The modulation of the cell-cycle: a sentinel to alert the NK cells of dangers

Natural killer (NK) cells are an essential component of innate immunity that provides a rapid response to detect stressed, infected, or transformed target cells. This system is controlled by a balance of inhibitory and activating signals transmitted by a myriad of receptors and their specific ligands. Inhibitory receptors mainly recognize self-MHC class-I molecules, whereas activating receptors, such as natural cytotoxic receptors, NKG2D, and DNAM-1, interact with self-proteins, normally not expressed on the cell surface of healthy cells, but up-regulated by cellular stress or infections and are frequently expressed on tumor cells. In these circumstances, regulatory controls ensure that specific ligands are induced mainly in diseased cells and not in normal cells. Each ligand seems to exhibit some distinct specializations providing broad “coverage” for numerous stresses associated with various diseases. Deregulated cell proliferation is a hallmark of these abnormal situations, and may serve as a sentinel for the elimination of the targets by NK cells. The purpose of this review is to discuss recent implications of cell-cycle to create a warning control system that relays various danger signals via specific ligands to the NK receptor system.

Constitutive expression of ligand for natural killer cell NKp44 receptor (NKp44L) by normal human articular chondrocytes

Normal chondrocytes display susceptibility to lysis by natural killer (NK) cells and this phenomenon may play a role in some inflammatory cartilage disorders. The mechanisms of chondrocyte recognition and killing by NK cells remain unclear. Using flow cytometry and immunohistochemical staining we found that normal human articular chondrocytes constitutively express a ligand for NKp44, one of stimulatory NK cell receptors involved in recognition and killing of target cells. Expression of NKp44 ligand by normal articular chondrocytes is not involved in their killing by unstimulated NK cells; however, it is responsible for anti-chondrocyte cytotoxicity mediated by long-term activated NK cells. Thus, expression of NKp44 ligand may play a role in chondrocyte destruction in course of chronic inflammatory cartilage disorders.

A single amino-acid change in a highly conserved motif of gp41 elicits HIV-1 neutralization and protects against CD4 depletion

BACKGROUND

The induction of neutralizing antibodies against conserved regions of the human immunodeficiency virus type 1 (HIV-1) envelope protein is a major goal of vaccine strategies. We previously identified 3S, a critical conserved motif of gp41 that induces the NKp44L ligand of an activating NK receptor. In vivo, anti-3S antibodies protect against the natural killer (NK) cell-mediated CD4 depletion that occurs without efficient viral neutralization.

METHODS

Specific substitutions within the 3S peptide motif were prepared by directed mutagenesis. Virus production was monitored by measuring the p24 production. Neutralization assays were performed with immune-purified antibodies from immunized mice and a cohort of HIV-infected patients. Expression of NKp44L on CD4(+) T cells and degranulation assay on activating NK cells were both performed by flow cytometry.

RESULTS

Here, we show that specific substitutions in the 3S motif reduce viral infection without affecting gp41 production, while decreasing both its capacity to induce NKp44L expression on CD4(+) T cells and its sensitivity to autologous NK cells. Generation of antibodies in mice against the W614 specific position in the 3S motif elicited a capacity to neutralize cross-clade viruses, notable in its magnitude, breadth, and durability. Antibodies against this 3S variant were also detected in sera from some HIV-1-infected patients, demonstrating both neutralization activity and protection against CD4 depletion.

CONCLUSIONS

These findings suggest that a specific substitution in a 3S-based immunogen might allow the generation of specific antibodies, providing a foundation for a rational vaccine that combine a capacity to neutralize HIV-1 and to protect CD4(+) T cells.

CMV drives clonal expansion of NKG2C+ NK cells expressing self-specific KIRs in chronic hepatitis patients

Natural killer (NK) cells are affected by infection with human cytomegalovirus (HCMV) manifested by increased expression of the HLA-E binding activating receptor NKG2C. We here show that HCMV seropositivity was associated with a profound expansion of NKG2C(+) CD56(dim) NK cells in patients with chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) infection. Multi-color flow cytometry revealed that the expanded NKG2C(+) CD56(dim) NK cells displayed a highly differentiated phenotype, expressed high amounts of granzyme B and exhibited polyfunctional responses (CD107a, IFN-γ, and TNF-α) to stimulation with antibody-coated as well as HLA-E expressing target cells but not when stimulated with IL-12/IL-18. More importantly, NKG2C(+) CD56(dim) NK cells had a clonal expression pattern of inhibitory killer cell immunoglobulin-like receptors (KIRs) specific for self-HLA class I molecules, with predominant usage of KIR2DL2/3. KIR engagement dampened NKG2C-mediated activation suggesting that such biased expression of self-specific KIRs may preserve self-tolerance and limit immune-pathology during viral infection. Together, these findings shed new light on how the human NK-cell compartment adjusts to HCMV infection resulting in clonal expansion and differentiation of educated and polyfunctional NK cells.

Viremic HIV infected individuals with high CD4 T cells and functional envelope proteins show anti-gp41 antibodies with unique specificity and function

BACKGROUND

CD4 T-cell decay is variable among HIV-infected individuals. In exceptional cases, CD4 T-cell counts remain stable despite high plasma viremia. HIV envelope glycoprotein (Env) properties, namely tropism, fusion or the ability to induce the NK ligand NKp44L, or host factors that modulate Env cytopathic mechanisms may be modified in such situation.

METHODS

We identified untreated HIV-infected individuals showing non-cytopathic replication (VL>10,000 copies/mL and CD4 T-cell decay<50 cells/µL/year, Viremic Non Progressors, VNP) or rapid progression (CD4 T-cells<350 cells/µL within three years post-infection, RP). We isolated full-length Env clones and analyzed their functions (tropism, fusion activity and capacity to induce NKp44L expression on CD4 cells). Anti-Env humoral responses were also analyzed.

RESULTS

Env clones isolated from VNP or RP individuals showed no major phenotypic differences. The percentage of functional clones was similar in both groups. All clones tested were CCR5-tropic and showed comparable expression and fusogenic activity. Moreover, no differences were observed in their capacity to induce NKp44L expression on CD4 T cells from healthy donors through the 3S epitope of gp41. In contrast, anti- Env antibodies showed clear functional differences: plasma from VNPs had significantly higher capacity than RPs to block NKp44L induction by autologous viruses. Consistently, CD4 T-cells isolated from VNPs showed undetectable NKp44L expression and specific antibodies against a variable region flanking the highly conserved 3S epitope were identified in plasma samples from these patients. Conversely, despite continuous antigen stimulation, VNPs were unable to mount a broad neutralizing response against HIV.

CONCLUSIONS

Env functions (fusion and induction of NKp44L) were similar in viremic patients with slow or rapid progression to AIDS. However, differences in humoral responses against gp41 epitopes nearby 3S sequence may contribute to the lack of CD4 T cell decay in VNPs by blocking the induction of NKp44L by gp41.

Unconventional repertoire profile is imprinted during acute chikungunya infection for natural killer cells polarization toward cytotoxicity

Chikungunya virus (CHIKV) is a worldwide emerging pathogen. In humans it causes a syndrome characterized by high fever, polyarthritis, and in some cases lethal encephalitis. Growing evidence indicates that the innate immune response plays a role in controlling CHIKV infection. We show here that CHIKV induces major but transient modifications in NK-cell phenotype and function soon after the onset of acute infection. We report a transient clonal expansion of NK cells that coexpress CD94/NKG2C and inhibitory receptors for HLA-C1 alleles and are correlated with the viral load. Functional tests reveal cytolytic capacity driven by NK cells in the absence of exogenous signals and severely impaired IFN-γ production. Collectively these data provide insight into the role of this unique subset of NK cells in controlling CHIKV infection by subset-specific expansion in response to acute infection, followed by a contraction phase after viral clearance.

Chikungunya virus (CHIKV) infection, which is responsible for devastating human illness, is rapidly becoming a global concern. The spread of this disease throughout tropical areas, where it now affects nearly 40 countries, underlines the need to improve our understanding of this infection. In 2008, CHIKV was listed as a US National Institute of Allergy and Infectious Disease (NIAID) category C priority pathogen. Natural killer (NK) cells are cytotoxic effector cells that play a vital role in the innate immune system by limiting acute infection, as previously described for several other diseases. This report describes the first phenotypic and functional analysis of NK cells soon after infection by this virus. The key element of this study was the detailed analysis of the expansion of NK cells. Coexpression of NKG2C activating receptors and HLA-C1 ligands is associated with viral load, impaired IFN-γ production, and significant cytolytic functions. We found that NK cells were able to sense CHIKV from the beginning of infection and contributed to the clearance of the infected cells through the expansion of a unique NK-cell subset.

Phenotype and function of natural killer cells in systemic lupus erythematosus: excess interferon-γ production in patients with active disease

OBJECTIVE

To determine the phenotype and the functionality of natural killer (NK) cells in patients with systemic lupus erythematosus (SLE).

METHODS

A total of 94 patients with SLE (91 women and 3 men) were compared with 26 healthy controls. Active SLE was defined by an SLE Disease Activity Index score≥4. Immunologic tests were performed using nonactivated and/or interleukin-2 (IL-2)-activated peripheral blood mononuclear cells. NK cell phenotype was determined by flow cytometry. NK cell natural cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC) were determined by 51Cr release and CD107a degranulation experiments. Intracellular interferon-γ (IFNγ) production by NK cells was evaluated after overnight stimulation with IL-12 and IL-18. IFNα levels were assessed using an antiviral cytopathic bioassay.

RESULTS

The absolute NK cell count was decreased in patients with active SLE, but the relative frequencies of total CD3-CD56bright NK cells and CD3-CD56dim NK cells were unaffected. The CD3-CD56dim NK cells in patients with active SLE displayed unique phenotypic characteristics, including significant increases in CD69 and NKG2A and decreased expression of Fcγ receptor type IIIa/CD16, CD8α, and the killer cell immunoglobulin-like receptor (KIR) KIR2DL1/KIR2DS1. Concomitant with these findings, NK cells from SLE patients had lower cytotoxicity but a normal level of ADCC compared with NK cells from healthy controls. There was a significant positive correlation between the increased level of IFNα in the serum and the enhanced frequency of IFNγ+ cells in patients with active SLE (r=0.370, P=0.04).

CONCLUSION

NK cells in patients with active SLE display phenotypic and functional features associated with activation. Furthermore, NK cells from patients with active SLE have the capacity to produce large amounts of IFNγ. This could contribute to the dysregulation of the link between innate and adaptive immunity seen in SLE.

Profound coordinated alterations of intratumoral NK cell phenotype and function in lung carcinoma

Both the innate and adaptive immune systems contribute to tumor immunosurveillance in mice and humans; however, there is a paucity of direct evidence of a role for natural killer (NK) cells in this important process. In this study, we investigated the intratumoral phenotypic profile and functions of NK cells in primary human tumor specimens of non-small cell lung carcinoma (NSCLC). We used in situ methods to quantify and localize NK cells using the NKp46 marker and we characterized their phenotype in blood, tumoral, and nontumoral samples of NSCLC patients. Intratumoral NK cells displayed a profound and coordinated alteration of their phenotype, with a drastic reduction of NK cell receptor expression specifically detected in the tumoral region. According to their altered phenotype, intratumoral NK cells exhibited profound defects in the ability to activate degranulation and IFN-γ production. We found that the presence of NK cells did not impact the clinical outcome of patients with NSCLC. Finally, we showed that tumor cells heterogeneously express ligands for both activating and inhibitory NK receptors. Taken together, our results suggest that the NSCLC tumor microenvironment locally impairs NK cells, rendering them less tumorcidal and thereby supportive to cancer progression.

CD56brightCD16+ NK cells: a functional intermediate stage of NK cell differentiation

Human NK cells comprise two main subsets, CD56(bright) and CD56(dim) cells, which differ in function, phenotype, and tissue localization. To further dissect the differentiation from CD56(bright) to CD56(dim) cells, we performed ex vivo and in vitro experiments demonstrating that the CD56(bright)CD16(+) cells are an intermediate stage of NK cell maturation. We observed that the maximal frequency of the CD56(bright)CD16(+) subset among NK cells, following unrelated cord blood transplantation, occurs later than this of the CD56(bright)CD16(-) subset. We next performed an extensive phenotypic and functional analysis of CD56(bright)CD16(+) cells in healthy donors, which displayed a phenotypic intermediary profile between CD56(bright)CD16(-) and CD56(dim)CD16(+) NK cells. We also demonstrated that CD56(bright)CD16(+) NK cells were fully able to kill target cells, both by Ab-dependent cell cytotoxicity (ADCC) and direct lysis, as compared with CD56(bright)CD16(-) cells. Importantly, in vitro differentiation experiments revealed that autologous T cells specifically encourage the differentiation from CD56(bright)CD16(-) to CD56(bright)CD16(+) cells. Finally, further investigations performed in elderly patients clearly showed that both CD56(bright)CD16(+) and CD56(dim)CD16(+) mature subsets were substantially increased in older individuals, whereas the CD56(bright)CD16(-) precursor subset was decreased. Altogether, these data provide evidence that the CD56(bright)CD16(+) NK cell subset is a functional intermediate between the CD56(bright) and CD56(dim) cells and is generated in the presence of autologous T CD3(+) cells.

Role of natural killer cells in hematopoietic stem cell transplantation: myth or reality?

Natural killer (NK) cells play a crucial role in the innate immune system and are responsible for the initial responses in the surveillance against malignant cells and virally infected cells. NK cells express their own repertoire of receptors, including activating and inhibitory receptors, which bind to major histocompatibility complex class I or class-I-related molecules. Binding of NK cell inhibitory receptors to their major histocompatibility complex class I ligands protects the target cells from NK cell-mediated cytotoxicity. NK cell alloreactivity has been put to use in allogeneic hematopoietic stem cell transplantation to reduce the rate of relapse and of graft-versus-host disease. A variety of findings have been observed in clinical studies, showing either beneficial or deleterious effects on clinical outcome. This article reviews the results of major clinical trials in relation to the model used to define NK cell alloreactivity.

Infusion of allogeneic natural killer cells in a patient with acute myeloid leukemia in relapse after haploidentical hematopoietic stem cell transplantation

BACKGROUND

Allogeneic donor natural killer (NK)-cell infusion (NK-DLI) is a promising immunotherapy for patients with hematologic disorders.

CASE REPORT

This report describes the case of a patient who received a single haploidentical NK-DLI for a relapse of acute myeloid leukemia (AML) after haploidentical hematopoietic stem cell transplantation. He underwent a cytoreductive, immunosuppressive regimen before NK-DLI and received high-dose interleukin-2 in vivo for 8 weeks afterward.

RESULTS

No major adverse effect was observed. Prospective phenotypic and functional studies of the NK cells showed major expansion of infused NK cells and, more importantly, of the alloreactive KIR2DL1+KIR2DL2/DL3-NKG2A- subset, which reached 117×10(6) cells/L on Day +14 after NK-DLI, the greatest expansion of infused alloreactive NK cells reported so far. Infused NK cells conserved their lytic capacities against K562 target cells and primary AML-mismatched blasts.

CONCLUSION

We review the literature to clarify these data and to detail the indications for allogeneic NK-DLI, the criteria for determining the most suitable donor, the types of conditioning regimens, and the procedures for selecting and activating NK cells.

Association of KIR2DS1 and KIR2DS3 with fatal outcome in Ebola virus infection

Zaïre ebolavirus (ZEBOV) infection rapidly outruns the host's immunity and leads to death within a week. Fatal cases have been associated with an aberrant innate, proinflammatory immune response followed by a suppressed adaptive response leading to the rapid depletion of peripheral NK cells and lymphocytes. A critical role for NK cells has been suggested but not elucidated. In this genetic study, we investigated the association of KIR genotype with disease outcome by comparing genotypes of a Gabonese control population, IgG+ contacts, survivors, and fatalities of ZEBOV infection. We showed that the activating KIR2DS1 and KIR2DS3 genes associate with fatal outcome in Ebola virus infection. In addition, this study brings supplemental evidence in favor of the specificity of the IgG+ contact population. The outcome of fulminating Ebola virus infection could depend in part on the host's inherited KIR gene repertoire. This supports a key role for KIRs in disease susceptibility to infections.

NK cell terminal differentiation: correlated stepwise decrease of NKG2A and acquisition of KIRs

BACKGROUND

Terminal differentiation of NK cells is crucial in maintaining broad responsiveness to pathogens and discriminating normal cells from cells in distress. Although it is well established that KIRs, in conjunction with NKG2A, play a major role in the NK cell education that determines whether cells will end up competent or hyporesponsive, the events underlying the differentiation are still debated.

METHODOLOGY/PRINCIPAL FINDINGS

A combination of complementary approaches to assess the kinetics of the appearance of each subset during development allowed us to obtain new insights into these terminal stages of differentiation, characterising their gene expression profiles at a pan-genomic level, their distinct surface receptor patterns and their prototypic effector functions. The present study supports the hypothesis that CD56dim cells derive from the CD56bright subset and suggests that NK cell responsiveness is determined by persistent inhibitory signals received during their education. We report here the inverse correlation of NKG2A expression with KIR expression and explore whether this correlation bestows functional competence on NK cells. We show that CD56dimNKG2A-KIR+ cells display the most differentiated phenotype associated to their unique ability to respond against HLA-E+ target cells. Importantly, after IL-12+IL-18 stimulation, reacquisition of NKG2A strongly correlates with IFN-gamma production in CD56dimNKG2A- NK cells.

CONCLUSIONS/SIGNIFICANCE

Together, these findings call for the reclassification of mature human NK cells into distinct subsets and support a new model, in which the NK cell differentiation and functional fate are based on a stepwise decrease of NKG2A and acquisition of KIRs.

Human NK cells display major phenotypic and functional changes over the life span

Aging is generally associated with an increased predisposition to infectious diseases and cancers, related in part to the development of immune senescence, a process that affects all cell compartments of the immune system. Although many studies have investigated the effects of age on natural killer (NK) cells, their conclusions remain controversial because the diverse health status of study subjects resulted in discordant findings. To clarify this situation, we conducted the first extensive phenotypic and functional analysis of NK cells from healthy subjects, comparing NK cells derived from newborn (cord blood), middle-aged (18-60 years), old (60-80 years), and very old (80-100 years) subjects. We found that NK cells in cord blood displayed specific features associated with immaturity, including poor expression of KIR and LIR-1/ILT-2 and high expression of both NKG2A and IFN-gamma. NK cells from older subjects, on the other hand, preserved their major phenotypic and functional characteristics, but with their mature features accentuated. These include a profound decline of the CD56(bright) subset, a specific increase in LIR-1/ILT-2, and a perfect recovering of NK-cell function following IL2-activation in very old subjects. We conclude that the preservation of NK cell features until very advanced age may contribute to longevity and successful aging.

HIV gp41 engages gC1qR on CD4+ T cells to induce the expression of an NK ligand through the PIP3/H2O2 pathway

CD4⁺ T cell loss is central to HIV pathogenesis. In the initial weeks post-infection, the great majority of dying cells are uninfected CD4⁺ T cells. We previously showed that the 3S motif of HIV-1 gp41 induces surface expression of NKp44L, a cellular ligand for an activating NK receptor, on uninfected bystander CD4⁺ T cells, rendering them susceptible to autologous NK killing. However, the mechanism of the 3S mediated NKp44L surface expression on CD4⁺ T cells remains unknown. Here, using immunoprecipitation, ELISA and blocking antibodies, we demonstrate that the 3S motif of HIV-1 gp41 binds to gC1qR on CD4⁺ T cells. We also show that the 3S peptide and two endogenous gC1qR ligands, C1q and HK, each trigger the translocation of pre-existing NKp44L molecules through a signaling cascade that involves sequential activation of PI3K, NADPH oxidase and p190 RhoGAP, and TC10 inactivation. The involvement of PI3K and NADPH oxidase derives from 2D PAGE experiments and the use of PIP3 and H2O2 as well as small molecule inhibitors to respectively induce and inhibit NKp44L surface expression. Using plasmid encoding wild type or mutated form of p190 RhoGAP, we show that 3S mediated NKp44L surface expression on CD4⁺ T cells is dependent on p190 RhoGAP. Finally, the role of TC10 in NKp44L surface induction was demonstrated by measuring Rho protein activity following 3S stimulation and using RNA interference. Thus, our results identify gC1qR as a new receptor of HIV-gp41 and demonstrate the signaling cascade it triggers. These findings identify potential mechanisms that new therapeutic strategies could use to prevent the CD4⁺ T cell depletion during HIV infection and provide further evidence of a detrimental role played by NK cells in CD4⁺ T cell depletion during HIV-1 infection.

HIV infected individuals suffer from a loss of CD4⁺ lymphocytes. Initially, dying CD4⁺ lymphocytes are mainly infected ones. Afterward, the great majority of dying CD4⁺ lymphocytes are uninfected. The cause of uninfected CD4⁺ lymphocyte death during HIV infection is still under debate. We previously showed that one of the HIV-1 envelop proteins, gp41, induces the expression of a stress molecule called NKp44L on the surface of uninfected CD4⁺ lymphocytes. Uninfected CD4⁺ lymphocytes expressing NKp44L are killed, in vitro and in vivo, by cells of the immune system called NK cells. In this report, we study the CD4⁺ lymphocyte's proteins involved in the expression of NKp44L. To do so, we used several techniques to identify interacting or differentially expressed proteins and to inhibit or monitor enzymes activity. We also induce NKp44L using the product of some of the proteins involved in NKp44L expression. We found that HIV-1 gp41 binds to its receptor gC1qR on CD4⁺ lymphocytes. This interaction respectively activates the PI3K, the NADPH oxidase and p190 RhoGAP which inactivates TC10. Using the obtained data we build a model of the protein cascade involved in NKp44L surface expression.

Persistent chronic inflammation and infection by Chikungunya arthritogenic alphavirus in spite of a robust host immune response

Alphaviruses, including Chikungunya virus (CHIKV), produce a transient illness in humans, but severe forms leading to chronic incapacitating arthralgia/arthritis have been reported by mechanisms largely ill-characterized. The pathogenesis of CHIKV was addressed in a prospective cohort study of 49 hospitalized patients from Reunion Island subsequently categorized into two distinct groups at 12 mo postinfection. Comprehensive analyses of the clinical and immunological parameters throughout the disease course were analyzed in either the "recovered" or the "chronic" groups to identify prognostic markers of arthritis-like pathology after CHIKV disease. We found that the chronic group consisted mainly of more elderly patients (>60 y) and with much higher viral loads (up to 10(10) viruses per milliliter of blood) during the acute phase. Remarkably, a rapid innate immune antiviral response was demonstrated by robust dendritic/NK/CD4/CD8 cell activation and accompanied by a rather weak Th1/Th2 cytokine response in both groups. Interestingly, the antiviral immune response witnessed by high levels of IFN-alpha mRNA in PBMCs and circulating IL-12 persisted for months only in the chronic group. CHIKV (RNA and proteins) was found in perivascular synovial macrophages in one chronic patient 18 mo postinfection surrounded by infiltrating NK and T cells (CD4(++) but rare cytotoxic CD8). Fibroblast hyperplasia, strong angiogenesis, tissue lesions given the high levels of matrix metalloproteinase 2, and acute cell death [high cleaved poly(ADP-ribose) polymerase staining] were observed in the injured synovial tissue. These observed cellular and molecular events may contribute to chronic arthralgia/arthritis targeted by methotrexate used empirically for effective treatment but with immunosuppressive function in a context of viral persistence.

HLA-E upregulation on IFN-gamma-activated AML blasts impairs CD94/NKG2A-dependent NK cytolysis after haplo-mismatched hematopoietic SCT

Natural killer (NK) cells generated after haploidentical hematopoietic SCT in patients with AML are characterized by specific phenotypic features and impaired functioning that may affect transplantation outcome. We show that IFN-gamma produced by immature CD56(bright) NK cells upregulates cell surface expression of HLA-E on AML blasts and that this upregulation protects leukemic cells from NK-mediated cell lysis through the mediation of CD94/NKG2A, an inhibitory receptor overexpressed on NK cells after haploidentical SCT. Two years after transplantation, however, maturing NK cells were functionally active, as evidenced by high cytotoxicity and poor IFN-gamma production. This implies that maturation of NK cells is the key to improved immune responses and transplantation outcome.

Fully functional NK cells after unrelated cord blood transplantation

Promising results of umbilical cord blood transplantation (UCBT) from unrelated donors have been reported in patients with hematologic disorders. These transplants, having potential to trigger beneficial donor-versus-recipient natural killer (NK) cell-mediated alloreaction, we have conducted the first extensive analysis of the phenotypic and functional properties of NK cells after UCBT. NK cells from 25 patients with high-risk hematologic malignancies were compared with cells derived from both healthy adult and CB cells. We found that following UCBT, NK cells display not only some phenotypic features associated with maturity but also unique characteristics that make them fully functional against leukemic blasts. We propose that this full functionality of alloreactive donor-derived NK may drive graft-versus-leukemia reactions after UCBT.

[Towards a vaccine for HIV infection: role of the gp41 envelope protein]

HIV infection leads to a gradual deterioration in immune status. The mechanisms underlying CD4 T cell depletion in this setting are controversial. One of the most intriguing phenomena is that many uninfected CD4 cells die prematurely in HIV-infected subjects. We therefore investigated the possibility that these cells are killed by a collateral effector mechanism. Here we show that a cellular ligand for the natural cytotoxicity receptor NKp44 (NKp44L) is expressed during HIV infection, and that its expression correlates both with CD4 T cell depletion and with an increase in viral load. CD4+ T cells expressing the NKp44L ligand are highly sensitive to the lytic activity of NKp44+ NK cells. NKp44L ligand expression is strongly induced by the highly conserved 3S motif of the HIV-1 envelope protein gp41. Anti-3S antibodies, detected early in the disease, protect CD4+ T cells from NK-mediated lysis during incubation with 3S. In addition, anti-3S antibody titers correlate positively with CD4+ T cell numbers and negatively with NKp44L expression on CD4 T cells. To determine whether anti-3S immunization might prevent NKp44L expression on CD4 T cells in vivo and thereby prevent the decline in CD4 T cells, macaques were immunized with 3S and then infected with the simian virus SHIV162P3. 3S peptide vaccination elicited antibodies that prevented CD4+ T cell depletion (percentage and absolute number), and also NK activation and cytotoxicity, without halting virus replication. These data raise new questions on HIV infection and point to novel preventive and therapeutic vaccine strategies.

NKG2C is a major triggering receptor involved in the V[delta]1 T cell-mediated cytotoxicity against HIV-infected CD4 T cells

BACKGROUND

Gammadelta T cells share with natural killer (NK) cells many effector capabilities and cell-surface proteins, including the NKG2 receptor family. A subset of gammadelta T cells that express the variable Vdelta1 region plays a critical role in immune regulation, tumour surveillance and viral infection. Dramatic expansion of Vdelta1 T cells has been observed in HIV disease.

OBJECTIVE

To determine if NKG2C expression on Vdelta1 T cells during HIV-1 infection is correlated with CD4 cell count and involved in lysis of CD4 T cells.

METHODS

gammadelta T cells from viraemic HIV-infected patients were examined. Expression of NK cell markers was analyzed by flow cytometry. The cytolytic activity of Vdelta1 T cells was determined by either Cr-release assays or degranulation assays against HLA-E-transfected 721.221 cells or HIV-infected CD4 primary T cells.

RESULTS

The expression of C-type lectin NKG2 receptors was sharply modulated on gammadelta T cells in patients with HIV infection. A profound decrease of Vdelta1 T cells bearing inhibitory NKG2A receptors corresponded to a drastic expansion of a distinct population of Vdelta1 T cells expressing a functional activating NKG2C receptor. Engagement of HLA-E, the ligand of both NKG2A and NKG2C, which is specifically induced on HIV-infected CD4 T cells, substantially enhanced the Vdelta1 T cell-mediated cytotoxicity.

CONCLUSIONS

These results raise the possibility that induction of NKG2C expression on Vdelta1 T cells plays a key role in the destruction of HIV-infected CD4 T cells during HIV disease.

Specific adaptive humoral response against a gp41 motif inhibits CD4 T-cell sensitivity to NK lysis during HIV-1 infection

OBJECTIVE

We have recently found that during HIV-1 infection, CD4 T cells overexpress a ligand of the NK activating receptor NKp44 (NKp44L) and are sensitized to NK lysis. Expression of NKp44L is triggered by a motif (3S) from the gp41, highly conserved in all HIV-1 clades. The objectives were to determine whether anti-3S antibodies were produced, could counteract 3S-CD4 interactions and were correlated to CD4 cell count and NKp44L expression in HIV-infected patients.

DESIGN

Anti-3S antibodie production was studied in HIV-infected patients at various stages of the disease, including a longitudinal study in Asymptomatiques à Long Terme (ALT) patients.

METHODS

Specimens from 193 HIV-1 infected patients were examined. Anti-3S antibodies were detected by ELISA, and NKp44L expression was analysed by flow cytometry. NK cytotoxicity against CD4NKp44L cells was determined in the presence of anti-3S antibodies.

RESULTS

Anti-3S antibodies were detected in 28.5% of HIV-infected patients. They were positively correlated to CD4 cell counts (P = 0.01) and inversely correlated to NKp44L expression (P = 0.007). Particularly, in ALT patients, a longitudinal study revealed that the CD4 cell count slope differed according to the presence or absence of anti-3S antibodies (-0.98 cells/month versus -7.48 cells/month, P > 0.001). In addition, a clear inhibition of CD4NKp44L NK lysis was observed in relationship to anti-3S antibodies titres.

CONCLUSIONS

These results strongly suggested that anti-3S antibodies might affect disease course in inhibiting NKp44L expression and CD4 sensitivity to NK lysis. In linking specific adaptive immunity to the innate immunity induced by the 3S motif, this study may have important implications for therapeutic vaccines against AIDS.

Persistence of CD16+/CD56-/2B4+ natural killer cells: a highly dysfunctional NK subset expanded in ocular myasthenia gravis

We report a case of myasthenia gravis associated with marked expansion of an unusual CD16(+)CD56(-)2B4(+) NK subset. These atypical cells were characterized by poor cytotoxicity against CD48(+) target cells and high proliferation due to 2B4/CD48 interaction. IL18, IFN-gamma and TGF-beta levels were profoundly different in this patient than in healthy donors. Immunosuppressive treatment induced disease remission and decreased the CD16(+)CD56(-)2B4(+)NK cells count. Our data suggest that expansion of this NK subset in myasthenia gravis patients may account for the deleterious NK cell functioning that occurs in this autoimmune disease.

NK cytotoxicity against CD4+ T cells during HIV-1 infection: a gp41 peptide induces the expression of an NKp44 ligand

HIV infection leads to a state of chronic immune activation and progressive deterioration in immune function, manifested most recognizably by the progressive depletion of CD4+ T cells. A substantial percentage of natural killer (NK) cells from patients with HIV infection are activated and express the natural cytotoxicity receptor (NCR) NKp44. Here we show that a cellular ligand for NKp44 (NKp44L) is expressed during HIV-1 infection and is correlated with both the progression of CD4+ T cell depletion and the increase of viral load. CD4+ T cells expressing this ligand are highly sensitive to the NK lysis activity mediated by NKp44+ NK cells. The expression of NKp44L is induced by the linear motif NH2-SWSNKS-COOH of the HIV-1 envelope gp41 protein. This highly conserved motif appears critical to the sharp increase in NK lysis of CD4+ T cells from HIV-infected patients. These studies strongly suggest that induction of NKp44L plays a key role in the lysis of CD4+ T cells by activated NK cells in HIV infection and consequently provide a framework for considering how HIV-1 may use NK cell immune surveillance to trigger CD4+ T cells. Understanding this mechanism may help to develop future therapeutic strategies and vaccines against HIV-1 infection.

NK-cell reconstitution after haploidentical hematopoietic stem-cell transplantations: immaturity of NK cells and inhibitory effect of NKG2A override GvL effect

Natural killer (NK) cell alloreactivity is reported to mediate strong GvL (graft versus leukemia) effect in patients after haploidentical stem-cell transplantation (SCT) for acute myeloid leukemia (AML). Because subsequent immune reconstitution remains a major concern, we studied NK-cell recovery in 10 patients with AML who received haplomismatched SC transplants, among whom no GvL effect was observed, despite the mismatched immunoglobulin-like receptor (KIR) ligand in the GvH direction for 8 of 10 patients. NK cells generated after SCT exhibited an immature phenotype: the cytotoxic CD3- CD56(dim) subset was small, expression of KIRs and NKp30 was reduced, while CD94/NKG2A expression was increased. This phenotype was associated to in vitro lower levels of cytotoxicity against a K562 cell line and against primary mismatched AML blasts than donor samples. This impaired lysis was correlated with CD94/NKG2A expression in NK cells. Blockading CD94/NKG2A restored lysis against the AML blasts, which all expressed HLA-E, the ligand for CD94/NKG2A. Our present study allows a better understanding of the NK-cell differentiation after SCT. These results revealed that the NK cells generated after haplomismatched SCT are blocked at an immature state characterized by specific phenotypic features and impaired functioning, having potential impact for immune responsiveness and transplantation outcome.

A non-classical ISRE/ISGF3 pathway mediates induction of RANTES gene transcription by type I IFNs

RANTES (regulated upon activation normal T cell expressed and secreted) is a chemoattractant cytokine important in the generation of inflammatory responses and human immunodeficiency virus resistance. In hematopoietic cells, RANTES is over-expressed by type I interferons (IFN-alpha and IFN-beta). The upstream region of the RANTES gene promoter contains a distal low affinity IFN-stimulated response element (ISRE). Specific mutagenesis in this ISRE-like motif abolished the activation of RANTES transcription by type I IFNs. Examination of the ISRE binding factors strongly suggested that signal transducer and activator of transcription (Stat)-2 and p48/IFN-stimulated gene factor 3gamma (ISGF3gamma) are not required for the induction of RANTES by type I IFNs. The specific requirement of Stat-1 was demonstrated using Stat-1-deficient U3A cells. These results revealed a non-classical ISRE/ISGF3 signal transduction pathway for the induction of RANTES by type I IFNs.

Inhibition of human immunodeficiency virus transmission to CD4+ T cells after gene transfer of constitutively expressed interferon beta to dendritic cells

CD34(+)-derived dendritic cells (DCs) can be infected by the T cell-tropic HIVLAI strain, but are poorly permissive for efficient virus production. However, HIVLAI-infected DCs are able to transmit a vigorous cytopathic infection to activated CD4(+) T cells. We show that DCs differentiated from CD34(+) cells can be efficiently transduced by a retroviral vector carrying the IFN-beta coding sequence. This results in resistance to infection by HIV as shown by a threefold reduction in the HIV DNA copy number per cell, and by inhibition of HIV transmission from DCs to CD4(+) T cells. Moreover, constitutive IFN-beta production by DCs increases the synthesis of IL-12 and IFN-gamma Th1-type cytokines and of the beta-chemokines MIP-1alpha, MIP-1beta, and RANTES. This indicates that IFN-beta transduction of DCs blocks HIV infection and viral transmission to CD4(+) T cells, and could favor cellular immune responses in HIV-infected patients.

Retrovirally mediated IFN-beta transduction of macrophages induces resistance to HIV, correlated with up-regulation of RANTES production and down-regulation of C-C chemokine receptor-5 expression

Constitutive expression of IFN-beta by HIV target cells may be an alternative or complementary therapeutic approach for the treatment of AIDS. We show that macrophages derived from CD34+ cells from umbilical cord blood can be efficiently transduced by a retroviral vector carrying the IFN-beta coding sequence. This results in resistance to infection by a macrophage-tropic HIV type 1, as shown by the drastic reduction in the HIV DNA copy number per cell and in p24 release. Moreover, IFN-beta transduction totally blocked secretion of proinflammatory cytokines after HIV infection. The constitutive IFN-beta production also resulted in an increased production of IL-12 and IFN-gamma Th1-type cytokines and of the beta-chemokines macrophage-inflammatory protein-1alpha, macrophage-inflammatory protein-1beta, and RANTES. RANTES was found to be involved in the HIV resistance observed, and this was correlated with a down-regulation of the CCR-5 HIV entry coreceptor. These results demonstrate the feasibility and the efficacy of such IFN-beta-mediated gene therapy. In addition to inhibiting HIV replication, IFN-beta transduction could have beneficial immune effects in HIV-infected patients by favoring cellular immune responses.

Transfer of human CD4(+) T lymphocytes producing beta interferon in Hu-PBL-SCID mice controls human immunodeficiency virus infection

Beta interferon (IFN-beta) exerts pleiotropic antiretroviral activities and affects many different stages of the human immunodeficiency virus (HIV) infectious cycle in IFN-treated cells. To explore whether transfer of genetically engineered human CD4(+) T cells producing constitutively low amounts of IFN-beta can eradicate HIV in vivo, we developed a new Hu-PBL-SCID mouse model supporting a persistent, replicative HIV infection maintained by periodic reinoculations of activated human CD4(+) T cells. Transferring human CD4(+) T cells containing the IFN-beta retroviral vector drastically reduced the preexisting HIV infection and enhanced CD4(+) T-cell survival and Th1 cytokine expression. Furthermore, in 40% of the Hu-PBL-SCID mice engrafted with IFN-beta-transduced CD4(+) T cells, HIV-1 was undetectable in vivo as well as after cocultivation of mouse tissues with human phytohemagglutinin-stimulated lymphoblasts. These results indicate that a therapeutic strategy based upon IFN-beta transduction of CD4(+) T cells may be an approach to controlling a preexisting HIV infection and allowing immune restoration.

Cutting Edge: RANTES Regulates Fas Ligand Expression and Killing by HIV-Specific CD8 Cytotoxic T Cells

Based on the previous observation that RANTES mediates the cytotoxic activity of human HIV-specific CD8+ T cells via the chemokine receptor CCR3, we studied the effect of this chemokine on different effector CD8+ cytolytic cells requiring Fas/Fas ligand (FasL) or perforin-dependent pathway. In CTLs derived from PBMCs of HIV-infected patients, both the spontaneous and the RANTES-induced cytotoxicity were inhibited by anti-FasL neutralizing Abs. In contrast, allogeneic CTLs or NK cells killing through perforin were not affected by RANTES and anti-FasL Ab. Accordingly, RANTES enhanced the expression of FasL in a concentration- and time-dependent manner in HIV-specific CTLs, whereas anti-RANTES Ab decreased markedly FasL expression. Finally, cell surface expression of FasL protein in HIV-specific CTLs was also up-regulated by eotaxin, a selective ligand for CCR3. Our observations show that the action of RANTES via CCR3 is necessary to regulate FasL expression on HIV-specific CD8+ T cells that kill through the Fas/FasL pathway.

Cutting edge: RANTES regulates Fas ligand expression and killing by HIV-specific CD8 cytotoxic T cells

Based on the previous observation that RANTES mediates the cytotoxic activity of human HIV-specific CD8+ T cells via the chemokine receptor CCR3, we studied the effect of this chemokine on different effector CD8+ cytolytic cells requiring Fas/Fas ligand (FasL) or perforin-dependent pathway. In CTLs derived from PBMCs of HIV-infected patients, both the spontaneous and the RANTES-induced cytotoxicity were inhibited by anti-FasL neutralizing Abs. In contrast, allogeneic CTLs or NK cells killing through perforin were not affected by RANTES and anti-FasL Ab. Accordingly, RANTES enhanced the expression of FasL in a concentration- and time-dependent manner in HIV-specific CTLs, whereas anti-RANTES Ab decreased markedly FasL expression. Finally, cell surface expression of FasL protein in HIV-specific CTLs was also up-regulated by eotaxin, a selective ligand for CCR3. Our observations show that the action of RANTES via CCR3 is necessary to regulate FasL expression on HIV-specific CD8+ T cells that kill through the Fas/FasL pathway.

Acquired constitutive expression of interferon beta after gene transduction enhances human immunodeficiency virus type 1-specific cytotoxic T lymphocyte activity by a RANTES-dependent mechanism

CTL lines directed against HIV-1 antigens were generated from infected individuals and were transduced by the HMB-K(b)HuIFNbeta vector, resulting in low, constitutive expression of interferon beta (IFN-beta). The IFN-beta-transduced cells showed markedly increased HIV-1-specific, MHC class I-restricted CTL activity against HIV-1-LAI Gag, Pol, or Env antigens. This effect of IFN-beta was correlated with an overexpression of RANTES and completely abrogated by RANTES-blocking antibody. The present results provide the first evidence that IFN-beta transduction of CTL lines enhances HIV-specific cytotoxic activities through an upregulation of RANTES production. The efficient elimination of HIV-infected cells by IFN-beta-transduced CTL lines makes this gene therapy approach an attractive treatment for AIDS.

Interferon-beta-induced human immunodeficiency virus resistance in CD34(+) human hematopoietic progenitor cells: correlation with a down-regulation of CCR-5 expression

To explore the possibility of conferring a long-term resistance against human immunodeficiency virus (HIV) by a low continuous production of interferon-beta (IFN-beta) in hematopoietic progenitor cells, we transduced the human CD34(+) TF-1 cells with a retroviral vector ensuring IFN-beta production. The IFN-beta-transduction of TF-1 cells resulted in resistance to infection with HIV-LAI, as shown by the selective survival of IFN-beta-transduced CD4(+) cells and the protection against HIV-induced apoptosis. A similar response against HIV-LAI infection was obtained after pretreatment with 100 U/ml of recombinant IFN-alpha2b or IFN-beta. In contrast, after the addition of macrophage cell tropic (M cell-tropic) HIV strain, a treatment with exogenous IFN-alpha2b resulted in a >==10-fold lower protection compared with exogenous IFN-beta or IFN-beta transduction. This specific effect of IFN-beta on M cell-tropic HIV strains was correlated with a down-regulation of the CCR-5 chemokine receptor expression, corresponding to a novel antiviral effect of IFN-beta.

HIV-specific T cell cytotoxicity mediated by RANTES via the chemokine receptor CCR3

CC chemokines produced by CD8(+) T cells are known to act as HIV-suppressive factors. We studied the possible role of these chemokines in HIV-1-specific killing of target cells. We found that the activity of cytotoxic T lymphocytes (CTLs) in CTL lines or freshly isolated peripheral blood mononuclear cells from HIV-1-infected individuals is markedly enhanced by RANTES (regulated on activation, normal T cell expressed and secreted) and virtually abolished by an antibody neutralizing RANTES or the RANTES receptor antagonist RANTES(9-68). Lysis was mediated by CD8(+) major histocompatibility complex class I-restricted T cells and was obtained with target cells expressing epitopes of the HIV-1LAI proteins Gag, Pol, Env, and Nef. The cytolytic activity observed in the presence or absence of added RANTES could be abolished by pretreatment of the CTLs with pertussis toxin, indicating that the effect is mediated by a G protein-coupled receptor. The chemokines monocyte chemotactic protein (MCP)-3, MCP-4, and eotaxin acted like RANTES, whereas macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, MCP-1, and stromal cell-derived factor 1 were inactive, suggesting a role for the eotaxin receptor, CCR3, and ruling out the involvement of CCR1, CCR2, CCR5, and CXCR4. CTL activity was abrogated by an antibody that blocks CCR3, further indicating that specific lysis is triggered via this chemokine receptor. These observations reveal a novel mechanism for the induction of HIV-1-specific cytotoxicity that depends on RANTES acting via CCR3.

Interferon beta transduction of peripheral blood lymphocytes from HIV-infected donors increases Th1-type cytokine production and improves the proliferative response to recall antigens

We are developing a gene therapy method of HIV infection based on the constitutive low production of interferon (IFN) beta. Peripheral blood lymphocytes (PBL) from HIV-infected patients at different clinical stages of infection were efficiently transduced with the HMB-HbHuIFNbeta retroviral vector. The constitutive low production of IFN-beta in cultured PBL from HIV-infected patients resulted in a decreased viral production and an enhanced survival of CD4+ cells, and this protective effect was observed only in the PBL derived from donors having a CD4+ cell count above 200 per mm3. In IFN-beta-transduced PBL from healthy and from HIV-infected donors, the production of the Th1-type cytokines IFN-gamma and interleukin (IL)-12 was enhanced. In IFN-beta-transduced PBL from HIV-infected donors, the production of IL-4, IL-6, IL-10, and tumor necrosis factor alpha was maintained at normal levels, contrary to the increased levels produced by the untransduced PBL. The proliferative response to recall antigens was partially restored in IFN-beta-transduced PBL from donors with an impaired antigen response. Thus, in addition to inhibiting HIV replication, IFN-beta transduction of PBL from HIV-infected donors improves several parameters of immune function.

[Development of an anti-HIV gene therapy based on the antiviral properties of beta interferon]

The aim of our work is to explore the use of IFN-beta for gene therapy in the HIV-infection. Transduction of various HIV target cells with a retroviral vector that carries the Hu-IFN-beta coding sequence under constitutive low expression control, confers resistance to HIV without affecting cell replication or function. After transduction, lymphocytes from HIV-infected patients develop resistance to the endogenous virus, provided the cells are derived from individuals with a CD4 cell count higher than 200 per mm3.

Autocrine interferon-beta synthesis for gene therapy of HIV infection: increased resistance to HIV-1 in lymphocytes from healthy and HIV-infected individuals

OBJECTIVE

To explore the possibility of gene therapy of HIV infection based on the multiple antiretroviral activities of interferon (IFN)-beta.

DESIGN

We introduced into HIV target cells an IFN-beta gene placed under an expression control ensuring a low and constitutive expression, sufficient to confer a permanent antiviral state without impeding normal cell function.

METHODS

We transformed, with an efficacy ranging from 20-55%, peripheral blood lymphocytes (PBL) derived from healthy, seronegative donors, and from asymptomatic HIV-infected individuals by the HMB-KbHuIFN beta retroviral vector carrying the human IFN-beta coding sequence driven by a fragment of the murine H-2Kb gene promoter.

RESULTS

The replication rate of the IFN-beta-expressing cells was no different from that of untransformed controls during the 21-day period of in vitro observation. When IFN-beta-transformed, purified CD4+ lymphocytes from healthy donors were HIV-1LAI-infected, virus replication was inhibited and most of the cells survived, in contrast to untransformed CD4+ cells which were all destroyed 12 days after infection. Protection of CD4+ cells from the same donors was also observed in suspensions of IFN-beta-transformed total PBL that were infected with HIV-1LAI. In IFN-beta-transformed PBL from four HIV-infected donors, endogenous HIV replication was decreased and 28-69% of the CD4+ cells survived at the end of the 21 days in culture. In the untransformed control PBL suspensions, all CD4+ cells were destroyed. In long-term experiments, HIV-infected, IFN-beta-transformed cell populations of the lymphocytic CEM and the promonocytic U937 line were kept in culture for 60 days, during which time they remained resistant to HIV infection.

CONCLUSION

These results indicate that further exploration of autocrine IFN-beta production for somatic cell gene therapy of HIV infection is warranted.