NK cell regulation of CD4 T cell-mediated graft-versus-host disease

The immunoglobulin superfamily ligand B7H6 subjects T cell responses to NK cell surveillance

Understanding the mechanisms that regulate T cell immunity is critical for the development of effective therapies for diseases associated with T cell dysfunction, including autoimmune diseases, chronic infections, and cancer. Co-inhibitory "checkpoint molecules," such as programmed cell death protein-1, balance excessive or prolonged immune activation by T cell-intrinsic signaling. Here, by screening for mediators of natural killer (NK) cell recognition on T cells, we identified the immunoglobulin superfamily ligand B7H6 to be highly expressed by activated T cells, including patient-infused CD19-targeting chimeric antigen receptor (CAR) T cells. Unlike other checkpoint molecules, B7H6 mediated NKp30-dependent recognition and subsequent cytolysis of activated T cells by NK cells. B7H6+ T cells were prevalent in the tissue and blood of several diseases, and their abundance in tumor tissue positively correlated with clinical response in a cohort of patients with immune checkpoint inhibitor-treated esophageal cancer. In humanized mouse models, NK cell surveillance via B7H6 limited the persistence and antitumor activity of CAR T cells, and its genetic deletion enhanced T cell proliferation and persistence. Together, we provide evidence of B7H6 protein expression by activated T cells and suggest the B7H6-NKp30 axis as a therapeutically actionable NK cell-dependent immune checkpoint that regulates human T cell function.

Balancing act: the complex role of NK cells in immune regulation

Natural killer (NK) cells, as fundamental components of innate immunity, can quickly react to abnormalities within the body. In-depth research has revealed that NK cells possess regulatory functions not only in innate immunity but also in adaptive immunity under various conditions. Multiple aspects of the adaptive immune process are regulated through NK cells. In our review, we have integrated multiple studies to illuminate the regulatory function of NK cells in regulating B cell and T cell responses during adaptive immune processes, focusing on aspects including viral infections and the tumor microenvironment (TME). These insights provide us with many new understandings on how NK cells regulate different phases of the adaptive immune response.

Hypoxia-inducing cryogels uncover key cancer-immune cell interactions in an oxygen-deficient tumor microenvironment

Hypoxia is a major factor shaping the immune landscape, and several cancer models have been developed to emulate hypoxic tumors. However, to date, they still have several limitations, such as the lack of reproducibility, inadequate biophysical cues, limited immune cell infiltration, and poor oxygen (O2) control, leading to non-pathophysiological tumor responses. Therefore, it is essential to develop better cancer models that mimic key features of the tumor extracellular matrix and recreate tumor-associated hypoxia while allowing cell infiltration and cancer-immune cell interactions. Herein, hypoxia-inducing cryogels (HICs) have been engineered using hyaluronic acid (HA) to fabricate three-dimensional microtissues and model a hypoxic tumor microenvironment. Specifically, tumor cell-laden HICs have been designed to deplete O2 locally and induce long-standing hypoxia. HICs promoted changes in hypoxia-responsive gene expression and phenotype, a metabolic adaptation to anaerobic glycolysis, and chemotherapy resistance. Additionally, HIC-supported tumor models induced dendritic cell (DC) inhibition, revealing a phenotypic change in the plasmacytoid DC (pDC) subset and an impaired conventional DC (cDC) response in hypoxia. Lastly, our HIC-based melanoma model induced CD8+ T cell inhibition, a condition associated with the downregulation of pro-inflammatory cytokine secretion, increased expression of immunomodulatory factors, and decreased degranulation and cytotoxic capacity of T cells. Overall, these data suggest that HICs can be used as a tool to model solid-like tumor microenvironments and has great potential to deepen our understanding of cancer-immune cell relationship in low O2 conditions and may pave the way for developing more effective therapies.

Mapping human natural killer cell development in pediatric tonsil by imaging mass cytometry and high-resolution microscopy

Natural killer (NK) cells develop from CD34+ progenitors in a stage-specific manner defined by changes in cell surface receptor expression and function. Secondary lymphoid tissues, including tonsil, are sites of human NK cell development. Here we present new insights into human NK cell development in pediatric tonsil using cyclic immunofluorescence and imaging mass cytometry. We show that NK cell subset localization and interactions are dependent on NK cell developmental stage and tissue residency. NK cell progenitors are found in the interfollicular domain in proximity to cytokine-expressing stromal cells that promote proliferation and maturation. Mature NK cells are primarily found in the T-cell rich parafollicular domain engaging in cell-cell interactions that differ depending on their stage and tissue residency. The presence of local inflammation results in changes in NK cell interactions, abundance, and localization. This study provides the first comprehensive atlas of human NK cell development in secondary lymphoid tissue.

Hypoxia-inducing cryogels uncover key cancer-immune cell interactions in an oxygen-deficient tumor microenvironment

Hypoxia, an important feature of solid tumors, is a major factor shaping the immune landscape, and several cancer models have been developed to emulate hypoxic tumors. However, to date, they still have several limitations, such as the lack of reproducibility, inadequate biophysical cues, limited immune cell infiltration, and poor oxygen (O 2 ) control, leading to non-pathophysiological tumor responses. As a result, it is essential to develop new and improved cancer models that mimic key features of the tumor extracellular matrix and recreate tumor-associated hypoxia while allowing cell infiltration and cancer-immune cell interactions. Herein, hypoxia-inducing cryogels (HICs) have been engineered using hyaluronic acid (HA) as macroporous scaffolds to fabricate three-dimensional microtissues and model a hypoxic tumor microenvironment. Specifically, tumor cell-laden HICs have been designed to deplete O 2 locally and induce long-standing hypoxia. This state of low oxygen tension, leading to HIF-1α stabilization in tumor cells, resulted in changes in hypoxia-responsive gene expression and phenotype, a metabolic adaptation to anaerobic glycolysis, and chemotherapy resistance. Additionally, HIC-supported tumor models induced dendritic cell (DC) inhibition, revealing a phenotypic change in plasmacytoid B220 + DC (pDC) subset and an impaired conventional B220 - DC (cDC) response in hypoxia. Lastly, our HIC-based melanoma model induced CD8+ T cell inhibition, a condition associated with the downregulation of pro-inflammatory cytokine secretion, increased expression of immunomodulatory factors, and decreased degranulation and cytotoxic capacity of T cells. Overall, these data suggest that HICs can be used as a tool to model solid-like tumor microenvironments and identify a phenotypic transition from cDC to pDC in hypoxia and the key contribution of HA in retaining cDC phenotype and inducing their hypoxia-mediated immunosuppression. This technology has great potential to deepen our understanding of the complex relationships between cancer and immune cells in low O 2 conditions and may pave the way for developing more effective therapies.

Regulation of Cytotoxic Immune Effector Function by AJ3 Probiotic Bacteria in Amyotrophic Lateral Sclerosis (ALS)

Our recent studies indicated that amyotrophic lateral sclerosis (ALS) patients suffer from significantly elevated levels of interferon-gamma (IFN-γ) secretion by natural killer (NK) and CD8+ T cells, which may be responsible for the immune-pathologies seen in central nervous system and in peripheral organs of the patients. In order to counter such elevated induction of IFN-γ in patients we designed a treatment strategy to increase anti-inflammatory cytokine interleukin-10 (IL-10) by the use of probiotic strains which significantly increase the levels of IL-10. Therefore, in this paper we demonstrate disease specific functions of Al-Pro (AJ3) formulated for the adjunct treatment of auto-immune diseases including ALS, and compared the function with CA/I-Pro (AJ4) for the treatment of cancer and viral diseases, and NK-CLK (AJ2) for maintenance of immune balance and promotion of disease prevention. The three different formulations of probiotic bacteria have distinct profiles of activation of peripheral blood mononuclear cells (PBMCs), NK, and CD8+ T cells, and their induced activation is different from those mediated by either IL-2 or IL-2 + anti-CD16 monoclonal antibodies (mAbs) or IL-2 + anti-CD3/CD28 mAbs. IL-2 + anti-CD16 mAb activation of PBMCs and NK cells had the highest IFN-γ/IL-10 ratio, whereas IL-2 combination with sAJ4 had the next highest followed by IL-2 + sAJ2 and the lowest was seen with IL-2 + sAJ3. Accordingly, the highest secretion of IFN-γ was seen when the PBMCs and NK cells were treated with IL-2 + sAJ4, intermediate for IL-2 + sAJ2 and the lowest with IL-2 + sAJ3. The levels of IFN-γ induction and the ratio of IFN-γ to IL-10 induced by different probiotic bacteria formulation in the absence of IL-2 treatment remained much lower when compared to those treated in the presence of IL-2. Of note is the difference between NK cells and CD8+ T cells in which synergistic induction of IFN-y by IL-2 + sAJ4 was significantly higher in NK cells than those seen by CD8+ T cells. Based on these results, sAJ3 should be effective in alleviating auto-immunity seen in ALS since it will greatly regulate the levels and function of IFN-γ negatively, decreasing overactivation of cytotoxic immune effectors and prevention of death in motor neurons.

Changes in HCMV immune cell frequency and phenotype are associated with chronic lung allograft dysfunction

Background

Human cytomegalovirus (HCMV) infection is common and often severe in lung transplant recipients (LTRs), and it is a risk factor associated with chronic lung allograft dysfunction (CLAD). The complex interplay between HCMV and allograft rejection is still unclear. Currently, no treatment is available to reverse CLAD after diagnosis, and the identification of reliable biomarkers that can predict the early development of CLAD is needed. This study investigated the HCMV immunity in LTRs who will develop CLAD.

Methods

This study quantified and phenotyped conventional (HLA-A2pp65) and HLA-E-restricted (HLA-EUL40) anti-HCMV CD8⁺ T (CD8 T) cell responses induced by infection in LTRs developing CLAD or maintaining a stable allograft. The homeostasis of immune subsets (B, CD4T, CD8 T, NK, and γδT cells) post-primary infection associated with CLAD was also investigated.

Results

At M18 post-transplantation, HLA-EUL40 CD8 T responses were less frequently found in HCMV⁺ LTRs (21.7%) developing CLAD (CLAD) than in LTRs (55%) keeping a functional graft (STABLE). In contrast, HLA-A2pp65 CD8 T was equally detected in 45% of STABLE and 47.8% of CLAD LTRs. The frequency of HLA-EUL40 and HLA-A2pp65 CD8 T among blood CD8 T cells shows lower median values in CLAD LTRs. Immunophenotype reveals an altered expression profile for HLA-EUL40 CD8 T in CLAD patients with a decreased expression for CD56 and the acquisition of PD-1. In STABLE LTRs, HCMV primary infection causes a decrease in B cells and inflation of CD8 T, CD57⁺/NKG2C⁺ NK, and δ2^-γδT cells. In CLAD LTRs, the regulation of B, total CD8 T, and δ2⁺γδT cells is maintained, but total NK, CD57⁺/NKG2C⁺ NK, and δ2^-γδT subsets are markedly reduced, while CD57 is overexpressed across T lymphocytes.

Conclusions

CLAD is associated with significant changes in anti-HCMV immune cell responses. Our findings propose that the presence of dysfunctional HCMV-specific HLA-E-restricted CD8 T cells together with post-infection changes in the immune cell distribution affecting NK and γδT cells defines an early immune signature for CLAD in HCMV⁺ LTRs. Such a signature may be of interest for the monitoring of LTRs and may allow an early stratification of LTRs at risk of CLAD.

LFA-1/ ICAM-1 promotes NK cell cytotoxicity associated with the pathogenesis of ocular toxoplasmosis in murine model

Ocular toxoplasmosis (OT) is one of the most common causes of posterior uveitis. However, the pathogenic mechanisms of OT have not been well elucidated. Here, we used C57BL/6 (B6) mice to establish OT by peroral infection with 20 cysts of the TgCtWh6 strain, and severe ocular damage was observed by histopathological analysis in the eyes of infected mice. RNA-sequencing results showed that infection with T. gondii increased the expression of the NK-mediated cytotoxicity gene pathway at Day 30 after ocular T. gondii infection. Both NK-cell and CD49a+ NK-cell subsets are increased in ocular tissues, and the expression levels of LFA-1 in NK cells and ICAM-1 in the OT murine model were upregulated upon infection. Furthermore, inhibition of the interaction between LFA-1 and ICAM-1 with lifitegrast, a novel small molecule integrin antagonist, inhibited the protein expression of LFA-1 and ICAM-1 in murine OT and NK cells, improved the pathology of murine OT and influenced the secretion of cytokines in the OT murine model. In conclusion, the interaction between LFA-1 and ICAM-1 plays a role in the early regulation of the CD49a+ NK-cell proportion in an OT murine model. LFA-1/ ICAM-1 may be a key molecule in the pathogenesis of OT, and may provide new insights for potential immunotherapy.

Natural Killer Cell-Mediated Immunotherapy for Leukemia

Simple Summary

Conventional therapies such as chemotherapy and radiation in leukemia increase infection susceptibility, adverse side effects and immune cell inactivation. Natural killer (NK) cells are the first line of defense against cancer and are critical in the recognition and cytolysis of rapidly dividing and abnormal cell populations. In this review, we describe NK cells and NK cell receptors, functional impairment of NK cells in leukemia, NK cell immunotherapies currently under investigation including monoclonal antibodies (mAbs), adoptive transfer, chimeric antigen receptor-NKs (CAR-NKs), bi-specific/tri-specific killer engagers (BiKEs/TriKEs) and potential targets of NK cell-mediated immunotherapy for leukemia in the future.

Abstract

Leukemia is a malignancy of the bone marrow and blood resulting from the abnormal differentiation of hematopoietic stem cells (HSCs). There are four main types of leukemia including acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CML), and chronic lymphocytic leukemia (CLL). While chemotherapy and radiation have been conventional forms of treatment for leukemia, these therapies increase infection susceptibility, adverse side effects and immune cell inactivation. Immunotherapies are becoming promising treatment options for leukemia, with natural killer (NK) cell-mediated therapy providing a specific direction of interest. The role of NK cells is critical for cancer cell elimination as these immune cells are the first line of defense against cancer proliferation and are involved in both recognition and cytolysis of rapidly dividing and abnormal cell populations. NK cells possess various activating and inhibitory receptors, which regulate NK cell function, signaling either inhibition and continued surveillance, or activation and subsequent cytotoxic activity. In this review, we describe NK cells and NK cell receptors, functional impairment of NK cells in leukemia, NK cell immunotherapies currently under investigation, including monoclonal antibodies (mAbs), adoptive transfer, chimeric antigen receptor-NKs (CAR-NKs), bi-specific/tri-specific killer engagers (BiKEs/TriKEs) and future potential targets of NK cell-based immunotherapy for leukemia.

Lymphocyte subset analysis to evaluate the prognosis of HIV-negative patients with pneumocystis pneumonia

Objectives

We analysed the peripheral blood lymphocyte subsets of human immunodeficiency virus (HIV)-negative patients infected with pneumocystis pneumonia (PCP) to determine the relationships between the levels of different types of lymphocytes and the prognosis of patients.

Methods

We retrospectively reviewed HIV-negative patients with PCP diagnosed in our department. All the eligible patients underwent lymphocyte subset analysis on admission.

Results

A total of 88 HIV-negative PCP patients were enrolled in the study. In univariate analyses, low CD4+ T cell count, low CD8+ T cell count, and low natural killer cell (NK cell) count were associated with higher in-hospital mortality. CD8+ T cell count ≤300/μL was found to be an independent risk factor for poor prognosis in multivariate logistical regression analysis (p = 0.015, OR = 11.526, 95% CI = 1.597–83.158). Although low CD4+ T cell and NK cell counts were not independent risk factors, the mortality rates of PCP patients decreased as the CD4+ T cell and NK cell counts increased.

Conclusion

The immune process of Pneumocystis jirovecii infection is complex but important. We propose that lymphocyte subsets could give clinicians a better understanding of patient immune status, helping with the early identification of potentially lethal infections and treatment decision making, such as adjusting the immunosuppressive regimen and choosing an appropriate patient monitoring level.

Recipient and donor genetic variants associated with mortality after allogeneic hematopoietic cell transplantation

Many studies have suggested that genetic variants in donors and recipients are associated with survival-related outcomes after allogeneic hematopoietic cell transplantation (HCT), but these results have not been confirmed. Therefore, the utility of testing genetic variants in donors and recipients for risk stratification or understanding mechanisms leading to mortality after HCT has not been established. We tested 122 recipient and donor candidate variants for association with nonrelapse mortality (NRM) and relapse mortality (RM) in a cohort of 2560 HCT recipients of European ancestry with related or unrelated donors. Associations discovered in this cohort were tested for replication in a separate cohort of 1710 HCT recipients. We found that the donor rs1051792 A allele in MICA was associated with a lower risk of NRM. Donor and recipient rs1051792 genotypes were highly correlated, making it statistically impossible to determine whether the donor or recipient genotype accounted for the association. Risks of grade 3 to 4 graft-versus-host disease (GVHD) and NRM in patients with grades 3 to 4 GVHD were lower with donor MICA-129Met but not with MICA-129Val, implicating MICA-129Met in the donor as an explanation for the decreased risk of NRM after HCT. Our analysis of candidate variants did not show any other association with NRM or RM. A genome-wide association study did not identify any other variants associated with NRM or RM.

Innate Lymphoid Cells and Adaptive Immune Cells Cross-Talk: A Secret Talk Revealed in Immune Homeostasis and Different Inflammatory Conditions

The inflammatory immune response has evolved to protect the host from different pathogens, allergens, and endogenous death or damage-associated molecular patterns. Both innate and adaptive immune components are crucial in inducing an inflammatory immune response depending on the stimulus type and its duration of exposure or the activation of the primary innate immune response. As the source of inflammation is removed, the aggravated immune response comes to its homeostatic level. However, the failure of the inflammatory immune response to subside to its normal level generates chronic inflammatory conditions, including autoimmune diseases and cancer. Innate lymphoid cells (ILCs) are newly discovered innate immune cells, which are present in abundance at mucosal surfaces, including lungs, gastrointestinal tract, and reproductive tract. Also, they are present in peripheral blood circulation, skin, and lymph nodes. They play a crucial role in generating the pro-inflammatory immune response during diverse conditions. On the other hand, adaptive immune cells, including different types of T and B cells are major players in the pathogenesis of autoimmune diseases (type 1 diabetes mellitus, rheumatoid arthritis, psoriasis, and systemic lupus erythematosus, etc.) and cancers. Thus the article is designed to discuss the immunological role of different ILCs and their interaction with adaptive immune cells in maintaining the immune homeostasis, and during inflammatory autoimmune diseases along with other inflammatory conditions (excluding pathogen-induced inflammation), including cancer, graft-versus-host diseases, and human pregnancy.

Immune reconstitution after T-cell replete HLA haploidentical hematopoietic stem cell transplantation using high-dose post-transplant cyclophosphamide

As HLA haploidentical related donors are quickly available, HLA haploidentical hematopoietic stem cell transplantation (haploHSCT) using high-dose post-transplant cyclophosphamide (PTCy) is now widely used. Recent basic and clinical studies revealed the details of immune reconstitution after T-cell replete haploHSCT using PTCy. T cells and NK cells in the graft proliferate abundantly at day 3 post-haploHSCT, and the PTCy eliminates these proliferating cells. After ablation of proliferating mature cells, donor-derived NK cell reconstitution occurs after the second week; however, recovering NK cells remain functionally impaired for at least several months after haploHSCT. PTCy depletes proliferating cells, resulting in the preferential accumulation of Treg and CD4+ T cells, especially the memory stem T cell (TSCM) phenotype. TSCM capable of both self-renewal and differentiation into effector T cells may play an important role in the first month of immune reconstitution. Subsequently, de novo T cells progressively recover but their levels remain well below those of donor CD4+ T cells at the first year after haploHSCT. The phenotype of recovering T cells after HSCT is predominantly effector memory, whereas B cells are predominantly phenotypically naive throughout the first year after haploHSCT. B cell recovery depends on de novo generation and they are not detected until week 4 after haploHSCT. At week 5, recovering B cells mostly exhibit an unconventional transitional cell phenotype and the cell subset undergoes maturation. Recent advances in immune reconstitution have improved our understanding of the relationship between haploHSCT with PTCy and the clinical outcome.

Osteoclast-expanded super-charged NK-cells preferentially select and expand CD8+ T cells

Osteoclasts (OCs) and much less dendritic cells (DCs) induce significant expansion and functional activation of NK cells, and furthermore, the OC-expanded NK cells preferentially increase the expansion and activation of CD8+ T cells by targeting CD4+ T cells. When autologous OCs were used to expand patient NK cells much lower percentages of expanded CD8+ T cells, decreased numbers of expanded NK cells and decreased functions of NK cells could be observed, and the addition of allogeneic healthy OCs increased the patients' NK function. Mechanistically, OC-expanded NK cells were found to lyse CD4+ T cells but not CD8+ T cells suggesting potential selection of CD8+ T cells before their expansion by OC activated NK cells. In agreement, Increased IFN-γ secretion, and NK cell-mediated cytotoxicity and higher percentages of CD8+ T cells, in various tissue compartments of oral tumor-bearing hu-BLT mice in response to immunotherapy by OC-expanded NK cells were observed. Thus, our results indicate an important relationship between NK and CD8+ T cells.

Killers at the crossroads: The use of innate immune cells in adoptive cellular therapy of cancer

Adoptive cell therapy (ACT) is an approach to cancer treatment that involves the use of antitumor immune cells to target residual disease in patients after completion of chemo/radiotherapy. ACT has several advantages compared with other approaches in cancer immunotherapy, including the ability to specifically expand effector cells in vitro before selection for adoptive transfer, as well as the opportunity for host manipulation in order to enhance the ability of transferred cells to recognize and kill established tumors. One of the main challenges to the success of ACT in cancer clinical trials is the identification and generation of antitumor effector cells with high avidity for tumor recognition. Natural killer (NK) cells, cytokine‐induced killers and natural killer T cells are key innate or innate‐like effector cells in cancer immunosurveillance that act at the interface between innate and adaptive immunity, to have a greater influence over immune responses to cancer. In this review, we discuss recent studies that highlight their potential in cancer therapy and summarize clinical trials using these effector immune cells in adoptive cellular therapy for the treatment of cancer.

S1PR5 regulates NK cell responses in preventing graft-versus-host disease while preserving graft-versus-tumour activity in a murine allogeneic haematopoietic stem cell transplantation model

Graft-versus-host disease (GVHD) remains a major complication following allogeneic haematopoietic stem cell transplantation (allo-HSCT) leading to high transplant-related mortality. Natural killer (NK) cells have been found to mitigate GVHD without attenuating the graft-versus-tumour (GVT) activity in the murine model of haematopoietic stem cell transplantation. Sphingosine-1-phosphate receptor 5 (S1PR5) is a very important chemokine receptor on NK cells that governs NK cell distribution in vivo and trafficking at lesion sites. Our preliminary studies showed that the incidence of GVHD was negatively correlated with S1PR5 expression in the NK cells of patients after allo-HSCT. In the present study, we found that S1PR5 deficiency in murine NK cells blocked the migration of NK cells from the bone marrow to the GVHD target organs and attenuated the inhibitory effects on the alloreactive T cells, especially CD3⁺ CD8⁺ T cells, which may be the reason why the loss of S1PR5 in NK cells could aggravate GVHD in recipient mice. Furthermore, we also demonstrated that the absence of S1PR5 expression in NK cells did not interfere with the antitumour effects of NK cells and T cells in vivo. Taken together, our data indicate that S1PR5 plays an essential role in balancing GVHD and GVT activity.

An Essential Role of Innate Lymphoid Cells in the Pathophysiology of Graft-vs.-Host Disease

Allogeneic hematopoietic stem cell transplantation (Allo-HSCT) is the only curative treatment for multiple hematologic malignancies and non-malignant hematological diseases. However, graft-vs.-host disease (GVHD), one of the main complications after allo-HSCT, remains the major reason for morbidity and non-relapse mortality. Emerging evidence has demonstrated that innate lymphoid cells (ILCs) play a non-redundant role in the pathophysiology of GVHD. In this review, we will summarize previously published data regarding the role of ILCs in the pathogenesis of GVHD.

Natural Killer Cells as Allogeneic Effectors in Adoptive Cancer Immunotherapy

Natural killer (NK) cells are attractive within adoptive transfer settings in cancer immunotherapy due to their potential for allogeneic use; their alloreactivity is enhanced under conditions of killer immunoglobulin-like receptor (KIR) mismatch with human leukocyte antigen (HLA) ligands on cancer cells. In addition to this, NK cells are platforms for genetic modification, and proliferate in vivo for a shorter time relative to T cells, limiting off-target activation. Current clinical studies have demonstrated the safety and efficacy of allogeneic NK cell adoptive transfer therapies as a means for treatment of hematologic malignancies and, to a lesser extent, solid tumors. However, challenges associated with sourcing allogeneic NK cells have given rise to controversy over the contribution of NK cells to graft-versus-host disease (GvHD). Specifically, blood-derived NK cell infusions contain contaminating T cells, whose activation with NK-stimulating cytokines has been known to lead to heightened release of proinflammatory cytokines and trigger the onset of GvHD in vivo. NK cells sourced from cell lines and stem cells lack contaminating T cells, but can also lack many phenotypic characteristics of mature NK cells. Here, we discuss the available published evidence for the varying roles of NK cells in GvHD and, more broadly, their use in allogeneic adoptive transfer settings to treat various cancers.

iNKT cells and hematopoietic stem cell transplantation: Two-phase activation of iNKT cells may improve outcome

Invariant natural killer T cells (iNKT) produce large amounts of different cytokines which can influence differentiation, polarization and activation of immune cells, particularly NK and T cells. iNKT have been shown to suppress GvHD and promote anti-tumor and anti-pathogen immunity. There are highly specific and safe synthetic ligands such as alpha-galactosylceramide (α-GalCer) and C20:2 which activate iNKT cells toward relatively Th1 and Th2 pathways, respectively. Bone marrow transplantation (BMT) or 'hematopoietic stem cell transplantation' (HSCT) is effective for leukemia and lymphoma through 'graft-versus-leukemia' (GVL) immunity. However, frequent serious complications include graft-versus-host-disease (GVHD), opportunistic infections and relapse. Both GVHD and GVL are mediated by T cells. Manipulating iNKT by different lipid analogues in early and late phases after transplantation may suppress GVHD and graft rejection and enhance GVL effect, as well as resistance to opportunistic infections and so, could be a novel and effective strategy for improving HSCT outcome.

CD83+ CCR7+ NK cells induced by interleukin 18 by dendritic cells promote experimental autoimmune uveitis

Natural killer (NK) cells have been reported to play a pathological role in autoimmune uveitis. However, the mechanisms regarding NK cells in uveitis and factors that affect NK-cell activation in this condition remain unclear. Here, we report that the number of CD3- NK1.1+ CD83+ CCR7+ cells is increased in the inflamed eyes within a mouse model of experimental autoimmune uveitis (EAU), and these cells express elevated levels of NKG2D, CD69 and IFN-γ. Adoptively transferring CD83+ CCR7+ NK cells aggravates EAU symptoms and increases the number of CD4+ IFN-γ+ T cells and dendritic cells (DCs) within the eye. These CD83+ CCR7+ NK cells then promote the maturation of DCs and IFN-γ expression within T cells as demonstrated in vitro. Furthermore, IL-18, as primarily secreted by DCs in the eyes, is detected to induce CD83+ CCR7+ NK cells. In EAU mice, anti-IL-18R antibody treatment also decreases retinal tissue damage, as well as the number of infiltrating CD83+ CCR7+ NK cells, T cells and DCs in the inflamed eyes and spleens of EAU mice. These results suggest that CD83+ CCR7+ NK cells, as induced by IL-18 that primarily secreted by DCs, play a critical pathological role in EAU. Anti-IL-18R antibody might serve as a potential therapeutic agent for uveitis through its capacity to inhibit CD83+ CCR7+ NK cells infiltration.

Impact of conditioning regimen on peripheral blood hematopoietic cell transplant

AIM

To investigate infused hematopoietic cell doses and their interaction with conditioning regimen intensity +/- total body irradiation (TBI) on outcomes after peripheral blood hematopoietic cell transplant (PBHCT).

METHODS

Our retrospective cohort included 247 patients receiving a first, T-replete, human leukocyte antigen-matched allogeneic PBHCT and treated between 2001 and 2012. Correlations were calculated using the Pearson product-moment correlation coefficient. Overall survival and progression free survival curves were generated using the Kaplan-Meier method and compared using the log-rank test.

RESULTS

Neutrophil engraftment was significantly faster after reduced intensity TBI based conditioning [reduced intensity conditioning (RIC) + TBI] and > 4 × 10⁶ CD34+ cells/kg infused. A higher total nucleated cell dose led to a higher incidence of grade II-IV acute graft-versus-host disease in the myeloablative + TBI regimen group (P = 0.03), but no significant difference in grade III-IV graft-versus-host disease. A higher total nucleated cell dose was also associated with increased incidence of moderate/severe chronic graft-versus-host disease, regardless of conditioning regimen. Overall and progression-free survival were significantly better in patients with a RIC + TBI regimen and total nucleated cell dose > 8 × 10⁸/kg (3 years, overall survival: 70% vs 38%, P = 0.02, 3 years, progression free survival: 64% vs 38%, P = 0.02).

CONCLUSION

TBI and conditioning intensity may alter the relationship between infused cell doses and outcomes after PBHCT. Immune cell subsets may predict improved survival after unmanipulated PBHCT.

NKG2D signaling certifies effector CD8 T cells for memory formation

BACKGROUND

The development of memory responses is an evolutionary function of the adaptive immune system. We propose that for the immune system to populate the memory compartment with the best-suited CD8 T cells it utilizes a process of certification or molecular accreditation mediated through Natural Killer Group 2D (NKG2D). This process of certification assures that the memory compartment is filled with CD8 T cells that have demonstrated their ability to kill their cognate targets through a two-step process that utilizes T cell receptor (TCR) and NKG2D signaling.

METHODS

One week after immunization with peptide-pulsed dendritic cells, NKG2D signaling was transiently blocked in vivo with a single injection of neutralizing antibodies. Under such conditions, we determined the importance of NKG2D signaling during the effector phase for memory formation without compromising NKG2D signaling at the memory phase. Both open (polyclonal) and closed (monoclonal) CD8 T cell repertoires were studied.

RESULTS

We show that signaling through NKG2D mediated this certification. Temporary blockade of NKG2D signaling during the effector phase resulted in the formation of highly defective memory CD8 T cells characterized by altered expression of the ribosomal protein S6 and epigenetic modifiers, suggesting modifications in the T cell translational machinery and epigenetic programming. Finally, these uncertified memory cells were not protective against a B16 tumor challenge.

CONCLUSION

Signaling through NKG2D during the effector phase (certification) favors the development of functional memory CD8 T cells, a previously undescribed role for NKG2D. Temporary blockade of NKG2D signaling during the effector phase results in the formation of highly defective memory CD8 T cells potentially by affecting the expression of the ribosomal protein S6 and epigenetic modifiers, suggesting alterations in T cell translational machinery and epigenetic programming.

Natural killer cells in lung transplantation

Natural killer (NK) cells are innate lymphoid cells that have been increasingly recognised as important in lung allograft tolerance and immune defence. These cells evolved to recognise alterations in self through a diverse set of germline-encoded activating and inhibitory receptors and display a broad range of effector functions that play important roles in responding to infections, malignancies and allogeneic tissue. Here, we review NK cells, their diverse receptors and the mechanisms through which NK cells are postulated to mediate important lung transplant clinical outcomes. NK cells can promote tolerance, such as through the depletion of donor antigen-presenting cells. Alternatively, these cells can drive rejection through cytotoxic effects on allograft tissue recognised as 'non-self' or 'stressed', via killer cell immunoglobulin-like receptor (KIR) or NKG2D receptor ligation, respectively. NK cells likely mediate complement-independent antibody-mediated rejection of allografts though CD16A Fc receptor-dependent activation induced by graft-specific antibodies. Finally, NK cells play an important role in response to infections, particularly by mediating cytomegalovirus infection through the CD94/NKG2C receptor. Despite these sometimes-conflicting effects on allograft function, enumeration of NK cells may have an important role in diagnosing allograft dysfunction. While the effects of immunosuppression agents on NK cells may currently be largely unintentional, further understanding of NK cell biology in lung allograft recipients may allow these cells to serve as biomarkers of graft injury and as therapeutic targets.

NK cells suppress CD8+ T cell immunity via NKG2D in severe aplastic anemia

The roles of natural killer (NK) cells in shaping the immune system had raised wide interests. Here we intended to explore the regulatory functions of NK cells on CD8⁺ T cells in severe aplastic anemia (SAA) using human participants and lymphocyte infusion-induced bone marrow failure (BMF) mouse model. In SAA patients, NK cells had over-expressions of NKG2D and NKp46, under-expression of NKG2A and enhanced cytotoxicity. NK cells limited autologous CD8⁺ T cell immunity in an effector/target ratio manner. The suppression was dependent on the existence of NKG2D. We also observed upregulated MICA expression on activated CD8⁺ T cells, which were susceptible to NK cell mediated lysis in SAA. Animal model concurred with the data from patients. Infusion of NK cells suppressed the proliferation of CD8⁺ T cells and decreased IFN-γ production. In conclusion, NK cells served NKG2D-dependent immunoregulatory roles by attenuating autologous CD8⁺ T cell response in SAA.

Effect of the in vivo application of granulocyte colony-stimulating factor on NK cells in bone marrow and peripheral blood

Granulocyte colony‐stimulating factor (G‐CSF) has been widely used in the field of allogeneic haematopoietic stem cell transplantation (allo‐HSCT) for priming donor stem cells from the bone marrow (BM) to peripheral blood (PB) to collect stem cells more conveniently. Donor‐derived natural killer (NK) cells have important antitumour functions and immune regulatory roles post‐allo‐HSCT. The aim of this study was to evaluate the effect of G‐CSF on donors' NK cells in BM and PB. The percentage of NK cells among nuclear cells and lymphocyte was significantly decreased and led to increased ratio of T and NK cells in BM and PB post‐G‐CSF in vivo application. Relative expansion of CD56^briNK cells led to a decreased ratio of CD56^dim and CD56^briNK subsets in BM and PB post‐G‐CSF in vivo application. The expression of CD62L, CD54, CD94, NKP30 and CXCR4 on NK cells was significantly increased in PB after G‐CSF treatment. G‐CSF treatment decreased the IFN‐γ‐secreting NK population (NK1) dramatically in BM and PB, but increased the IL‐13‐secreting NK (NK2), TGF‐β‐secreting NK (NK3) and IL‐10‐secreting NK (NKr) populations significantly in BM. Clinical data demonstrated that higher doses of NK1 infused into the allograft correlated with an increased incidence of chronic graft‐vs‐host disease post‐transplantation. Taken together, our results show that the in vivo application of G‐CSF can modulate NK subpopulations, leading to an increased ratio of T and NK cells and decreased ratio of CD56^dim and CD56^briNK cells as well as decreased NK1 populations in both PB and BM.

Rapid reconstitution of NK1 cells after allogeneic transplantation is associated with a reduced incidence of graft-versus-host disease

The balance between immunostimulation and immunoregulation in T cell immunity is achieved by maintaining specific ratios of Th1, Th2, Th3 and Tr1 cells. Here, we investigate levels of type 1 (IFN-gamma; NK1), type 2 (IL-13; NK2), type 3 (TGF-beta; NK3) and regulatory (IL-10; NKr) cytokines in peripheral blood to assess the cytokine profiles of natural killer (NK) cells following human allogeneic hematopoietic stem cell transplantation (allo-HSCT). NK2 and NK3 cell expansion was observed after allo-HSCT; levels of NKr cells reached donor levels at day 15, though levels of NK1 cells were consistently lower than donor levels until day 60 after allo-HSCT. Multivariate analysis showed that a higher level of NK1 cells by day 15 was associated with a lower overall risk of acute graft-versus-host disease (GVHD) (HR 0.157, P=0.010) as well as II-IV acute GVHD (HR 0.260, P=0.059). Furthermore, higher levels of NK1 cells by day 15 were correlated with lower rates of cytomegalovirus (CMV) reactivation (HR 0.040, 0.005-0.348, P=0.003). These results indicate that rapid reconstitution of NK cells, especially NK1 cells, can help prevent the development of GVHD as well as CMV reactivation after allogeneic transplantation.

More than Decoration: Roles for Natural Killer Group 2 Member D Ligand Expression by Immune Cells

The activating immune receptor natural killer group 2 member D (NKG2D), which is expressed by natural killer cells and T cell subsets, recognizes a number of ligands expressed by "stressed" or damaged cells. NKG2D has been extensively studied for its role in tumor immunosurveillance and antiviral immunity. To date, the majority of studies have focused on NKG2D-mediated killing of target cells expressing NKG2D ligands. However, with a number of reports describing expression of NKG2D ligands by cells that are not generally considered stressed, it is becoming clear that some healthy cells also express NKG2D ligands. Expression of these ligands by cells within the skin, intestinal epithelium, and the immune system suggests other immune functions for NKG2D ligand expression in addition to its canonical role as a "kill me" signal. How NKG2D ligands function in this capacity is just now starting to be unraveled. In this review, we examine the expression of NKG2D ligands by immune cells and discuss current literature describing the effects of this expression on immunity and immune regulation.

IL-12/IL-18-preactivated donor NK cells enhance GVL effects and mitigate GvHD after allogeneic hematopoietic stem cell transplantation

Adoptive transfer of donor NK cells has the potential of mediating graft-versus-leukemia (GVL) effect while suppressing acute graft-versus-host-disease (aGVHD) during allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, these beneficial effects are limited by the transient function of adoptively transferred NK cells. Previous studies demonstrate that cytokine-induced memory-like NK cells that are preactivated by IL-12, IL-15, and IL-18 have enhanced effector functions and long life span in vivo. Here, we investigated the effects of IL-12/18-preactivated and IL-12/15/18-preactivated donor NK cells on GVL and aGVHD in a murine model of allo-HSCT. We found that both IL-12/18- and IL-12/15/18-preactivated NK cells mediated stronger GVL effect than control NK cells mainly due to their elevated activation/cytotoxicity and sustained proliferative potential. Interestingly, we observed that although both IL-12/18- and IL-12/15/18-preactivated NK cells significantly inhibited severe aGVHD, only the IL-12/18-preactivated NK cells maintained the beneficial effect of donor NK cells on mild aGVHD. The IL-12/15/18-preactivated NK cell infusion accelerated aGVHD in the fully-mismatched mild aGVHD model. Our results demonstrated that IL-12/18-preactivated NK cells displayed sustained and enhanced GVL functions, and could mitigate aGVHD despite the severity of the disease. IL-12/18-preactivated donor NK cell infusion may be an effective and safe adoptive therapy after allo-HSCT.

Prior to Peripheral Tolerance, Newly Generated CD4 T Cells Maintain Dangerous Autoimmune Potential: Fas- and Perforin-Independent Autoimmunity Controlled by Programmed Death-1

Lymphopenia can result from various factors, including viral infections, clinical interventions, or as a normal property of the fetal/neonatal period. T cells in a lymphopenic environment undergo lymphopenia-induced proliferation (LIP) to fill the available “niche” as defined by peptide–MHC and homeostatic cytokine resources. We recently reported systemic autoimmunity following reconstitution of the lymphoid compartment of Rag1^−/− mice with PD-1^−/− hematopoietic stem cells or by transfer of thymocytes, but not splenocytes, suggesting that programmed death-1 (PD-1) plays a crucial role in controlling recent thymic emigrants (RTE) and preventing autoimmunity upon their LIP. However, it is unclear whether RTE residing within the periphery of a lymphoreplete host maintain enhanced autoimmune generating potential or if this property only manifests if RTE experience a lymphopenic periphery immediately after export from the thymus. Furthermore, it is unclear which of a variety of T cell effector mechanisms generate pathology when control of RTE by PD-1 is lacking. Herein, we determined that PD-1 is upregulated on CD4 T cells undergoing the natural LIP characteristic of the neonatal period. Newly generated T cells lacking PD-1 maintained an enhanced autoimmune potential even after residence in a lymphoreplete periphery, emphasizing the importance of PD-1 in the establishment of peripheral tolerance. Neither Fas nor perforin-dependent killing mechanisms were required for autoimmunity, while host MHC-II expression was critical, suggesting that LIP-driven autoimmunity in the absence of PD-1 may primarily result from a CD4 T cell-mediated systemic cytokinemia, a feature potentially shared by other autoimmune or inflammatory syndromes associated with immune reconstitution and LIP.

NK cells are negatively regulated by sCD83 in experimental autoimmune uveitis

Natural killer (NK) cells represent a subset of lymphocytes that contribute to innate immunity and have been reported to play a role in autoimmune uveitis. However, the mechanisms regulating NK cellular function in this condition remain unclear. Herein, we investigated the status of NK cells in experimental autoimmune uveitis (EAU). We found that the number of CD83+CD3-NK1.1+ cells was increased in the inflamed eyes and spleens of the EAU mouse model. At the recovery stage of EAU, serum concentrations of soluble CD83 (sCD83) were increased. sCD83 treatment relieved retinal tissue damage and decreased the number of infiltrating NK cells in inflamed eyes. Further analysis of the effects of sCD83 treatment in EAU revealed that it reduced: 1) the expressions of CD11b and CD83 in NK cells, 2) the percent of CD11bhighCD27lowCD3-NK1.1+ cells and 3) the secretion of granzyme B, perforin and IFN-γ in NK cells as demonstrated both in vivo and in vitro. When sCD83 treated-NK cells were transferred into EAU mice, retinal tissue damage was relieved. These results demonstrate sCD83 down-regulate NK cellular function and thus provide important, new information regarding the means for the beneficial effects of this agent in the treatment of autoimmune uveitis.

PD-1 Controls Tonic Signaling and Lymphopenia-Induced Proliferation of T Lymphocytes

Recovery of the T lymphocyte compartment within a lymphopenic host by lymphopenia-induced proliferation (LIP) is regulated by inter- and intraclonal competition for limited resources, including homeostatic cytokines and peptide:MHC (pMHC) complexes with which the TCR can interact at least weakly to yield a tonic signal. Importantly, the process of LIP can synergize with other factors that promote T cell activation to drive inflammatory disease. While reconstitution of the lymphoid compartment of immune deficient Rag^-/- mice by transfer of wild-type hematopoietic stem cells (HSC) does not generally result in an overt disease phenotype, transfer of HSC deficient in expression of the co-inhibitory molecule PD-1 results in severe systemic autoimmunity driven by newly generated T cells that emerge from the thymus into the periphery and undergo LIP. Importantly, autoimmunity does not appear to depend on a response to exogenous (i.e., gut flora-derived) antigens. PD-1 is well known to be upregulated during T cell activation in response to cognate antigens, but it is unclear whether PD-1 has a role in controlling LIP of T cells in the absence of cognate antigen, i.e., in response to tonic pMHC. We examined whether PD-1 controls LIP of newly generated T cells by controlling the response to tonic pMHC or the homeostatic cytokine IL-7. We found that PD-1-deficient T cells have a proliferative advantage over WT T cells during LIP and this effect is MHC-II dependent and independent of IL-7Rα signaling. Furthermore, our data suggest that signals through IL-7Rα can be dispensable for LIP and may instead be of increased importance for T cell survival in conditions of high competition for limited pMHC (e.g., post-LIP, in a lymphoreplete host). We hypothesize that autoimmunity post-PD-1^-/- HSC transplant is the result of an overzealous T cell response to normally tonic self-pMHC precipitated by the synergy of LIP and PD-1 deficiency. Furthermore, potentiation of TCR signals in response to normally tonic self-pMHC may contribute to the success of PD-1 blockade in cancer immunotherapy.

Allogeneic Reduced-Intensity Hematopoietic Stem Cell Transplantation for Chronic Granulomatous Disease: a Single-Center Prospective Trial

PURPOSE

The purpose of this study was to evaluate engraftment and adverse events with a conditioning and prophylactic regimen intended to achieve high rates of engraftment with minimal graft-versus-host disease (GVHD) in allogeneic transplantation for chronic granulomatous disease in a single center.

METHODS

Forty patients, 37 male, with chronic granulomatous disease were transplanted. Transplant products were matched sibling peripheral blood stem cells (PBSCs) in four and matched unrelated donor (MUD) bone marrow in three, and one patient received mismatched unrelated PBSCs. Thirty-two patients received MUD PBSCs. All patients received a conditioning regimen of busulfan/alemtuzumab (with low-dose total body irradiation for MUD recipients) with sirolimus graft-versus-host disease prophylaxis.

RESULTS

Engraftment occured in 38/40 recipients (95%). Acute or chronic GVHD occurred in 18 (45%) and 5 (12.5%), respectively, with 6 episodes of grades III-IV and/or steroid refractory GVHD. Overall survival was 33/40 (82.5%) and event-free survival was 30/40 (80%). Successful engraftment was associated with myeloid and NK cell, but not CD3+ chimerism. Myeloid engraftment was greater than 70% in 30/32 recipients at mean follow-up of 3.4 years. Evidence of persistent immunodeficiency was not seen in successful transplants. Attempts to rescue failed or poorly functioning grafts were associated with unacceptable morbidity and mortality.

CONCLUSIONS

A reduced-intensity allogeneic transplant protocol based on alemtuzumab and busulfan with sirolimus GVHD prophylaxis produced high rates of successful engraftment and minimal regimen-related toxicity. Prolonged clinical follow-up has confirmed its efficacy in ameliorating CGD-related disease. Outcomes were not acceptable with donor cell infusion rescue of cause with poor graft function.

Host-Derived CD70 Suppresses Murine Graft-versus-Host Disease by Limiting Donor T Cell Expansion and Effector Function

Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative treatment for hematologic and immunologic diseases. However, graft-versus-host disease (GVHD) may develop when donor-derived T cells recognize and damage genetically distinct normal host tissues. In addition to TCR signaling, costimulatory pathways are involved in T cell activation. CD27 is a TNFR family member expressed on T cells, and its ligand, CD70, is expressed on APCs. The CD27/CD70 costimulatory pathway was shown to be critical for T cell function and survival in viral infection models. However, the role of this pathway in allo-HCT is previously unknown. In this study, we have examined its contribution in GVHD pathogenesis. Surprisingly, Ab blockade of CD70 after allo-HCT significantly increases GVHD. Interestingly, whereas donor T cell- or bone marrow-derived CD70 plays no role in GVHD, host-derived CD70 inhibits GVHD as CD70^-/- hosts show significantly increased GVHD. This is evidenced by reduced survival, more severe weight loss, and increased histopathologic damage compared with wild-type hosts. In addition, CD70^-/- hosts have higher levels of proinflammatory cytokines TNF-α, IFN-γ, IL-2, and IL-17. Moreover, accumulation of donor CD4⁺ and CD8⁺ effector T cells is increased in CD70^-/- versus wild-type hosts. Mechanistic analyses suggest that CD70 expressed by host hematopoietic cells is involved in the control of alloreactive T cell apoptosis and expansion. Together, our findings demonstrate that host CD70 serves as a unique negative regulator of allogeneic T cell response by contributing to donor T cell apoptosis and inhibiting expansion of donor effector T cells.

Natural Killer Cells in Graft-versus-Host-Disease after Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (HCT) is a well-established therapeutic modality effective for a variety of hematological malignancies but, unfortunately, is associated with significant morbidity and mortality related to cancer relapse as well as to transplant-related complications including graft-versus-host-disease (GvHD). Natural killer (NK) cells are the first donor-derived lymphocyte subset to recover after HCT, and their crucial role in protection against cancer relapse and infections is well established. Conversely, the role played by NK cells in GvHD is still controversial. Early studies suggested a participation of NK cells in GvHD induction or exacerbation. Subsequently, experimental evidence obtained in mice as well observational studies performed in humans led to a model in which NK cells play a regulatory role in GvHD by repressing alloreactive T cell responses. This widely accepted model has been recently challenged by clinical evidence indicating that NK cells can in some cases promote GvHD. In this review, we summarize available knowledge about the role of NK cells in GVHD pathogenesis. We review studies uncovering cellular mechanisms through which NK cells interact with other immune cell subsets during GvHD leading to a model in which NK cells naturally suppress GvHD through their cytotoxic ability to inhibit T cell activation unless exogenous hyperactivation lead them to produce proinflammatory cytokines that can conversely sustain T cell-mediated GvHD induction.

Thymus-Derived Regulatory T Cell Development Is Regulated by C-Type Lectin-Mediated BIC/MicroRNA 155 Expression

Thymus-derived regulatory T (tTreg) cells are key to preventing autoimmune diseases, but the mechanisms involved in their development remain unsolved. Here, we show that the C-type lectin receptor CD69 controls tTreg cell development and peripheral Treg cell homeostasis through the regulation of BIC/microRNA 155 (miR-155) and its target, suppressor of cytokine signaling 1 (SOCS-1). Using Foxp3-mRFP/cd69^+/- or Foxp3-mRFP/cd69^-/- reporter mice and short hairpin RNA (shRNA)-mediated silencing and miR-155 transfection approaches, we found that CD69 deficiency impaired the signal transducer and activator of transcription 5 (STAT5) pathway in Foxp3⁺ cells. This results in BIC/miR-155 inhibition, increased SOCS-1 expression, and severely impaired tTreg cell development in embryos, adults, and Rag2^-/- γc^-/- hematopoietic chimeras reconstituted with cd69^-/- stem cells. Accordingly, mirn155^-/- mice have an impaired development of CD69⁺ tTreg cells and overexpression of the miR-155-induced CD69 pathway, suggesting that both molecules might be concomitantly activated in a positive-feedback loop. Moreover, in vitro-inducible CD25⁺ Treg (iTreg) cell development is inhibited in Il2rγ^-/-/cd69^-/- mice. Our data highlight the contribution of CD69 as a nonredundant key regulator of BIC/miR-155-dependent Treg cell development and homeostasis.

A distinct innate lymphoid cell population regulates tumor-associated T cells

Antitumor T cells are subject to multiple mechanisms of negative regulation. Recent findings that innate lymphoid cells (ILCs) regulate adaptive T cell responses led us to examine the regulatory potential of ILCs in the context of cancer. We identified a unique ILC population that inhibits tumor-infiltrating lymphocytes (TILs) from high-grade serous tumors, defined their suppressive capacity in vitro, and performed a comprehensive analysis of their phenotype. Notably, the presence of this CD56+CD3- population in TIL cultures was associated with reduced T cell numbers, and further functional studies demonstrated that this population suppressed TIL expansion and altered TIL cytokine production. Transcriptome analysis and phenotypic characterization determined that regulatory CD56+CD3- cells exhibit low cytotoxic activity, produce IL-22, and have an expression profile that overlaps with those of natural killer (NK) cells and other ILCs. NKp46 was highly expressed by these cells, and addition of anti-NKp46 antibodies to TIL cultures abrogated the ability of these regulatory ILCs to suppress T cell expansion. Notably, the presence of these regulatory ILCs in TIL cultures corresponded with a striking reduction in the time to disease recurrence. These studies demonstrate that a previously uncharacterized ILC population regulates the activity and expansion of tumor-associated T cells.

Old game, new players: Linking classical theories to new trends in transplant immunology

The evolutionary emergence of an efficient immune system has a fundamental role in our survival against pathogenic attacks. Nevertheless, this same protective mechanism may also establish a negative consequence in the setting of disorders such as autoimmunity and transplant rejection. In light of the latter, although research has long uncovered main concepts of allogeneic recognition, immune rejection is still the main obstacle to long-term graft survival. Therefore, in order to define effective therapies that prolong graft viability, it is essential that we understand the underlying mediators and mechanisms that participate in transplant rejection. This multifaceted process is characterized by diverse cellular and humoral participants with innate and adaptive functions that can determine the type of rejection or promote graft acceptance. Although a number of mediators of graft recognition have been described in traditional immunology, recent studies indicate that defining rigid roles for certain immune cells and factors may be more complicated than originally conceived. Current research has also targeted specific cells and drugs that regulate immune activation and induce tolerance. This review will give a broad view of the most recent understanding of the allogeneic inflammatory/tolerogenic response and current insights into cellular and drug therapies that modulate immune activation that may prove to be useful in the induction of tolerance in the clinical setting.

Chronic graft-versus-host disease: biological insights from preclinical and clinical studies

With the increasing use of mismatched, unrelated, and granulocyte colony-stimulating factor-mobilized peripheral blood stem cell donor grafts and successful treatment of older recipients, chronic graft-versus-host disease (cGVHD) has emerged as the major cause of nonrelapse mortality and morbidity. cGVHD is characterized by lichenoid changes and fibrosis that affects a multitude of tissues, compromising organ function. Beyond steroids, effective treatment options are limited. Thus, new strategies to both prevent and treat disease are urgently required. Over the last 5 years, our understanding of cGVHD pathogenesis and basic biology, born out of a combination of mouse models and correlative clinical studies, has radically improved. We now understand that cGVHD is initiated by naive T cells, differentiating predominantly within highly inflammatory T-helper 17/T-cytotoxic 17 and T-follicular helper paradigms with consequent thymic damage and impaired donor antigen presentation in the periphery. This leads to aberrant T- and B-cell activation and differentiation, which cooperate to generate antibody-secreting cells that cause the deposition of antibodies to polymorphic recipient antigens (ie, alloantibody) or nonpolymorphic antigens common to both recipient and donor (ie, autoantibody). It is now clear that alloantibody can, in concert with colony-stimulating factor 1 (CSF-1)-dependent donor macrophages, induce a transforming growth factor β-high environment locally within target tissue that results in scleroderma and bronchiolitis obliterans, diagnostic features of cGVHD. These findings have yielded a raft of potential new therapeutics, centered on naive T-cell depletion, interleukin-17/21 inhibition, kinase inhibition, regulatory T-cell restoration, and CSF-1 inhibition. This new understanding of cGVHD finally gives hope that effective therapies are imminent for this devastating transplant complication.

Granulysin expressed in a humanized mouse model induces apoptotic cell death and suppresses tumorigenicity

Granulysin (GNLY) is a cytolytic and proinflammatory protein expressed in activated human cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. Conventional mouse models cannot adequately address the triggering mechanism and immunopathological pathways in GNLY-associated diseases due to lack of the GNLY gene in the mouse genome. Therefore, we generated a humanized immune system (HIS) mouse model by transplanting human umbilical cord blood mononuclear cells into NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ (NSG) mice after sublethally irradiation. We examined the GNLY expression and its effects on tumor growth using this system. Our HIS mice expressed human CD45⁺, CD4⁺, CD8⁺ and CD56⁺ cells in the peripheral blood and spleen. A high expression level of human Th1/Th2 and NK cytokines was detected, indicating the activation of both T and NK cells. Importantly, we found an elevated level of GNLY in the serum and it was produced by human CTLs and NK cells obtained from the peripheral blood mononuclear cells and spleen cells in the HIS mice. The serum level of GNLY was negatively correlated with the proliferation of transplanted tumor cells in HIS mice. Collectively, our findings strongly supported that HIS mouse as a valuable model for studying human cancer under an intact immune system and the role of GNLY in tumorigenesis.

Extracorporeal photopheresis as an immunomodulatory agent: Haematocrit-dependent effects on natural killer cells

The GvHD is a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). Extracorporeal photopheresis (ECP) represents an alternative therapeutic strategy to immunosuppressive therapy. Although ECP is used since 1990s, the mechanism of action has not yet been completely clarified. We analyzed cells collected from 20 ECP procedures of 4 patients affected by chronic GvHD and, for comparison, Peripheral Blood Mononuclear Cells (PBMCs) of 10 healthy donors undergoing from same type of photochemiotherapy, evaluating by flow cytometry, the effects before and after photoactivation with 8-MOP. The analysis showed a significant increase in cell death after ECP in particular in CD4 T lymphocytes as described in literature correlated with haematocrit value. Most interesting data emerge from the analysis of cytotoxic activity of NK cells, using flow cytometry analysis of surface expression of CD107a in the presence of target cells (K562). In all analyzed samples it was possible to document a statistically significant reduction of the cytotoxic activity of NK cells after photoactivation. The decrease of the cytotoxic activity was related to hematocrit value of leukoapheresis: in fact, lower HCT values were associated with a more marked reduction of cytotoxic activity. The study confirms literature data about the increase of cellular mortality induce by ECP. Furthermore, for the first time it is demonstrated that the ECP exerts a marked and significant inhibitory effect on the cytotoxic activity of NK cells. Our study suggests that lower values of hematocrit are associated with better treatment outcome.

"Natural Regulators": NK Cells as Modulators of T Cell Immunity

Natural killer (NK) cells are known as frontline responders capable of rapidly mediating a response upon encountering transformed or infected cells. Recent findings indicate that NK cells, in addition to acting as innate effectors, can also regulate adaptive immune responses. Here, we review recent studies on the immunoregulatory function of NK cells with a specific focus on their ability to affect the generation of early, as well as long-term antiviral T cell responses, and their role in modulating immune pathology and disease. In addition, we summarize the current knowledge of the factors governing regulatory NK cell responses and discuss origin, tissue specificity, and open questions about the classification of regulatory NK cells as classical NK cells versus group 1 innate lymphoid cells.

Resistance of novel mouse strains different in MHC class I and the NKC domain to the development of experimental tumors

To elucidate the immunological mechanisms critical for tumor progression, we bred novel mouse strains, different in the NKC and H-2D domains. We used inbreeding to generate hybrids of Balb/c and C57BL/6 of stable H-2Db+d-NK1.1neg and H-2Db-d+NK1.1high phenotypes. We analyzed the growth of three established MHC class I-deficient tumor cell lines: TC-1/A9 tumor (HPV-associated) and B16F10 melanoma, both syngeneic to C57BL/6, and the MCB8 (3-methycholanthrene-induced tumor) syngeneic to Balb/c. Furthermore, we induced colorectal carcinoma by azoxymethane-DSS treatment to test the susceptibility to chemically-induced primary cancer. We found that the novel strains spontaneously regressed the tumor transplants syngeneic to both Balb/c (MCB8) and C57BL/6 (B16F10 and TC-1/A9) mice. The H2-Db+d-NK1.1neg, but not the H2-Db-d+NK1.1high strain was also highly resistant to chemically-induced colorectal cancer in comparison to the parental mice. The immune changes during TC-1/A9 cancer development involved an increase of the NK cell distribution in the peripheral blood and spleen along with higher expression of NKG2D activation antigen; this was in correlation with the time-dependent rise of cytotoxic activity in comparison to C57BL/6 mice. The TC-1/A9 cancer regression was accompanied by higher proportion of B cells in the spleen and B220+/CD86+ activated antigen-presenting B cells distributed in the lymphoid organs, as well as in the periphery. The changes in the T-cell population were represented mainly by the prevalence of T helper cells reflected by grown CD4/CD8 ratio, most prominent in the b+d-NK1.1neg strain. The results of the present study imply usefulness of the two novel mouse strains as an experimental model for further studies of tumor resistance mechanisms.

Exploitation of natural killer cells for the treatment of acute leukemia

Natural killer (NK) cells play an important role in surveillance and elimination of malignant cells. Their spontaneous cytotoxicity was first demonstrated in vitro against leukemia cell lines, and NK cells might play a crucial role in the therapy of leukemia. NK cell activity is controlled by an array of germ line-encoded activating and inhibitory receptors, as well as modulating coreceptors. This biologic feature can be exploited in allogeneic cell therapy, and the recognition of "missing-self" on target cells is crucial for promoting NK cell-mediated graft-versus-leukemia effects. In this regard, NK cells that express an inhibitory killer immunoglobulin-like receptor (iKIR) for which the respective major histocompatibility complex class I ligand is absent on leukemic target cells can exert alloreactivity in vitro and in vivo. Several models regarding potential donor-patient constellations have been described that have demonstrated the clinical benefit of such alloreactivity of the donor-derived NK cell system in patients with adult acute myeloid leukemia and pediatric B-cell precursor acute lymphoblastic leukemia after allogeneic stem cell transplantation. Moreover, adoptive transfer of mature allogeneic NK cells in the nontransplant or transplant setting has been shown to be safe and feasible, whereas its effectivity needs further evaluation. NK cell therapy can be further improved by optimal donor selection based on phenotypic and genotypic properties, by adoptive transfer of NK cells with ex vivo or in vivo cytokine stimulation, by the use of antibodies to induce antibody-dependent cellular cytotoxicity or to block iKIRs, or by transduction of chimeric antigen receptors.

A role for pre-mNK cells in tumor progression

The innate and adaptive immune systems have evolved together to fight infection and cancerous tissues. The innate immune system emerges first with the adaptive immune system following, both ostensibly being bridged by dendritic cells (DC). Recently cells have emerged that possess characteristics of both innate and adaptive immune cell qualities, termed interferon-producing killer dendritic cells (IKDCs). These cells have an indistinct origin that is not well understood. They appear to have more NK cell attributes than DC but purportedly can regulate the immune system similar to immunoregulatory NK cells. Because of this, they have been renamed pre-mNK cells (pre-mature NK cells). We argue in this commentary that pre-mNK cells may contribute to cancer recurrence.

T-bet Promotes Acute Graft-versus-Host Disease by Regulating Recipient Hematopoietic Cells in Mice

Beyond its critical role in T cells, T-bet regulates the functions of APCs including dendritic cells and B cells, as well as NK cells. Given that recipient APCs are essential for priming allogeneic T cells and recipient NK or T cells are able to reject allogeneic donor cells, we evaluated the role of T-bet on the host in acute graft-versus-host disease (GVHD) using murine models of allogeneic bone marrow transplantation. T-bet(-/-) recipients developed significantly milder GVHD than their wild type counterparts in MHC-mismatched or CD4-dependent minor histocompatibility Ag-mismatched models. Allogeneic donor T cells, in particular, CD4 subset, significantly reduced IFN-γ production, proliferation and migration, and caused less injury in liver and gut of T-bet(-/-) recipients. We further observed that T-bet on recipient hematopoietic cells was primarily responsible for the donor T cell response and pathogenicity in GVHD. T-bet(-/-) dendritic cells expressed higher levels of Trail, whereas they produced lower levels of IFN-γ and IL-12/23 p40, as well as chemokine CXCL9, resulting in significantly higher levels of apoptosis, less priming, and infiltration of donor T cells. Meanwhile, NK cells in T-bet(-/-) hosts partially contribute to the decreased donor T cell proliferation. Furthermore, although T-bet on hematopoietic cells was required for GVHD development, it was largely dispensable for the graft-versus-leukemia effect. Taken together with our previous findings, we propose that T-bet is a potential therapeutic target for the control of GVHD through regulating donor T cells and recipient hematopoietic cells.

Negative Impact of Unidirectional Host-versus-Graft Killer Cell Immunoglobulin-like Receptor Ligand Mismatch on Transplantation Outcomes after Unmanipulated Haploidentical Peripheral Blood Stem Cell Transplantation for Acute Myeloid Leukemia

This study explored the influence of mismatched inhibitory killer cell immunoglobulin-like receptor (KIR) ligands on the outcome of haploidentical transplantation using T cell-replete, granulocyte colony-stimulating factor-mobilized peripheral blood stem cells in adult patients with acute myeloid leukemia (AML). Three groups were examined: unidirectional graft-versus-host KIR ligand mismatched (GVH-KIR-MM; n = 33), bidirectional KIR ligand matched (KIR-M; n = 41), and unidirectional host-versus-graft KIR ligand mismatched (HVG-KIR-MM; n = 26). All recipients were treated with the same conditioning regimen (800 cGy total body irradiation, fludarabine, busulfan, and antithymocyte globulin). After a median follow-up of 26 months, the 2-year cumulative incidence of relapse was significantly higher in HVG-KIR-MM (40.3% ± 10.3%) versus others (18.9% ± 4.8%, P = .044). In the standard-risk group, the 2-year disease-free survival (DFS) was significantly lower in HVG-KIR-MM (51.8% ± 11.2%) compared with GVH-KIR-MM (88% ± 8.1%, P = .025). Multivariate analysis showed that HVG-KIR-MM was significantly associated with higher relapse (hazard ratio [HR], 10.7; P = .002) and lower DFS (HR, 3.4; P = .012). Subgroup analysis revealed increased DFS with higher doses of CD3(+)CD8(+) and CD3(-)CD56(+) grafts in GVH-KIR-MM (90.9% ± 8.7%, P = .006); there was no such effect in the other groups. Although our conclusions are limited by the absence of donor KIR genotype data, our study suggests unidirectional KIR ligand incompatibility in the host-versus-graft vector has a detrimental effect on T cell-replete haploidentical transplantation outcomes in adult patients with AML.

Intestinal barrier loss as a critical pathogenic link between inflammatory bowel disease and graft-versus-host disease

Compromised intestinal barrier function is a prominent feature of inflammatory bowel disease (IBD). However, links between intestinal barrier loss and disease extend much further, including documented associations with celiac disease, type I diabetes, rheumatoid arthritis, and multiple sclerosis. Intestinal barrier loss has also been proposed to have a critical role in the pathogenesis of graft-versus-host disease (GVHD), a serious, potentially fatal consequence of hematopoietic stem cell transplantation. Experimental evidence has begun to support this view, as barrier loss and its role in initiating and establishing a pathogenic inflammatory cycle in GVHD is emerging. Here we discuss similarities between IBD and GVHD, mechanisms of intestinal barrier loss in these diseases, and the crosstalk between barrier loss and the immune system, with a special focus on natural killer (NK) cells. Unanswered questions and future research directions on the topic are discussed along with implications for treatment.