated patient-derived PBMCs (n=5) with overlapping peptide libraries (pepmixes) spanning immunogenic AdV, CMV, EBV, BK and HHV-6 antigens. Similar to healthy donor-derived T cell lines (n=5, 3 specific for 4 viruses and 2 for 5 viruses), all 5 MDS patient-derived lines demonstrated specificity for one or more of the target viruses (1 for 5 viruses, 1 for 4, 2 for 3 and 1 for 1 virus) as observed by IFNγ ELISpot assay with comparable magnitude (range Adv: 43-730 vs 384-941 in healthy donors, CMV: 0-1599 vs 0-3002, EBV: 0-1486 vs 0-541, BK: 0-839 vs 38-275 and HHV6: 0-794 vs 5-407 SFU/2x105 cells, respectively). We next examined the feasibility of expanding autologous MDS-antigen directed T cell products (n=10) to determine whether an adoptive immunotherapeutic approach might be applicable for MDS treatment. Thus, we exposed patient-derived PBMCs to autologous dendritic cells (DC) loaded with pepmixes spanning 6 MDS-associated antigens (CCNA1, survivin, WT1, PRAME, PR3 and NYESO1). After 3 rounds of stimulation, the products obtained were predominantly CD3+ T cells (mean 88±1.3%) that were polyclonal (CD4: 46±5% and CD8: 41±4%) containing predominantly memory T cells (TEM: 36±6% TCM: 37±5% and Tnaïve =13±3%). Six lines (60%) showed specific recognition to at least one of the target antigens: 4 lines specific for PRAME, 1 for CCNA1, 1 for WT1 and 1 for NYESO1 (range 0-40, 0-184, 0-1386 and 0-179 SFU/2x105 cells, respectively by IFNγ ELIspot). T cell lines were capable of specifically secreting multiple effector cytokines in response to targets (TNFα: 12% and IFNγ: 16% in response to PRAME in a representative patient-derived T cell line). Furthermore, this line was capable of killing PRAME+ targets in a 4hr 51Cr release assay [60% specific lysis, E:T 20:1]. In conclusion, functional virus-directed T cell immunity in patients with MDS is preserved, potentially explaining the lower rates of viral reactivation seen in these patients compared with other infections. Moreover, T cells specific for MDS-expressed tumor antigens can also be successfully expanded ex vivo from patients. Taken together this raises the possibility of applying an adoptive immunotherapeutic approach for the treatment of MDS. Disclosures Ramos: Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Tessa Therapeutics: Research Funding. Leen:Allovir: Consultancy, Other: Cofounder, Ownership Interest; Marker Therapeutics: Consultancy, Other: Cofounder, Ownership Interest.

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CD4+ T Cell Fate in Multiple Myeloma

Blood ◽

10.1182/blood-2018-99-117674 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 4494-4494

Author(s):

Rachel Elizabeth Cooke ◽

Jessica Chung ◽

Sarah Gabriel ◽

Hang Quach ◽

Simon J. Harrison ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Board Of Directors ◽

Cd8 T Cells ◽

Cd4 T Cells ◽

Research Funding ◽

Flow Cytometric Analysis ◽

Advisory Committees ◽

Mitochondrial Mass ◽

Flow Cytometric

Abstract The average incidence of multiple myeloma (MM) is in the 7th decade that coincides with the development of immunosenescence and thymic atrophy, meaning that lymphocyte recovery after lymphopenia-inducing therapies (most notably autologous stem cell transplant, ASCT) is largely reliant on homeostatic proliferation of peripheral T cells rather than replenishing the T cell pool with new thymic emigrants. We have previously shown that there is a significant reduction in circulating naïve T cells with a reciprocal expansion of antigen-experienced cells from newly diagnosed MM (NDMM) to relapsed/refractory disease (RRMM). This results in a reduced TCR repertoire and the accumulation of senescence-associated secretory phenotype cytotoxic T cells, which maintain the ability to produce IFNγ but lose proliferative potential. A reduction in CD4:8 ratio is also a characteristic finding in MM with disease progression, which can be explained by high IL-15 levels in lymphopenic states that preferentially drive expansion of CD8+ memory T cells. We wanted to further evaluate what changes were occurring in the CD4+ T cell population with disease progression in MM. We analyzed paired peripheral blood (PB) samples from patients with NDMM and RRMM, and compared with age-matched normal donors (ND). In the NDMM cohort, we examined T cells from PB samples at baseline, after 4 cycles of lenalidomide and dexamethasone (len/dex), and after ASCT; and in the RRMM cohort samples from baseline and after 6 cycles of len/dex. We firstly confirmed in flow cytometric analysis of T cells at serial intervals in NDMM patients that the reduction in circulating naïve T cells and in CD4:8 ratio occurs post ASCT and does not recover by time of last follow-up. We next utilised RNA-seq to analyse differences in CD4+ T cells from NDMM, RRMM and ND. CD4+ T cells from RRMM showed downregulation of cytosolic ribosomal activity but maintenance of mitochondrial ribosomal activity and significant upregulation of pathways involved with calcium signalling. To this end, we evaluated mitochondrial biogenesis and metabolic pathways involved with mitochondrial respiration. Flow cytometric analysis of mitochondrial mass showed a marked increase in RRMM compared with ND, in keeping with a shift towards memory phenotype. Key rate-limiting enzymes in fatty acid β-oxidation (CPT1-A, ACAA2 and ACADVL) were all significantly increased in RRMM compared with ND. To analyse whether these cells were metabolically active, we also measured mitochondrial membrane potential and reactive oxygen species (ROS), gating on cells with high mitochondrial mass. Mitochondrial membrane potential was significantly increased in RRMM compared with ND, although ROS was reduced. The significance of this is not clear, as ROS are not only implicated in cell senescence and activation-induced cell death, but are also positively involved in tyrosine kinase and PI3K-signalling pathways. PD-1 has been shown to play a role in transitioning activated CD4+ T cells from glycolysis to FAO metabolism, and elevating ROS in activated CD8+ T cells. We analysed PD-1 expression on T cells in RRMM and at treatment intervals in NDMM (as described earlier). The proportion of CD4+ and CD8+ T cells expressing PD-1 was increased 4-6 months post-ASCT and remained elevated in CD4+ T cells 9-12 months post-ASCT, but normalised to baseline levels in CD8+ T cells. Increased PD-1 expressing CD4+ T cells was also evident in RRMM patient samples. This may suggest that in the lymphopenic state, PD-1 expression enhances longevity in a subset of CD4+ T cells by promoting reliance on mitochondrial respiration; however, their ability to undergo homeostatic proliferation is impaired. In CD8+ T cells, high PD-1 expression may lead to cell death via ROS accumulation, and these cells do not persist. ASCT remains a backbone of myeloma treatment in medically fit patients. However, this leads to significant permanent defects in the T cell repertoire, which may have unintended adverse outcomes. Additionally, T cells post-ASCT may not be metabolically adequate for the production of CAR-T cells, nor respond to checkpoint blockade therapies. Disclosures Quach: Amgen: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Sanofi Genzyme: Research Funding; Janssen Cilag: Consultancy. Harrison:Janssen-Cilag: Other: Scientific advisory board. Prince:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen Cilag: Honoraria, Membership on an entity's Board of Directors or advisory committees.

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Combinatorial Cytokine Secretion Signature of Donor-Derived T Cells Infused with the Graft: A New Potential Biomarker of Acute Graft-Versus-Host Disease in Αβt-Cell/CD19 B-Cell Depleted Hematopoietic Stem Cell Transplant Recipients

Blood ◽

10.1182/blood-2021-149948 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 1684-1684

Author(s):

Raul Montiel-Esparza ◽

Giulia Barbarito ◽

Samantha Peck ◽

Magali Bazzano ◽

Rachana Patil ◽

...

Keyword(s):

T Cells ◽

Stem Cell ◽

T Cell ◽

Single Cell ◽

Board Of Directors ◽

Cd8 T Cells ◽

Cytokine Secretion ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Tnf Α

Abstract Background: Hematopoietic stem cell graft manipulation strategies, such as αβT-cell/CD19 B-cell depleted hematopoietic stem cell transplantation (αβhaplo-HSCT), address the lack of matched donors and reduce the incidence of severe acute graft-versus-host disease (aGvHD). However, grade II-IV aGvHD still occurs in 25-30% of αβhaplo-HSCT recipients . Studies aimed at understanding the pathogenesis underlying aGVHD in αβhaplo-HSCT are lacking. We hypothesized that αβT cells adoptively transferred with the HSCT (<1x10 5/Kg) have unique combinatorial cytokine secretion signatures that may predict the occurrence of aGvHD. Here we used the IsoPlexis single-cell proteomics for CD4 + and CD8 + T cells to identify those putative signatures . Methods: Six patients with hematologic malignancies receiving fully myeloablative αβhaplo-HSCT at Lucile Packard Children's Hospital, Stanford, between 08/2018 and 05/2020 were enrolled upon signing IRB approved informed consent. Three patients developed grade II-IV aGvHD, while three did not. Aliquot of the graft and of peripheral blood collected at the time of aGvHD onset or at corresponding time points for the patients who did not develop aGvHD, were analyzed. Single sorted CD4 + and CD8 + T cells were profiled by single-cell barcode chip assay from IsoPlexis system (IsoPlexis, Branford, CT) after stimulation with PMA (50 ng/mL) and Ionomycin (1mcg/mL). Following the Human Adaptive Immune Panel, cytokines from CD4 + and CD8 + single T cells were captured by fluorescence ELISA, which measured the numbers of cytokine-producing cells (secretion frequency) and numbers of cytokines produced by individual cells across five functional groups: effector, stimulatory, chemoattractive, regulatory and inflammatory (Table 1). Polyfunctionality was defined as the secretion of 2+ cytokines from each CD4 + and CD8 + T cell. The T cell polyfunctional strength Index (PSI) was defined as the percentage of polyfunctional cells, multiplied by the sum of the mean fluorescence intensity of the proteins secreted by those cells. Additional statistical analysis was performed using the Student's t test. Results: We compared the combinatorial cytokine secretion signature of individual CD4 + and CD8 + T cells isolated from grafts infused into patients, who eventually did or didn't develop aGvHD. We are comparing the signature of post-HSCT CD4 + and CD8 + T cells isolated from patients who did or did not develop aGvHD. Collectively, we considered three variables: cytokine secretion frequency, numbers of cytokines produced by individual cells and characteristics of the cytokines secreted (functional group) upon stimulation. Single-cell functional heterogeneity evaluated by t-Distributed Stochastic Neighbor Embedding (t-SNE), showed higher CD4 + and CD8 + T-cell polyfunctionality (up to 4+ cytokines) with effector and stimulatory dominant functions in the grafts of patients who developed aGvHD, compared to those who did not develop aGvHD (Fig1). The average PSI (driven by Granzyme B, TNF-α, IFN-γ, MIP-1β, IL2, and IL-8) was found to be higher in both CD4 + and CD8 + T cells from the grafts of patients who developed aGvHD (Fig 2). Combinatorial cytokine secretion analysis showed that T cells from grafts of patients who did not develop aGvHD had unique signatures with CD4 + T cells having the predominant cytokine secretion signature of IL2 and TNF-α, and CD8 + T cells having three predominant cytokine secretion signatures: IL2, IL8, TNF-α; MIP-1β, IL8; and MIP-1β, IFN-γ (Fig3). Conclusions: Preliminary data from αβhaplo-HSCT pediatric recipients obtained using IsoPlexis single-cell functional proteomics for CD4 + and CD8 + T cells showed that an increased donor T-cell polyfunctionality with a Th1 dominant functional phenotype may be predictive of an increased risk of aGvHD, while CD4 + and CD8 + T cells infused into patients who didn't develop aGvHD, had combinations with limited cytokine secretion signatures. Ongoing analysis suggest that polyfunctional CD8 + T cells present in the graft of patients who developed aGvHD, are present at the time of aGvHD initiation, while the polyfunctional CD4 + T cell are not present at the onset of aGvHD. Correlation with ongoing studies on circulating cytokines and clonotypic analysis of αβT cells infused with the graft will be crucial to elucidate the cross talking between the donor's immune system and recipient's inflammatory milieu. Figure 1 Figure 1. Disclosures Parkman: Jasper Biotech: Consultancy. Bertaina: Cellevolve Bio: Membership on an entity's Board of Directors or advisory committees; Neovii: Membership on an entity's Board of Directors or advisory committees; AdicetBio: Membership on an entity's Board of Directors or advisory committees.

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Phase 1/2 Study of Nexi-001 Donor-Derived Multi-Antigen Specific CD8+ T Cells for the Treatment of Relapsed Acute Myeloid Leukemia (AML) after Allogeneic Hematopoietic Transplantation

Blood ◽

10.1182/blood-2021-152419 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 4819-4819

Author(s):

Monzr M. Al Malki ◽

Sumithira Vasu ◽

Dipenkumar Modi ◽

Miguel-Angel Perales ◽

Lucy Y Ghoda ◽

...

Keyword(s):

Bone Marrow ◽

T Cells ◽

T Cell ◽

Board Of Directors ◽

Cd8 T Cells ◽

Research Funding ◽

Phase 1 ◽

Clinical Activity ◽

Advisory Committees ◽

Over Time

Abstract Patients who relapse after allogeneic HCT have a poor prognosis and few effective treatment options. Responses to salvage therapy with donor lymphocyte infusions (DLI) are driven by a graft versus leukemia (GvL) effect. However, relapses and moderate to severe graft versus host disease (GVHD) are common. Therapies that increase the GvL effect without inducing GVHD are needed. The NEXI-001 study is a prospective, multicenter, open-label phase 1/2 trial designed to characterize the safety, immunogenic, and antitumor activity of the NEXI-001 antigen specific T-cell product. This product is a donor-derived non-genetically engineered therapy that consists of populations of CD8+ T cells that recognize HLA 02.01-restricted peptides from the WT1, PRAME, and Cyclin A1 antigens. These T cells consist of populations with key memory phenotypes, including stem-like memory, central memory, and effector memory cells, with a low proportion (<5%) of potentially allogeneic-reactive T-naïve cells. Patients enrolled into the first cohort of the dose escalation phase received a single infusion of 50 million (M) to 100M cells of the NEXI-001 product. Bridging anti-AML treatment was permitted during the manufacture of the cellular product with a wash-out period of at least 14 days prior to lymphodepletion (LD) chemotherapy (intravenous fludarabine 30 mg/m 2 and cyclophosphamide 300 mg/m 2) that was administered on Days -5, -4, and -3 prior to the infusion of the NEXI-001 product up to 72 hours later (Day1). Lymphocyte recovery to baseline levels occurred as early as three days after the NEXI-001 product infusion with robust CD4 and CD8 T cell reconstitution after LD chemotherapy. NEXI-001 antigen specific T cells were detectable in peripheral blood (PB) by multimer staining and were found to proliferate over time and to traffic to bone marrow. The phenotype composition of detectable antigen specific T cells at both sites was that of the infused product. T-cell receptor (TCR) sequencing assays revealed T cell clones in the NEXI-001 product that were not detected in PB of patients tested at baseline. These unique clones subsequently expanded in PB and bone marrow (BM) and persisted over time. Neutrophil recovery, decreased transfusion burden of platelets and red blood cells, and increased donor chimerism were observed. Decreases in myeloblasts and reduction in the size of an extramedullary myeloid sarcoma were suggestive of clinical activity. One patient, a 23-year- old with MRD+ disease at baseline, received two doses of 200M NEXI-001 cells separated by approximately 2 months. Following the first infusion, antigen specific CD8+ T cells increased gradually in PB to 9% of the total CD3+ T cell population just prior to the second infusion and were found to have trafficked to bone marrow. By Day 2 following the second infusion, which was not preceded by LD chemotherapy, the antigen specific CD8+ T cells again increased to 9% of the total CD3+ T cell population in PB and remained at ≥5% until the end of study visit a month later. The absolute lymphocyte count increased by 50% highlighting continued expansion of the NEXI-001 T cells. These cells also maintained significant Tscm populations. Treatment related adverse events, including infusion reactions, GVHD, CRS, and neurotoxicity (ICANS), have not developed in these patients who have received 50M to 200M T cells of the NEXI-001 product either as single or repeat infusions. In conclusion, these results show that infusion of the NEXI-001 product is safe and capable of generating a cell-mediated immune response with early signs of clinical activity. A second infusion is associated with increasing the level of antigen specific CD8+ T cells and their persistence in PB and BM. TCR sequencing and RNA Seq transcriptional profiling of the CD8+ T cells are planned, and these data will be available for presentation during the ASH conference. At least two cycles of 200M NEXI-001 cells weekly x 3 weeks of a 4-week cycle is planned for the next dose-escalation cohort. Early data suggest that the NEXI-001 product has the potential to enhance a GvL effect with minimal GVHD-associated toxicities. Disclosures Al Malki: Jazz Pharmaceuticals, Inc.: Consultancy; Neximmune: Consultancy; Hansa Biopharma: Consultancy; CareDx: Consultancy; Rigel Pharma: Consultancy. Vasu: Boehringer Ingelheim: Other: Travel support; Seattle Genetics: Other: travel support; Kiadis, Inc.: Research Funding; Omeros, Inc.: Membership on an entity's Board of Directors or advisory committees. Modi: MorphoSys: Membership on an entity's Board of Directors or advisory committees; Seagen: Membership on an entity's Board of Directors or advisory committees; Genentech: Research Funding. Perales: Sellas Life Sciences: Honoraria; Novartis: Honoraria, Other; Omeros: Honoraria; Merck: Honoraria; Takeda: Honoraria; Karyopharm: Honoraria; Incyte: Honoraria, Other; Equilium: Honoraria; MorphoSys: Honoraria; Kite/Gilead: Honoraria, Other; Bristol-Myers Squibb: Honoraria; Celgene: Honoraria; Medigene: Honoraria; NexImmune: Honoraria; Cidara: Honoraria; Nektar Therapeutics: Honoraria, Other; Servier: Honoraria; Miltenyi Biotec: Honoraria, Other. Edavana: Neximmune, Inc: Current Employment. Lu: Neximmune, Inc: Current Employment. Kim: Neximmune, Inc: Current Employment. Suarez: Neximmune, Inc: Current Employment. Oelke: Neximmune, Inc: Current Employment. Bednarik: Neximmune, Inc: Current Employment. Knight: Neximmune, Inc: Current Employment. Varela: Kite: Speakers Bureau; Nexlmmune: Current equity holder in publicly-traded company, Honoraria, Membership on an entity's Board of Directors or advisory committees.

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The Innate Immune Sensor Sting Promotes Donor CD8+ T Cell Activation and Recipient APC Death Early after Preclinical Allogeneic Hematopoietic Stem Cell Transplantation

Blood ◽

10.1182/blood-2019-130197 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 3202-3202

Author(s):

Cameron S. Bader ◽

Henry Barreras ◽

Casey O. Lightbourn ◽

Sabrina N. Copsel ◽

Dietlinde Wolf ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Board Of Directors ◽

T Cell Activation ◽

Cd8 T Cells ◽

Research Funding ◽

Cell Activation ◽

Cd8 T Cell ◽

Advisory Committees ◽

Hematopoietic Stem

Graft-versus-host disease (GVHD) remains a significant cause of morbidity and mortality in patients receiving allogeneic hematopoietic stem cell transplants (aHSCTs). Pre-HSCT conditioning typically consists of irradiation and drug administration resulting in the death of rapidly dividing cells and release of endogenous danger signals. These molecules drive the activation of antigen presenting cells (APCs) and the differentiation of allo-reactive donor T cells, leading to damage of particular host tissues characteristic of GVHD. Cell death following conditioning has promoted the hypothesis that sensors of cytoplasmic DNA damage in GVHD target tissues contribute to pro-inflammatory cytokine production. We identified a role for Stimulator of Interferon Genes (STING), an innate immune sensor, in GVHD using pre-clinical MHC-matched unrelated donor (MUD) aHSCT models. Here we show that STING rapidly promotes donor CD8+ T cell activation and recipient APC death early after aHSCT. To assess STING involvement immediately post-HSCT, cytokine mRNA expression was examined 48 hrs after transplant of MUD C3H.SW bone marrow (BM) + T cells into irradiated B6 wildtype (WT) or STING-/- recipients. Colon tissue from STING-/- recipients had >2x reduction in IFNβ, TNFα and IL-6 mRNA vs WT. MUD STING-/- HSCT recipients also experienced decreased weight loss, GVHD scores and skin pathology 6 wks post-HSCT vs WT. Double chimerism studies showed that the absence of STING in non-hematopoietic cells was responsible for GVHD amelioration. Conversely, a single dose of the highly specific STING agonist DMXAA given in vivo increased IFNβ, TNFα and IL-6 mRNA expression in WT, but not STING-/-, colon tissue 48 hrs after transplant and increased GVHD scores and lethality post-HSCT. Post-transplant cytoxan treatment abolished the ability of DMXAA to augment GVHD, supporting the notion that STING signaling increases donor T cell activation during aHSCT. To evaluate the potential impact of STING in the clinical setting, we transplanted C3H.SW BM + T cells into mice homozygous for a murine homologue of a human allele associated with diminished STING activity (STINGHAQ/HAQ) and found that these mice also exhibited diminished GVHD. Interestingly, our findings that STING deficiency ameliorates GVHD in MUD aHSCT contrasts to reported observations that STING deficiency can exacerbate GVHD after MHC-mismatched (MMUD) aHSCT (Fischer J, et al, Sci. Transl. Med. 2017). Since CD4+ and CD8+ T cells are central in MMUD and MUD GVHD, respectively, we hypothesized that STING's effect on the predominant T cell subset in each model may explain these seemingly paradoxical results in STING-/- vs WT recipients. Therefore, we transplanted MMUD BALB/c BM + CD8+ T cells into B6-WT and STING-/- mice and found that - in contrast to MMUD recipients of combined CD4+ and CD8+ T cells - STING-/- recipients developed lower GVHD clinical scores, reduced skin pathology and had lower frequencies of activated T cells 8 wks post-HSCT vs WT, supporting a role for STING in the promotion of CD8+ T cell-mediated GVHD. Next, we investigated if recipient APCs played a role in STING's enhancement of CD8+ T cell-mediatedGVHD. We found that STING-/- mice had greater frequencies and numbers of recipient splenic CD11b+CD11c+ APCs 1 day after MMUD B6 into BALB/c aHSCT (Fig. A). BALB/c-STING-/- APCs also expressed reduced MHC class I protein levels (Fig. B). Moreover, STING-/- recipient spleens contained lower numbers of donor CD8+ T cells producing IFNγ and TNFα (Fig. C). These data support the hypothesis that STING contributes to early activation of donor CD8+ T cells and elimination of recipient APCs. Next, to identify if the loss of host MHC II+ APCs affected subsequent donor CD4+ T cell activation, B6-Nur77GFP transgenic donor T cells were used to explicitly monitor T cell receptor signaling. Consistent with increased numbers of host MHC II+ APCs in the spleens of STING-/- recipients 1 day post-aHSCT, we found greater frequencies and numbers of donor Nur77GFP CD4+ T cells expressing GFP, CD69 and IFNγ in STING-/- spleens 6 days after transplant (Fig. D). In summary, our studies demonstrate that STING plays an important role in regulating aHSCT and provide one potential mechanism by which STING could promote CD8+ T cell-mediated GVHD yet diminish CD4+-mediated GVHD. Overall, our studies suggest this pathway can provide a target for new therapeutic strategies to ameliorate GVHD. Disclosures Blazar: BlueRock Therapeutics: Membership on an entity's Board of Directors or advisory committees; Childrens' Cancer Research Fund: Research Funding; KidsFirst Fund: Research Funding; Tmunity: Other: Co-Founder; Kamon Pharmaceuticals, Inc: Membership on an entity's Board of Directors or advisory committees; Regeneron Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Five Prime Therapeutics Inc: Co-Founder, Membership on an entity's Board of Directors or advisory committees; Magenta Therapeutics and BlueRock Therapeuetics: Membership on an entity's Board of Directors or advisory committees; Fate Therapeutics, Inc.: Research Funding; RXi Pharmaceuticals: Research Funding; Alpine Immune Sciences, Inc.: Research Funding; Abbvie Inc: Research Funding; Leukemia and Lymphoma Society: Research Funding. Levy:Heat Biologics: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pelican Therapeutics: Consultancy, Research Funding.

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Nivolumab for Relapsed or Residual Haematological Malignancies after Allogeneic Haematopoietic Stem Cell Transplantation (NIVALLO)

Blood ◽

10.1182/blood-2018-99-112310 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 4633-4633 ◽

Cited By ~ 4

Author(s):

Eric Wong ◽

Emily Dawson ◽

Joanne Davis ◽

Rachel Koldej ◽

Mandy Ludford-Menting ◽

...

Keyword(s):

Clinical Trial ◽

T Cells ◽

Stem Cell ◽

T Cell ◽

Board Of Directors ◽

Cd8 T Cells ◽

Acute Gvhd ◽

Haematological Malignancies ◽

Advisory Committees ◽

Safety And Efficacy

Abstract Aim: To evaluate the safety and efficacy of nivolumab for the treatment of relapsed or residual haematological malignancies after allogeneic stem cell transplantation (alloSCT). Background: Relapse of haematological malignancies following alloSCT is a major cause of post-transplant mortality. Interaction between programmed cell death protein-1 (PD-1) and its ligand (PD-L1) inhibits T-cell alloreactivity and contributes to immune escape. Nivolumab inhibits PD-1 signalling and augments T-cell cytotoxicity. The safety and efficacy of nivolumab post-alloSCT has not been evaluated in a clinical trial. Method: In this investigator-initiated phase IIa clinical trial, patients with relapsed or persistent haematological malignancies following alloSCT receive nivolumab 3mg/kg for up to 48 weeks. Patients with current graft-versus-host disease (GVHD) or prior grade ≥2 acute GVHD or chronic GVHD are excluded. Results: Six participants have received at least one dose of nivolumab at this interim assessment. Primary haematological malignancies relapsing post-alloSCT included Hodgkin lymphoma (HL, 2 patients), acute myeloid leukaemia (AML, 2), transformed chronic lymphocytic leukaemia (tCLL, 1) and mantle cell lymphoma (MCL, 1). The median time from alloSCT to first dose of nivolumab was 25.5 months. Two participants developed grade 3 acute GVHD at 6 days and 13 days following the first dose of nivolumab. Complete or partial responses were observed in 3 participants (50%). Two participants with HL achieved complete responses. One participant with MCL had a complete nodal response with small volume persistent bone marrow disease. One participant with monosomal karyotype AML achieved initial blast reduction (23% to 13%) however subsequently developed progressive AML. T-cell phenotyping at first AML relapse (prior to nivolumab) demonstrated a high proportion of CD8+ T cells that expressed PD-1 and T-cell immunoglobulin and mucin domain 3 (TIM-3) consistent with T-cell exhaustion. Following treatment with nivolumab there was an increase in TNFα production by CD8+ T-cells at day 7 post nivolumab, demonstrating augmentation of T-cell activity. Despite continued nivolumab treatment TNFα production subsequently declined and correlated with loss of clinical response. TIM-3 expression was further upregulated at post-nivolumab progression suggesting this inhibitory checkpoint receptor may have contributed to nivolumab resistance. Conclusion: Nivolumab treatment after alloSCT results in potent immune stimulation with a high rate of clinical responses, albeit with a risk of GVHD. Acquired resistance to nivolumab may develop via upregulation of alternative inhibitory checkpoints. Disclosures Szer: Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Other: Travel Support , Research Funding. Grigg:BMS: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees.

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Early Mycosis Fungoides Lesions with Increased CD3-CD4+ Histiocytes Are Associated with Dyslipidemia and Use of Statins

Blood ◽

10.1182/blood.v126.23.4609.4609 ◽

2015 ◽

Vol 126 (23) ◽

pp. 4609-4609

Author(s):

Chee Won Oh ◽

Carlos Torres-Cabala ◽

Mikyoung Chang ◽

Madeleine Duvic

Keyword(s):

T Cells ◽

T Cell ◽

Board Of Directors ◽

Cd8 T Cells ◽

Research Funding ◽

Skin Lesions ◽

Medication History ◽

Advisory Committees ◽

History Of ◽

Skin Biopsies

Abstract Background The term "histiocyte" includes cells of the monocyte/macrophage series as antigen processing cells and the Langerhans cell/DC series as antigen-presenting cells. At least three DC subsets exist in skin: two expressing either CD1a or CD14 are dermal and Langerhans cells expressing CD1a are epidermal. Since the phenotype of histiocytic cells is typically CD3-CD4+, an estimation of the CD4+ histiocytic population can be made by comparing the numbers of CD3+ T cells with CD4+ cells. Programmed Cell Death 1 (PD-1) is an inhibitory receptor expressed on T cells, B cells, and some myeloid cells. During chronic antigen exposure, expression of PD-1 is sustained. Statins, inhibitors of cholesterol biosynthesis, are immunomodulatory agents acting on T cells and DCs, but their effects on skin immunology are unknown. Objectives To investigate whether infiltrates of CD3-CD4+histiocytes in early mycosis fungoides (MF) lesional skin biopsies are associated with any other factors, including history of medication and to reveal their histopathological pattern. Methods From Jan to Dec 2014, we identified cases of early MF from the clinic in which CD4+ cells exceeded CD3+ cells with biopsies to identify increased histiocytic population. Exclusion criteria included Sézary syndrome, granulomatous MF, T cell receptor beta monoclonality, abnormal T cell populations by flow cytometry, retinoid treatment, and progression of disease after treatment (n=12). Clinical and laboratory findings were retrospectively reviewed. Skin biopsies stained for H&E, CD3, CD4, CD7, and CD8 were reviewed. In 3 cases with paraffin blocks available, immunohistochemical stains for CD68, CD1a, CD163, PD-1, and PD-1 ligand PD-L1 were done. Results Clinical manifestations of early MF were pink scaly patches (9/12), capillaritis (2/12), and annular erythema - like patches (1/12). Eleven also had an increased monocytes in peripheral blood. All cases had a medication history of taking statins (atorvastatin 5/12; simvastatin 2/12; rosuvastatin 1/12) for dyslipidemia (hypercholesterolemia 7/12; both hypercholesterolemia and hypertriglyceridemia 3/12). In 9/12, symptoms persisted after MF treatment. A lichenoid or superficial perivascular lymphohistiocytic infiltration was observed in skin lesions. Focal basal vacuolization was found in all 12 patients. Upper dermal perivascular extravasation of RBCs suggesting vasculopathy was also found in 12/12 cases. All twelve cases showed predominant CD4+ T cells compared to CD8+ T cells in dermis and the CD4+ T cells were more prominent in dermis rather than in epidermis. CD7+ T cells were preserved (3/12) or partially lost (9/12). In all 3 cases, macrophage markers CD68 and CD163 were positive in dermal infiltrates. CD1a+ DCs were increased in both epidermis and dermis in all 3/3. Only one case of three showed PD1/PD-L1+ T cells in dermis. Discussion and Conclusion All our cases had a medication history of statins for dyslipidemia. Of interest, skin biopsies showed a vasculopathy previously reported during high-dose atorvastatin treatment (Tehrani et al, 2013) and infiltration of CD4/CD8+ T cells, CD1a+DCs and CD163/CD68+ macrophages. We hypothesize that statins or dyslipidemia in early MF were associated with cutaneous T cell immune reaction. In support of our hypothesis that dyslipidemia is associated with histiocytosis, we found a report of nine cases of granulomatous pigmented purpuric dermatosis with concurrent hyperlipidemia (Battle et al, 2015). Cholesterol induces monocytosis and M1 macrophages in mice. One study showed that predominant migration of mature CD1a+ DC is associated with release of IL-12p70 and efficient expansion of Th 1 cells and functional CD8+ T cells. On the contrary, IL-10 up-regulates migration of immature CD14+ DC, expression of the M2 macrophage marker CD163, poor expansion of CD4+ and CD8+ T cells, and skewing of Th responses conducive to expression of PD-L1. We cannot know whether skin lesions are secondary to hyperlipidemia or to treatment with statins. Although M1 and M2 macrophages can be distinguished by diverse markers, none of these antigens are suitable for single-marker identification by immunohistochemistry in paraffin embedded tissue blocks. Further study of the cutaneous effect and immunologic mechanisms leading to increased expression of DCs and T cell dysfunction after statin medication is necessary. Disclosures Duvic: Oncoceutics: Research Funding; Therakos: Research Funding, Speakers Bureau; Huya Bioscience Int'l: Consultancy; Tetralogics SHAPE: Research Funding; Innate Pharma: Research Funding; Cell Medica Ltd: Consultancy; Celgene: Membership on an entity's Board of Directors or advisory committees; MiRagen Therapeutics: Consultancy; Soligenics: Research Funding; Allos (spectrum): Research Funding; Array Biopharma: Consultancy; Spatz Foundation: Research Funding; Rhizen Pharma: Research Funding; Eisai: Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Kyowa Hakko Kirin, Co: Membership on an entity's Board of Directors or advisory committees, Research Funding.

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CD4+ Regulatory T Cells Specific for the WT1 Antigen Are Present in Acute Myeloid Leukemia Patients: Implication for Immunotherapy.

Blood ◽

10.1182/blood.v112.11.1933.1933 ◽

2008 ◽

Vol 112 (11) ◽

pp. 1933-1933

Author(s):

Said Dermime ◽

Cynthia Lehe ◽

Hazem Ghebeh ◽

Abdullah Al-Sulaiman ◽

Ghofran Al Qudaihi ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Regulatory T Cells ◽

Cytotoxic Activity ◽

Cd8 T Cells ◽

Ex Vivo ◽

Granzyme B ◽

Critical Role ◽

Leukemic Cells ◽

Cell Contact

Abstract Compelling evidences indicate a key role for regulatory T cells (Tregs) on the host response to cancer and recent studies indicated that the generation of effective WT1-specific cytotoxic T cells can be largely affected by the presence of Tregs. This is the first study to describe human Tregs generated specifically against the WT1 antigen which is overexpressed in several human leukemias and provide the mechanism by which these anti-WT1 Tregs inhibit the immune response in leukemia patients. We have generated T cell lines and clones that specifically recognized a WT1-84 peptide in an HLA DRB1*0402/TCR-Vb8-restricted manner. Importantly, they recognized HLADRB1* 04-matched fresh leukemic cells expressing the WT1 antigen. These clones exerted a Th2 cytokine profile, had a CD4+CD25+Foxp3+GITR+CD127− Tregs phenotype, and significantly inhibited the proliferative activity of allogeneic T cells independently of cell-contact. Priming of allo-reactive T cells in the presence of Tregs strongly inhibited the expansion of NK; NK-T and CD8+ T cells, had an inhibitory effect on NK/NK-T cytotoxic activity but not on CD8+ T cells. Furthermore, priming of T cells with the WT1- 126 HLA-A0201-restricted peptide in the presence of Tregs strongly inhibited the induction of anti-WT1-126 CD8+ CTL responses as evidenced by both very low cytotoxic activity and IFN-g production. Moreover, these Tregs clones specifically produced Granzyme-B and selectively induced apoptosis in WT1-84 pulsed-autologous APCs but not in apoptoticresistant DR4-matched leukemic cells. Importantly, we have also detected anti-WT1-84 IL-5+/Granzyme-B+/Foxp3+ CD4+ Tregs in 5 out of 8 HLA-DR4+ AML patients. These findings suggest a critical role for anti-WT1 Tregs in the inhibition of T cell responses against leukemia. This study may have important implications for the clinical manipulation of Tregs such as immuno-targeting of TCR-Vb-8 with mAbs to eliminate anti-WT1 Tregs in leukemia patients in order to enhance GVL before vaccination with the WT1 antigen. On the other hand, leukemia patients with GVHD should be clinically-tried for vaccination with the current WT1-84 peptide or adoptively-treated with ex-vivo anti-WT1 Treg cells to specifically enhance their frequency, which is known to be very low in these patients.

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