Mouse NK cell-mediated rejection of bone marrow allografts exhibits patterns consistent with Ly49 subset licensing

A promising natural killer cell-based model and a nomogram for the prognostic prediction of clear-cell renal cell carcinoma

BACKGROUND

Clear-cell renal cell carcinoma (ccRCC) is one of prevalent kidney malignancies with an unfavorable prognosis. There is a need for a robust model to predict ccRCC patient survival and guide treatment decisions.

METHODS

RNA-seq data and clinical information of ccRCC were obtained from the TCGA and ICGC databases. Expression profiles of genes related to natural killer (NK) cells were collected from the Immunology Database and Analysis Portal database. Key NK cell-related genes were identified using consensus clustering algorithms to classify patients into distinct clusters. A NK cell-related risk model was then developed using Least Absolute Shrinkage and Selection Operator (LASSO) Cox regression to predict ccRCC patient prognosis. The relationship between the NK cell-related risk score and overall survival, clinical features, tumor immune characteristics, as well as response to commonly used immunotherapies and chemotherapy, was explored. Finally, the NK cell-related risk score was validated using decision tree and nomogram analyses.

RESULTS

ccRCC patients were stratified into 3 molecular clusters based on expression of NK cell-related genes. Significant differences were observed among the clusters in terms of prognosis, clinical characteristics, immune infiltration, and therapeutic response. Furthermore, six NK cell-related genes (DPYSL3, SLPI, SLC44A4, ZNF521, LIMCH1, and AHR) were identified to construct a prognostic model for ccRCC prediction. The high-risk group exhibited poor survival outcomes, lower immune cell infiltration, and decreased sensitivity to conventional chemotherapies and immunotherapies. Importantly, the quantitative real-time polymerase chain reaction (qRT-PCR) confirmed significantly high DPYSL3 expression and low SLC44A4 expression in ACHN cells. Finally, the decision tree and nomogram consistently show the dramatic prediction performance of the risk score on the survival outcome of the ccRCC patients.

CONCLUSIONS

The six-gene model based on NK cell-related gene expression was validated and found to accurately mirror immune microenvironment and predict clinical outcomes, contributing to enhanced risk stratification and therapy response for ccRCC patients.

Killers on the loose: Immunotherapeutic strategies to improve NK cell-based therapy for cancer treatment

Natural killer (NK) cells are innate lymphocytes that control tumor progression by not only directly killing cancer cells, but also by regulating other immune cells, helping to orchestrate a coordinated anti-tumor response. However, despite the tremendous potential that this cell type has, the clinical results obtained from diverse NK cell-based immunotherapeutic strategies have been, until recent years, rather modest. The intrinsic regulatory mechanisms that are involved in the control of their activation as well as the multiple mechanisms that tumor cells have developed to escape NK cell-mediated cytotoxicity likely account for the unsatisfactory clinical outcomes. The current approaches to improve long-term NK cell function are centered on modulating different molecules involved in both the activation and inhibition of NK cells, and the latest data seems to advocate for combining strategies that target multiple aspects of NK cell regulation. In this review, we summarize the different strategies (such as engineered NK cells, CAR-NK, NK cell immune engagers) that are currently being used to take advantage of this potent and complex immune cell.

Improved hematopoietic stem cell transplantation upon inhibition of natural killer cell-derived interferon-gamma

Hematopoietic stem cell transplantation (HSCT) is a frequent therapeutic approach to restore hematopoiesis in patients with hematologic diseases. Patients receive a hematopoietic stem cell (HSC)-enriched donor cell infusion also containing immune cells, which may have a beneficial effect by eliminating residual neoplastic cells. However, the effect that donor innate immune cells may have on the donor HSCs has not been deeply explored. Here, we evaluate the influence of donor natural killer (NK) cells on HSC fate, concluded that NK cells negatively affect HSC frequency and function, and identified interferon-gamma (IFNγ) as a potential mediator. Interestingly, improved HSC fitness was achieved by NK cell depletion from murine and human donor infusions or by blocking IFNγ activity. Thus, our data suggest that suppression of inflammatory signals generated by donor innate immune cells can enhance engraftment and hematopoietic reconstitution during HSCT, which is particularly critical when limited HSC numbers are available and the risk of engraftment failure is high.

Trained Innate Immunity in Hematopoietic Stem Cell and Solid Organ Transplantation

Although significant progress has been made to improve short-term survival of transplant patients, long-term acceptance of allografts in solid organ and hematopoietic stem cell (HSC) transplantation is still a significant challenge. Current therapeutics for preventing or treating allograft rejection rely on potent immunosuppressive drugs that primarily target T cells of the adaptive immune response. Promising advances in transplant immunology have highlighted the importance of innate immune responses in allograft acceptance and rejection. Recent studies have demonstrated that innate immune cells are capable of mediating memory-like responses during inflammation, a term known as trained innate immunity. In this process, innate immune cells, such as macrophages and monocytes, undergo metabolic and epigenetic changes in response to a primary stimulus with a pathogen or their products that result in faster and more robust responses to a secondary stimulus. There is also some evidence to suggest that innate immune cells or their progenitors may be more anti-inflammatory after initial stimulation with appropriate agents, such as helminth products. Although this phenomenon has primarily been studied in the context of infection, there is emerging evidence to suggest that it could play a vital role in transplantation rejection and tolerance. Mechanisms of training innate immune cells and their progenitors in the bone marrow are therefore attractive targets for mediating long-term solid organ and HSC transplant tolerance. In this review, we highlight the potential role of proinflammatory and anti-inflammatory mechanisms of trained innate immunity in solid organ and HSC transplantation.

Control of Viral Infection by Natural Killer Cell Inhibitory Receptors

Major histocompatibility complex class I (MHC-I)-restricted immune responses are largely attributed to cytotoxic T lymphocytes (CTLs). However, natural killer (NK) cells, as predicted by the missing-self hypothesis, have opposing requirements for MHC-I, suggesting that they may also demonstrate MHC-I-restricted effects. In mice, the Ly49 inhibitory receptors prevent NK cell killing of missing-self targets in effector responses, and they have a proposed second function in licensing or educating NK cells via self-MHC-I in vivo. Here we show MHC-I-restricted control of murine cytomegalovirus (MCMV) infection in vivo that is NK cell dependent. Using mice lacking specific Ly49 receptors, we show that control of MCMV requires inhibitory Ly49 receptors and an inhibitory signaling motif and the capacity for MCMV to downregulate MHC-I. Taken together, these data provide definitive evidence that the inhibitory receptors are required for missing-self rejection and are relevant to MHC-I-restricted NK cell control of a viral infection in vivo.

Parikh et al. show that major histocompatibility complex class I (MHC-I)-restricted control of viral infection is due to natural killer (NK) cells rather than cytotoxic T cells. Inhibitory NK cell receptors are essential for protection, requiring NK cell licensing (education) by self-MHC-I and missing-self recognition due to virus-induced MHC-I downregulation.

Infusion of Host-Derived Unlicensed NK Cells Improves Donor Engraftment in Non-Myeloablative Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) is an efficacious and frequently the only treatment option for some hematological malignances. However, it often faces severe morbidities and/or mortalities due to graft versus host disease, and the severity of the conditioning regiment needed, that result in toxicity-related issues poorly tolerable for some patients. These shortcomings have led to the development of less aggressive alternatives like non-myeloablative (NMAC) or reduced-intensity conditioning regiments (RIC). However, these approaches tend to have an increase of cancer relapse and limited persistence of donor-specific chimerism. Thus, strategies that lead towards an accelerated and more durable donor engraftment are still needed. Here, we took advantage of the ability of host-derived unlicensed NK (UnLicNK) cells to favor donor cell engraftment during myeloablative allo-HCT, and evaluated if the adoptive transfer of this cell type can improve donor chimerism in NAMC settings. Indeed, the infusion of these cells significantly increased mixed chimerism in a sublethal allo-HCT mouse model, resulting in a more sustainable donor cell engraftment when compared to the administration of licensed NK cells or HCT controls. We observed an overall increase in the total number and proportion of donor B, NK and myeloid cells after UnLicNK cell infusion. Additionally, the extension and durability of donor chimerism was similar to the one obtained after the tolerogenic Tregs infusion. These results serve as the needed bases for the implementation of the adoptive transfer of UnLicNK cells to upgrade NMAC protocols and enhance allogeneic engraftment during HCT.

Impaired Hematopoiesis after Allogeneic Hematopoietic Stem Cell Transplantation: Its Pathogenesis and Potential Treatments

Impaired hematopoiesis is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Bone marrow aplasia and peripheral cytopenias arise from primary and secondary graft failure or primary and secondary poor graft function. Chimerism analysis is useful to discriminate these conditions. By determining the pathogenesis of impaired hematopoiesis, a timely and appropriate treatment can be performed. Hematopoietic system principally consists of hematopoietic stem cells and bone marrow microenvironment termed niches. Abnormality in hematopoietic stem and progenitor cells and/or abnormality in the relevant niches give rise to hematological diseases. Allo-HSCT is intended to cure each hematological disease, replacing abnormal hematopoietic stem cells and bone marrow niches with hematopoietic stem cells and bone marrow niches derived from normal donors. Therefore, treatment for graft failure and poor graft function after allo-HSCT is required to proceed based on determining the pathogenesis of impaired hematopoiesis. Recent progress in this area suggests promising treatment manipulations for graft failure and poor graft function.

IL-2 and Anti-TGF-β Promote NK Cell Reconstitution and Anti-tumor Effects after Syngeneic Hematopoietic Stem Cell Transplantation

Simple Summary

Hematopoietic stem cell transplantation (HSCT) causes early immune deficiency and susceptibility to both opportunistic infections and cancer relapse. In this study, using a mouse model where donor cells can be tracked over time, we have observed that the combination of IL-2 (a cytokine which activates the immune system) combined with the blockade of TGF-β (a cytokine which suppresses the immune system) increased immune recovery and resulted in greater anti-tumor efficacy. The combination of IL-2 and anti-TGF-β accelerated NK cell and myeloid cell reconstitution after HSCT.

Abstract

The failure of autologous hematopoietic stem cell transplantation (HSCT) has been associated with a profound immunodeficiency that follows shortly after treatment, which renders patients susceptible to opportunistic infections and/or cancer relapse. Thus, given the additional immunosuppressive pathways involved in immune evasion in cancer, strategies that induce a faster reconstitution of key immune effector cells are needed. Natural killer (NK) cells mediate potent anti-tumor effector functions and are the first immune cells to repopulate after HSCT. TGF-β is a potent immunosuppressive cytokine that can impede both the development and function of immune cells. Here, we evaluated the use of an immunotherapeutic regimen that combines low dose of IL-2, an NK cell stimulatory signal, with TGF-β neutralization, in order to accelerate NK cell reconstitution following congenic HSCT in mice by providing stimulatory signals yet also abrogating inhibitory ones. This therapy led to a marked expansion of NK cells and accelerated NK cell maturation. Following HSCT, mature NK cells from the treated recipients displayed an activated phenotype and enhanced anti-tumor responses both in vitro and in vivo. No overt toxicities or adverse effects were observed in the treated recipients. However, these stimulatory effects on NK cell recovery were predicated upon continuous treatment as cessation of treatment led to return to baseline levels and to no improvement of overall immune recovery when assessed at later time-points, indicating strict regulatory control of the NK cell compartment. Overall, this study still demonstrates that therapies that combine positive and negative signals can be plausible strategies to accelerate NK cell reconstitution following HSCT and augment anti-tumor efficacy.

Natural Killer Cells Expanded and Preactivated Exhibit Enhanced Antitumor Activity against Different Tumor Cells in Vitro

One of the emerging treatment strategies for cancer particularly for haematological malignancies is natural killer (NK) cell therapy. However, the availability of a best approach to maximize NK cell anticancer potential is still awaited. It is well established that cytokine-induced memory-like NK cells have the potential to differentiate after a short period of preactivation with interleukins-IL-12, IL-15, and IL-18 and exhibit increased responses to cytokine or activating receptor restimulation for weeks to months after preactivation. We demonstrated that NK cells differentiated from CD34+ cells isolated from cord blood show increased antitumor potential in vitro against different cancer cells. Using flow cytometry, we found that NK cells were able to induce apoptosis in cancer cells in vitro. We further analysed surviving gene expression by quantitative real time PCR and reported that NK cells cause down regulation of survivin gene expression in tumor cells. Therefore, NK cell therapy represents a promising immunotherapy for cancers like AML and other haematological malignancies. It concluded that NK cells can be differentiated from CD34+ cells isolated from cord blood ,are able to induce apoptosis and induce increased antitumor potential in vitro against different cancer cells besides cause downregulation of survivin gene expression in tumor cells. Therefore, NK cell therapy represents a promising immunotherapy for different cancer types and haematological malignancies. Furthers studies are necessary to confirm our findings.

Rapid isolation and enrichment of mouse NK cells for experimental purposes

Natural killer (NK) cells have shown to play a critical, but as yet poorly defined, role in the process by which the immune system controls tumor progression. Indeed, NK cell-based immunotherapy, particularly NK cell adoptive transfer therapy, has become a very attractive cancer weapon against multiple types of cancers such as metastatic and hematological cancers. Unfortunately, the implementation of these therapies has been challenged by the existence of immunosuppression mechanisms that have prevented NK cell functionality. Additionally, the development of protocols to obtain purified and functional NK cells has faced some difficulties due to the limitations in the numbers of cells that can be obtained and the development of an exhaustion phenotype with impaired proliferative and functional capabilities during lengthy ex vivo NK cell expansion protocols. Thus, the development of new strategies to obtain a rapid expansion of highly functional NK cells without the appearance of exhaustion is still much needed. This is particularly true in the case of mouse NK cells, a surrogate commonly used to evaluate NK cell biology and human NK cell-based immunotherapeutic alternatives. Here, we describe a feasible and rapid protocol to produce strongly activated mouse NK cells in vivo taking advantage of the hydrodynamic delivery of a plasmid that contains interleukin-15, a cytokine known to cause NK cell expansion and activation, fused with the binding domain of the IL-15Rα ("sushi" domain) and apolipoprotein A-I.

Regulation of murine NK cell exhaustion through the activation of the DNA damage repair pathway

NK cell exhaustion (NCE) due to sustained proliferation results in impaired NK cell function with loss of cytokine production and lytic activity. Using murine models of chronic NK cell stimulation, we have identified a phenotypic signature of NCE characterized by up-regulation of the terminal differentiation marker KLRG1 and by down-regulation of eomesodermin and the activating receptor NKG2D. Chronic stimulation of mice lacking NKG2D resulted in minimized NCE compared to control mice, thus identifying NKG2D as a crucial mediator of NCE. NKG2D internalization and downregulations on NK cells has been previously observed in the presence of tumor cells with high expression of NKG2D ligands (NKG2DL) due to the activation of the DNA damage repair pathways. Interestingly, our study revealed that during NK cell activation there is an increase of MULT1, and NKG2DL, that correlates with an induction of DNA damage. Treatment with the ATM DNA damage repair pathway inhibitor KU55933 (KU) during activation reduced NCE by improving expression of activation markers and genes involved in cell survival, by sustaining NKG2D expression and by preserving cell functionality. Importantly, NK cells expanded ex vivo in the presence of KU displayed increased anti-tumor efficacy in both NKG2D-dependent and -independent mouse models. Collectively, these data demonstrate that NCE is caused by DNA damage and regulated, at least in part, by NKG2D. Further, the prevention of NCE is a promising strategy to improve NK cell-based immunotherapy.

Innate Immune Determinants of Graft-Versus-Host Disease and Bidirectional Immune Tolerance in Allogeneic Transplantation

The success of tissue transplantation from a healthy donor to a diseased individual (allo-transplantation) is regulated by the immune systems of both donor and recipient. Developing a state of specific non-reactivity between donor and recipient, while maintaining the salutary effects of immune function in the recipient, is called “immune (transplantation) tolerance”. In the classic early post-transplant period, minimizing bidirectional donor ←→ recipient reactivity requires the administration of immunosuppressive drugs, which have deleterious side effects (severe immunodeficiency, opportunistic infections, and neoplasia, in addition to drug-specific reactions and organ toxicities). Inducing immune tolerance directly through donor and recipient immune cells, particularly via subsets of immune regulatory cells, has helped to significantly reduce side effects associated with multiple immunosuppressive drugs after allo-transplantation. The innate and adaptive arms of the immune system are both implicated in inducing immune tolerance. In the present article, we will review innate immune subset manipulations and their potential applications in hematopoietic stem cell transplantation (HSCT) to cure malignant and non-malignant hematological disorders by inducing long-lasting donor ←→ recipient (bidirectional) immune tolerance and reduced graft-versus-host disease (GVHD). These innate immunotherapeutic strategies to promote long-term immune allo-transplant tolerance include myeloid-derived suppressor cells (MDSCs), regulatory macrophages, tolerogenic dendritic cells (tDCs), Natural Killer (NK) cells, invariant Natural Killer T (iNKT) cells, gamma delta T (γδ-T) cells and mesenchymal stromal cells (MSCs).

Immunoreceptor tyrosine-based inhibitory motif-dependent functions of an MHC class I-specific NK cell receptor

Natural killer (NK) cells express MHC class I (MHC-I)-specific receptors, such as Ly49A, that inhibit killing of cells expressing self-MHC-I. Self-MHC-I also "licenses" NK cells to become responsive to activating stimuli and regulates the surface level of NK-cell inhibitory receptors. However, the mechanisms of action resulting from these interactions of the Ly49s with their MHC-I ligands, particularly in vivo, have been controversial. Definitive studies could be derived from mice with targeted mutations in inhibitory Ly49s, but there are inherent challenges in specifically altering a single gene within a multigene family. Herein, we generated a knock-in mouse with a targeted mutation in the immunoreceptor tyrosine-based inhibitory motif (ITIM) of Ly49A that abolished the inhibitory function of Ly49A in cytotoxicity assays. This mutant Ly49A caused a licensing defect in NK cells, but the surface expression of Ly49A was unaltered. Moreover, NK cells that expressed this mutant Ly49A exhibited an altered inhibitory receptor repertoire. These results demonstrate that Ly49A ITIM signaling is critical for NK-cell effector inhibition, licensing, and receptor repertoire development.

Immunological Basis of Bone Marrow Failure after Allogeneic Hematopoietic Stem Cell Transplantation

Bone marrow failure (BMF) syndromes are severe complications of allogeneic hematopoietic stem cell transplantation (allo-HSCT). In this paper, we distinguish two different entities, the graft failure (GF) and the poor graft function (PGF), and we review the current understanding of the interactions between the immune and hematopoietic compartments in these conditions. We first discuss how GF occurs as the result of classical alloreactive immune responses mediated by residual host cellular and humoral immunity persisting after conditioning and prevented by host and donor regulatory T cells. We next summarize the current knowledge about the contribution of inflammatory mediators to the development of PGF. In situations of chronic inflammation complicating allo-HSCT, such as graft-versus-host disease or infections, PGF seems to be essentially the result of a sustained impairment of hematopoietic stem cells (HSC) self-renewal and proliferation caused by inflammatory mediators, such as interferon-γ (IFN-γ) and tumor necrosis factor-α, and of induction of apoptosis through the Fas/Fas ligand pathway. Interestingly, the production of inflammatory molecules leads to a non-MHC restricted, bystander inhibition of hematopoiesis, therefore, representing a promising target for immunological interventions. Finally, we discuss immune-mediated impairment of bone marrow microenvironment as a potential mechanism hampering hematopoietic recovery. Better understanding of immunological mechanisms responsible for BMF syndromes after allo-HSCT may lead to the development of more efficient immunotherapeutic interventions.

NK cells pave the road for alloengraftment

In this issue of Blood, Alvarez et al describe a novel inhibitory receptor-mediated role for unlicensed natural killer (U-NK) cells in allogeneic graft facilitation.

Licensed and Unlicensed NK Cells: Differential Roles in Cancer and Viral Control

Natural killer (NK) cells are known for their well characterized ability to control viral infections and eliminate tumor cells. Through their repertoire of activating and inhibitory receptors, NK cells are able to survey different potential target cells for various surface markers, such as MHC-I – which signals to the NK cell that the target is healthy – as well as stress ligands or viral proteins, which alert the NK cell to the aberrant state of the target and initiate a response. According to the “licensing” hypothesis, interactions between self-specific MHC-I receptors – Ly49 in mice and KIR in humans – and self-MHC-I molecules during NK cell development is crucial for NK cell functionality. However, there also exists a large proportion of NK cells in mice and humans, which lack self-specific MHC-I receptors and are consequentially “unlicensed.” While the licensed NK cell subset plays a major role in the control of MHC-I-deficient tumors, this review will go on to highlight the important role of the unlicensed NK cell subset in the control of MHC-I-expressing tumors, as well as in viral control. Unlike the licensed NK cells, unlicensed NK cells seem to benefit from the lack of self-specific inhibitory receptors, which could otherwise be exploited by some aberrant cells for immunoevasion by upregulating the expression of ligands or mimic ligands for these receptors.

NLRC5 shields T lymphocytes from NK-cell-mediated elimination under inflammatory conditions

NLRC5 is a transcriptional regulator of MHC class I (MHCI), which maintains high MHCI expression particularly in T cells. Recent evidence highlights an important NK–T-cell crosstalk, raising the question on whether NLRC5 specifically modulates this interaction. Here we show that NK cells from Nlrc5-deficient mice exhibit moderate alterations in inhibitory receptor expression and responsiveness. Interestingly, NLRC5 expression in T cells is required to protect them from NK-cell-mediated elimination upon inflammation. Using T-cell-specific Nlrc5-deficient mice, we show that NK cells surprisingly break tolerance even towards ‘self' Nlrc5-deficient T cells under inflammatory conditions. Furthermore, during chronic LCMV infection, the total CD8⁺ T-cell population is severely decreased in these mice, a phenotype reverted by NK-cell depletion. These findings strongly suggest that endogenous T cells with low MHCI expression become NK-cell targets, having thus important implications for T-cell responses in naturally or therapeutically induced inflammatory conditions.

NK cell tolerance to self-MHCI levels is calibrated during their development. Here the authors show that this tolerance is overcome by an inflammatory environment and that NLRC5 protects T cells from NK cell-mediated elimination by maintaining high MHCI expression.

Mouse host unlicensed NK cells promote donor allogeneic bone marrow engraftment

Natural killer (NK) cells exist as subsets based on expression of inhibitory receptors that recognize major histocompatibility complex I (MHCI) molecules. NK cell subsets bearing MHCI binding receptors for self-MHCI have been termed as "licensed" and exhibit a higher ability to respond to stimuli. In the context of bone marrow transplantation (BMT), host licensed-NK (L-NK) cells have also been demonstrated to be responsible for the acute rejection of allogeneic and MHCI-deficient BM cells (BMCs) in mice after lethal irradiation. However, the role of recipient unlicensed-NK (U-NK) cells has not been well established with regard to allogeneic BMC resistance. After NK cell stimulation, the prior depletion of host L-NK cells resulted in a marked increase of donor engraftment compared with the untreated group. Surprisingly, this increased donor engraftment was reduced after total host NK cell depletion, indicating that U-NK cells can actually promote donor allogeneic BMC engraftment. Furthermore, direct coculture of U-NK cells with allogeneic but not syngeneic BMCs resulted in increased colony-forming unit cell growth in vitro, which was at least partially mediated by granulocyte macrophage colony-stimulating factor (GM-CSF) production. These data demonstrate that host NK cell subsets exert markedly different roles in allogeneic BMC engraftment where host L- and U-NK cells reject or promote donor allogeneic BMC engraftment, respectively.

NK Cell and CD4+FoxP3+ Regulatory T Cell Based Therapies for Hematopoietic Stem Cell Engraftment

Allogeneic hematopoietic cell transplantation (HCT) is a powerful therapy to treat multiple hematological diseases. The intensive conditioning regimens used to allow for donor hematopoietic stem cell (HSC) engraftment are often associated with severe toxicity, delayed immune reconstitution, life-threatening infections, and thus higher relapse rates. Additionally, due to the high incidence of graft versus host disease (GvHD), HCT protocols have evolved to prevent such disease that has a detrimental impact on antitumor and antiviral responses. Here, we analyzed the role of host T and natural killer (NK) cells in the rejection of donor HSC engraftment as well as the impact of donor regulatory T cells (Treg) and NK cells on HSC engraftment. We review some of the current strategies that utilize NK or Treg to improve allogeneic HCT therapy in order to accomplish better HSC engraftment and immune reconstitution and achieve a lower incidence of cancer relapse, opportunistic infections, and GvHD.

Donor Requirements for Regulatory T Cell Suppression of Murine Graft-versus-Host Disease

Adoptive transfer of freshly isolated natural occurring CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) prevents graft-versus-host disease (GVHD) in several animal models and following hematopoietic cell transplantation (HCT) in clinical trials. Donor-derived Treg have been mainly used, as they share the same MHC with CD4(+) and CD8(+) conventional T cells (Tcon) that are primarily responsible for GVHD. Third party-derived Treg are a promising alternative for cellular therapy, as they can be prepared in advance, screened for pathogens and activity, and banked. We explored MHC disparities between Treg and Tcon in HCT to evaluate the impact of different Treg populations in GVHD prevention and survival. Third-party Treg and donor Treg are equally suppressive in ex vivo assays, whereas both donor and third-party but not host Treg protect from GVHD in allogeneic HCT, with donor Treg being the most effective. In an MHC minor mismatched transplantation model (C57BL/6 → BALB/b), donor and third-party Treg were equally effective in controlling GVHD. Furthermore, using an in vivo Treg depletion mouse model, we found that Treg exert their main suppressive activity in the first 2 d after transplantation. Third-party Treg survive for a shorter period of time after adoptive transfer, but despite the shorter survival, they control Tcon proliferation in the early phases of HCT. These studies provide relevant insights on the mechanisms of Treg-mediated protection from GVHD and support for the use of third-party Treg in clinical trials.

Genetic investigation of MHC-independent missing-self recognition by mouse NK cells using an in vivo bone marrow transplantation model

MHC-I-specific receptors play a vital role in NK cell-mediated "missing-self" recognition, which contributes to NK cell activation. In contrast, MHC-independent NK recognition mechanisms are less well characterized. In this study, we investigated the role of NKR-P1B:Clr-b (Klrb1:Clec2d) interactions in determining the outcome of murine hematopoietic cell transplantation in vivo. Using a competitive transplant assay, we show that Clr-b(-/-) bone marrow (BM) cells were selectively rejected by wild-type B6 recipients, to a similar extent as H-2D(b-/-) MHC-I-deficient BM cells. Selective rejection of Clr-b(-/-) BM cells was mitigated by NK depletion of recipient mice. Competitive rejection of Clr-b(-/-) BM cells also occurred in allogeneic transplant recipients, where it was reversed by selective depletion of NKR-P1B(hi) NK cells, leaving the remaining NKR-P1B(lo) NK subset and MHC-I-dependent missing-self recognition intact. Moreover, competitive rejection of Clr-b(-/-) hematopoietic cells was abrogated in Nkrp1b-deficient recipients, which lack the receptor for Clr-b. Of interest, similar to MHC-I-deficient NK cells, Clr-b(-/-) NK cells were hyporesponsive to both NK1.1 (NKR-P1C)-stimulated and IL-12/18 cytokine-primed IFN-γ production. These findings support a unique and nonredundant role for NKR-P1B:Clr-b interactions in missing-self recognition of normal hematopoietic cells and suggest that optimal BM transplant success relies on MHC-independent tolerance mechanisms. These findings provide a model for human NKR-P1A:LLT1 (KLRB1:CLEC2D) interactions in human hematopoietic cell transplants.

Elevation of MMP-9 and IDO induced by pancreatic cancer cells mediates natural killer cell dysfunction

Background

Natural killer (NK) cells play a key role in non-specific immune response in different cancers, including pancreatic cancer. However the anti-tumor effect of NK cells decreases during pancreatic cancer progression. The regulatory pathways by which NK cells facilitate tumor immune escape are unclear, therefore our purpose was to investigate the roles of the contributory factors.

Methods

NK cells isolated from fresh healthy peripheral blood were co-cultured with normal human pancreatic ductal cells hTERT-HPNE and human pancreatic cancer cell lines SW1990 and BxPc-3 in vitro. Then NK cell function was determined by Flow cytometric analysis of surface receptors and cytotoxic granules in NK cells, NK cell apoptosis and cytotoxicity, and Enzyme-linked immunosorbent assay of cytokines. Expression level of MMP-9, IDO and COX-2 in hTERT-HPNE and SW1990 cells were detected by quantitative RT-PCR. Statistical differences between data groups were determined by independent t-tests using SPSS 19.0 software.

Results

Our results showed that NK cell function was significantly downregulated following exposure to pancreatic cancer cells compared to normal pancreatic cells, as demonstrated by lower expressions of activating surface receptors (NKG2D, DNAM-1, NKp30 and NKp46) and cytotoxic granules (Perforin and Granzyme B); decreased secretion of cytokines (TNF-α and IFN-γ); and reduced cytotoxicity against myelogenous leukemia K562 cells. Further investigations revealed that MMP-9 and IDO may be implicated in SW1990 cell-induced NK cell dysfunction by facilitating tumor immune evasion. Blockade by TIMP-1 and/or 1-MT could partially restore NK function.

Conclusions

Taken together, elevation of MMP-9 and IDO induced by pancreatic cancer cells mediates NK cell dysfunction. Our findings could contribute to the development of NK cell-based immunotherapy in patients with pancreatic cancer.

Positive and negative regulation by NK cells in cancer

Our understanding of NK biology has expanded immensely since the initial discovery of natural killer cells in 1975. New studies have uncovered various levels of immune regulation both on and by unique subsets of NK cells, which go well beyond simple receptor-ligand interactions between NK cells and target cancer cells. Distinct suppressor and effector populations of NK cells have been delineated in both viral and tumor models. Interactions between NK cells and dendritic cells, T cells, and B cells also dramatically alter the overall immune response to cancer. To exploit the diverse functional abilities of NK cell subsets for cancer immunotherapies, it is important to understand NK cell biology and NK regulator mechanisms.

Natural killer cell subsets differentially reject embryonic stem cells based on licensing

BACKGROUND

Embryonic stem cells (ESC) and induced pluripotent stem cells provide great promise to the future of medicine. Because immune rejection represents a major obstacle to the success of all stem cell-based therapies, many recent studies have sought to determine the key immune mediators involved in ESC rejection. The role of natural killer (NK) cells and specifically the role of NK cell licensing is not well understood in ESC rejection.

METHODS

Mouse or human ESCs were subjected to cytotoxicity assays involving their respective species-matched activated NK cells. Mouse ESCs were then transplanted to allogeneic recipients after depletion of NK cell subsets in the host. ESC engraftment was analyzed by bioluminescent imaging.

RESULTS

Depletion of all NK cells in vivo resulted in the greatest amount of ESC engraftment, confirming a role for NK cells in ESC rejection. Importantly, depletion of the Ly49C/I or Ly49G2 NK cell subsets resulted in differential ESC engraftment and rejection. This indicates that NK cell rejection of allogeneic ESC is highly differential based on the presence of licensed NK cells. Blocking NKG2D in vitro resulted in less killing of mESC by allogeneic NK cells, indicating NKG2D is a likely mechanism for NK-mediated killing of mESC.

CONCLUSIONS

In this study, we show that expression of inhibitory Ly49s correlates with the ability of NK cells to kill murine ESC in an NKG2D-dependent manner. This further suggests that the rejection of similar stem cell transplants in humans will be dependent upon the presence of licensed NK cells.

Innate immune cells in transplantation

PURPOSE OF REVIEW

To examine the recent literature on the role of innate cells in immunity to transplanted tissue. It specifically addresses the impact of monocytes/macrophages, neutrophils, natural killer cells, and platelets.

RECENT FINDINGS

Current research indicates that innate immunity plays a dual role in response to transplanted tissue with the ability to either facilitate rejection or promote tolerance. Intriguingly, some of these cells are even capable of reacting to allogeneic cells, a feature usually only attributed to cells of the adaptive immune system.

SUMMARY

This review highlights the new therapeutic targets in the innate immune system that may be useful in the treatment of transplant recipients. It also emphasizes the need to use caution in exploring these new therapeutics.

Advantages and clinical applications of natural killer cells in cancer immunotherapy

The past decade has witnessed a burgeoning of research and further insight into the biology and clinical applications of natural killer (NK) cells. Once thought to be simple innate cells important only as cytotoxic effector cells, our understanding of NK cells has grown to include memory-like responses, the guidance of adaptive responses, tissue repair, and a delicate paradigm for how NK cells become activated now termed "licensing" or "arming." Although these cells were initially discovered and named for their spontaneous ability to kill tumor cells, manipulating NK cells in therapeutic settings has proved difficult and complex in part due to our emerging understanding of their biology. Therapies involving NK cells may either activate endogenous NK cells or involve transfers of exogenous cells by hematopoietic stem cell transplantation or adoptive cell therapy. Here, we review the basic biology of NK cells, highlighting characteristics which make NK cells particularly useful in cancer therapies. We also explore current treatment strategies that have been used for cancer as well as discuss potential future directions for the field.

Contrasting effects of anti-Ly49A due to MHC class I cis binding on NK cell-mediated allogeneic bone marrow cell resistance

NK subsets have activating and inhibitory receptors that bind MHC-I. Ly49A is a mouse inhibitory receptor that binds with high affinity to H2(d) in both a cis- and trans-manner. Ly49A cis-associations limit trans-interactions with H2(d)-expressing targets as well as mAb binding. We demonstrate that cis-interactions affect mAb effector functions. In vivo administration of anti-Ly49A depleted NK cells in H2(b) but not H2(d) mice. Despite lack of depletion, in vivo treatment with anti-Ly49A reduced NK killing capabilities and inhibited activation, partially due to its agonistic effect. These data explain the previously described in vivo effects on bone marrow allograft rejection observed with anti-Ly49A treatment in H2(d)-haplotype mice. However, prior treatment of mice with poly(I:C) or mouse CMV infection resulted in increased Ly49A expression and Ly49A(+) NK cell depletion in H2(d) mice. These data indicate that, although Ly49 mAbs can exert similar in vivo effects in mice with different MHC haplotypes, these effects are mediated via different mechanisms of action correlating with Ly49A expression levels and can be altered within the same strain contingent on stimuli. This illustrates the marked diversity of mAb effector functions due to the regulation of the level of expression of target Ags and responses by stimulatory incidents such as infection.

The Rac activator DOCK2 regulates natural killer cell-mediated cytotoxicity in mice through the lytic synapse formation

Natural killer (NK) cells play an important role in protective immunity against viral infection and tumor progression, but they also contribute to rejection of bone marrow grafts via contact-dependent cytotoxicity. Ligation of activating NK receptors with their ligands expressed on target cells induces receptor clustering and actin reorganization at the interface and triggers polarized movement of lytic granules to the contact site. Although activation of the small GTPase Rac has been implicated in NK cell-mediated cytotoxicity, its precise role and the upstream regulator remain elusive. Here, we show that DOCK2, an atypical guanine nucleotide exchange factor for Rac, plays a key role in NK cell-mediated cytotoxicity. We found that although DOCK2 deficiency in NK cells did not affect conjugate formation with target cells, DOCK2-deficienct NK cells failed to effectively kill leukemia cells in vitro and major histocompatibility complex class I-deficient bone marrow cells in vivo, regardless of the sorts of activating receptors. In DOCK2-deficient NK cells, NKG2D-mediated Rac activation was almost completely lost, resulting in a severe defect in the lytic synapse formation. Similar results were obtained when the Rac guanine nucleotide exchange factor activity of DOCK2 was selectively abrogated. These results indicate that DOCK2-Rac axis controls NK cell-mediated cytotoxicity through the lytic synapse formation.

Murine natural killer cell licensing and regulation by T regulatory cells in viral responses

Natural killer (NK) cells show differential functionality based on their capability of binding to self-MHC consistent with licensing. Here we show in vivo confirmation of the physiologic effects of licensing with differential effects of NK subsets on anti-murine cytomegalovirus (anti-MCMV) responses after syngeneic hematopoietic stem cell transplantation (HSCT) or regulatory T-cell (Treg) depletion. After HSCT, depletion of licensed NK cells led to far greater viral loads in target organs early after infection compared with nondepleted and unlicensed depleted mice. There was a preferential expansion of licensed, C-type lectin-like activating receptor Ly49H+ NK cells with increased IFNγ production after infection in nondepleted mice post-HSCT and after Treg depletion. Adoptive transfer of licensed NK subsets into immunodeficient hosts provided significantly greater MCMV resistance compared with transfer of total NK populations or unlicensed subsets. In non-HSCT mice, only concurrent depletion of Tregs or TGF-β neutralization resulted in detection of NK licensing effects. This suggests that licensed NK cells are the initial and rapidly responding population of NK cells to MCMV infection, but are highly regulated by Tregs and TGF-β.

Utilization of mouse models to decipher natural killer cell biology and potential clinical applications

Natural killer (NK) cells represent a key component of innate immunity. The utility of mouse models to recapitulate the human immune response has been a matter of ongoing debate, especially with regard to NK cells. However, mouse models of NK cells have provided significant advancements in our understanding of the biology of the cells that bridge these species. Initial characterization of NK cell activity was in mouse hematopoietic stem cell transplantation models. Recent findings include uncovering functionally disparate subsets of NK cells based on unique inhibitory receptor expression patterns, the existence of memory-like NK cells, and immunoregulatory NK cells that affect hematopoiesis and T-cell function. In addition, the biology of these cells with regard to MHC-binding receptors that affect NK cell subset maturation and function in the context of licensing, the importance of cytokines such as IL-15 in their development and maintenance, and evidence of NK exhaustion have been initially studied in mice. Many of these findings have been validated in clinical studies and demonstrate the significant wealth of knowledge that can be obtained by mouse models. However, it is important to understand the limitations and conditions of the mouse models, particularly when studying NK cells in hematopoietic stem cell transplantation and cancer.

Recognition of the nonclassical MHC class I molecule H2-M3 by the receptor Ly49A regulates the licensing and activation of NK cells

The development and function of natural killer (NK) cells is regulated by the interaction of inhibitory receptors of the Ly49 family with distinct peptide-laden major histocompatibility complex (MHC) class I molecules, although whether the Ly49 family is able bind to other MHC class I-like molecules is unclear. Here we found that the prototypic inhibitory receptor Ly49A bound the highly conserved nonclassical MHC class I molecule H2-M3 with an affinity similar to its affinity for H-2D(d). The specific recognition of H2-M3 by Ly49A regulated the 'licensing' of NK cells and mediated 'missing-self' recognition of H2-M3-deficient bone marrow. Host peptide-H2-M3 was required for optimal NK cell activity against experimental metastases and carcinogenesis. Thus, nonclassical MHC class I molecules can act as cognate ligands for Ly49 molecules. Our results provide insight into the various mechanisms that lead to NK cell tolerance.

Late effects and healthcare needs of survivors of allogeneic stem cell transplantation: a qualitative study

PURPOSE

This qualitative study of survivors of allogeneic stem cell transplantation (SCT) for haematological malignancy explored attitudes about late effects of therapy, healthcare issues and information needs.

METHODS

We conducted 12 indepth cognitive interviews and three focus groups of patients who had previously had SCT and were without recurrence of their primary disease. We used grounded theory methods, where themes emerged from consensus between cocoders. Health-related quality of life was assessed with the short-form 36 (SF-36).

RESULTS

The study included 22 patients (50% female; 95% white; mean age 47 years). The mean time from SCT was 5.2 years (±1.4 years). Most had low SF-36 scores. Participants discussed late effects of therapy, most commonly graft-versus-host disease, and how they impacted their quality of life. They reported frequent healthcare use and cancer screening after SCT and discussed problems affording care and interacting with insurance companies. Participants shared sources of health information (eg, preferring providers as their primary sources of information, but also learnt from websites, medical journals and peer experiences) and identified information barriers (eg, feeling 'on their own' insofar as they did not have targeted care for their needs), and expressed importance of anticipatory guidance regarding infertility. Overall, participants' personal issues and social influences impacted survivors' needs and attitudes.

CONCLUSIONS

SCT survivors face continuing and lasting health effects. The factors impacting survivorship needs are complex and may be interrelated. Future research should study the affect of incorporating personal and social issues into existing clinical SCT programmes on survivors' quality of life.