Immunomonitoring of graft‐versus‐host minor histocompatibility antigen correlates with graft‐versus‐host disease and absence of relapse after graft

BACKGROUND: After HLA‐identical hematopoietic stem cell transplantation, minor histocompatibility (mH) antigen alloreactivity plays a dominant role in the development of graft‐versus‐host disease (GVHD) and graft versus leukemia (GVL). STUDY DESIGN AND METHODS: We have analyzed the mH alloreactivity (enzyme‐linked immunospot [ELISpot] for interferon‐γ[IFN‐γ] assay) from 24 donor/recipient pairs over a period of 2 years of follow‐up and correlated such alloreactivity with the development of GVHD or absence of relapse. Circulating specific T cells anti‐mH with multimer HLA‐peptides were also studied. RESULTS: We show by ELISpot IFN‐γ assay that alloreactivity during the first 3 months from donor versus recipient or donor versus mismatched identified mH antigens is associated with acute GVHD and GVL effect. In addition, we demonstrate that the donor‐versus‐recipient reactivity observed after the third month is highly associated with chronic GVHD and GVL (p = 0.0007). Finally, we show by multimer HLA‐peptide assay that mH epitope‐specific T cells present after 3 months are statistically related to the GVL effect. CONCLUSIONS: Our results provide a robust method to monitor mH antigen graft‐versus‐host reaction and suggest that current identified mH have predictive value on GVHD and GVL.     

Generation of leukemia-reactive cytotoxic T lymphocyte clones from the HLA-identical bone marrow donor of a patient with leukemia.

Allogeneic bone marrow transplantation (BMT) has been associated with a graft-vs.-leukemia (GVL) reactivity. Since T cell depletion of the bone marrow graft has decreased the risk of graft-vs.-host disease (GVHD), but has been associated with higher rates of leukemia relapse, GVL reactivity is probably caused by donor-derived T lymphocytes. Previously, we demonstrated that minor histocompatibility (mH) antigen-specific cytotoxic T lymphocyte (CTL) clones, generated from patients after BMT, are capable of major histocompatibility complex-(MHC) restricted lysis of (clonogenic) myeloid leukemic cells. Here, we investigated whether donor-derived leukemia-specific CTL clones can be generated in vitro, before BMT, using irradiated leukemic cells from a patient with acute myeloid leukemia as stimulator cells, and peripheral blood or bone marrow from the HLA genotypically identical sibling donor as responder cells. Several CTL lines were generated that showed specific lysis (> 50%) of the recipient leukemic cells in a 51Cr-release assay. Two of these CTL lines were cloned by limiting dilution in the presence of the irradiated recipient cells. Multiple leukemia-reactive, HLA class I and II-restricted clones with various specificities could be established. These alloreactive, antileukemic CTL clones may cause GVL reactivity after BMT, and may be used as adjuvant immunotherapy in the treatment of leukemia.     

Alloantigen expression on non-hematopoietic cells reduces graft-versus-leukemia effects in mice

Allogeneic hematopoietic stem cell transplantation (HSCT) is used effectively to treat a number of hematological malignancies. Its beneficial effects rely on donor-derived T cell–targeted leukemic cells, the so-called graft-versus-leukemia (GVL) effect. Induction of GVL is usually associated with concomitant development of graft-versus-host disease (GVHD), a major complication of allogeneic HSCT. The T cells that mediate GVL and GVHD are activated by alloantigen presented on host antigen-presenting cells of hematopoietic origin, and it is not well understood how alloantigen expression on non-hematopoietic cells affects GVL activity. Here we show, in mouse models of MHC-matched, minor histocompatibility antigen–mismatched bone marrow transplantation, that alloantigen expression on host epithelium drives donor T cells into apoptosis and dysfunction during GVHD, resulting in a loss of GVL activity. During GVHD, programmed death–1 (PD-1) and PD ligand–1 (PD-L1), molecules implicated in inducing T cell exhaustion, were upregulated on activated T cells and the target tissue, respectively, suggesting that the T cell defects driven by host epithelial alloantigen expression might be mediated by the PD-1/PD-L1 pathway. Consistent with this, blockade of PD-1/PD-L1 interactions partially restored T cell effector functions and improved GVL. These results elucidate a previously unrecognized significance of alloantigen expression on non-hematopoietic cells in GVL and suggest that separation of GVL from GVHD for more effective HSCT may be possible in human patients.     

T-cell lines specific for peptides of adenovirus hexon protein and devoid of alloreactivity against recipient cells can be obtained from HLA-haploidentical donors

Human adenovirus (HAdV) infection may cause life-threatening complications in recipients of hematopoietic stem cell transplantation (HSCT), the highest risk being observed in children given T-cell depleted haploidentical allografts. The effectiveness of pharmacologic therapy for HAdV infection is suboptimal. Recently, cell therapy was demonstrated to offer a unique opportunity to restore antiviral immune surveillance, leading to clearance of infection and prevention/treatment of disease. However, infusion of insufficiently selected HAdV-specific T cells in haplo-HSCT may increase the risk of graft-versus-host disease. We conducted scale-up experiments to validate a method of in vitro culture to expand T cells specific for HAdV from donor peripheral blood mononuclear cells (PBMC), based on stimulation with a pool of five 30-mer peptides derived from HAdV5 hexon protein, for use in recipients of haplo-HSCT. A total of 21 T-cell lines that included a majority of CD4 T lymphocytes, were generated. Nineteen of the 21 T-cell lines proliferated specifically against HAdV. The 2 nonspecific, and 3 T-cell lines with lower specific activity, included a median of 48% CD8 T cells. The 19 HAdV-specific T-cell lines showed a median 357-fold decrease in alloreactivity, compared with proliferation of noncultured donor PBMC in response to recipient PBMC, only 4/19 T-cell lines showing residual alloreactivity. Our data indicate that HAdV-specific CD4 T-cell lines with efficient in vitro antiviral response and low/undetectable alloreactivity against recipient targets may be expanded from PBMC of most human leukocyte antigen-haploidentical HSCT donors after stimulation with HAdV hexon protein-derived peptides. These T cells may be safely employed for adoptive treatment of HAdV complications.     

PKCθ is required for alloreactivity and GVHD but not for immune responses toward leukemia and infection in mice

When used as therapy for hematopoietic malignancies, allogeneic BM transplantation (BMT) relies on the graft-versus-leukemia (GVL) effect to eradicate residual tumor cells through immunologic mechanisms. However, graft-versus-host disease (GVHD), which is initiated by alloreactive donor T cells that recognize mismatched major and/or minor histocompatibility antigens and cause severe damage to hematopoietic and epithelial tissues, is a potentially lethal complication of allogeneic BMT. To enhance the therapeutic potential of BMT, we sought to find therapeutic targets that could inhibit GVHD while preserving GVL and immune responses to infectious agents. We show here that T cell responses triggered in mice by either Listeria monocytogenes or administration of antigen and adjuvant were relatively well preserved in the absence of PKC isoform θ (PKCθ), a key regulator of TCR signaling. In contrast, PKCθ was required for alloreactivity and GVHD induction. Furthermore, absence of PKCθ raised the threshold for T cell activation, which selectively affected alloresponses. Most importantly, PKCθ-deficient T cells retained the ability to respond to virus infection and to induce GVL effect after BMT. These findings suggest PKCθ is a potentially unique therapeutic target required for GVHD induction but not for GVL or protective responses to infectious agents.     

杀伤细胞免疫球蛋白样受体与供者特异性人类白细胞抗原抗体在单倍体相合造血干细胞移植供者选择中的研究进展

目前,单倍体相合造血干细胞移植(haplo-HSCT)为治疗血液系统恶性疾病的重要手段之一,其为需要接受异基因造血干细胞移植(allo-HSCT)患者解决了供者缺乏的问题.但是移植排斥、移植物抗宿主病(GVHD)、植入失败(GF)、植入功能不良均为haplo-HSCT相关不良反应.目前,对于影响非人类白细胞抗原(HLA)相合程度的因素,如供者性别、年龄、供者特异性人类白细胞抗原抗体(DSA)及杀伤细胞免疫球蛋白样受体(KIR)匹配程度等,在haplo-HSCT供者选择方面的作用越来越受到研究者的关注.KIR3DL1为自然杀伤(NK)细胞表面重要的抑制性受体之一,在诱导异源反应性NK细胞中发挥重要作用.为了优化haplo-HSCT的供者选择,笔者拟就DSA、KIR匹配程度在haplo-HSCT供者选择中的作用进行综述.     

In Vivo Proof of Concept of Adoptive Immunotherapy for Hepatocellular Carcinoma Using Allogeneic Suicide Gene-modified Killer Cells

Cell therapy based on alloreactivity has completed clinical proof of concept against hematological malignancies. However, the efficacy of alloreactivity as a therapeutic approach to treat solid tumors is unknown. Using cell culture and animal models, we aimed to investigate the efficacy and safety of allogeneic suicide gene-modified killer cells as a cell-based therapy for hepatocellular carcinoma (HCC), for which treatment options are limited. Allogeneic killer cells from healthy donors were isolated, expanded, and phenotypically characterized. Antitumor cytotoxic activity and safety were studied using a panel of human or murine HCC cell lines engrafted in immunodeficient or immunocompetent mouse models. Human allogeneic suicide gene-modified killer cells (aSGMKCs) exhibit a high, rapid, interleukin-2–dependent, and non–major histocompatibility complex class I-restricted in vitro cytotoxicity toward human hepatoma cells, mainly mediated by natural killer (NK) and NK-like T cells. In vivo evaluation of this cell therapy product demonstrates a marked, rapid, and sustained regression of HCC. Preferential liver homing of effector cells contributed to its marked efficacy. Calcineurin inhibitors allowed preventing rejection of allogeneic lymphocytes by the host immune system without impairing their antitumor activity. Our results demonstrate proof of concept for aSGMKCs as immunotherapy for HCC and open perspectives for the clinical development of this approach.     

Minor histocompatibility antigen-specific cytotoxic T cell lines, capable of lysing human hematopoietic progenitor cells, can be generated in vitro by stimulation with HLA-identical bone marrow cells

Recipient-antidonor alloreactivity before HLA genotypically identical bone marrow transplantation (BMT) between donor-recipient pairs that are negative in the mixed lymphocyte reaction (MLR), the cell-mediated lympholysis (CML) assay, and the lymphocyte crossmatch was not detectable in the majority of cases, using recipient peripheral blood lymphocytes (PBL) collected before BMT as responder cells and donor PBL as stimulator cells. However, when donor bone marrow mononuclear cells (BMMNC) instead of PBL were used as stimulator cells, we could detect donor-specific alloreactivity in 7 of 10 HLA genotypically identical donor-recipient pairs. To demonstrate that this alloreactivity was minor histocompatibility (mH) antigen specific and not directed against HLA class I splits or variants, two cytotoxic T lymphocyte (CTL) lines were tested in further detail against phytohemagglutinin (PHA) blasts from pairs of HLA genotypically identical siblings positive for the HLA class I restriction molecule. Both CTL lines recognized mH antigens, as illustrated by the differential recognition of PHA blasts of one of the two siblings from several pairs. The potential role of these mH antigen-specific CTLs in bone marrow graft rejection was demonstrated by the mH antigen-specific growth inhibition of hematopoietic progenitor cells from the original bone marrow donor and from HLA class I restriction molecule-positive individuals who expressed the mH antigens on their PBL and BMMNC. Our assay can be used in HLA genotypically identical BMT to detect a recipient-antidonor response, directed against cellularly defined mH antigens expressed on donor HPC, BMMNC, and PBL, before transplantation.     

Graft Versus Leukemia Response Without Graft-versus-host Disease Elicited By Adoptively Transferred Multivirus-specific T-cells

A 12-year-old boy with refractory acute lymphoblastic leukemia received a haploidentical transplant from his mother. As prophylaxis for Epstein-Barr virus (EBV), cytomegalovirus (CMV) and adenovirus, he received ex vivo expanded virus-specific donor T cells 3.5 months after transplant. Four weeks later leukemic blasts bearing the E2A deletion, identified by fluorescent in situ hybridization (FISH), appeared transiently in the blood followed by a FISH-negative hematological remission, which was sustained until a testicular relapse 3.5 months later. Clearance of the circulating leukemic cells coincided with a marked increase in circulating virus-specific T cells. The virus-specific cytotoxic T-cell (CTL) line showed strong polyfunctional reactivity with the patient''s leukemic cells but not phytohemagglutinin (PHA) blasts, suggesting that virus-specific CTL lines may have clinically significant antileukemia activity.     

NKT cell-dependent leukemia eradication following stem cell mobilization with potent G-CSF analogs

NKT cells have pivotal roles in immune regulation and tumor immunosurveillance. We report that the G-CSF and FMS-like tyrosine kinase 3 ligand (Flt-3L) chimeric cytokine, progenipoietin-1, markedly expands the splenic and hepatic NKT cell population and enhances functional responses to alpha-galactosylceramide. In a murine model of allogeneic stem cell transplantation, donor NKT cells promoted host DC activation and enhanced perforin-restricted CD8+ T cell cytotoxicity against host-type antigens. Following leukemic challenge, donor treatment with progenipoietin-1 significantly improved overall survival when compared with G-CSF or control, attributable to reduced graft-versus-host disease mortality and paradoxical augmentation of graft-versus-leukemia (GVL) effects. Enhanced cellular cytotoxicity was dependent on donor NKT cells, and leukemia clearance was profoundly impaired in recipients of NKT cell-deficient grafts. Enhanced cytotoxicity and GVL effects were not associated with Flt-3L signaling or effects on DCs but were reproduced by prolonged G-CSF receptor engagement with pegylated G-CSF. Thus, modified G-CSF signaling during stem cell mobilization augments NKT cell-dependent CD8+ cytotoxicity, effectively separating graft-versus-host disease and GVL and greatly expanding the potential applicability of allogeneic stem cell transplantation for the therapy of malignant disease.     

Differential roles of IL-1 and TNF-α on graft-versus-host disease and graft versus leukemia

We demonstrate an increase in graft-versus-host disease (GVHD) after experimental bone marrow transplant (BMT) when cyclophosphamide (Cy) is added to an otherwise well-tolerated dose (900 cGy) of total body irradiation (TBI). Donor T cell expansion on day +13 was increased after conditioning with Cy/TBI compared with Cy or TBI alone, although cytotoxic T lymphocyte (CTL) function was not altered. Histological analysis of the gastrointestinal tract demonstrated synergistic damage by Cy/TBI and allogeneic donor cells, which permitted increased translocation of LPS into the systemic circulation. TNF-alpha and IL-1 production in response to LPS was increased in BMT recipients after Cy/TBI conditioning. Neutralization of IL-1 significantly reduced serum LPS levels and GVHD mortality, but it did not affect donor CTL activity. By contrast, neutralization of TNF-alpha did not prevent GVHD mortality but did impair CTL activity after BMT. When P815 leukemia cells were added to the bone marrow inoculum, allogeneic BMT recipients given the TNF-alpha inhibitor relapsed at a significantly faster rate than those given the IL-1 inhibitor. To confirm that the role of TNF-alpha in graft versus leukemia (GVL) was due to effects on donor T cells, cohorts of animals were transplanted with T cells from either wild-type mice or p55 TNF-alpha receptor-deficient mice. Recipients of TNF-alpha p55 receptor-deficient T cells demonstrated a significant impairment in donor CTL activity after BMT and an increased rate of leukemic relapse compared with recipients of wild-type T cells. These data highlight the importance of conditioning in GVHD pathophysiology, and demonstrate that TNF-alpha is critical to GVL mediated by donor T cells, whereas IL-1 is not.     

Donor T cell DNMT3a regulates alloreactivity in mouse models of hematopoietic stem cell transplantation

DNA methyltransferase 3a (DNMT3a) is an important part of the epigenetic machinery that stabilizes patterns of activated T cell responses. We hypothesized that donor T cell DNMT3a regulates alloreactivity after allogeneic blood and marrow transplantation (allo-BMT). T cell conditional Dnmt3a KO mice were used as donors in allo-BMT models. Mice receiving allo-BMT from KO donors developed severe acute graft-versus-host disease (aGVHD), with increases in inflammatory cytokine levels and organ histopathology scores. KO T cells migrated and proliferated in secondary lymphoid organs earlier and demonstrated an advantage in trafficking to the small intestine. Donor T cell subsets were purified after BMT for whole-genome bisulfite sequencing (WGBS) and RNA-Seq. KO T cells had global methylation similar to that of WT cells, with distinct, localized areas of hypomethylation. Using a highly sensitive computational method, we produced a comprehensive profile of the altered epigenome landscape. Hypomethylation corresponded with changes in gene expression in several pathways of T cell signaling and differentiation. Additionally, Dnmt3a-KO T cells resulted in superior graft-versus-tumor activity. Our findings demonstrate a critical role for DNMT3a in regulating T cell alloreactivity and reveal pathways that control T cell tolerance. These results also provide a platform for deciphering clinical data that associate donor DNMT3a mutations with increased GVHD, decreased relapse, and improved survival.     

Reduced graft-versus-host disease-inducing capacity of T cells after activation, culturing, and magnetic cell sorting selection in an allogeneic bone marrow transplantation model in rats.

Graft-versus-host disease (GvHD), a major complication of allogeneic bone marrow transplantation, has been ascribed to mature T cells in the graft. Because T cells play an important role in engraftment of the bone marrow and decrease the probability of relapse of leukemia, a treatment strategy was developed to preserve the benefits of T cells in the graft and to control the severe complications of GvHD. This can be accomplished by the genetic modification of donor T cells with a suicide gene that allows their selective in vivo elimination and subsequently the abrogation of GvHD. For clinical benefit the alloreactivity of herpes simplex virus thymidine kinase (HSV-TK) gene-transduced T cells should be retained. Therefore, we investigated the influence of gene transduction and the selection procedure on T cells. We demonstrated that activation and culturing of T cells reduce their capacity to induce lethal GvHD in an allogeneic rat bone marrow transplantation model. Furthermore, positive immunomagnetic selection of gene-transduced T cells resulted in loss of the GvHD-inducing capacity of HSV-TK(+) T cells directly after MACS (magnetic cell sorting) selection; this loss could be recovered by a 1-day expansion of the selected T cells. No effect on alloreactivity was observed to be caused by the gene transduction procedure. Our study resulted in the development of an optimized culture and gene transduction protocol with preservation of T cell alloreactivity. Treatment of transplanted rats with ganciclovir resulted in a rapid reduction in the number of HSV-TK(+) T cells in the peripheral blood and in increased survival of the animals.     

[18F]FHBG PET/CT Imaging of CD34-TK75 Transduced Donor T Cells in Relapsed Allogeneic Stem Cell Transplant Patients: Safety and Feasibility

Described herein is a first-in-man attempt to both genetically modify T cells with an imagable suicide gene and track these transduced donor T cells in allogeneic stem cell transplantation recipients using noninvasive positron emission tomography/computerized tomography (PET/CT) imaging. A suicide gene encoding a human CD34-Herpes Simplex Virus-1-thymidine kinase (CD34-TK75) fusion enabled enrichment of retrovirally transduced T cells (TdT), control of graft-versus-host disease and imaging of TdT migration and expansion in vivo in mice and man. Analysis confirmed that CD34-TK75-enriched TdT contained no replication competent γ-retrovirus, were sensitive to ganciclovir, and displayed characteristic retroviral insertion sites (by targeted sequencing). Affinity-purified CD34-TK75⁺-selected donor T cells (1.0–13 × 10⁵)/kg were infused into eight patients who relapsed after allogeneic stem cell transplantation. Six patients also were administered 9-[4-(¹⁸F)fluoro-3-hydroxymethyl-butyl]guanine ([¹⁸F]FHBG) to specifically track the genetically modified donor T cells by PET/CT at several time points after infusion. All patients were assessed for graft-versus-host disease, response to ganciclovir, circulating TdT cells (using both quantitative polymerase chain reaction and [¹⁸F]FHBG PET/CT imaging), TdT cell clonal expansion, and immune response to the TdT. This phase 1 trial demonstrated that genetically modified T cells and [¹⁸F]FHBG can be safely infused in patients with relapsed hematologic malignancies after allogeneic stem cell transplantation.     

Identification of conserved SARS-CoV-2 spike epitopes that expand public cTfh clonotypes in mild COVID-19 patients

Adaptive immunity is a fundamental component in controlling COVID-19. In this process, follicular helper T (Tfh) cells are a subset of CD4⁺ T cells that mediate the production of protective antibodies; however, the SARS-CoV-2 epitopes activating Tfh cells are not well characterized. Here, we identified and crystallized TCRs of public circulating Tfh (cTfh) clonotypes that are expanded in patients who have recovered from mild symptoms. These public clonotypes recognized the SARS-CoV-2 spike (S) epitopes conserved across emerging variants. The epitope of the most prevalent cTfh clonotype, S_864–882, was presented by multiple HLAs and activated T cells in most healthy donors, suggesting that this S region is a universal T cell epitope useful for booster antigen. SARS-CoV-2–specific public cTfh clonotypes also cross-reacted with specific commensal bacteria. In this study, we identified conserved SARS-CoV-2 S epitopes that activate public cTfh clonotypes associated with mild symptoms.     

FBC预处理方案在HLA半相合异基因外周血干细胞移植中的应用

目的　观察降低预处理强度对HLA半相合异基因干细胞植入的影响。方法　用氟达拉宾 (30mg m2 × 6d)、白消安 (4mg kg× 2d)、环磷酰胺 [(30～ 6 0 )mg kg× 2d]组成FBC方案。将 12例白血病患者分成两组 ,HLA完全相合移植组 4例 ,移植前患者处完全缓解状态 ;HLA半相合移植组 8例 ,皆为难治性白血病 ,其中 1例HLA 3个位点不合 ,6例二个位点不合 ,1例一个位点不合 ,接受本处理方案后 ,进行G CSF动员的异基因外周血干细胞移植 ,并于移植后第 30天 (+30天 )、+6 0天、+90天输注供者淋巴细胞 ,观察异基因干细胞植入和长期植入情况。结果　HLA半相合组患者平均接受 4.87× 10 8 kg供者外周血单个核细胞 ,其中CD3 4+细胞平均数为 4.5 8× 10 6 kg,HLA全相合组平均接受 4.85× 10 8 kg供者外周血单个核细胞 ,其中CD3 4+细胞 4.47× 10 6 kg。HLA半相合组 7例白细胞升至 1.0×10 9 L的平均时间为 2 9d(11～ 90d) ,血小板升至 2 0× 10 9 L的时间为 36d(14～ 96d) ,1例HLA 3个位点不合的患者移植失败 ,但该患者于 +5 0天恢复自体造血。而HLA全相合的 4例患者白细胞升至 1.0×10 9 L平均需 14d(11～ 18d) ,血小板升至 2 0× 10 9 L平均需 15d(11～ 18d)。经STR PCR检测 ,两组患者除 1例表现为混合嵌合体 ,其余均呈完     

HLA Engineering of Human Pluripotent Stem Cells

The clinical use of human pluripotent stem cells and their derivatives is limited by the rejection of transplanted cells due to differences in their human leukocyte antigen (HLA) genes. This has led to the proposed use of histocompatible, patient-specific stem cells; however, the preparation of many different stem cell lines for clinical use is a daunting task. Here, we develop two distinct genetic engineering approaches that address this problem. First, we use a combination of gene targeting and mitotic recombination to derive HLA-homozygous embryonic stem cell (ESC) subclones from an HLA-heterozygous parental line. A small bank of HLA-homozygous stem cells with common haplotypes would match a significant proportion of the population. Second, we derive HLA class I–negative cells by targeted disruption of both alleles of the Beta-2 Microglobulin (B2M) gene in ESCs. Mixed leukocyte reactions and peptide-specific HLA-restricted CD8⁺ T cell responses were reduced in class I–negative cells that had undergone differentiation in embryoid bodies. These B2M^−/− ESCs could act as universal donor cells in applications where the transplanted cells do not express HLA class II genes. Both approaches used adeno-associated virus (AAV) vectors for efficient gene targeting in the absence of potentially genotoxic nucleases, and produced pluripotent, transgene-free cell lines.     

Recent progress in allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (ASCT) is a well-established treatment for patients with malignant and non-malignant immunohematopoietic diseases. Matched unrelated donors are increasingly used and improved HLA matching has led to increased survival. In addition, stem cells derived from peripheral blood and cord blood are being utilized to a greater extent. During the last decade, reduced-intensity conditioning, which is preferentially used in older patients or those with organ dysfunction, was introduced as an alternative to standard myeloablative regimens. In addition, the isolation of patients after transplant has been challenged by allowing patients to be treated at home after ASCT. Analysis of mutations in caspase recruitment domain containing protein 15 and levels of regulatory T-cells may be important in identifying patients at risk for acute graft-versus-host disease (GVHD). Mesenchymal stem cells that have immunomodulatory effects home in to injured tissues and may be used in the treatment of patients with steroid-refractory GVHD. In addition, the graft-versus-tumor (GVT) or graft-versus-leukemia (GVL) effect (ie, the attack of the transplanted immune system against the tumor or leukemia), is of major importance for the success of ASCT in patients with malignant disease. GVT and GVL effects may be improved by utilizing differences in minor histocompatibility antigens between the patients and the donor or by using natural killer cell alloreactivity. ASCT has shown GVT effects in patients with solid tumors. New developments in clinical ASCT have been highlighted in this review.     

Programmed death ligand-1 expression on donor T cells drives graft-versus-host disease lethality

Programmed death ligand-1 (PD-L1) interaction with PD-1 induces T cell exhaustion and is a therapeutic target to enhance immune responses against cancer and chronic infections. In murine bone marrow transplant models, PD-L1 expression on host target tissues reduces the incidence of graft-versus-host disease (GVHD). PD-L1 is also expressed on T cells; however, it is unclear whether PD-L1 on this population influences immune function. Here, we examined the effects of PD-L1 modulation of T cell function in GVHD. In patients with severe GVHD, PD-L1 expression was increased on donor T cells. Compared with mice that received WT T cells, GVHD was reduced in animals that received T cells from Pdl1^–/– donors. PD-L1–deficient T cells had reduced expression of gut homing receptors, diminished production of inflammatory cytokines, and enhanced rates of apoptosis. Moreover, multiple bioenergetic pathways, including aerobic glycolysis, oxidative phosphorylation, and fatty acid metabolism, were also reduced in T cells lacking PD-L1. Finally, the reduction of acute GVHD lethality in mice that received Pdl1^–/– donor cells did not affect graft-versus-leukemia responses. These data demonstrate that PD-L1 selectively enhances T cell–mediated immune responses, suggesting a context-dependent function of the PD-1/PD-L1 axis, and suggest selective inhibition of PD-L1 on donor T cells as a potential strategy to prevent or ameliorate GVHD.     

HTLV-1 infection promotes excessive T cell activation and transformation into adult T cell leukemia/lymphoma

Human T cell leukemia virus type 1 (HTLV-1) mainly infects CD4⁺ T cells and induces chronic, persistent infection in infected individuals, with some developing adult T cell leukemia/lymphoma (ATL). HTLV-1 alters cellular differentiation, activation, and survival; however, it is unknown whether and how these changes contribute to the malignant transformation of infected cells. In this study, we used single-cell RNA-sequencing and T cell receptor–sequencing to investigate the differentiation and HTLV-1–mediated transformation of T cells. We analyzed 87,742 PBMCs from 12 infected and 3 uninfected individuals. Using multiple independent bioinformatics methods, we demonstrated the seamless transition of naive T cells into activated T cells, whereby HTLV-1–infected cells in an activated state further transformed into ATL cells, which are characterized as clonally expanded, highly activated T cells. Notably, the greater the activation state of ATL cells, the more they acquire Treg signatures. Intriguingly, the expression of HLA class II genes in HTLV-1–infected cells was uniquely induced by the viral protein Tax and further upregulated in ATL cells. Functional assays revealed that HTLV-1–infected cells upregulated HLA class II molecules and acted as tolerogenic antigen-presenting cells to induce anergy of antigen-specific T cells. In conclusion, our study revealed the in vivo mechanisms of HTLV-1–mediated transformation and immune escape at the single-cell level.