Optimizing the therapeutic window of sirolimus by monitoring blood concentration for the treatment of immune thrombocytopenia

Previous studies have demonstrated that sirolimus (SRL) is an effective agent for the treatment of refractory/relapsed (R/R) ITP. However, the therapeutic window of sirolimus in the treatment of ITP has not been established. As the toxicity of sirolimus increases with higher blood concentrations, it is crucial to determine the optimal therapeutic concentration of SRL for the treatment of ITP. Thus, in this study, we used a retrospective cohort of ITP patients treated with sirolimus to propose the therapeutic dosage window for sirolimus. A total of 275 laboratory results of SRL blood concentration from 63 ITP patients treated with SRL were analyzed retrospectively. The ITP patients were divided into five groups based on their SRL blood concentration: 0-4 ng/ml, 4-8 ng/ml, 8-12 ng/ml, 12-16 ng/ml and ≥16 ng/ml. In addition to the SRL blood concentration, platelet counts and adverse events that occurred during the first 6 weeks of SRL treatment were analyzed. These findings were then used to establish the decision matrix tables and ROC curves, which helped identify the therapeutic window of SRL. Based on the values and trends of true-positive rate (TPR) and false-positive rate (FPR) in the ROC curve, patients who achieved a SRL blood concentration of 4-12 ng/ml displayed a higher response rate compared to those with a SRL concentration of 0-4 ng/ml or ≥16ng/ml. Additionally, the response rate was better for patients with a SRL concentration of 8-12 ng/ml compared to 4-8 ng/ml. Adverse events were related to the concentration of SRL; however, there was no significant difference in the incidence of adverse events between the concentrations of 4-8 ng/ml and 8-12 ng/ml (P > .05). Regression analysis suggested that the concentration of SRL correlated with the patient's age, PLT count at the start of SRL administration, and the dose of SRL. It is suggested that the optimal blood concentration of SRL monotherapy for managing ITP is 8-12 ng/ml. This range may achieve a favorable balance between clinical efficacy and the severity of adverse events.

Donor T cell STAT3 deficiency enables tissue PD-L1-dependent prevention of graft-versus-host disease while preserving graft-versus-leukemia activity

STAT3 deficiency (STAT3-/-) in donor T cells prevents graft-versus-host disease (GVHD), but the impact on graft-versus-leukemia (GVL) activity and mechanisms of GVHD prevention remains unclear. Here, using murine models of GVHD, we show that STAT3-/- donor T cells induced only mild reversible acute GVHD while preserving GVL effects against nonsusceptible acute lymphoblastic leukemia (ALL) cells in a donor T cell dose-dependent manner. GVHD prevention depended on programmed death ligand 1/programmed cell death protein 1 (PD-L1/PD-1) signaling. In GVHD target tissues, STAT3 deficiency amplified PD-L1/PD-1 inhibition of glutathione (GSH)/Myc pathways that regulate metabolic reprogramming in activated T cells, with decreased glycolytic and mitochondrial ATP production and increased mitochondrial ROS production and dysfunction, leading to tissue-specific deletion of host-reactive T cells and prevention of GVHD. Mitochondrial STAT3 deficiency alone did not reduce GSH expression or prevent GVHD. In lymphoid tissues, the lack of host-tissue PD-L1 interaction with PD-1 reduced the inhibition of the GSH/Myc pathway despite reduced GSH production caused by STAT3 deficiency and allowed donor T cell functions that mediate GVL activity. Therefore, STAT3 deficiency in donor T cells augments PD-1 signaling-mediated inhibition of GSH/Myc pathways and augments dysfunction of T cells in GVHD target tissues while sparing T cells in lymphoid tissues, leading to prevention of GVHD while preserving GVL effects.

Azacitidine and lenalidomide combination: a novel relapse prophylaxis regimen after allogeneic hematopoietic stem-cell transplantation in patients with acute myeloid leukemia

Introduction

While allogeneic hematopoietic stem cell transplantation (allo-HSCT) can be a curative regimen for acute myeloid leukemia (AML), relapse of AML remains a serious risk post-transplantation. Once relapsed, salvage options are limited and management of AML is difficult. Here we designed a prospective study to examine the efficacy and tolerability of maintenance therapy with azacytidine (AZA) plus low-dose lenalidomide (LEN) to prevent relapse after allo-HSCT for AML patients (ChiCTR2200061803).

Methods

AML patients post-allo-HSCT were treated with AZA (75 mg/m² for 7 days), followed by LEN (5 mg/m², day 10-28), and a 4-week resting interval, which was defined as one treatment cycle. A total of 8 cycles was recommended.

Results

37 patients were enrolled, 25 patients received at least 5 cycles, and 16 patients finished all 8 cycles. With a median follow-up time of 608 (43-1440) days, the estimated 1-year disease free survival (DFS) was 82%, cumulative incidence of relapse (CIR) was 18%, and overall survival (OS) was 100%. Three patients (8%) had grade 1-2 neutropenia without fever; one patient developed grade 3-4 thrombocytopenia and minor subdural hematoma; 4/37 patients (11%) developed chronic GVHD with a score of 1-2, without requiring systemic treatment; No patient developed acute GVHD. After AZA/LEN prophylaxis, increasing numbers of CD56⁺NK and CD8⁺ T, and decreasing of CD19⁺ B cells were observed.

Discussion

Azacitidine combined with low-dose lenalidomide was observed to be an effective relapse prophylaxis option after allo-HSCT in AML patients, and can be administered safely without significantly increasing the risk of GVHD, infection and other AEs.

Clinical Trial Registration

www.chictr.org, identifier ChiCTR2200061803.

Blockade of trans PD-L1 interaction with CD80 augments antitumor immunity

PD-L1 has two receptors: PD-1 and CD80. Previous reports assumed that PD-L1 and CD80 interacted in trans, but recent reports showed that only cis PD-L1/CD80 interactions existed, and prevention of cis PD-L1/CD80 interactions on antigen-presenting cells (APCs) reduced antitumor immunity via augmenting PD-L1/PD-1 and CD80/CTLA4 interactions between T and APCs. Here, using tumor-bearing mice capable of cis and trans or trans only PD-L1/CD80 interactions, we show that trans PD-L1/CD80 interactions do exist between tumor and T cells, and the effects of trans PD-L1/CD80 interactions require tumor cell expression of MHC-I and T cell expression of CD28. The blockade of PD-L1/CD80 interactions in mice with both cis and trans interactions or with only trans interactions augments antitumor immunity by expanding IFN-γ-producing CD8⁺ T cells and IFN-γ-dependent NOS2-expressing tumor-associated macrophages. Our studies indicate that although cis and trans PD-L1/CD80 interactions may have opposite effects on antitumor immunity, the net effect of blocking PD-L1/CD80 interactions in vivo augments CD8⁺ T cell-mediated antitumor immunity.

Trafficking between clonally related peripheral T-helper cells and tissue-resident T-helper cells in chronic GVHD

Chronic graft-versus-host disease (cGVHD) is an autoimmune-like syndrome. CXCR5-PD-1hi peripheral T-helper (Tph) cells have an important pathogenic role in autoimmune diseases, but the role of Tph cells in cGVHD remains unknown. We show that in patients with cGVHD, expansion of Tph cells among blood CD4+ T cells was associated with cGVHD severity. These cells augmented memory B-cell differentiation and production of immunoglobulin G via interleukin 21 (IL-21). Tph cell expansion was also observed in a murine model of cGVHD. This Tph cell expansion in the blood is associated with the expansion of pathogenic tissue-resident T-helper (Trh) cells that form lymphoid aggregates surrounded by collagen in graft-versus-host disease (GVHD) target tissues. Adoptive transfer experiments showed that Trh cells from GVHD target tissues give rise to Tph cells in the blood, and conversely, Tph cells from the blood give rise to Trh cells in GVHD target tissues. Tph cells in the blood and Trh cells in GVHD target tissues had highly overlapping T-cell receptor α and β repertoires. Deficiency of IL-21R, B-cell lymphoma 6 (BCL6), or T-bet in donor T cells markedly reduced the proportions of Tph cells in the blood and Trh cells in GVHD target tissues and reduced T-B interaction in the lymphoid aggregates. These results indicate that clonally related pathogenic Tph cells and Trh cells traffic between the blood and cGVHD target tissues, and that IL-21R-BCL6 signaling and T-bet are required for the development and expansion of Tph and Trh cells in the pathogenesis of cGVHD.

Clinical characteristics in immune thrombocytopenia patients after COVID-19 vaccination

It is well documented that COVID-19 vaccines greatly reduce the severity and complications of SARS-CoV-2 infection. However, it has been reported that COVID-19 related vaccines may induce or exacerbate autoimmune hematological disorders, for example, a decrease in platelet numbers characteristic of immune thrombocytopenia (ITP). To investigate this, we retrospectively reported, for the first time, the clinical characteristics of 42 ITP patients after COVID-19 vaccination in southwest China. Of the 42 patients, 28 patients were historically diagnosed ITP, and their platelet counts (PC) decrease mainly occurred after the first-dose vaccinations. The average PC after vaccination was 39.5 × 10⁹/L and recovered to an average of 80.6 × 10⁹/L after treatment. Efficacy of treatment was 90%, and only 10% maintained low PC at the third month of treatment. More interestingly, of the 42 patients, 14 were newly diagnosed ITP following vaccination. Of these 14 patients, 6 patients (43%) were found PC deterioration after the first vaccine dose, and 7 patients (50%) after the second dose. Fortunately, the peripheral PC of all 14 patients recovered significantly after treatment, and the average PC was 139.4 × 10⁹/L, including 8 CRs (complete response) and 6 PRs (partial response). Notably, 9 of the 14 cases were found to have abnormal immune indices when thrombocytopenia diagnosed. No severe organ hemorrhage was found in either subgroup. These results are reassuring the vaccine safety for ITP patients, in that the risks of aggravating thrombocytopenia by COVID-19 vaccination do exist, but it was transient and can be effectively controlled through intensive clinical monitoring and management.

Pretransplantation minimal residual disease monitoring by multiparameter flow cytometry predicts outcomes of AML patients receiving allogeneic hematopoietic stem cell transplantation

BACKGROUND AND PURPOSE

Is minimal residual disease (MRD) monitoring by multiparameter flow cytometry (MFC) prognostic for acute myeloid leukemia (AML) patients before allogeneic hemopoietic stem cell transplantation (allo-HSCT)? And if so, what level of MRD eradication can be used to help guide the timing of HSCT? Can haplo-HSCT improve the prognosis of AML patients with MRD positive? To figure out these questions, we initiated this retrospective study.

METHODS

96 AML patients were included retrospectively and divided into 5 groups, according to pre-transplantation MRD levels (from 5 × 10^-2 to <1 × 10^-4), to analyze the overall survival (OS), disease-free survival (DFS) and cumulative incidence of relapse (CIR). Secondly, we compared the prognosis of MRD-negative (MRD^neg) and MRD-positive (MRD^pos) AML patients (cutoff value = 1 × 10^-3) who underwent allo-HSCT, and further analyzed the prognosis of MRD^pos patients after received different transplantation modalities.

RESULTS

It is found that the 2-year OS and DFS of MRD negative group were better than the MRD positive group, and that the deeper the eradication of MRD before transplantation, the better the prognosis of patients. The CIR in patients received HLA-identical transplantation, was higher in the MRD^pos than in the MRD^neg. Haploid transplantation reduced the CIR disparity between MRD^pos and MRD^neg group. Subsequently, in AML patients who remain MRD positive before HSCT, we show that haplo-HSCT offered a better prognosis than HLA-identical transplantation (MSDT and MUDT).

CONCLUSION

It is suggested that achieving MFC-MRD <10^-3 (10^-4 or even better) before allo-HSCT could reduce the relapse of AML and improve OS and DFS significantly, while haplo-HSCT may be preferred for patients not achieving MRD negativity.

microRNA-142 guards against autoimmunity by controlling Treg cell homeostasis and function

Regulatory T (Treg) cells are critical in preventing aberrant immune responses. Posttranscriptional control of gene expression by microRNA (miRNA) has recently emerged as an essential genetic element for Treg cell function. Here, we report that mice with Treg cell-specific ablation of miR-142 (hereafter Foxp3CremiR-142fl/fl mice) developed a fatal systemic autoimmune disorder due to a breakdown in peripheral T-cell tolerance. Foxp3CremiR-142fl/fl mice displayed a significant decrease in the abundance and suppressive capacity of Treg cells. Expression profiling of miR-142-deficient Treg cells revealed an up-regulation of multiple genes in the interferon gamma (IFNγ) signaling network. We identified several of these IFNγ-associated genes as direct miR-142-3p targets and observed excessive IFNγ production and signaling in miR-142-deficient Treg cells. Ifng ablation rescued the Treg cell homeostatic defect and alleviated development of autoimmunity in Foxp3CremiR-142fl/fl mice. Thus, our findings implicate miR-142 as an indispensable regulator of Treg cell homeostasis that exerts its function by attenuating IFNγ responses.

The Addition of Sirolimus to GVHD Prophylaxis After Allogeneic Hematopoietic Stem Cell Transplantation: A Meta-Analysis of Efficacy and Safety

Objective

The objective of this study was to evaluate the safety and efficacy of sirolimus (SRL) in the prevention of graft-versus-host disease (GVHD) in recipients following allogeneic hematopoietic stem cell transplantation (allo-HSCT).

Methods

Randomized controlled trials (RCTs) evaluating the safety and efficacy of SRL-based prophylaxis regimens in patients receiving allo-HSCT were obtained from PubMed, Embase, and the Cochrane database. Following specific inclusion and exclusion criteria, studies were selected and screened by two independent reviewers who subsequently extracted the study data. The Cochrane risk bias evaluation tool was used for quality evaluation, and RevMan 5.3 software was used for statistical analysis comparing the effects of SRL-based and non–SRL-based regimens on acute GVHD, chronic GVHD, overall survival (OS), relapse rate, non-relapse mortality (NRM), thrombotic microangiopathy (TMA), and veno-occlusive disease (VOD).

Results

Seven studies were included in this meta-analysis, with a total sample size of 1,673 cases, including 778 cases of patients receiving SRL-based regimens and 895 cases in which patients received non-SRL-based regimens. Our data revealed that SRL containing prophylaxis can effectively reduce the incidence of grade II–IV acute GVHD (RR = 0.75, 95% CI: 0.68∼0.82, p < 0.0001). SRL-based prophylaxis was not associated with an improvement of grade III–IV acute GVHD (RR = 0.78, 95% CI: 0.59∼1.03, p = 0.08), chronic GVHD (p = 0.89), OS (p = 0.98), and relapse rate (p = 0.16). Despite its immunosuppressant effects, SRL-based regimens did not increase bacterial (p = 0.68), fungal (p = 0.70), or CMV (p = 0.10) infections. However, patients receiving SRL-based regimens had increased TMA (p < 0.00001) and VOD (p < 0.00001).

Conclusions

This meta-analysis indicates that addition of sirolimus is an effective alternative prophylaxis strategy for II–IV aGVHD but may cause endothelial cell injury and result in secondary TMA or VOD events.

Case Report: PD-1 Blockade Combined Autologous Hematopoietic Stem Cell Transplantation With Modified BEAM Regimen Containing High-Dose Cytarabine to Treat R/R Hodgkin's Lymphoma

The emergence of new drugs has provided additional options in the treatment of relapsed and refractory (R/R) Hodgkin's lymphoma (HL). However, the use of autologous stem cell transplantation (ASCT) has not been completely replaced in this setting. The use of anti-programmed death-1 (PD-1) antibody bridging to ASCT and as maintenance after transplantation is a novel approach in HL treatment. In this case, we report that PD-1 monoclonal antibody (mAb) plus ASCT with modified BEAM regimen (carmustine + etoposide + cytarabine + melphalan) containing high-dose cytarabine to treat R/R HL may represent a promising regimen in this difficult-to-treat setting.

Abstract 3180: Blockade of PD-L1 interaction with CD80 in trans augments anti-tumor immunity by increasing NOS2 in tumor-associated macrophages

Programmed death ligand 1(PD-L1) has two receptors: programmed death receptor 1 (PD-1) and CD80. Both PD-L1 and CD80 are expressed by activated T-cells, antigen presenting cells (APCs) and tumor cells. Although the role of PD-L1/PD-1 interaction in regulation of tumor immunity has been well characterized, role of PD-L1/CD80 interaction remains largely unknown. The interaction mode of PD-L1 with CD80 is also controversial. Our previous studies showed that in murine model of acute graft versus host disease, PD-L1 interact with CD80 on different cells (Deng et al: J. Immunol. 2015); but a recent report showed that PD-L1 interacts with CD80 in cis on the same cell (Sugiura et al: Science 2019). In the current studies, we tested the role of PD-L1/CD80 interaction in trans in regulation of tumor immunity. WT, PD-L1-/-, and CD80-/- C57BL/6 mice were inoculated with WT or PD-L1-/- MC38 tumor cells and intraperitoneally injected with 200μg anti-PD-L1(43H12) that specifically block PD-L1/CD80 interactions or control IgG, starting on D7 after tumor inoculation, every 3 days, total of 5 times. Tumor volume was monitored every 3 days for up to D20. Tumor and tumor draining lymph nodes were harvested on D14 or D15 after tumor inoculation for mechanism studies. We observed that administration of 43H12 resulted in inhibition of tumor growth in WT MC38→WT Rec model; as well as in models of WT MC38→PD-L1-/- Rec (no PD-L1 on APCs or T cells), WT MC38→CD80-/- Rec (no CD80 on APCs or T cells), and PD-L1-/-MC38→CD80-/- Rec (no PD-L1 on tumor cells and no CD80 on APCs or T cells, truly PD-L1 interaction with CD80 in trans). These results indicate that blockade of PD-L1 interaction with CD80 in trans inhibits tumor growth. Furthermore, we found that blockade of PD-L1/CD80 interaction by 43H12 mAb increased percentage of CD8+ effector memory T (Tem) that produce IFN-γ and tumor-associated macrophages (TAMs) that express NOS2. Administration of anti-IFN-γ eliminated increase of NOS2 and anti-tumor effect, and administration of NOS2 inhibitor (1400W) also eliminated the anti-tumor effect mediated by injection of 43H12 mAb. Therefore, PD-L1 interaction with CD80 in trans regulate tumor immunity; and blockade of this interaction augments anti-tumor immunity via augmenting CD8+ Tem expansion and their production of IFN-γ, and subsequently augmenting tumoricidal NOS2 expressed in TAMs.

Citation Format: Yuankun Zhang, Qingxiao Song, Michael Lee, Haidong Tang, Kaniel Cassady, Yang-Xin Fu, Dustin E. Schones, Arthur Riggs, Ru Feng, Defu Zeng. Blockade of PD-L1 interaction with CD80 in trans augments anti-tumor immunity by increasing NOS2 in tumor-associated macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3180.

The Role of mTOR Inhibitors in Hematologic Disease: From Bench to Bedside

The mTOR pathway plays a central role in many cellular processes, such as cellular growth, protein synthesis, glucose, and lipid metabolism. Aberrant regulation of mTOR is a hallmark of many cancers, including hematological malignancies. mTOR inhibitors, such as Rapamycin and Rapamycin analogs (Rapalogs), have become a promising class of agents to treat malignant blood diseases-either alone or in combination with other treatment regimens. This review highlights experimental evidence underlying the molecular mechanisms of mTOR inhibitors and summarizes their evolving role in the treatment of hematologic disease, including leukemia, lymphoma, myeloma, immune hemocytopenia, and graft-versus-host disease (GVHD). Based on data presented in this review, we believe that mTOR inhibitors are becoming a trusted therapeutic in the clinical hematologist's toolbelt and should be considered more routinely in combination therapy for the management of hematologic disease.

Effect of rhG-CSF Combined With Decitabine Prophylaxis on Relapse of Patients With High-Risk MRD-Negative AML After HSCT: An Open-Label, Multicenter, Randomized Controlled Trial

Relapse is a major cause of treatment failure after allogeneic hematopoietic stem-cell transplantation (allo-HSCT) for high-risk acute myeloid leukemia (HR-AML). The aim of this study was to explore the effect of recombinant human granulocyte colony-stimulating factor (rhG-CSF) combined with minimal-dose decitabine (Dec) on the prevention of HR-AML relapse after allo-HSCT.

Blockade of CD80 interaction with PD-L1 between T and tumor cells augments effector T expansion and tumor immunity in a PD-1-dependent manner

PD-L1 interactions with PD-1 and CD80 play a critical role in regulating tumor immunity. Blockade of PD-L1 interaction with PD-1 between tumor and T cells augments tumor immunity. Cis-PD-L1/CD80 interactions reduce PD-L1 interaction with PD-1 on T cells and augment tumor immunity. However, whether trans-PD-L1 interaction with CD80 between tumor and T cells play a role in regulating tumor immunity remains unknown. In the current studies, using B16 and MC38 tumor lines in C57BL/6 mice with or without PD-1 or PD-L1 deficiency, we show that administration of anti-PD-L1 (43H12), a monoclonal antibody that specifically blocks PD-L1 interaction with CD80, augments tumor immunity. The effect is tumor PD-L1 interaction with PD-1 on T cells-dependent, because although 43H12 blockade does not augment tumor immunity in PD-1−/− mice or in PD-L1−/− mice with PD-L1 KO tumor lines, 43H12 blockade does augment tumor immunity in PD-L1−/− mice with wild-type tumor lines. Furthermore, consistent with CD28 requirement for augmenting anti-tumor immunity during blocking anti-PD-1 treatment, 43H12 blockade of PD-L1/CD80 interaction does not augment tumor immunity in CD28−/− mice. Finally, 43H12 blockade augments CD8+ T effector expansion in the tumor draining lymph nodes, with increased production of IFN-g and down-regulation of ps21-EZH2. These results indicate that blockade of PD-L1 interaction with CD80 can augment tumor immunity via down-regulating the effect of PD-L1 interaction with PD-1. (This work is supported by DMRI institutional funds and NIH 1R01CA228465-01 to Zeng).

Sirolimus as Rescue Therapy for Refractory/Relapsed Immune Thrombocytopenia: Results of a Single-Center, Prospective, Single-Arm Study

Immune thrombocytopenia (ITP) is an autoimmune disease which arises due to self-destruction of circulating platelets. Failure to respond or maintain a response to first-line treatment can lead to refractory/relapsed (R/R) ITP. The mechanism remains complicated and lacks a standard clinical treatment. Sirolimus (SRL) is a mammalian target of rapamycin (mTOR) inhibitor that has been demonstrated to inhibit lymphocyte activity, indicating potential for SRL in treatment of ITP. Activation of the mTOR pathway in autoimmune diseases suggests that SRL might be a useful agent for treating ITP. Accordingly, we initiated an open-label, prospective clinical trial using SRL for patients with R/R ITP (ChiCTR-ONC-17012126). The trial enrolled 86 patients, each dosed with 2–4 mg/day of SRL. By the third month, 40% of patients (34 of 86) achieved complete remission (CR) and 45% of patients (39 of 86) achieved partial remission (PR), whereby establishing an overall response rate (ORR) of 85%. By 6 months of treatment, 41% of patients (32 of 78) achieved CR and 29% of patients (23 of 78) achieved PR, establishing an ORR of 70% without serious side effects. After 12 months follow-up, the ORR remained at 65%. We also found that SRL treatment exhibited higher efficacy in achieving CR in ITP patients who were younger than 40 years old or steroid dependent by univariate analysis. Importantly, in patients who responded, SRL treatment was associated with a reduction in the percentage of Th2, Th17 cells, and increase in the percentage of M-MDSCs and Tregs, indicating that SRL may reestablish peripheral tolerance. Taken together, Sirolimus demonstrated efficacy as a second-line agent for R/R ITP.

TET2 Function in Hematopoietic Malignancies, Immune Regulation, and DNA Repair

Over the last decade, investigation of Ten-Eleven Translocation 2 (TET2) gene function and TET2 mutation have become of increasing interest in the field of hematology. This heightened interest was sparked by the seminal discoveries that (1) TET2 mutation is associated with development of hematological malignancies and that (2) the TET family of proteins is critical in promoting DNA demethylation and immune homeostasis. Since then, additional studies have begun to unravel the question “Does TET2 have additional biological functions in the regulation of hematopoiesis?” Here, we present a mini-review focused on the current understanding of TET2 in hematopoiesis, hematological malignancies, and immune regulation. Importantly, we highlight the critical function that TET2 facilitates in maintaining the stability of the genome. Based on our review of the literature, we provide a new hypothesis that loss of TET2 may lead to dysregulation of the DNA repair response, augment genome instability, and subsequently sensitize myeloid leukemia cells to PARP inhibitor treatment.

Regulation of GVHD and GVL Activity via PD-L1 Interaction With PD-1 and CD80

Allogeneic hematopoietic cell transplantation (HCT) is a curative therapy for hematological malignancies (i.e. leukemia and lymphoma), because graft-versus-leukemia (GVL) activity mediated by alloreactive T cells can eliminate residual malignant cells and prevent relapse. However, the same alloreactive T cells also mediate a severe side effect, graft-versus-host disease (GVHD), and prevention of GVHD while preserving GVL activity remains an elusive goal. The immune checkpoint molecule PD-L1 and its interaction with PD-1 receptor in regulating cancer immunity is under intensive and wide-spread study, but knowledge about this interaction in regulating GVHD and GVL activity is very limited. In this review, we summarize the literature exploring how PD-L1 interaction with its receptors PD-1 and CD80 regulate GVHD and GVL activities, how PD-L1 signaling regulates T cell metabolic profiles, and how a differential role of PD-L1 interaction with PD-1, CD80 or both may provide a novel avenue to prevent GVHD while preserving strong GVL effects.

MicroRNA-142 guards against autoimmunity by controlling Treg cell development and function

Regulatory T (Treg) cells are critical in preventing aberrant immune responses. Post-transcriptional gene control by microRNA (miRNA), a large class of small regulatory RNA, has recently emerged as a key genetic element required for Treg cell function. Nevertheless, specific miRNA gene(s) that play a vital role in the regulation of Treg cell activity are still unknown. Here we report that mice with Treg cell-specific ablation of miR-142 (hereafter Foxp3CremiR-142fl/fl mice) developed a fatal systemic autoimmune disorder due to a breakdown in peripheral T cell tolerance. Foxp3CremiR-142fl/fl mice displayed a sharp decrease in abundance and suppressive capacity of Treg cells. Analysis of miR-142-deficient Treg cells revealed excessive IFNγ production and dysregulated IFNγ signaling. We have identified several of the derepressed IFNγ-related genes, including Ifngr2 receptor and Hif1a transcription factor, as direct miR-142 targets. Furthermore, lowering the Hif1a gene dose in Treg cells significantly diminished the hyperactivation of peripheral effector T cells in Foxp3CremiR-142fl/flmice. Thus, miR-142 is an indispensable regulator of Treg cell development and function that mediates its control by attenuating IFNg response.

PD-L1/CD80 interaction differentially regulates CD8+ T cell metabolism, survival and GVHD capacity in the presence or absence of PD-1

Purified alloreactive CD8+ T cells induce no acute GVHD, but the mechanisms remain unknown. PD-L1 interacts with PD-1 and CD80. Here we show that, sorted C57BL/6 donor CD8+ T cells (1.25 ×106) expanded in wild-type MHC-mismatched BALB/c recipients but induced no acute GVHD. In PD-L1−/− recipients, donor CD8+ T cells expanded and induced lethal acute GVHD. PD-1−/−CD8+ T cells induced lethal acute GVHD in wild-type recipients. Blockade of PD-L1/CD80 interactions on days 0 and 2 prevented expansion of wild-type and PD-1−/− CD8+ T cells in wild type recipients and prevented acute GVHD caused by PD-1−/− CD8+ T cells. On the other hand, blockade of PD-L1/CD80 interaction after CD8+ T activation on day 5 caused lethal acute GVHD in wild-type recipients that usually have no acute GVHD. Naïve CD8+ T cells express much higher levels of CD80 than PD-1, whereas activated CD8+ T cells express higher levels of PD-1 than CD80. PD-L1/CD80 interaction augmented glycolysis in naïve WT and PD-1−/− CD8+T cells. This interaction was associated with increased phosphorylation of PLC-γ and activation of the AKT/mTOR pathway in a CD28-dependent manner. This interaction increased mitochondrial numbers and volume and augmented ROS production and apoptosis at the peak of CD8+ T cell activation, such that CD8+T cells did not over-expand to cause GVHD. Conversely, blockade of PD-L1/CD80 after CD8+ T activation in the presence of high PD-1 expression led to increased mitophagy, reduced apoptosis and overexpansion of CD8+ T cells, resulting in lethal GVHD. These results indicate that PD-L1/ CD80 interaction is dependent on PD-1 expression to differentially regulate glycolysis and mitophagy as well as expansion, survival and acute GVHD capacity of alloreactive CD8+ T cells.

PD-L1 interacts with CD80 to regulate graft-versus-leukemia activity of donor CD8+ T cells

Programmed death ligand-1 (PD-L1) interacts with programmed death-1 (PD-1) and the immunostimulatory molecule CD80 and functions as a checkpoint to regulate immune responses. The interaction of PD-L1 with CD80 alone has been shown to exacerbate the severity of graft-versus-host disease (GVHD), whereas costimulation of CD80 and PD-1 ameliorates GVHD. Here we have demonstrated that temporary depletion of donor CD4+ T cells early after hematopoietic cell transplantation effectively prevents GVHD while preserving strong graft-versus-leukemia (GVL) effects in allogeneic and xenogeneic murine GVHD models. Depletion of donor CD4+ T cells increased serum IFN-γ but reduced IL-2 concentrations, leading to upregulation of PD-L1 expression by recipient tissues and donor CD8+ T cells. In GVHD target tissues, the interactions of PD-L1 with PD-1 on donor CD8+ T cells cause anergy, exhaustion, and apoptosis, thereby preventing GVHD. In lymphoid tissues, the interactions of PD-L1 with CD80 augment CD8+ T cell expansion without increasing anergy, exhaustion, or apoptosis, resulting in strong GVL effects. These results indicate that the outcome of PD-L1-mediated signaling in CD8+ T cells depends on the presence or absence of CD4+ T cells, the nature of the interacting receptor expressed by CD8+ T cells, and the tissue environment in which the signaling occurs.

Increased Expression of System xc- in Glioblastoma Confers an Altered Metabolic State and Temozolomide Resistance

Glioblastoma multiforme is the most aggressive malignant primary brain tumor in adults. Several studies have shown that glioma cells upregulate the expression of xCT (SLC7A11), the catalytic subunit of system x_c^-, a transporter involved in cystine import, that modulates glutathione production and glioma growth. However, the role of system x_c^- in regulating the sensitivity of glioma cells to chemotherapy is currently debated. Inhibiting system x_c^- with sulfasalazine decreased glioma growth and survival via redox modulation, and use of the chemotherapeutic agent temozolomide together with sulfasalazine had a synergistic effect on cell killing. To better understand the functional consequences of system x_c^- in glioma, stable SLC7A11-knockdown and -overexpressing U251 glioma cells were generated. Modulation of SLC7A11 did not alter cellar proliferation but overexpression did increase anchorage-independent cell growth. Knockdown of SLC7A11 increased basal reactive oxygen species (ROS) and decreased glutathione generation resulting in increased cell death under oxidative and genotoxic stress. Overexpression of SLC7A11 resulted in increased resistance to oxidative stress and decreased chemosensitivity to temozolomide. In addition, SLC7A11 overexpression was associated with altered cellular metabolism including increased mitochondrial biogenesis, oxidative phosphorylation, and ATP generation. These results suggest that expression of SLC7A11 in the context of glioma contributes to tumorigenesis, tumor progression, and resistance to standard chemotherapy.

IMPLICATIONS

SLC7A11, in addition to redox modulation, appears to be associated with increased cellular metabolism and is a mediator of temozolomide resistance in human glioma, thus making system x_C^- a potential therapeutic target in glioblastoma multiforme. Mol Cancer Res; 14(12); 1229-42. ©2016 AACR.

Transient depletion of donor CD4+ T cells early after HCT allows recipient tissue PD-L1 to tolerize infiltrating CD8+ T cells and to prevent acute GVHD while preserving GVL effect

Prevention of graft-versus-host-disease (GVHD) while preserving graft-versus-leukemia/lymphoma (GVL) effect remains the Holy Grail for allogeneic hematopoietic cell transplantation (HCT). Purified donor CD4+ T cells induce strong but CD8+ T cells induce little acute GVHD (aGVHD); however, the mechanisms remain unknown. Recipient tissue expression of PD-L1 (B7H1) down-regulates aGVHD via simultaneous PD-L1 interactions with CD80 and PD-1 on donor T cells, but whether this mechanism impacts on GVL effect remains unclear. In the current studies, with MHC-mismatched HCT model of C57BL/6 donor to BALB/c recipient, we observed that 1) although sorted wild-type (WT) CD8+T cells induced no signs of aGVHD, purified PD-1−/− CD8+ T cells induced lethal aGVHD; 2) while WTCD8+ T or very low-dose (0.1×106) CD4+ T cells alone induced little signs of aGVHD, co-transplantation of them induced lethal aGVHD; 3) depletion of CD4+ T cells by anti-CD4 mAb early after HCT prevented aGVHD in wild-type but not in PD-L1−/− recipients, and the GVHD prevention is associated with increase of serum IFN-γ, upregulation of host tissue PD-L1, upregulation of CD80 and PD-1 by CD8+ T cells, as well as increase of apoptosis and anergy of tissue infiltrating CD8+ T cells; 4) interestingly, the depletion of donor CD4+ T cells augmented donor CD8+T cell proliferation without increasing anergy or apoptosis in the lymphoid tissue and preserved strong GVL effect. These results indicate that depletion of donor CD4+ T cells early after HCT leads to increasing susceptibility of donor CD8+ T cells to host tissue PD-L1-mediated apoptosis and anergy in GVHD target tissues but not in the lymphoid tissues, such that GVHD is prevented and GVL effect is preserved.

B7H1/CD80 interaction augments PD-1-dependent T cell apoptosis and ameliorates graft-versus-host disease

Interactions of B7H1 (programmed death ligand 1 [PD-L1]) with its two ligands, PD-1 and CD80, on T cells play a pivotal role in controlling T cell activation, proliferation, anergy, and apoptosis. However, the interactions between the two pathways remain unknown. Using an alloimmune response model of graft-versus-host disease (GVHD), we report in this study that: 1) Comparison of proliferation and apoptosis of wild-type (WT) and PD-1(-/-)CD4(+) conventional T (Tcon) cells in WT and B7H1(-/-) recipients revealed that B7H1/CD80 interaction per se augments T cell proliferation, and this interaction augments T cell apoptosis mediated by B7H1/PD-1 interaction. This observation was recapitulated in an in vitro MLR assay. 2) Specific blockade of the B7H1/CD80 axis by anti-B7H1 mAb reduces WT-alloreactive Tcon cell proliferation, IL-2 production, expression of PD-1, and apoptosis, resulting in worsening GVHD. In contrast, specific blockade of B7H1/CD80 interaction reduces donor PD-1(-/-) Tcon cell proliferation without an impact on apoptosis, resulting in ameliorating GVHD. 3) B7H1 fused to an Ig Fc domain (B7H1-Ig), when produced in vivo by hydrodynamic injection of B7H1-Ig plasmid, ameliorates GVHD by augmenting proliferation and apoptosis of WT- alloreactive Tcon cells. Conversely, B7H1-Ig treatment has no impact on apoptosis but augments PD-1(-/-) T cell proliferation and worsens GVHD. These results indicate that B7H1/CD80 interaction augments Tcon cell proliferation, IL-2 production, and expression of PD-1, which leads to increased apoptosis mediated by the B7H1/PD-1 pathway. Additionally, by engaging both PD-1 and CD80, B7H1-Ig can be a powerful therapeutic reagent for downregulating the T cell immune response.

Administration of anti-CD20 mAb is highly effective in preventing but ineffective in treating chronic graft-versus-host disease while preserving strong graft-versus-leukemia effects

Chronic graft-versus-host disease (cGVHD) is an autoimmune-like syndrome, and donor B cells play important roles in augmenting its pathogenesis. B cell-depleting anti-CD20 mAb has been administered before or after cGVHD onset for preventing or treating cGVHD in the clinic. Although administration before onset appeared to be more effective, the effect is variable and sometimes minimal. Here, we used 2 mouse cGVHD models to evaluate the preventive and therapeutic effect of anti-CD20 mAb. With the model of DBA/2 donor to MHC-matched BALB/c recipient, 1 intravenous injection of anti-CD20 mAb (40 mg/kg) the following day or on day 7 after hematopoietic cell transplantation when serum autoantibodies were undetectable effectively prevented induction of cGVHD and preserved a strong graft-versus-leukemia (GVL) effect. The separation of GVL effect from GVHD was associated with a significant reduction of donor CD4(+) T cell proliferation and expansion and protection of host thymic medullary epithelial cells. Anti-CD20 mAb administration also prevented expansion of donor T cells and induction of cGVHD in another mouse model of C57BL/6 donor to MHC-mismatched BALB/c recipients. In contrast, administration of anti-CD20 mAb after GVHD onset was not able to effectively deplete donor B cells or ameliorate cGVHD in either model. These results indicate that administration of anti-CD20 mAb before signs of cGVHD can prevent induction of autoimmune-like cGVHD while preserving a GVL effect; there is little effect if administered after cGVHD onset. This provides new insights into clinical prevention and therapy of cGVHD with B cell-depleting reagents.