High eomesodermin expression among CD57+ CD8+ T cells identifies a CD8+ T cell subset associated with viral control during chronic human immunodeficiency virus infection

The role of TEMRA cell-mediated immune senescence in the development and treatment of HIV disease

Human Immunodeficiency Virus (HIV) has plagued human society for a long time since its discovery, causing a large number of patients to suffer and costing hundreds of millions of medical services every year. Scientists have found that HIV and antiretroviral therapy accelerate immune aging by inducing mitochondrial dysfunction, and that terminal effector memory T cells (TEMRA cells) are crucial in immune aging. This specific subset of effector memory T cells has terminally differentiated properties and exhibits high cytotoxicity and proinflammatory capacity. We therefore explored and described the interplay between exhaustion features, essential markers, functions, and signaling pathways from previous studies on HIV, antiretroviral therapy, immune senescence, and TEMRA cells. Their remarkable antiviral capacity is then highlighted by elucidating phenotypic changes in TEMRA cells during HIV infection, describing changes in TEMRA cells before, during, and after antiretroviral therapy and other drug treatments. Their critical role in complications and cytomegalovirus (CMV)-HIV superinfection is highlighted. These studies demonstrate that TEMRA cells play a key role in the antiviral response and immune senescence during HIV infection. Finally, we review current therapeutic strategies targeting TEMRA cells that may be clinically beneficial, highlight their potential role in HIV-1 vaccine development, and provide perspectives and predictions for related future applications.

Comparison of the Biological Basis for Non-HIV Transmission to HIV-Exposed Seronegative Individuals, Disease Non-Progression in HIV Long-Term Non-Progressors and Elite Controllers

HIV-exposed seronegative individuals (HESIs) are a small fraction of persons who are multiply exposed to human immunodeficiency virus (HIV), but do not exhibit serological or clinical evidence of HIV infection. In other words, they are groups of people maintaining an uninfected status for a long time, even after being exposed to HIV several times. The long-term non-progressors (LTNPs), on the other hand, are a group of HIV-infected individuals (approx. 5%) who remain clinically and immunologically stable for an extended number of years without combination antiretroviral therapy (cART). Meanwhile, elite controllers are comprise a much lower number (0.5%) of HIV-infected persons who spontaneously and durably control viremia to below levels of detection for at least 12 months, even when using the most sensitive assays, such as polymerase chain reaction (PCR) in the absence of cART. Despite the fact that there is no universal agreement regarding the mechanisms by which these groups of individuals are able to control HIV infection and/or disease progression, there is a general consensus that the mechanisms of protection are multifaceted and include genetic, immunological as well as viral factors. In this review, we analyze and compare the biological factors responsible for the control of HIV in these unique groups of individuals.

Alterations in high-dimensional T-cell profile and gene signature of immune aging in HIV-infected older adults without viremia

Alterations in the components of the immune system occur with aging. The introduction of combination antiretroviral therapy (ART) has dramatically improved life expectancy in human immunodeficiency virus (HIV) infected individuals by suppressing viral replication and increasing CD4+ T-cell counts. Immunosenescence-like changes, including the expansion of memory CD8+ T cells with senescent features, are reported in young HIV-infected individuals who do not have clinically detectable viremia on ART. However, it is less known whether HIV infection affects the immunosenescent status in older HIV-infected individuals. Here, we addressed this question in older HIV-infected, HIV-uninfected, and frail individuals (all groups age ≥65 years) by examining a set of aging-associated genes in peripheral blood mononuclear cells (PBMCs) as well as by analyzing subsets of CD4+ and CD8+ T cells in depth using high-dimensional CyTOF analysis. Older HIV-infected individuals had increased expression of aging-associated genes such as CX3CR1 in PBMCs which are related to IL-7 receptor low effector memory (IL-7Rαlow EM) CD8+ T cells, a cell population known to expand with age. The subsets of IL-7Rαlow EM CD8+ T cells expressing senescent, cytotoxic, and inflammatory molecules, including CD57, perforin, and CX3CR1, as well as memory CD4+ T cells expressing CD161 and CXCR3, molecules associated with replication-competent HIV-1 harboring cells, were increased in older HIV-infected individuals. Overall, older HIV-infected individuals without detectable viremia on ART had augmented levels of age-associated immune alterations in PBMCs, suggesting that HIV infection has a persistent impact on senescence in older HIV-infected individuals despite the clinically controlled viremia.

Peptide Centric Vβ Specific Germline Contacts Shape a Specialist T Cell Response

Certain CD8 T cell responses are particularly effective at controlling infection, as exemplified by elite control of HIV in individuals harboring HLA-B57. To understand the structural features that contribute to CD8 T cell elite control, we focused on a strongly protective CD8 T cell response directed against a parasite-derived peptide (HF10) presented by an atypical MHC-I molecule, H-2Ld. This response exhibits a focused TCR repertoire dominated by Vβ2, and a representative TCR (TG6) in complex with Ld-HF10 reveals an unusual structure in which both MHC and TCR contribute extensively to peptide specificity, along with a parallel footprint of TCR on its pMHC ligand. The parallel footprint is a common feature of Vβ2-containing TCRs and correlates with an unusual Vα-Vβ interface, CDR loop conformations, and Vβ2-specific germline contacts with peptides. Vβ2 and Ld may represent "specialist" components for antigen recognition that allows for particularly strong and focused T cell responses.

How elite controllers and posttreatment controllers inform our search for an HIV-1 cure

A small percentage of people living with HIV-1 can control viral replication without antiretroviral therapy (ART). These patients are called elite controllers (ECs) if they are able to maintain viral suppression without initiating ART and posttreatment controllers (PTCs) if they control HIV replication after ART has been discontinued. Both types of controllers may serve as a model of a functional cure for HIV-1 but the mechanisms responsible for viral control have not been fully elucidated. In this review, we highlight key lessons that have been learned so far in the study of ECs and PTCs and their implications for HIV cure research.

Optimal Maturation of the SIV-Specific CD8+ T Cell Response after Primary Infection Is Associated with Natural Control of SIV: ANRS SIC Study

Highly efficient CD8⁺ T cells are associated with natural HIV control, but it has remained unclear how these cells are generated and maintained. We have used a macaque model of spontaneous SIVmac251 control to monitor the development of efficient CD8⁺ T cell responses. Our results show that SIV-specific CD8⁺ T cells emerge during primary infection in all animals. The ability of CD8⁺ T cells to suppress SIV is suboptimal in the acute phase but increases progressively in controller macaques before the establishment of sustained low-level viremia. Controller macaques develop optimal memory-like SIV-specific CD8⁺ T cells early after infection. In contrast, a persistently skewed differentiation phenotype characterizes memory SIV-specific CD8⁺ T cells in non-controller macaques. Accordingly, the phenotype of SIV-specific CD8⁺ T cells defined early after infection appears to favor the development of protective immunity in controllers, whereas SIV-specific CD8⁺ T cells in non-controllers fail to gain antiviral potency, feasibly as a consequence of early defects imprinted in the memory pool.

Circulating mucosal-associated invariant T cells identify patients responding to anti-PD-1 therapy

Immune checkpoint inhibitors are used for treating patients with metastatic melanoma. Since the response to treatment is variable, biomarkers are urgently needed to identify patients who may benefit from such therapy. Here, we combine single-cell RNA-sequencing and multiparameter flow cytometry to assess changes in circulating CD8⁺ T cells in 28 patients with metastatic melanoma starting anti-PD-1 therapy, followed for 6 months: 17 responded to therapy, whilst 11 did not. Proportions of activated and proliferating CD8⁺ T cells and of mucosal-associated invariant T (MAIT) cells are significantly higher in responders, prior to and throughout therapy duration. MAIT cells from responders express higher level of CXCR4 and produce more granzyme B. In silico analysis support MAIT presence in the tumor microenvironment. Finally, patients with >1.7% of MAIT among peripheral CD8⁺ population show a better response to treatment. Our results thus suggest that MAIT cells may be considered a biomarker for patients responding to anti-PD-1 therapy.

The T cell differentiation landscape is shaped by tumour mutations in lung cancer

Tumour mutational burden (TMB) predicts immunotherapy outcome in non-small cell lung cancer (NSCLC), consistent with immune recognition of tumour neoantigens. However, persistent antigen exposure is detrimental for T cell function. How TMB affects CD4 and CD8 T cell differentiation in untreated tumours, and whether this affects patient outcomes is unknown. Here we paired high-dimensional flow cytometry, exome, single-cell and bulk RNA sequencing from patients with resected, untreated NSCLC to examine these relationships. TMB was associated with compartment-wide T cell differentiation skewing, characterized by loss of TCF7-expressing progenitor-like CD4 T cells, and an increased abundance of dysfunctional CD8 and CD4 T cell subsets, with significant phenotypic and transcriptional similarity to neoantigen-reactive CD8 T cells. A gene signature of redistribution from progenitor-like to dysfunctional states associated with poor survival in lung and other cancer cohorts. Single-cell characterization of these populations informs potential strategies for therapeutic manipulation in NSCLC.

The proportion of CD57+ cells among effector CD8+ T cells is lower in HIV controllers compared with antiretroviral therapy-treated patients

BACKGROUND

HIV infection has often been linked to faster immune ageing. We sought to determine whether or not treatment-naive spontaneous HIV-1 controllers (HICs) and ART-exposed patients differ with regard to the expression of cell senescence markers.

METHODS

Eighty-eight chronically infected HICs and ART-exposed patients (median time since infection: 15 years) with an undetectable plasma HIV RNA load (at least for the previous 2 years) were included. We used flow cytometry to measure immunosenescence markers (KLRG-1 and CD57) expression in fresh blood samples collected from patients and healthy donors.

RESULTS

For the CD8 T-cell population as a whole, the ART-exposed but not the HIC patients exhibited a much higher proportion of KLRG-1 and CD57 CD8 T cells than healthy blood donors. For the CD8 T-cell subsets, HICs had a lower proportion of CD57 effector CD8 T cells than ART patients or healthy blood donors, whereas the proportions of KLRG-1 effector were similar. A similar trend was observed for terminal effectors. No impact of age, sex or standard parameters of infection (CD4 percentage, protective HLA allele, viral blips) was observed. The difference in the proportion of CD57 cells between HICs and ART was observed more specifically in long-term infected patients (>20 years). However, whenever considering the CD57 effector memory and effector subsets, the cytotoxic granule content was greater in HICs than in ART.

CONCLUSION

The proportion of CD57 effector CD8 T cells is lower in HICs than in ART-exposed patients. This profile may be beneficial by ensuring limited senescence associated with consistent cytotoxic potential.

HLA class II-Restricted CD8+ T cells in HIV-1 Virus Controllers

A paradigm shifting study demonstrated that induction of MHC class E and II-restricted CD8+ T cells was associated with the clearance of SIV infection in rhesus macaques. Another recent study highlighted the presence of HIV-1-specific class II-restricted CD8+ T cells in HIV-1 patients who naturally control infection (virus controllers; VCs). However, questions regarding class II-restricted CD8+ T cells ontogeny, distribution across different HIV-1 disease states and their role in viral control remain unclear. In this study, we investigated the distribution and anti-viral properties of HLA-DRB1*0701 and DQB1*0501 class II-restricted CD8+ T cells in different HIV-1 patient cohorts; and whether class II-restricted CD8+ T cells represent a unique T cell subset. We show that memory class II-restricted CD8+ T cell responses were more often detectable in VCs than in chronically infected patients, but not in healthy seronegative donors. We also demonstrate that VC CD8+ T cells inhibit virus replication in both a class I- and class II-dependent manner, and that in two VC patients the class II-restricted CD8+ T cells with an anti-viral gene signature expressed both CD4+ and CD8+ T cell lineage-specific genes. These data demonstrated that anti-viral memory class II-restricted CD8+ T cells with hybrid CD4+ and CD8+ features are present during natural HIV-1 infection.

In-vitro viral suppressive capacity correlates with immune checkpoint marker expression on peripheral CD8+ T cells in treated HIV-positive patients

OBJECTIVE

To determine whether viral suppressive capacity (VSC) of CD8+ T cells can be boosted by stimulation with HIV-1 peptides and whether the ability to control HIV-1 replication correlates with immunological (cytokine production and CD8+ T-cell phenotype) and viral reservoir measures (total HIV-1 DNA and cell-associated RNA) in well treated HIV-infected chronic progressors.

DESIGN

We compared VSC of peripheral CD8+ T cells to cytokine production profile in response to peptide stimulation, detailed phenotype (17-color flow-cytometry), reservoir size (total HIV-1 DNA), basal viral transcription (unspliced cell-associated RNA) and inducible viral transcription (tat/rev induced limiting dilution assay) in 36 HIV+ patients on cART and six healthy donors.

RESULTS

We found that the VSC of CD8+ T cells can be increased by prior stimulation with a pool of consensus HIV-1 gag peptides in a significant proportion of progressor patients. We also found that VSC after peptide stimulation was correlated with higher expression of immune checkpoint markers on subsets of terminally differentiated effector memory (TEMRA) CD8 T cells as well as with production of IFN-γ, TNF-α and IL-10. We did not find a correlation between VSC and viral reservoir measures.

CONCLUSION

These results add to a small body of evidence that the capacity of CD8+ T cells to suppress viral replication is increased after stimulation with HIV-1 peptides. Interestingly, this VSC was correlated with expression of immune checkpoint markers, which are generally considered to be markers of exhaustion. Our findings may guide further investigations into immune phenotypes correlated with viral suppression.

An altered cytotoxic program of CD8+ T-cells in HIV-infected patients despite HAART-induced viral suppression

Despite the suppression of viral replication induced by the highly active anti-retroviral therapy (HAART), an increased immune activation and inflammatory state persists in HIV-infected patients, contributing to lower treatment response and immune reconstitution, and development of non-AIDS conditions. The chronic activation and inflammation affect the functionality and differentiation of CD8+ T-cells, particularly reducing their cytotoxic capacity, which is critical in the control of HIV replication. Although previous studies have shown that HAART induce a partial immune reconstitution, its effect on CD8+ T-cells cytotoxic function, as well as its relationship with the inflammatory state, is yet to be defined. Here, we characterized the functional profile of polyclonal and HIV-specific CD8+ T cells, based on the expression of cell activation and differentiation markers, in individuals chronically infected with HIV, under HAART. Compared with seronegative controls, CD8+ T-cells from patients on HAART exhibited a low degranulation capacity (surface expression of CD107a), with consequent low secreted levels and high intracellular expression of granzyme B and perforin. This degranulation defect was particularly observed in those cells expressing the activation marker HLA-DR, which were further characterized as effector memory cells with high expression of CD57. The expression of CD107a, but not of granzyme B and perforin, in CD8+ T-cells from HIV-infected patients on HAART reached levels similar to those in seronegative controls when the treatment duration was higher than 25 months. In addition, the expression of CD107a was negatively correlated with the expression of exhaustion markers on CD8+ T-cells and the plasma inflammatory molecule sCD14. Thus, despite HAART-induced viral suppression, CD8+ T-cells from HIV-infected patients have an alteration in their cytotoxic program. This defect is associated with the cellular activation, differentiation and exhaustion state, as well as with the inflammation levels, and can be partially recovered with a long and continuous treatment.

Assessing the role of the T-box transcription factor Eomes in B cell differentiation during either Th1 or Th2 cell-biased responses

Successful T-dependent humoral responses require the production of antibody-secreting plasmablasts, as well as the formation of germinal centers which eventually form high-affinity B cell memory. The ability of B cells to differentiate into germinal center and plasma cells, as well as the ability to tailor responses to different pathogens, is driven by transcription factors. In T cells, the T-box transcription factors T-bet and Eomesodermin (Eomes) regulate effector and memory T cell differentiation, respectively. While T-bet has a critical role in regulating anti-viral B cell responses, a role for Eomes in B cells has yet to be described. We therefore investigated whether Eomes was required for B cell differentiation during either Th1 or Th2 cell-biased immune responses. Here, we demonstrate that deletion of Eomes specifically in B cells did not affect B cell differentiation in response to vaccination, as well as following viral or helminth infection. In contrast to its established role in CD8⁺ T cells, Eomes did not influence memory B cell differentiation. Finally, the use of an Eomes reporter mouse confirmed the lack of Eomes expression during immune responses. Thus, germinal center and plasma cell differentiation and the formation of isotype-switched memory B cells in response to infection are independent of Eomes expression.

Characterization of eomesodermin and T-bet expression by allostimulated CD8+ T cells of healthy volunteers and kidney transplant patients in relation to graft outcome

Memory T cell (Tmem) responses play a critical role in the outcome of allo-transplantation. While the role of the T-box transcription factor Eomesodermin (Eomes) in the maintenance of antigen-specific Tmem is well studied, little is known about Eomes⁺ CD8⁺ T cell responses after transplantation. We evaluated the phenotype and function of allo-reactive Eomes⁺ CD8⁺ T cells in healthy volunteers and kidney transplant patients and their relation to transplant outcome. High Eomes expression by steady-state CD8⁺ T cells correlated with effector and memory phenotype. Following allo-stimulation, the expression of both the T-box proteins Eomes and T-bet by proliferating cells increased significantly, where high expression of Eomes and T-bet correlated with higher incidence of allo-stimulated IFNγ⁺ TNFα⁺ CD8⁺ T cells. In patients with no subsequent rejection, Eomes but not T-bet expression by donor-stimulated CD8⁺ T cells, increased significantly after transplantation. This was characterized by increased Eomes^hi T-bet^-/lo and decreased Eomes^-/lo T-bet^hi CD8⁺ T cell subsets, with no significant changes in the Eomes^hi T-bet^hi CD8⁺ T cell subset. No upregulation of exhaustion markers programmed-death-1 (PD-1) and cytotoxic-T-lymphocyte-associated-antigen-4 (CTLA4) by donor-stimulated Eomes⁺ CD8⁺ T cells was observed. Before transplantation, in patients without rejection, there were higher incidences of Eomes^hi T-bet^-/lo , and lower incidences of Eomes^hi T-bet^hi and Eomes^-/lo T-bet^hi donor-stimulated CD8⁺ T cell subsets, compared to those with subsequent rejection. Overall, our findings indicate that high Eomes expression by allo-stimulated T-bet⁺ CD8⁺ T cells is associated with enhanced effector function, and that an elevated incidence of donor-stimulated CD8⁺ T cells co-expressing high levels of Eomes and T-bet before transplantation, may correlate with an increased incidence of acute cellular rejection.

The function and dysfunction of memory CD8+ T cells in tumor immunity

The generation and maintenance of CD8+ T cell memory is crucial to long-term host survival, yet the basic tenets of CD8+ T cell immunity are still being established. Recent work has led to the discovery of tissue-resident memory cells and refined our understanding of the transcriptional and epigenetic basis of CD8+ T cell differentiation and dysregulation. In parallel, the unprecedented clinical success of immunotherapy has galvanized an intense, global research effort to decipher and de-repress the anti-tumor response. However, the progress of immunotherapy is at a critical juncture, since the efficacy of immuno-oncology agents remains confined to a fraction of patients and often fails to provide durable benefit. Unlocking the potential of immunotherapy requires the design of strategies that both induce a potent effector response and reliably forge stable, functional memory T cell pools capable of protecting from recurrence or relapse. It is therefore essential that basic and emerging concepts of memory T cell biology are rapidly and faithfully transposed to advance therapeutic development in cancer immunotherapy. This review highlights seminal and recent reports in CD8+ T cell memory and tumor immunology, and evaluates recent data from solid cancer specimens in the context of the key paradigms from preclinical models. We elucidate the potential significance of circulating effector cells poised downstream of neoantigen recognition and upstream of T cell dysfunction and propose that cells in this immunological 'sweet spot' may be key anti-tumor effectors.

Adaptive Memory of Human NK-like CD8+ T-Cells to Aging, and Viral and Tumor Antigens

Human natural killer (NK)-like CD8⁺ T-cells are singular T-cells that express both T and NK cell markers such as CD56; their frequencies depend on their differentiation and activation during their lifetime. There is evidence of the presence of these innate CD8⁺ T-cells in the human umbilical cord, highlighting the necessity of investigating whether the NK-like CD8⁺ T-cells arise in the early stages of life (gestation). Based on the presence of cell surface markers, these cells have also been referred to as CD8⁺KIR⁺ T-cells, innate CD8⁺ T-cells, CD8⁺CD28⁻KIR⁺ T-cells or NKT-like CD8⁺CD56⁺ cells. However, the functional and co-signaling significance of these NK cell receptors on NK-like CD8⁺ T-cells is less clear. Also, the diverse array of costimulatory and co-inhibitory receptors are spatially and temporally regulated and may have distinct overlapping functions on NK-like CD8⁺ T-cell priming, activation, differentiation, and memory responses associated with different cell phenotypes. Currently, there is no consensus regarding the functional properties and phenotypic characterization of human NK-like CD8⁺ T-cells. Environmental factors, such as aging, autoimmunity, inflammation, viral antigen re-exposure, or the presence of persistent tumor antigens have been shown to allow differentiation (“adaptation”) of the NK-like CD8⁺ T-cells; the elucidation of this differentiation process and a greater understanding of the characteristics of these cells could be important for their eventual in potential therapeutic applications aimed at improving protective immunity. This review will attempt to elucidate an understanding of the characteristics of these cells with the goal toward their eventual use in potential therapeutic applications aimed at improving protective immunity.

Continuous Effector CD8(+) T Cell Production in a Controlled Persistent Infection Is Sustained by a Proliferative Intermediate Population

Highly functional CD8(+) effector T (Teff) cells can persist in large numbers during controlled persistent infections, as exemplified by rare HIV-infected individuals who control the virus. Here we examined the cellular mechanisms that maintain ongoing T effector responses using a mouse model for persistent Toxoplasma gondii infection. In mice expressing the protective MHC-I molecule, H-2L(d), a dominant T effector response against a single parasite antigen was maintained without a contraction phase, correlating with ongoing presentation of the dominant antigen. Large numbers of short-lived Teff cells were continuously produced via a proliferative, antigen-dependent intermediate (Tint) population with a memory-effector hybrid phenotype. During an acute, resolved infection, decreasing antigen load correlated with a sharp drop in the Tint cell population and subsequent loss of the ongoing effector response. Vaccination approaches aimed at the development of Tint populations might prove effective against pathogens that lead to chronic infection.

HIV-Specific CD8+ T Cell-Mediated Viral Suppression Correlates With the Expression of CD57

BACKGROUND

Virus-specific CD8(+) T-cell responses are believed to play an important role in the control of HIV-1 infection; however, what constitutes an effective HIV-1 CD8(+) T-cell response remains a topic of debate. The ex vivo viral suppressive capacity was measured of CD8(+) T cells from 44 HIV-1-positive individuals. The phenotypic and cytokine profiles, and also the specificity of the CD8(+) T cells, were correlated with the suppression of HIV-1 replication. We also aimed to determine whether antiretroviral therapy (ART) had any positive effect on the HIV-1 suppressive CD8(+) T cells.

METHOD

Ex vivo suppression assay was used to evaluate the ability of CD8(+) T cells to suppress HIV-1 replication in autologous CD4(+) T cells. The CD107a, interferon-γ, interleukin-2, tumor necrosis factor-α (TNF-α), and macrophage inflammatory protein-1β (MIP-1β) responses to HIV-1 were evaluated by intracellular staining. The phenotypic profile of CD8(+) T cells was determined by whole blood staining.

RESULTS

The expression of CD57 on effector CD8(+) T cells correlated with the suppression of HIV-1 replication and to the duration of ART. CD107a and tumor necrosis factor-α expression levels were significantly higher in individuals with ex vivo suppressive activity compared with individuals without suppressive activity.

CONCLUSIONS

Standard in vitro assays measuring one or several cytokines do not correlate with the functional viral suppressive capacity of CD8(+) T cells from HIV-1-positive individuals. The best correlation of viral suppression was found to be CD57 expression. CD57 expression correlated with the duration of ART, suggesting that ART restores the cytotoxic capacity of CD8(+) T lymphocytes.

Regulation of CD8+ T-cell cytotoxicity in HIV-1 infection

Understanding the mechanisms involved in cellular immune responses against control of human immunodeficiency virus (HIV) infection is key to development of effective immunotherapeutic strategies against viral proliferation. Clear insights into the regulation of cytotoxic CD8+ T cells is crucial to development of effective immunotherapeutic strategies due to their unique ability to eliminate virus-infected cells during the course of infection. Here, we reviewed the roles of transcription factors, co-inhibitory molecules and regulatory cytokines following HIV infection and their potential significance in regulating the cytotoxic potentials of CD8+ T cells.

NK Cell Functional Impairment after Allogeneic Hematopoietic Stem Cell Transplantation Is Associated with Reduced Levels of T-bet and Eomesodermin

NK cells play a major role in protection against tumor recurrence and infection after allogeneic hematopoietic stem cell transplantation (HSCT). It has been shown that NK cell function after HSCT is impaired, but underlying molecular mechanisms are not well-known. In this report we show that the level of T-bet and Eomesodermin (Eomes), two T-box transcription factors regulating lymphocyte effector functions, is strongly reduced in NK cells from HSCT recipients compared with healthy control subjects. Reduction of T-bet and Eomes expression appeared early and persisted for years after HSCT, affecting all peripheral blood NK cells independently of their differentiation status. Reduced T-bet levels in NK cells from allogeneic HSCT recipients significantly correlated with reduced perforin expression. Acute, but not chronic, graft-versus-host disease, as well as CMV reactivation, was associated with further downregulation of T-bet expression in NK cells. Lower levels of T-bet expression in NK cells were associated with less favorable outcome after HSCT as a result of increased nonrelapse mortality. Collectively, our results provide a possible molecular explanation for the previously reported functional exhaustion of NK cells after allogeneic HSCT and suggest an impact of the NK transcriptional machinery status on HSCT outcome.