Rapamycin and MPA, but not CsA, impair human NK cell cytotoxicity due to differential effects on NK cell phenotype

Tumour-associated neutrophils: Potential therapeutic targets in pancreatic cancer immunotherapy

Pancreatic cancer (PC) is a highly malignant tumour of the digestive system with poor therapeutic response and low survival rates. Immunotherapy has rapidly developed in recent years and has achieved significant outcomes in numerous malignant neoplasms. However, responses to immunotherapy in PC are rare, and the immunosuppressive and desmoplastic tumour microenvironment (TME) significantly hinders their efficacy in PC. Tumour-associated neutrophils (TANs) play a crucial role in the PC microenvironment and exert a profound influence on PC immunotherapy by establishing a robust stromal shelter and restraining immune cells to assist PC cells in immune escape, which may subvert the current status of PC immunotherapy. The present review aims to offer a comprehensive summary of the latest progress in understanding the involvement of TANs in PC desmoplastic and immunosuppressive functions and to emphasise the potential therapeutic implications of focusing on TANs in the immunotherapy of this deleterious disease. Finally, we provide an outlook for the future use of TANs in PC immunotherapy.

Examining the impact of immunosuppressive drugs on antibody-dependent cellular cytotoxicity (ADCC) of human peripheral blood natural killer (NK) cells and gamma delta (γδ) T cells

BACKGROUND

Human natural killer (NK) cells and gamma delta (γδ) T cells may impact outcomes of solid organ transplantation (SOT) such as lung transplantation (LTx) following the differential engagement of an array of activating and inhibitory receptors. Amongst these, CD16 may be particularly important due to its capacity to bind IgG to trigger antibody-dependent cellular cytotoxicity (ADCC) and the production of proinflammatory cytokines. While the use of immunosuppressive drugs (ISDs) is an integral component of SOT practice, their relative impact on various immune cells, especially γδT cells and CD16-induced functional responses, is still unclear.

METHODS

The ADCC responses of peripheral blood NK cells and γδT cells from both healthy blood donors and adult lung transplant recipients (LTRs) were assessed by flow cytometry. Specifically, the degranulation response, as reflected in the expression of CD107a, and the capacity of both NK cells and γδT cells to produce IFN-γ and TNF-α was assessed following rituximab (RTX)-induced activation. Additionally, the effect of cyclosporine A (CsA), tacrolimus (TAC), prednisolone (Prdl) and azathioprine (AZA) at the concentration of 1 ng/ml, 10 ng/ml, 100 ng/ml, and 1000 ng/ml on these responses was also compared in both cell types.

RESULTS

Flow cytometric analyses of CD16 expresion showed that its expression on γδT cells was both at lower levels and more variable than that on peripheral blood NK cells. Nevertheless functional analyses showed that despite these differences, γδT cells like NK cells can be readily activated by engagement with RTX to degranulate and produce cytokines such as IFNg and TNF-a. RTX-induced degranulation by either NK cells or γδT cells from healthy donors was not impacted by co-culture with individual ISDs. However, CsA and TAC but not Prdl and AZA did inhibit the production of IFN-γ and TNF-α by both cell types. Flow cytometric analyses of RTX-induced activation of NK cells and γδT cells from LTRs suggested their capacity to degranulate was not markedly impacted by transplantation with similar levels of cells expressing CD107 pre- and post-LTx. However an impairment in the ability of NK cells to produce cytokines was observed in samples obtained post LTx whereas γδT cell cytokine responses were not significantly impacted.

CONCLUSIONS

In conclusion, the findings show that despite differences in the expression levels of CD16, γδT cells like NK cells can be readily activated by engagement with RTX and that in vitro exposure to CsA and TAC (calcineurin inhibitors) had a measurable effect on cytokine production but not degranulation by both NK cells and gdT cells from healthy donors. Finally the observation that in PBMC obtained from LTx recipients, NK cells but not γδT cells exhibited impaired cytokine reponses suggests that transplantation or chronic exposure to ISDs differentially impacts their potential to respond to the introduction of an allograft and/or transplant-associated infections.

Chimeric HLA antibody receptor T cells for targeted therapy of antibody-mediated rejection in transplantation

The presence of donor-specific antibodies (DSA), mainly against HLA, increases the risk of allograft rejection. Moreover, antibody-mediated rejection (ABMR) remains an important barrier to optimal long-term outcomes after solid organ transplantation. The development of chimeric autoantibody receptor T lymphocytes has been postulated for targeted therapy of autoimmune diseases. We aimed to develop a targeted therapy for DSA desensitization and ABMR, generating T cells with a chimeric HLA antibody receptor (CHAR) that specifically eliminates DSA-producing B cells. We have genetically engineered an HLA-A2-specific CHAR (A2-CHAR) and transduced it into human T cells. Then, we have performed in vitro experiments such as cytokine measurement, effector cell activation, and cytotoxicity against anti-HLA-A2 antibody-expressing target cells. In addition, we have performed A2-CHAR-Tc cytotoxic assays in an immunodeficient mouse model. A2-CHAR expressing T cells could selectively eliminate HLA-A2 antibody-producing B cells in vitro. The cytotoxic capacity of A2-CHAR expressing T cells mainly depended on Granzyme B release. In the NSG mouse model, A2-CHAR-T cells could identify and eradicate HLA-A2 antibody-producing B cells even when those cells are localized in the bone marrow. This ability is effector:target ratio dependent. CHAR technology generates potent and functional human cytotoxic T cells to target alloreactive HLA class I antibody-producing B cells. Thus, we consider that CHAR technology may be used as a selective desensitization protocol or an ABMR therapy in transplantation.

CD16+ natural killer cells in bronchoalveolar lavage are associated with antibody-mediated rejection and chronic lung allograft dysfunction

Acute and chronic rejections limit the long-term survival after lung transplant. Pulmonary antibody-mediated rejection (AMR) is an incompletely understood driver of long-term outcomes characterized by donor-specific antibodies (DSAs), innate immune infiltration, and evidence of complement activation. Natural killer (NK) cells may recognize DSAs via the CD16 receptor, but this complement-independent mechanism of injury has not been explored in pulmonary AMR. CD16⁺ NK cells were quantified in 508 prospectively collected bronchoalveolar lavage fluid samples from 195 lung transplant recipients. Associations between CD16⁺ NK cells and human leukocyte antigen mismatches, DSAs, and AMR grade were assessed by linear models adjusted for participant characteristics and repeat measures. Cox proportional hazards models were used to assess CD16⁺ NK cell association with chronic lung allograft dysfunction and survival. Bronchoalveolar lavage fluid CD16⁺ NK cell frequency was associated with increasing human leukocyte antigens mismatches and increased AMR grade. Although NK frequencies were similar between DSA+ and DSA- recipients, CD16⁺ NK cell frequencies were greater in recipients with AMR and those with concomitant allograft dysfunction. CD16⁺ NK cells were associated with long-term graft dysfunction after AMR and decreased chronic lung allograft dysfunction-free survival. These data support the role of CD16⁺ NK cells in pulmonary AMR.

Conditional Knockout of Hypoxia-Inducible Factor 1-Alpha in Tumor-Infiltrating Neutrophils Protects against Pancreatic Ductal Adenocarcinoma

Large numbers of neutrophils infiltrate tumors and comprise a notable component of the inflammatory tumor microenvironment. While it is established that tumor cells exhibit the Warburg effect for energy production, the contribution of the neutrophil metabolic state to tumorigenesis is unknown. Here, we investigated whether neutrophil infiltration and metabolic status promotes tumor progression in an orthotopic mouse model of pancreatic ductal adenocarcinoma (PDAC). We observed a large increase in the proportion of neutrophils in the blood and tumor upon orthotopic transplantation. Intriguingly, these tumor-infiltrating neutrophils up-regulated glycolytic factors and hypoxia-inducible factor 1-alpha (HIF-1α) expression compared to neutrophils from the bone marrow and blood of the same mouse. This enhanced glycolytic signature was also observed in human PDAC tissue samples. Strikingly, neutrophil-specific deletion of HIF-1α (HIF-1αΔNφ) significantly reduced tumor burden and improved overall survival in orthotopic transplanted mice, by converting the pro-tumorigenic neutrophil phenotype to an anti-tumorigenic phenotype. This outcome was associated with elevated reactive oxygen species production and activated natural killer cells and CD8+ cytotoxic T cells compared to littermate control mice. These data suggest a role for HIF-1α in neutrophil metabolism, which could be exploited as a target for metabolic modulation in cancer.

How to improve results after DCD (donation after circulation death)

The shortage of organs for transplantation has led health professionals to look for alternative sources of donors. One of the avenues concerns donors who have died after circulatory arrest. This is a special situation because the organs from these donors are exposed to warm ischaemia-reperfusion lesions that are unavoidable during the journey of the organs from the donor to the moment of transplantation in the recipient. We will address and discuss the key issues from the perspective of team organization, legislation and its evolution, and the ethical framework. In a second part, the avenues to improve the quality of organs will be presented following the itinerary of the organs between the donor and the recipient. The important moments from the point of view of therapeutic strategy will be put into perspective. New connections between key players involved in pathophysiological mechanisms and implications for innate immunity and injury processes are among the avenues to explore. Technological developments to improve the quality of organs from these recipients will be analyzed, such as perfusion techniques with new modalities of temperatures and oxygenation. New molecules are being investigated for their potential role in protecting these organs and an analysis of potential prospects will be proposed. Finally, the important perspectives that seem to be favored will be discussed in order to reposition the use of deceased donors after circulatory arrest. The use of these organs has become a routine procedure and improving their quality and providing the means for their evaluation is absolutely inevitable.

Association of IL-15 and IP-10 Serum Levels with Cytomegalovirus Infection, CMV Viral Load and Cyclosporine Level after Kidney Transplantation

BACKGROUND

Cytomegalovirus (CMV) infection is the most common complications following kidney transplantation. Natural killer (NK) cells demonstrated critical anti-viral role in controlling and elimination of CMV after transplantation. Interleukin-15 (IL-15) is a pleiotropic cytokine that promotes the activity of NK cells and strengthens the acquired immune system. Also, IP10 (CXCL10) is a chemotactic factor which regulates NK cell recruitment and antiviral immune response. We aimed to determine the correlation between the serum levels of IL-15 and IP-10 cytokines with CMV infection, CMV viral load, and cyclosporine as a major immunosuppressive treatment after transplantation.

METHODS

Fifty-eight kidney transplant recipient patients without evidence of CMV virus disease before transplantation surgery were included in the study. From the day of transplant surgery, the patients were evaluated based on the presence of CMV Ag pp65, CMV viral load, serum levels of IL-15 & IP-10, Cyclosporine levels (C0 & C2), Glomerular Filtration Rate (GFR), and hematological & biochemical Index, up to 75 days.

RESULTS

Comparison analysis of serum levels of IL-15 and IP-10 showed no significant association with CMV infection in kidney transplant recipients. In addition, CMV viral load and cyclosporine levels at C0 and C2 did not affect patients' IL-15 and IP-10 levels.

CONCLUSION

The levels of IP-10 and IL-15 cytokines are not affected with CMV infection, even if a viral infection occurs in the early days after transplantation or long afterwards. In addition, taking the different levels of cyclosporine did not affect the cytokines levels. Other mechanisms may play a role in maintaining the levels of these cytokines.

Histologic Antibody-Mediated Kidney Allograft Rejection in the Absence of Donor Specific HLA Antibodies

Histologic antibody-mediated rejection (hAMR) is defined as a kidney allograft biopsy satisfying the first 2 Banff criteria for diagnosing antibody-mediated rejection (AMR): tissue injury and evidence of current/recent antibody interaction with the endothelium. In approximately one-half of such cases, circulating HLA donor specific antibodies (DSA) are not detectable by current methodology at the time of biopsy. Some studies indicated a better prognosis for HLA-DSA-negative cases of hAMR compared to those with detectable HLA-DSA, whereas others found equally poor survival compared to hAMR-negative cases. We reviewed the literature regarding the pathophysiology of HLA-DSA-negative hAMR. We find 3 nonmutually exclusive possibilities: 1) HLA-DSA are involved, but just not detected; 2) non-HLA DSA (allo- or autoantibodies) are pathogenically involved; and/or 3) antibody-independent NK cell activation is mediating the process through "missing self" or other activating mechanisms. These possibilities are discussed in detail. Recommendations regarding the approach to such patients are made. Clearly, more research is necessary regarding the measurement of non-HLA antibodies, recipient/donor NK cell genotyping, and the use of antibody reduction therapy or other immunosuppression in any subset of patients with HLA-DSA-negative hAMR.

Natural Killer Cell Alloreactivity Against Human Induced Pluripotent Stem Cells and Their Neuronal Derivatives into Dopaminergic Neurons

In recent years, great hope has arisen surrounding human stem cells, particularly human induced pluripotent stem (hiPS) cells, as nearly all human tissues can be derived from hiPS cells, using a specific protocol. Therefore, hiPS cells can be a source for replacing defective tissues and make up for the lack of organ donors. However, the alloreactivity of hiPS cells and their derivatives in the context of transplantation remain unclear. Although immunosuppressive drugs can inhibit the T cell compartment, these drugs inhibit partially or not at all natural killer (NK) cells activity. Therefore, the alloreactivity of NK cells against transplanted cells remains to be established. To partially answer this question, we choose, as a model, the potential of cellular therapy for Parkinson's disease (PD). First, we established the in vitro derivation of hiPS cells into mature dopaminergic (mDOPA) neurons, going through an intermediate step called neurosphere (NS) cells. These different cells population were cultured with or without interferon gamma (IFN-γ). They were characterized phenotypically regarding their morphology, and the expression of specific ligands for NK cell receptors expressed by these cells types was investigated. NK cells were isolated from the peripheral blood of healthy donors and cultured in the presence of interleukin 15, to be activated. To test NK cell alloreactivity, a cytotoxic assay was performed with hiPS cells, NS cells, and mDOPA neurons (IFN-γ treated or not) cocultured with allogenic NK cells. Our results show that allogenic NK cells kill hiPS cells (IFN-γ treated or not), but IFN-γ-treated NS cells were protected from killing by allogenic NK cells, compared with untreated NS cells. Finally, mDOPA neurons (IFN-γ treated or not) were partially protected against allogenic NK cell killing. These results indicate that derivatives of hiPS cells, especially NS cells, could be a good product for allogenic transplantation in cellular therapy for PD.

Effects of Antirejection Drugs on Innate Immune Cells After Kidney Transplantation

Over the last decades, our understanding of adaptive immune responses to solid organ transplantation increased considerably and allowed development of immunosuppressive drugs targeting key alloreactive T cells mechanism. As a result, rates of acute rejection dropped and short-term graft survival improved significantly. However, long-term outcomes are still disappointing. Recently, increasing evidence supports that innate immune responses plays roles in allograft rejection and represents a valuable target to further improve long-term allograft survival. Innate immune cells are activated by molecules with stereotypical motifs produced during injury (i.e., damage-associated molecular patterns, DAMPS) or infection (i.e., pathogen-associated molecular patterns, PAMPs). Activated innate immune cells can exert direct pro- and anti-inflammatory effects, while also priming adaptive immune responses. These cells are activated after transplantation by multiple stimuli, including ischemia-reperfusion injury, rejection, and infections. Data from animal models of graft rejection, show that inhibition of innate immunity promotes development of tolerance. Therefore, understanding mechanisms of innate immunity is important to improve graft outcomes. This review discusses effects of currently used immunosuppressive agents on innate immune responses in kidney transplantation.

Distinct Effects of Immunosuppressive Drugs on the Anti-Aspergillus Activity of Human Natural Killer Cells

As the prognosis of invasive aspergillosis remains unacceptably poor in patients undergoing hematopoietic stem cell transplantation (HSCT), there is a growing interest in the adoptive transfer of antifungal effector cells, such as Natural Killer (NK) cells. Because immunosuppressive agents are required in most HSCT recipients, knowledge of the impact of these compounds on the antifungal activity of NK cells is a prerequisite for clinical trials. We, therefore, assessed the effect of methylprednisolone (mPRED), cyclosporin A (CsA) and mycophenolic acid (MPA) at different concentrations on proliferation, apoptosis/necrosis, and the direct and indirect anti-Aspergillus activity of human NK cells. Methylprednisolone decreased proliferation and increased apoptosis of NK cells in a significant manner. After seven days, a reduction of viable NK cells was seen for all three immunosuppressants, which was significant for MPA only. Cyclosporin A significantly inhibited the direct hyphal damage by NK cells in a dose-dependent manner. None of the immunosuppressive compounds had a major impact on the measured levels of interferon-γ, granulocyte-macrophage colony-stimulating factor and RANTES (regulated on activation, normal T cell expressed and secreted; CCL5). Our data demonstrate that commonly used immunosuppressive compounds have distinct effects on proliferation, viability and antifungal activity of human NK cells, which should be considered in designing studies on the use of NK cells for adoptive antifungal immunotherapy.

Natural Killer Cells Promote Kidney Graft Rejection Independently of Cyclosporine A Therapy

Natural Killer (NK) cells have recently been recognized as key players in antibody-mediated chronic allograft failure, thus requiring a comprehensive understanding whether NK cells can escape conventional immunosuppressive regimens. Influence of cyclosporine A (CyA) on NK cell function was studied in a mouse model of allogeneic kidney transplantation (KTX, BALB/c to C57BL/6). Recipients were treated daily with CyA (10 mg/kg) for seven or 14 days for long term survival (day 56). Administration of CyA in recipients resulted in significantly reduced frequencies of intragraft and splenic CD8⁺ T cells, whereas the latter illustrated reduced IFNγ production. In contrast, intragraft and splenic NK cell frequencies remained unaffected in CyA recipients and IFNγ production and degranulation of NK cells were not reduced as compared with controls. Depletion of NK cells in combination with CyA resulted in an improvement in kidney function until day 7 and prolonged graft survival until day 56 as compared to untreated controls. Surviving animals demonstrated higher intragraft frequencies of proliferating CD4⁺FoxP3⁺Ki67⁺ regulatory T (T_REG) cells as well as higher frequencies of CD8⁺CD122⁺ T_REG. We here demonstrate that NK cell depletion combined with CyA synergistically improves graft function and prolongs graft survival, suggesting that NK cell targeting constitutes a novel approach for improving KTX outcomes.

Delay expression of NKp30 on NK cells correlates with long-term mycophenolate mofetil treatment and higher EBV viremia post allogenic hematological stem cells transplantation

Mycophenolate mofetil (MMF) is an immunosuppressive agent that is widely used in graft-versus-host disease prophylaxis because of its inhibitory function on T cells and B cells. However, the effect of MMF on natural killer cell reconstitution after allogenic hematological transplantation is largely unknown. The present study examined the effects of different MMF administration durations after haploidentical allo-HSCT on NK cell reconstitution. Ninety patients were enrolled in this study and defined into two groups in term of MMF duration. We found that MMF patients in the long-term MMF group were associated with a poor reconstitution of NK cells and a significantly lower cytotoxicity from day 30 to day 180 post-transplantation. Especially, the long-term MMF group inhibits reconstitution of NKp30 NK subsets, which correlated with higher risk of EBV viremia. Multivariate analysis showed that a better reconstitution of NKp30 cells was associated with lower EBV viremia (HR0.957, p = .04). In vitro experiments demonstrated that the active metabolite of MMF, mycophenolic acid (MPA), inhibited the proliferation and cytotoxicity of NK cells from healthy donors or patients at day 30 post-transplantation. In summary, our findings demonstrated that long-term MMF administration delayed the quality and quantity of NK cells, especially NKp30 subpopulations, which was associated with decreased EBV viremia post allogeneic HSCT.

Rapamycin downregulates NKG2D ligands in acute myeloid leukemia cells via an activation of the STAT3 pathway: a potential mechanism for rapamycin-induced immune escape in leukemia

Background

The constitutive activation of the mammalian target of rapamycin (mTOR) is involved in the pathogenesis of many cancers. Rapamycin (RAPA), a specific inhibitor of mTOR, has been applied to the clinical treatment of tumors, and its anti-leukemia effect has also been confirmed.

Methods

We detected apoptosis and the NKG2D ligands expression in acute myeloid leukemia (AML) cells using flow cytometry and investigated the cytotoxicity of AML cells that had been co-cultured with natural killer (NK) cells using CFSE staining. We evaluated the signal pathways with a western blot assay.

Results

In this study, we found that RAPA can significantly inhibit the proliferation of AML cells. Further studies showed that the use of RAPA alone reduced the expression of NKG2D ligands on the membranes of HL-60 and THP-1 AML cells. Also, RAPA blocked the upregulation of the NKG2D ligand when AML cells were cultured with the demethylation drug decitabine (DAC). We found that RAPA decreased the expression of the NKG2D ligands by inducing the STAT3 phosphorylation of AML cells.

Conclusions

The discovery of this mechanism might further optimize the clinical use of RAPA for the treatment of AML.

Small-Molecule Immunosuppressive Drugs and Therapeutic Immunoglobulins Differentially Inhibit NK Cell Effector Functions in vitro

Small-molecule immunosuppressive drugs (ISD) prevent graft rejection mainly by inhibiting T lymphocytes. Therapeutic immunoglobulins (IVIg) are used for substitution, antibody-mediated rejection (AbMR) and HLA-sensitized recipients by targeting distinct cell types. Since the effect of ISD and IVIg on natural killer (NK) cells remains somewhat controversial in the current literature, the aim of this comparative study was to investigate healthy donor's human NK cell functions after exposure to ISD and IVIg, and to comprehensively review the current literature. NK cells were incubated overnight with IL2/IL12 and different doses and combinations of ISD and IVIg. Proliferation was evaluated by ³[H]-thymidine incorporation; phenotype, degranulation and interferon gamma (IFNγ) production by flow cytometry and ELISA; direct NK cytotoxicity by standard ⁵¹[Cr]-release and non-radioactive DELFIA assays using K562 as stimulator and target cells; porcine endothelial cells coated with human anti-pig antibodies were used as targets in antibody-dependent cellular cytotoxicity (ADCC) assays. We found that CD69, CD25, CD54, and NKG2D were downregulated by ISD. Proliferation was inhibited by methylprednisolone (MePRD), mycophenolic acid (MPA), and everolimus (EVE). MePRD and MPA reduced degranulation, MPA only of CD56^bright NK cells. MePRD and IVIg inhibited direct cytotoxicity and ADCC. Combinations of ISD demonstrated cumulative inhibitory effects. IFNγ production was inhibited by MePRD and ISD combinations, but not by IVIg. In conclusion, IVIg, ISD and combinations thereof differentially inhibit NK cell functions. The most potent drug with an effect on all NK functions was MePRD. The fact that MePRD and IVIg significantly block NK cytotoxicity, especially ADCC, has major implications for AbMR as well as therapeutic strategies targeting cancer and immune cells with monoclonal antibodies.

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.

Early Everolimus Initiation Fails to Counteract the Cytotoxic Response Mediated by CD8+ T and NK Cells in Heart Transplant Patients

The positive long-term effects of conversion to everolimus (EVL) after heart transplantation (HT) have been evaluated in several studies. However, the timing of EVL initiation, the best way to combine it with other immunosuppressive treatments, and the impact of these combinations on the immune response are poorly understood aspects. Here, we analyzed the immune phenotype and function of HT patients (n = 56) at short and long terms (prospective and retrospective cohorts), taking into account the time of EVL initiation: early (3 months post-transplant, EVL-E group) or late (>1 year post-transplant, EVL-L group) compared with mycophenolate mofetil treatment (MMF group). We show that early EVL conversion from MMF allows the increase of cytotoxic (CD56^dim CD16⁺) NK and effector-memory (EM, CD45RA⁻ CCR7⁻) CD8⁺ T cell subsets, which show a significantly higher level of expression of cytotoxic molecules, IFN-γ production and degranulation ability under activation. NK cell expansion is accompanied by an altered balance of receptor expression, increasing the activation state, and lytic activity of those cells. Those changes are detected after as little as 1 month after EVL conversion in association with the expansion of regulatory T cells and the decrease in B cell frequency. However, no changes in the immune cells subsets were observed after late EVL initiation (EVL-L) compared with the MMF group. Our results imply that only early EVL conversion induces key changes in the post-transplant immune response, preserving an efficient anti-viral response, but simultaneously showing a limited ability to counteract the cytotoxic response to the allograft.

Impact of Steroids on Natural Killer Cells Against Cytotoxicity and Hepatitis C Virus Replication

BACKGROUND

Natural killer (NK) cells play important roles in killing tumor and virus-infected cells. Immunosuppression used after organ transplantation is thought to increase the risk of tumor recurrence and viral infections. However, the effect of immunosuppressive drugs on NK cells has not yet been clearly established. Therefore, we examined the effect of immunosuppression on NK cells.

METHODS

NK cells were cultured for 7 days in the presence of interleukin-2 (100 U/mL) with or without the following immunosuppressive drugs: tacrolimus, cyclosporine A, corticosteroid (methylprednisolone [MP]), mycophenolate mofetil, and rapamycin. The effect of the drugs on NK cell activation was tested on the basis of the following: NK cell phenotype, NK cell proliferation, cytotoxicity against K562 cells, cytokine production by NK cells, and anti-hepatitis C virus (HCV) activity with HCV genomic replicon cells.

RESULTS

NK cells showed relatively robust functions in the presence of tacrolimus and cyclosporine A. Mycophenolate mofetil and rapamycin significantly prevented only NK cell proliferation (P < .05). In contrast, MP significantly inhibited the proliferation, cytotoxicity, and anti-HCV effect (10.9%, 18.5%, and 1.9%, respectively) of NK cells. Furthermore, MP specifically inhibited the expression of NK cell activation markers and the production of interferon-γ (P < .05).

CONCLUSIONS

Corticosteroids have distinct effects on NK cells, which may have important implications for NK cell function in cytotoxicity and HCV effect after transplantation.

The Role of NK Cells in Pig-to-Human Xenotransplantation

Recruitment of human NK cells to porcine tissues has been demonstrated in pig organs perfused ex vivo with human blood in the early 1990s. Subsequently, the molecular mechanisms leading to adhesion and cytotoxicity in human NK cell-porcine endothelial cell (pEC) interactions have been elucidated in vitro to identify targets for therapeutic interventions. Specific molecular strategies to overcome human anti-pig NK cell responses include (1) blocking of the molecular events leading to recruitment (chemotaxis, adhesion, and transmigration), (2) expression of human MHC class I molecules on pECs that inhibit NK cells, and (3) elimination or blocking of pig ligands for activating human NK receptors. The potential of cell-based strategies including tolerogenic dendritic cells (DC) and regulatory T cells (Treg) and the latest progress using transgenic pigs genetically modified to reduce xenogeneic NK cell responses are discussed. Finally, we present the status of phenotypic and functional characterization of nonhuman primate (NHP) NK cells, essential for studying their role in xenograft rejection using preclinical pig-to-NHP models, and summarize key advances and important perspectives for future research.

KIR and their HLA Class I ligands: Two more pieces towards completing the puzzle of chronic rejection and graft loss in kidney transplantation

BACKGROUND

Kidney transplantation is a life-saving treatment for patients with end-stage renal disease. However, despite progress in surgical techniques and patient management, immunological rejection continues to have a negative impact on graft function and overall survival. Incompatibility between donors and recipients for human leukocyte antigens (HLA) of the major histocompatibility complex (MHC) generates a series of complex cellular and humoral immune response mechanisms that are largely responsible for rejection and loss of graft function. Within this context, a growing amount of evidence shows that alloreactive natural killer (NK) cells play a critical role in the immune response mechanisms elicited by the allograft. Killer immunoglobulin-like receptors (KIRs) are prominent mediators of NK cell alloreactivity.

METHODS AND FINDINGS

A cohort of 174 first cadaveric kidney allograft recipients and their donors were selected from a total cohort of 657 transplanted patients for retrospective immunogenetic analyses. Patients with HLA Class II mismatches were excluded. HLA Class I allele frequencies were compared among patients with chronic rejection, patients with stable graft function and a group of 2388 healthy controls. Activating and inhibitory KIR gene frequencies, KIR haplotypes, KIR-HLA ligand matches/mismatches and combinations of recipient KIRs and donor HLA Class I ligands were compared among patients with and without chronic rejection and a group of 221 healthy controls. Patients transplanted from donors homozygous for HLA-C1 antigens had a significantly higher risk for chronic rejection than patients transplanted from donors homozygous or heterozygous for HLA-C2 antigens or with epitopes belonging to the HLA-Bw4 ligand group. The Kaplan-Meier curves obtained by dividing the patients into 3 groups according to the presence or absence of one or both of the combinations of recipient KIRs and donor HLA ligands (rKIR2DL1/dHLA-C2 and rKIR3DL1/dHLA-Bw4) showed a significantly higher cumulative incidence of chronic rejection in the group of patients completely lacking these functional units. These patients showed a progressively stronger decline in modification of diet in renal disease-estimated glomerular filtration rate.

CONCLUSIONS

KIR genotyping should be performed at the time of enrolment of patients on the waiting list for organ transplantation. In our study, a significantly higher risk of chronic rejection after kidney transplantation was observed when recipient (r) and donor (d) pairs completely lacked the two functional rKIR-dHLA ligand combinations rKIR2DL1/dHLA-C2 and rKIR3DL1/dHLA-Bw4. This immunogenetic profile corresponds to low levels of NK cell inhibition. Therefore, patients with this high risk profile could benefit from immunosuppressive therapy aimed at reducing NK-cell cytotoxicity.

In-vitro influence of mycophenolate mofetil (MMF) and Ciclosporin A (CsA) on cytokine induced killer (CIK) cell immunotherapy

Background

Cytokine-induced-killer (CIK) cells are a promising immunotherapeutic approach for impending relapse following hematopoietic stem cell transplantation (HSCT). However, there is a high risk for treatment failure associated with severe graft versus host disease (GvHD) necessitating pharmaceutical intervention post-transplant. Whether immunosuppression with mycophenolate mofetil (MMF) or Ciclosporin A (CsA) influences the cytotoxic effect of CIK cell immunotherapy is still an open issue.

Methods

CIK cells were generated from PBMC as previously described followed by co-incubation with mycophenolic acid (MPA) or CsA. Proliferation, cytotoxicity and receptor expression were investigated following short- (24 h), intermediate- (3 days) and long-term (7 days) MPA incubation with the intention to simulate the in vivo situation when CIK cells were given to a patient with relevant MPA/CsA plasma levels.

Results

Short-term MPA treatment led to unchanged proliferation capacity and barely had any effect on viability and cytotoxic capability in vitro. The composition of CIK cells with respect to T-, NK-like T- and NK cells remained stable. Intermediate MPA treatment lacked effects on NKG2D, FasL and TRAIL receptor expression, while an influence on proliferation and viability was detectable. Furthermore, long-term treatment significantly impaired proliferation, restricted viability and drastically reduced migration-relevant receptors accompanied by an alteration in the CD4/CD8 ratio. CD3⁺CD56⁺ cells upregulated receptors relevant for CIK cell killing and migration, whereas T cells showed the most interference through significant reductions in receptor expression. Interestingly, CsA treatment had no significant influence on CIK cell viability and the cytotoxic potential against K562.

Conclusions

Our data indicate that if immunosuppressant therapy is indispensable, efficacy of CIK cells is maintained at least short-term, although more frequent dosing might be necessary.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1024-4) contains supplementary material, which is available to authorized users.

mTOR Regulation of Lymphoid Cells in Immunity to Pathogens

Immunity to pathogens exists as a fine balance between promoting activation and expansion of effector cells, while simultaneously limiting normal and aberrant responses. These seemingly opposing functions are kept in check by immune regulators. The mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that senses nutrient availability and, in turn, regulates cell metabolism, growth, and survival accordingly. mTOR plays a pivotal role in facilitating immune defense against invading pathogens by regulating the differentiation, activation, and effector functions of lymphoid cells. Here, we focus on the emerging and sometimes contradictory roles of mTOR in orchestrating lymphoid cell-mediated host immune responses to pathogens. A thorough understanding of how mTOR impacts lymphoid cells in pathogen defense will provide the necessary base for developing therapeutic interventions for infectious diseases.

Added effects of dexamethasone and mesenchymal stem cells on early Natural Killer cell activation

Graft rejection and graft-versus-host disease are leading causes of transplant related mortality despite advancements in immunosuppressive therapy. Mesenchymal stem cells (MSCs) offer a promising addition to immunosuppressive drugs (ISD), while NK-cells are increasingly used as effector cells in graft-versus-leukemia. Combined therapy of ISD, NK-cells and/or MSCs is used in clinical practice. Here, we examined the effects of MSCs and selected ISD (tacrolimus, cyclosporin A, mycophenolic acid, dexamethasone) treatment on early NK-cell activation. We assessed STAT4 and STAT5 phosphorylation triggered by IL-12 and IL-2, respectively. Furthermore, we determined IFNγ, perforin production and the expression pattern of selected NK-cell receptors. Of all drugs tested, only dexamethasone inhibited NK-cell STAT4 and STAT5 phosphorylation. All ISD, with the exception of MPA, significantly inhibited IFNγ, and only dexamethasone inhibited upregulation of early activation markers CD69 and CD25 (IL-2 condition only). MSCs inhibited IL-2 induced NK cell STAT5 phosphorylation, IFNγ production and CD69 upregulation, and IL-12 induced IFNγ and perforin production. While MSCs mediated inhibition of CD69 expression was cell contact dependent, inhibition of IFNγ and perforin production, as well as STAT5 phosphorylation was cell-contact independent. Importantly, dexamethasone augmented MSCs mediated inhibition of both IL-12 and IL-2 induced CD69 expression and IFNγ production, as well as IL-2 induced STAT5 phosphorylation. Taken together, these novel insights may help the design of future NK-cell and MSCs based immunotherapy.

The Role of Natural Killer Cells in Humoral Rejection

Antibody-mediated rejection (AMR) has been identified among the most important factors limiting long-term outcome in cardiac and renal transplantation. Therapeutic management remains challenging and the development of effective treatment modalities is hampered by insufficient understanding of the underlying pathophysiology. However, recent findings indicate that in addition to AMR-triggered activation of the classical complement pathway, antibody-dependent cellular cytotoxicity by innate immune cell subsets also promotes vascular graft injury. This review summarizes the accumulating evidence for the contribution of natural killer cells, the key mediators of antibody-dependent cellular cytotoxicity, to human AMR in allotransplantation and xenotransplantation and illustrates the current mechanistic conceptions drawn from animal models.

NK Cell Subgroups, Phenotype, and Functions After Autologous Stem Cell Transplantation

High-dose chemotherapy with consecutive autologous stem cell transplantation (autoSCT) is a well-established treatment option for patients suffering from malignant lymphoma or multiple myeloma. Natural killer (NK) cells are an important part of the immune surveillance, and their cell number after autoSCT is predictive for progression-free and overall survival. To improve knowledge about the role of NK cells after autoSCT, we investigated different NK cell subgroups, their phenotype, and their functions in patients treated with autoSCT. Directly after leukocyte regeneration (>1000 leukocytes/μl) following autoSCT, CD56⁺⁺ NK cells were the major NK cell subset. Surprisingly, these cells showed unusually high surface expression levels of CD57 and killer Ig-like receptors (KIRs) compared to expression levels before or at later time points after autoSCT. Moreover, these NK cells strongly upregulated KIR2DL2/3/S2 and KIR3DL1, whereas KIR2DL1/S1 remained constant, indicating that this cell population arose from more immature NK cells instead of from activated mature ones. Remarkably, NK cells were already able to degranulate and produce IFN-γ and MIP-1β upon tumor interaction early after leukocyte regeneration. In conclusion, we describe an unusual upregulation of CD57 and KIRs on CD56⁺⁺ NK cells shortly after autoSCT. Importantly, these NK cells were functionally competent upon tumor interaction at this early time point.

The Aryl Hydrocarbon Receptor Antagonist StemRegenin1 Improves In Vitro Generation of Highly Functional Natural Killer Cells from CD34(+) Hematopoietic Stem and Progenitor Cells

Early natural killer (NK)-cell repopulation after allogeneic stem cell transplantation (allo-SCT) has been associated with reduced relapse rates without an increased risk of graft-versus-host disease, indicating that donor NK cells have specific antileukemic activity. Therefore, adoptive transfer of donor NK cells is an attractive strategy to reduce relapse rates after allo-SCT. Since NK cells of donor origin will not be rejected, multiple NK-cell infusions could be administered in this setting. However, isolation of high numbers of functional NK cells from transplant donors is challenging. Hence, we developed a cytokine-based ex vivo culture protocol to generate high numbers of functional NK cells from granulocyte colony-stimulating factor (G-CSF)-mobilized CD34(+) hematopoietic stem and progenitor cells (HSPCs). In this study, we demonstrate that addition of aryl hydrocarbon receptor antagonist StemRegenin1 (SR1) to our culture protocol potently enhances expansion of CD34(+) HSPCs and induces expression of NK-cell-associated transcription factors promoting NK-cell differentiation. As a result, high numbers of NK cells with an active phenotype can be generated using this culture protocol. These SR1-generated NK cells exert efficient cytolytic activity and interferon-γ production toward acute myeloid leukemia and multiple myeloma cells. Importantly, we observed that NK-cell proliferation and function are not inhibited by cyclosporin A, an immunosuppressive drug often used after allo-SCT. These findings demonstrate that SR1 can be exploited to generate high numbers of functional NK cells from G-CSF-mobilized CD34(+) HSPCs, providing great promise for effective NK-cell-based immunotherapy after allo-SCT.

A phase I/II trial of interleukin-15--stimulated natural killer cell infusion after haplo-identical stem cell transplantation for pediatric refractory solid tumors

BACKGROUND AIMS

Preliminary data suggest that T-cell-depleted haplo-identical stem cell transplantation (haplo-SCT) has a clinically beneficial allograft-versus-tumor effect associated with natural killer (NK) cell immune reconstitution.

METHODS

This phase I/II trial descriptively evaluates the feasibility of interleukin (IL)-15-stimulated NK cell infusion after haplo-SCT in pediatric patients with refractory solid tumors.

RESULTS

Six patients received an IL-15-stimulated NK cell infusion at 30 days after haplo-SCT. The mean number of infused NK cells per product was 11.3 × 10(6)/kg (range, 3-27 × 10(6)/kg). The T-cell count was <1 × 10(3)/kg in all patients (range, 0-0.75 × 10(3)/kg). No toxic effects related to IL-15--stimulated NK cell infusion were observed. Four of the six patients showed a clinical response (one achieved very good partial remission, two achieved partial remission and one had stable disease). One patient had progressive disease, and the response was not evaluated in the remaining patient. After a median follow-up period of 310 days, all patients had died: four of cancer relapse, one of cancer-associated thrombotic micro-angiopathy and one of acute graft-versus-host disease.

CONCLUSIONS

The adoptive transfer of allogeneic IL-15--stimulated NK cells might be feasible and safe in heavily pretreated pediatric patients with refractory solid tumors, though the advanced stage of disease and toxic effects of haplo-SCT may limit the efficacy of NK cell infusion in this population.

Reconstitution of natural killer cells in HLA-matched HSCT after reduced-intensity conditioning: impact on clinical outcome

Recent advances in the development of reduced-intensity conditioning (RIC) have allowed a broader range of patients to access allogeneic hematopoietic stem cell transplantation (HSCT). Reconstitution of an effective immune system post-transplant, including natural killer (NK) cells, is critical for both tumor control and infectious disease control or prevention. The development and functions of NK cells in such settings remain elusive. Here we analyzed NK cell development in HLA-matched HSCT from related or unrelated donors, after RIC that included antithymocyte globulin (N = 45 patients). Our data reveal that NK cells quickly recover after RIC-HSCT, irrespective of donor type. Rapidly re-emerging NK cells, however, remain immature for more than 6 months. Effector functions resemble that of immature NK cells because they poorly produce IFN-γ and TNF-α in response to target cell stimulation, despite a rapid acquisition of degranulation ability and MIP-1β production. Strikingly, rapid reconstitution of cytokine production correlates with a lower relapse incidence (P = .01) and a better survival rate (P < .0001) at 1 year post-transplant, whereas degranulation capacity was associated with less relapse (P = .05). Our study demonstrates rapid quantitative reconstitution of the NK cell compartment despite administration of potent immune suppressive drugs as part of the conditioning regimen and after transplantation. However, there is a prolonged persistence of functional defects, the correction of which positively correlates with clinical outcome.

IL-27 stimulates human NK-cell effector functions and primes NK cells for IL-18 responsiveness

IL-27, a member of the IL-12 family of cytokines, is produced by APCs, and displays pro- and anti-inflammatory effects. How IL-27 affects human NK cells still remains unknown. In this study, we observed that mature DCs secreted IL-27 and that blockade of IL-27R (CD130) reduced the amount of IFN-γ produced by NK cells during their coculture, showing the importance of IL-27 during DC-NK-cell crosstalk. Accordingly, human rIL-27 stimulated IFN-γ secretion by NK cells in a STAT1-dependent manner, induced upregulation of CD25 and CD69 on NK cells, and displayed a synergistic effect with IL-18. Preincubation experiments demonstrated that IL-27 primed NK cells for IL-18-induced IFN-γ secretion, which was associated with an IL-27-driven upregulation of T-bet expression. Also, IL-27 triggered NKp46-dependent NK-cell-mediated cytotoxicity against Raji, T-47D, and HCT116 cells, and IL-18 enhanced this cytotoxic response. Such NK-cell-mediated cytotoxicity involved upregulation of perforin, granule exocytosis, and TRAIL-mediated cytotoxicity but not Fas-FasL interaction. Moreover, IL-27 also potentiated Ab-dependent cell-mediated cytotoxicity against mAb-coated target cells. Taken together, IL-27 stimulates NK-cell effector functions, which might be relevant in different physiological and pathological situations.

mTORC1-dependent metabolic reprogramming is a prerequisite for NK cell effector function

The mammalian target of rapamycin complex 1 (mTORC1) is a key regulator of cellular metabolism and also has fundamental roles in controlling immune responses. Emerging evidence suggests that these two functions of mTORC1 are integrally linked. However, little is known regarding mTORC1 function in controlling the metabolism and function of NK cells, lymphocytes that play key roles in antiviral and antitumor immunity. This study investigated the hypothesis that mTORC1-controlled metabolism underpins normal NK cell proinflammatory function. We demonstrate that mTORC1 is robustly stimulated in NK cells activated in vivo and in vitro. This mTORC1 activity is required for the production of the key NK cell effector molecules IFN-γ, which is important in delivering antimicrobial and immunoregulatory functions, and granzyme B, a critical component of NK cell cytotoxic granules. The data reveal that NK cells undergo dramatic metabolic reprogramming upon activation, upregulating rates of glucose uptake and glycolysis, and that mTORC1 activity is essential for attaining this elevated glycolytic state. Directly limiting the rate of glycolysis is sufficient to inhibit IFN-γ production and granzyme B expression. This study provides the highly novel insight that mTORC1-mediated metabolic reprogramming of NK cells is a prerequisite for the acquisition of normal effector functions.

Interleukin-2-stimulated natural killer cells are less susceptible to mycophenolate mofetil than non-activated NK cells: possible consequences for immunotherapy

In a clinical phase I/II trial, pediatric patients with high-risk malignancies were treated with ex vivo IL-2-stimulated donor natural killer (NK) cells after transplantation with haploidentical stem cells. To evaluate the potential negative effects of the immunosuppressive drug mycophenolate mofetil (MMF) used for immunotherapy, the functionality and signaling of ex vivo NK cells was investigated. Our results show that during NK cell expansion, long-term (9 days) incubation with mycophenolic acid (MPA), the active metabolite of MMF, in therapeutically relevant concentrations led to the severe inhibition of NK cell proliferation. This correlated with a significantly reduced cytokine/chemokine secretion and the inhibited acquisition of surface receptors regarding cytotoxicity (e.g., NKp30, NKp44, NKp46, NKG2D), adhesion/migration (e.g., ICAM-1/CD54, LFA-1/CD11a, CD62L, CXCR3) and activation (e.g., CD25). Moreover, MPA prevented phosphorylation of the central signaling molecules STAT-3/-4/-5, AKT and ERK1/2. In contrast, short-term (24 h) MPA incubation of IL-2-stimulated NK cells had no or only marginal effects on the activated NK cell phenotype, including receptor expression, cytokine/chemokine secretion and intracellular signaling. Further, short-term MPA incubation only moderately affected the highly cytotoxic activity of previously IL-2-stimulated NK cells. In conclusion, while long-term MPA incubation significantly compromised ex vivo NK cell functionality, previously IL-2-activated NK cells seemed to be rather resistant to short-term MPA treatment. This finding supports the use of IL-2-activated NK cells as immunotherapy, especially for patients treated with MMF after haploidentical stem cell transplantation.

Limited efficacy of immunosuppressive drugs on CD8+ T cell-mediated and natural killer cell-mediated lysis of human renal tubular epithelial cells

BACKGROUND

Although CD8+ T cell-mediated and natural killer (NK) cell-mediated cytotoxicity against renal tubular epithelial cells (TECs) plays a crucial role during rejection, the degree of inhibition of these lytic immune responses by immunosuppressive drugs is unknown. We investigated the CD8 T-cell and NK cell responses induced by TECs in vitro and questioned how these processes are affected by immunosuppressive drugs.

METHODS

Donor-derived TECs were co-cultured with recipient peripheral blood monocyte cells. Proliferation of CD8+ T cells and NK cell subsets was assessed using PKH dilution assay. CD107a degranulation and europium release assay were performed to explore CD8+-mediated and NK cell-mediated TEC lysis. Experiments were conducted in the absence or presence of tacrolimus (10 ng/mL), everolimus (10 ng/mL), and prednisolone (200 ng/mL).

RESULTS

Tubular epithelial cells induce significant CD8+ T-cell and NK cell proliferation. All immunosuppressive drugs significantly inhibited TEC-induced CD8+ T-cell proliferation. Interestingly, prednisolone was the most powerful inhibitor of NK cell proliferation. CD8-mediated and NK cell-mediated early lytic responses were marked by strong degranulation after an encounter of unstimulated TECs, represented by a high cell surface expression of CD107a. However, with the use of interferon-γ-activated and tumor necrosis factor-α-activated TECs, the NK degranulation response was significantly reduced and CD8 degranulation response was even more enhanced (P<0.05). Tubular epithelial cell-induced CD8 degranulation and CD8-mediated TEC lysis were preferentially inhibited by tacrolimus and prednisolone, and not by everolimus. Although tacrolimus showed the most inhibitory effect on the degranulation of NK cells, NK cell-mediated TEC lysis was efficiently inhibited by prednisolone (P<0.05).

CONCLUSION

Overall, our data point to a limited efficacy of immunosuppressive drugs on CD8+ T cell-mediated and NK cell-mediated lysis of human renal TECs.

Differential effects of mycophenolate mofetil and cyclosporine A on peripheral blood and cord blood natural killer cells activated with interleukin-2

BACKGROUND AIMS

Graft-versus-host disease remains a major cause of death after hematopoietic stem cell transplantation. Cyclosporine (CsA) and mycophenolate mofetil (MMF) have been successfully used alone or in combination as prophylaxis for graft-versus-host disease. Although the effects of these drugs on T cells have been studied, little is known about the effects of both drugs on natural killer (NK) cells. We examined if the sensitivity of umbilical cord blood (CB) NK cells to MMF and/or CsA differs from their adult counterparts.

METHODS

An approach that was based on flow cytometry and real-time polymerase chain reaction was used to assess the effects of MMF, CsA and the combination of both drugs on the viability, activation, proliferation and cytotoxicity of peripheral blood (PB) and CB NK cells after culture with interleukin-2.

RESULTS

MMF alone or together with CsA induced cell death of CB NK cells but not of PB NK cells. MMF and CsA had differential effects on NK cell activation but significantly reduced proliferation of CB NK cells. MMF reduced perforin expression by PB NK cells, whereas CsA alone or together with MMF drastically decreased degranulation of CB and PB NK cells. However, neither affected cytokine secretion by PB and CB NK cells.

CONCLUSIONS

This study showed that CB NK cells were more sensitive to MMF and CsA than were PB NK cells. MMF and CsA had significant effects on NK cells that could jeopardize the beneficial effects of NK cells after hematopoietic stem cell transplantation.

Alloimmune activation promotes anti-cancer cytotoxicity after rat liver transplantation

Liver transplantation for hepatocellular carcinoma (HCC) results in a specific condition where the immune response is potentially directed against both allogeneic and cancer antigens. We have investigated the level of anti-cancer immunity during allogeneic immune response. Dark Agouti-to-Lewis and Lewis-to-Lewis rat liver transplantations were performed and the recipients anti-cancer immunity was analysed at the time of alloimmune activation. The occurrence of rejection in the allogeneic recipients was confirmed by a shorter survival (p<0.01), increased liver function tests (p<0.01), the presence of signs of rejection on histology, and a donor-specific ex vivo mixed lymphocyte reaction. At the time of alloimmune activation, blood mononuclear cells of the allogeneic group demonstrated increased anti-cancer cytotoxicity (p<0.005), which was related to an increased natural killer (NK) cell frequency (p<0.05) and a higher monocyte/macrophage activation level (p<0.01). Similarly, liver NK cell anti-cancer cytotoxicity (p<0.005), and liver monocyte/macrophage activation levels (p<0.01) were also increased. The alloimmune-associated cytotoxicity was mediated through the NKG2D receptor, whose expression was increased in the rejected graft (p<0.05) and on NK cells and monocyte/macrophages. NKG2D ligands were expressed on rat HCC cells, and its inhibition prevented the alloimmune-associated cytotoxicity. Although waiting for in vivo validation, alloimmune-associated cytotoxicity after rat liver transplantation appears to be linked to increased frequencies and levels of activation of NK cells and monocyte/macrophages, and is at least in part mediated through the NKG2D receptor.

Fcγ-receptor IIIA polymorphism p.158F has no negative predictive impact on rituximab therapy with and without sequential chemotherapy in CD20-positive posttransplant lymphoproliferative disorder

We retrospectively analyzed the p.V158F polymorphism of Fcγ-receptor IIIA (FCGR3A, CD16) in patients with PTLD treated with rituximab monotherapy. Previous reports had indicated that the lower affinity F allele affects rituximab-mediated antibody-dependent cellular cytotoxicity (ADCC) and is linked to inferior outcome of rituximab monotherapy in B cell malignancies. 25 patients with PTLD after solid organ transplantation were included in this analysis. They had received 4 weekly doses of rituximab as part of two clinical trials, which had a rituximab monotherapy induction regimen in common. 16/25 patients received further treatment with CHOP-21 after rituximab monotherapy (PTLD-1, NCT01458548). The FCGR3A status was correlated to the response after 4 cycles of rituximab monotherapy. Response to rituximab monotherapy was not affected by F carrier status. This is in contrast to previous findings in B cell malignancies where investigators found a predictive impact of FCGR3A status on outcome to rituximab monotherapy. One explanation for this finding could be that ADCC is impaired in transplant recipients receiving immunosuppression. These results suggest that carrying a FCRG3A F allele does not negatively affect rituximab therapy in immunosuppressed patients.

Cyclosporine and tacrolimus have inhibitory effects on toll-like receptor signaling after liver transplantation

Toll-like receptors (TLRs) play a key role in transplantation biology. The effect of immunosuppression on TLR function after liver transplantation is unknown. Peripheral blood mononuclear cells (PBMCs) from 113 post-liver transplant patients and 13 healthy controls were stimulated with TLR-specific ligands [lipopolysaccharide (TLR4), pan-3-cys (P3C) (TLR2), Poly (I:C) (PIC) (TLR3), R848 (TLR7/8), and CpG (TLR9)] for 24 hours. PBMCs from 5 healthy controls were also cultured with therapeutic concentrations of cyclosporine A (CYA) and tacrolimus (TAC). Cytokine production was measured with enzyme-linked immunosorbent assays and flow cytometry. PBMCs from patients on calcineurin inhibitors after liver transplantation produced less interleukin-6 (IL-6) and tumor necrosis factor α (TNFα) in response to TLR2 stimulation (IL-6: P=0.02; TNFα: P=0.01), TLR4 stimulation (IL-6: P=0.02; TNFα: P=0.01), and TLR7/8 stimulation (IL-6: P=0.02; TNFα: P=0.02), compared with healthy controls. Both CD56(bright) and CD56(dim) natural killer (NK) cells from patients on calcineurin inhibitors also produced less interferon-γ (IFNγ) with TLR7/8 stimulation compared with healthy controls (CD56(bright) : P=0.002; CD56(dim) : P=0.004). Similar findings were demonstrated in healthy PBMCs cultured with CYA (PBMCs: TLR2, IL-6: P=0.005; TLR4, IL-6: P=0.03, TNFα: P=0.03; TLR7/8, IL-6: P=0.02, TNFα: P=0.01; CD56(dim) NK cells: TLR7/8, IFNγ: P=0.03). TAC impaired TLR4-mediated IL-6 and TNFα production by PBMCs (IL-6; P = 0.02; TNFα P = 0.009). In conclusion, patients on calcineurin inhibitors had impaired inflammatory cytokine production in response to TLR2, TLR4, and TLR7/8 stimulation compared comparison with healthy controls. Importantly, TAC and CYA appear to have different effects on TLR signaling. Impaired TLR function has important repercussions for risk of infection, graft rejection, and disease recurrence after transplantation, and the different immunosuppressive profiles of CYA and TAC may guide the choice of therapy to improve disease outcomes.

Impact of commonly used transplant immunosuppressive drugs on human NK cell function is dependent upon stimulation condition

Lung transplantation is a recognised treatment for patients with end stage pulmonary disease. Transplant recipients receive life-long administration of immunosuppressive drugs that target T cell mediated graft rejection. However little is known of the impact on NK cells, which have the potential to be alloreactive in response to HLA-mismatched ligands on the lung allograft and in doing so, may impact negatively on allograft survival. NK cells from 20 healthy controls were assessed in response to Cyclosporine A, Mycophenolic acid (MPA; active form of Mycophenolate mofetil) and Prednisolone at a range of concentrations. The impact of these clinically used immunosuppressive drugs on cytotoxicity (measured by CD107a expression), IFN-γ production and CFSE proliferation was assessed in response to various stimuli including MHC class-I negative cell lines, IL-2/IL-12 cytokines and PMA/Ionomycin. Treatment with MPA and Prednisolone revealed significantly reduced CD107a expression in response to cell line stimulation. In comparison, addition of MPA and Cyclosporine A displayed reduced CD107a expression and IFN-γ production following PMA/Ionomycin stimulation. Diminished proliferation was observed in response to treatment with each drug. Additional functional inhibitors (LY294002, PD98059, Rottlerin, Rapamycin) were used to elucidate intracellular pathways of NK cell activation in response to stimulation with K562 or PMA-I. CD107a expression was significantly decreased with the addition of PD98059 following K562 stimulation. Similarly, CD107a expression significantly decreased following PMA-I stimulation with the addition of LY294002, PD98059 and Rottlerin. Ten lung transplant patients, not receiving immunosuppressive drugs pre-transplant, were assessed for longitudinal changes post-transplant in relation to the administration of immunosuppressive drugs. Individual patient dynamics revealed different longitudinal patterns of NK cell function post-transplantation. These results provide mechanistic insights into pathways of NK cell activation and show commonly administered transplant immunosuppression agents and clinical rejection/infection events have differential effects on NK cell function that may impact the immune response following lung transplantation.

The Peripheral NK Cell Repertoire after Kidney Transplantation is Modulated by Different Immunosuppressive Drugs

In the context of kidney transplantation, little is known about the involvement of natural killer (NK) cells in the immune reaction leading to either rejection or immunological tolerance under immunosuppression. Therefore, the peripheral NK cell repertoire of patients after kidney transplantation was investigated in order to identify NK cell subsets that may be associated with the individual immune status at the time of their protocol biopsies for histopathological evaluation of the graft. Alterations in the peripheral NK cell repertoire could be correlated to the type of immunosuppression, i.e., calcineurin-inhibitors like Cyclosporin A vs. Tacrolimus with or without addition of mTOR inhibitors. Here, we could demonstrate that the NK cell repertoire in peripheral blood of kidney transplant patients differs significantly from healthy individuals. The presence of donor-specific antibodies was associated with reduced numbers of CD56^dim NK cells. Moreover, in patients, down-modulation of CD16 and CD6 on CD56^dim NK cells was observed with significant differences between Cyclosporin A- and Tac-treated patients. Tac-treatment was associated with decreased CD69, HLA-DR, and increased CD94/NKG2A expression in CD56^dim NK cells indicating that the quality of the immunosuppressive treatment impinges on the peripheral NK cell repertoire. In vitro studies with peripheral blood mononuclear cells of healthy donors showed that this modulation of CD16, CD6, CD69, and HLA-DR could also be induced experimentally. The presence of calcineurin or mTOR inhibitors had also functional consequences regarding degranulation and interferon-γ-production against K562 target cells, respectively. In summary, we postulate that the NK cell composition in peripheral blood of kidney transplanted patients represents an important hallmark of the efficacy of immunosuppression and may be even informative for the immune status after transplantation in terms of rejection vs. drug-induced allograft tolerance. Thus, NK cells can serve as sensors for immunosuppression and may be utilized for future strategies of an individualized adjustment of immunosuppression.

Clinical relevance of natural killer cells following hematopoietic stem cell transplantation

Natural killer (NK) cells are one of the first cells to recover following allogeneic hematopoietic stem cell transplantation (HSCT), and are believed to play an important role in facilitating engraftment or preventing post-transplant infection and tumor recurrence. Recent studies have provided novel insights into the mechanisms by which NK cells mediate these highly clinically relevant immunological functions. In particular, the ability of NK cells to reduce the risk of graft versus host disease (GVHD) and increase the graft versus leukemia effect (GVL) in the setting of human leukocyte antigen (HLA)-haploidentical HSCT highlights their clinical potentials. NK cells also mediate anti-viral protection, in particular against cytomegalovirus (CMV), an infection that causes significant morbidity and mortality following transplant. Another crucial function of NK cells is providing protection against bacterial infections at the mucosal barriers. NK cells achieve this by promoting anti-microbial defenses and regeneration of epithelial cells. These recent exciting findings provide a strong basis for the formulation of novel NK cell-based immunotherapies. In this review, we summarize the recent advances related to the mechanisms, functions, and future clinical prospects of NK cells that can impact post-transplant outcomes.

Nonobese diabetic natural killer cells: a barrier to allogeneic chimerism that can be reduced by rapamycin

BACKGROUND

Induction of allogeneic hematopoietic chimerism is a promising strategy to induce tolerance to donor islets for treating type 1 diabetes. Successful induction of chimerism requires overcoming host alloimmunity. In diabetes-prone nonobese diabetic (NOD) mice, this is challenging due to their general tolerance resistance. Although the adaptive alloimmunity of NOD mice is a known barrier to allogeneic chimerism, whether NOD natural killer (NK) cells are an additional barrier has not been examined. Because NOD NK cells exhibit functional defects, they may not inhibit chimerism generation.

METHODS

Antibody depletion of NK cells in vivo, or transplantation of F1 hybrid donor cells to eliminate the "missing-self" trigger of NK cells, was preformed to test the NK-mediated rejection of donor bone marrow cells. We also studied the capacity of rapamycin to block the NK cell response against allogeneic cells in vivo.

RESULTS

Depleting NK cells or rendering them unresponsive to the donor greatly improved the level of chimerism obtained in NOD mice. Rapamycin significantly reduced the resistance to allogeneic chimerism mounted by NOD NK cells; however, it was much less effective than NK cell depletion by antibodies.

CONCLUSIONS

Contrary to the view that NOD NK cells are defective, we found these cells to be a substantial barrier to allogeneic chimerism in the presence or absence of adaptive immunity. Moreover, rapamycin will need to be combined with other approaches to fully overcome the NK cell barrier.

In situ induction of dendritic cell-based T cell tolerance in humanized mice and nonhuman primates

Administration of an ICAM-1–specific antibody arrests dendritic cells in a semi-immature state and facilitates antigen-specific T cell tolerance to islet allografts in humanized mice and Rhesus monkeys.

Induction of antigen-specific T cell tolerance would aid treatment of diverse immunological disorders and help prevent allograft rejection and graft versus host disease. In this study, we establish a method of inducing antigen-specific T cell tolerance in situ in diabetic humanized mice and Rhesus monkeys receiving porcine islet xenografts. Antigen-specific T cell tolerance is induced by administration of an antibody ligating a particular epitope on ICAM-1 (intercellular adhesion molecule 1). Antibody-mediated ligation of ICAM-1 on dendritic cells (DCs) led to the arrest of DCs in a semimature stage in vitro and in vivo. Ablation of DCs from mice completely abrogated anti–ICAM-1–induced antigen-specific T cell tolerance. T cell responses to unrelated antigens remained unaffected. In situ induction of DC-mediated T cell tolerance using this method may represent a potent therapeutic tool for preventing graft rejection.

Liver transplantation for hepatocellular carcinoma: five steps to prevent recurrence

Liver transplantation is the best treatment of patients with unresectable early hepatocellular carcinoma, allowing disease-free survival rates of 60-80% at 5 years. Despite these good results, some 10% of recipients experience a posttransplant HCC recurrence, which leads to death in almost all patients. Recurrence is either due to the growth of occult metastases or to the engraftment of circulating tumor cells. It can be hypothesized that strategies to decrease the engraftment of circulating tumor cells could decrease the risk of recurrence and, in addition, extend access to transplantation to patients with more advanced HCC. These potential strategies can be schematized into five steps, including (1) selecting recipients with low baseline levels of circulating HCC cells, by adding biological markers (such as alpha fetoprotein or molecular signatures) to the accepted combination of morphological criteria; (2) decreasing the perioperative release of HCC cells, with careful perioperative handling of the tumors; (3) preventing the engraftment of circulating HCC cells by decreasing liver graft ischemia-reperfusion injury, which has been shown to promote cancer cell engraftment and growth; (4) using anticancer drugs, including mammalian target of rapamycin inhibitors and (5) tuning immunity toward HCC clearance.

KIR-ligand mismatches are associated with reduced long-term graft survival in HLA-compatible kidney transplantation

Natural killer (NK) cells are cytotoxic lymphocytes of the innate immune system with the ability to detect HLA class I disparities via killer-cell immunoglobulin-like receptors (KIR). To test whether such KIR-ligand mismatches contribute to the rejection of human solid allografts, we did a retrospective cohort study of 397 HLA-DR-compatible kidney transplantations and determined the KIR and HLA genotypes of recipients and the HLA genotypes of donors. In transplantations compatible for HLA-A, HLA-B and HLA-DR (n = 137), in which a role for T cells and HLA antibodies in rejection was minimized, KIR-ligand mismatches were associated with an approximately 25% reduction in 10-year death-censored graft survival (p = 0.043). This effect was comparable to the effect of classical HLA-A and HLA-B incompatibility, and in HLA-A,-B-incompatible transplantations (n = 260) no significant additional effect of KIR-ligand mismatches was observed. Multivariate Cox regression analysis confirmed the effect of KIR-ligand mismatching as an independent risk factor in HLA-A,-B,-DR-compatible transplantations (hazard ratio 2.29, range 1.03-5.10, p = 0.043). This finding constitutes the first indication that alloreactive NK cells may thwart the success of HLA-compatible kidney transplantations, and suggests that suppression of NK-cell activity can improve the survival of such kidney grafts.