Human CD8+ T lymphocyte subsets that express HLA class I-specific inhibitory receptors represent oligoclonally or monoclonally expanded cell populations

Engineered NKG2C + NK-like T cells exhibit superior antitumor efficacy while mitigating cytokine release syndrome

Engineered T and NK cell therapies have widely been used to treat hematologic malignancies and solid tumors, with promising clinical results. Current chimeric antigen receptor (CAR) T cell therapeutics have, however, been associated with treatment-related adverse events such as cytokine release syndrome (CRS) and are prone to immunologic exhaustion. CAR-NK therapeutics, while not associated with CRS, have limited in vivo persistence. We now demonstrate that an NK-like TCRαβ + CD8 T cell subset, identified and expanded ex vivo through its expression of the activating receptor NKG2C (NKG2C + NK-like T cells), can be transduced to express a second-generation CD19 CAR (1928z), resulting in superior tumor clearance, longer persistence and decreased exhaustion compared to conventional 1928z CAR + CD8 T cells and 1928z CAR+ NK cells. Moreover, CAR-modified NKG2C + NK-like T cells resulted in significantly reduced CRS compared to conventional CAR + CD8 T cells. Similarly, NKG2C + NK-like T cells engineered with a TCR targeting the NY-ESO-1 antigen exhibit robust tumor control and minimal exhaustion compared to TCR-engineered conventional CD8 T cells. These data establish NKG2C + NK-like T cells as a robust platform for cell engineering, and offer a safer, more durable alternative to conventional CAR-T and CAR-NK therapies.

Heterogeneity of memory T cells in aging

Immune memory is a requisite and remarkable property of the immune system and is the biological foundation of the success of vaccinations in reducing morbidity from infectious diseases. Some vaccines and infections induce long-lasting protection, but immunity to other vaccines and particularly in older adults rarely persists over long time periods. Failed induction of an immune response and accelerated waning of immune memory both contribute to the immuno-compromised state of the older population. Here we review how T cell memory is influenced by age. T cell memory is maintained by a dynamic population of T cells that are heterogeneous in their kinetic parameters under homeostatic condition and their function. Durability of T cell memory can be influenced not only by the loss of a clonal progeny, but also by broader changes in the composition of functional states and transition of T cells to a dysfunctional state. Genome-wide single cell studies on total T cells have started to provide insights on the influence of age on cell heterogeneity over time. The most striking findings were a trend to progressive effector differentiation and the activation of pro-inflammatory pathways, including the emergence of CD4+ and CD8+ cytotoxic subsets. Genome-wide data on antigen-specific memory T cells are currently limited but can be expected to provide insights on how changes in T cell subset heterogeneity and transcriptome relate to durability of immune protection.

Innate receptors modulating adaptive T cell responses: KIR-HLA interactions and T cell-mediated control of chronic viral infections

Killer-cell immunoglobulin-like receptors (KIRs) are mainly expressed on natural killer (NK) cells and are key regulators of innate immune responses. NK cells are the first responders in the face of infection and help promote placentation during pregnancy; the importance of KIRs in these NK-mediated processes is well-established. However, mounting evidence suggests that KIRs also have a prominent and long-lasting effect on the adaptive immune system. Here, we review the evidence for the impact of KIRs on T cell responses with a focus on the clinical significance of this interaction.

The impact of killer cell immunoglobulin-like receptor (KIR) genes and human leukocyte antigen (HLA) class I ligands on predisposition or protection against prostate cancer

Natural killer (NK) cell development largely depends on killer cell immunoglobulin-like receptors (KIRs) and human leukocyte antigen (HLA) class I ligands. In the current study, we investigated the role of KIR genes, HLA ligands, and KIR-HLA combinations in vulnerability or protection against prostate cancer (PC). To analyze the frequency of 16 KIR genes and 5 HLA ligands, polymerase chain reaction with sequence-specific primers (PCR-SSP) was conducted in 150 PC patients and 200 healthy controls (CNs). KIR2DL5 (p = 0.0346, OR = 0.606, CI = 0.3916-0.9336), KIR2DS5 (p = 0.0227, OR = 0.587, CI = 0.3793-0.9139), HLA-B Bw4^Thr80 (p = 0.0401, OR = 0.3552, CI = 0.1466-0.9059), HLA Bw4 (p = 0.0190, OR = 0.4744, CI = 0.2656-0.8521), and T4 gene cluster (including KIR2DS5-2DL5-3DS1-2DS1 genes) (p = 0.0194, OR = 0.5575, CI = 0.3449-0.8938) had a lower frequency in the PC patients compared to the control group. Moreover, a lower frequency of the genotypes contacting activating KIR (aKIR) > inhibitory KIR (iKIR) (p = 0.0298, OR = 0.5291, CI = 0.3056-0.9174) and iKIR + HLA < aKIR + HLA (p = 0.0183, OR = 0.2197, CI = 0.0672-0.7001) in PC patients compared to the CNs implies a protective role for aKIR genes. In the case of KIR-HLA interactions, we detected a significant association between KIR3DS1⁺ + HLA-A Bw4⁺ (p = 0.0113, OR = 0.5093, CI = 0.3124-0.8416) and KIR3DL1^- + HLA-A Bw4⁺ (p = 0.0306, OR = 0.1153, CI = 0.0106-0.6537) combinations and resistance to prostate cancer. In contrast, the presence of KIR3DL1 in the absence of HLA-A Bw4 (p = 0.0040, OR = 2.00, CI = 1.264-3.111), HLA Bw4 (p = 0.0296, OR = 2.066, CI = 1.094-3.906), and HLA-Bw4^Thr80 (p = 0.0071, OR = 2.505, CI = 1.319-4.703) genes probably predisposes to prostate cancer. Carrying the CxT4 genotype in PC patients was positively associated with lower tumor grades (Gleason score ≤ 6) (p = 0.0331, OR = 3.290, and CI = 1.181-8.395). Altogether, our data suggest a protective role for aKIRs, HLA-B Bw4^Thr80, and HLA Bw4 ligands as well as a predisposing role for certain KIR-HLA combinations in prostate cancer. The findings of this study offer new insight into the population's risk assessment for prostate cancer in men. Additionally, predicting immunotherapy response based on KIR-HLA combinations aids in implementing the most effective therapeutic approach in the early stages of the disease.

Natural Killer T-like Cells: Immunobiology and Role in Disease

CD56+ T cells are generally recognized as a distinct population of T cells and are categorized as NKT-like cells. Although our understanding of NKT-like cells is far from satisfactory, it has been shown that aging and a number of disease situations have impacted these cells. To construct an overview of what is currently known, we reviewed the literature on human NKT-like cells. NKT-like cells are highly differentiated T cells with "CD1d-independent" antigen recognition and MHC-unrestricted cell killing. The genesis of NKT-like cells is unclear; however, it is proposed that the acquisition of innate characteristics by T cells could represent a remodeling process leading to successful aging. Additionally, it has been shown that NKT-like cells may play a significant role in several pathological conditions, making it necessary to comprehend whether these cells might function as prognostic markers. The quantification and characterization of these cells might serve as a cutting-edge indicator of individual immune health. Additionally, exploring the mechanisms that can control their killing activity in different contexts may therefore result in innovative therapeutic alternatives in a wide range of disease settings.

Immunogenomics of Killer Cell Immunoglobulin-Like Receptor (KIR) and HLA Class I: Coevolution and Consequences for Human Health

Interactions of killer cell immunoglobin-like receptors (KIR) with human leukocyte antigens (HLA) class I regulate effector functions of key cytotoxic cells of innate and adaptive immunity. The extreme diversity of this interaction is genetically determined, having evolved in the ever-changing environment of pathogen exposure. Diversity of KIR and HLA genes is further facilitated by their independent segregation on separate chromosomes. That fetal implantation relies on many of the same types of immune cells as infection control places certain constraints on the evolution of KIR interactions with HLA. Consequently, specific inherited combinations of receptors and ligands may predispose to specific immune-mediated diseases, including autoimmunity. Combinatorial diversity of KIR and HLA class I can also differentiate success rates of immunotherapy directed to these diseases. Progress toward both etiopathology and predicting response to therapy is being achieved through detailed characterization of the extent and consequences of the combinatorial diversity of KIR and HLA. Achieving these goals is more tractable with the development of integrated analyses of molecular evolution, function, and pathology that will establish guidelines for understanding and managing risks. Here, we present what is known about the coevolution of KIR with HLA class I and the impact of their complexity on immune function and homeostasis.

[Role of innate receptors in chronic inflammation and autoimmunity]

Elucidating the basis of chronic disease courses and the development of appropriate treatment methods for inflammatory diseases still represent a big challenge for medical science, as the mechanisms driving aberrant immune reactions are mostly still unknown. Of particular interest is the identification of checkpoints that regulate the function and differentiation of proinflammatory cells during the pathogenesis, along with methods for modulation of specific checkpoints as a treatment approach. Innate receptors, such as members of the natural killer group 2 family (NKG2X), natural cytotoxicity receptors (NCR) or Toll-like receptors (TLRs), play an important role in modulating the immune response. NKG2 member D (NKG2D) is a potent activating receptor of the immune system, known as a sentinel for cellular danger signals presented by cells exposed to endoplasmic reticulum (ER) stress, cell death or an inflammatory cytokine milieu. NKG2A/C bind the non-classical HLA class I molecule, sense changes in ligand expression associated with malignant transformation and cellular stress and their main function is to send inhibitory or activating signals to NK cells and subsets of T cells. In this review, we present our latest knowledge on the understanding of the role of innate receptors in the context of chronic inflammation and autoimmunity with special emphasis on danger sensor receptors NKG2D and NKG2A/C.

Human cytomegalovirus expands a CD8+ T cell population with loss of BCL11B expression and gain of NK cell identity

[Figure: see text].

Association of killer cell immunoglobulin-like receptors with endemic Burkitt lymphoma in Kenyan children

Endemic Burkitt lymphoma (eBL) is an aggressive pediatric B cell lymphoma, common in Equatorial Africa. Co-infections with Epstein-Barr virus (EBV) and Plasmodium falciparum, coupled with c-myc translocation are involved in eBL etiology. Infection-induced immune evasion mechanisms to avoid T cell cytotoxicity may increase the role of Natural killer (NK) cells in anti-tumor immunosurveillance. Killer immunoglobulin-like receptor (KIR) genes on NK cells exhibit genotypic and allelic variations and are associated with susceptibility to diseases and malignancies. However, their role in eBL pathogenesis remains undefined. This retrospective study genotyped sixteen KIR genes and compared their frequencies in eBL patients (n = 104) and healthy geographically-matched children (n = 104) using sequence-specific primers polymerase chain reaction (SSP-PCR) technique. The relationship between KIR polymorphisms with EBV loads and eBL pathogenesis was investigated. Possession of ≥ 4 activating KIRs predisposed individuals to eBL (OR = 3.340; 95% CI 1.530-7.825; p = 0.004). High EBV levels were observed in Bx haplogroup (p = 0.016) and AB genotypes (p = 0.042) relative to AA haplogroup and AA genotype respectively, in eBL patients but not in healthy controls. Our results suggest that KIR-mediated NK cell stimulation could mute EBV control, contributing to eBL pathogenesis.

Surface NKG2C Identifies Differentiated αβT-Cell Clones Expanded in Peripheral Blood

T cells that express CD56 in peripheral blood of healthy humans represent a heterogeneous and poorly studied subset. In this work, we analyzed this subset for NKG2C expression. In both CD56+ and CD56- subsets most of the NKG2C+ T cells had a phenotype of highly differentiated CD8+ TEMRA cells. The CD56+NKG2C+ T cells also expressed a number of NK cell receptors, such as NKG2D, CD16, KIR2DL2/DL3, and maturation marker CD57 more often than the CD56-NKG2C+CD3+ cells. TCR β-chain repertoire of the CD3+CD56+NKG2C+ cell fraction was limited by the prevalence of one or several clonotypes which can be found within the most abundant clonotypes in total or CD8+ T cell fraction TCRβ repertoire. Thus, NKG2C expression in highly differentiated CD56+ T cells was associated with the most expanded αβ T cell clones. NKG2C+ T cells produced almost no IFN-γ in response to stimulation with HCMV pp65-derived peptides. This may be partially due to the high content of CD45RA+CD57+ cells in the fraction. CD3+NKG2C+ cells showed signs of activation, and the frequency of this T-cell subset in HCMV-positive individuals was positively correlated with the frequency of NKG2C+ NK cells that may imply a coordinated in a certain extent development of the NKG2C+ T and NK cell subsets under HCMV infection.

KIR3DL3 Is an Inhibitory Receptor for HHLA2 that Mediates an Alternative Immunoinhibitory Pathway to PD1

Blockade of the PD1 pathway is a broadly effective cancer therapy, but additional immune-inhibitory pathways contribute to tumor immune evasion. HERV-H LTR-associating 2 (HHLA2; also known as B7H5 and B7H7) is a member of the B7 family of immunoregulatory ligands that mediates costimulatory effects through its interaction with the CD28 family member transmembrane and immunoglobulin domain containing 2 (TMIGD2). However, HHLA2 has also been known to have inhibitory effects on T cells. Here, we report that we have identified killer cell immunoglobulin-like receptor, three immunoglobulin domains and long cytoplasmic tail 3 (KIR3DL3) as an inhibitory receptor for HHLA2 in T cells and natural killer (NK) cells and have generated HHLA2 and KIR3DL3 antibodies that block the immune-inhibitory activity of HHLA2, preserving the costimulatory signal. It is known that HHLA2 is frequently expressed in several tumor types, including clear cell renal cell carcinoma (ccRCC). We found that HHLA2 expression was nonoverlapping with PDL1 expression in ccRCC, suggesting that HHLA2 mediates a mechanism of tumor immune evasion that is independent from PDL1. Blockade of both the PD1 and KIR3DL3 pathways may be a more effective way to reverse tumor immune evasion.See related Spotlight on p. 128.

Killer Ig-Like Receptors (KIRs): Their Role in NK Cell Modulation and Developments Leading to Their Clinical Exploitation

Natural killer (NK) cells contribute to the first line of defense against viruses and to the control of tumor growth and metastasis spread. The discovery of HLA class I specific inhibitory receptors, primarily of killer Ig-like receptors (KIRs), and of activating receptors has been fundamental to unravel NK cell function and the molecular mechanisms of tumor cell killing. Stemmed from the seminal discoveries in early '90s, in which Alessandro Moretta was the major actor, an extraordinary amount of research on KIR specificity, genetics, polymorphism, and repertoire has followed. These basic notions on NK cells and their receptors have been successfully translated to clinical applications, primarily to the haploidentical hematopoietic stem cell transplantation to cure otherwise fatal leukemia in patients with no HLA compatible donors. The finding that NK cells may express the PD-1 inhibitory checkpoint, particularly in cancer patients, may allow understanding how anti-PD-1 therapy could function also in case of HLA class Ineg tumors, usually susceptible to NK-mediated killing. This, together with the synergy of therapeutic anti-checkpoint monoclonal antibodies, including those directed against NKG2A or KIRs, emerging in recent or ongoing studies, opened new solid perspectives in cancer therapy.

Human NK cells: surface receptors, inhibitory checkpoints, and translational applications

NK cells play important roles in innate defenses against viruses and in the control of tumor growth and metastasis. The regulation/induction of NK cell function is mediated by an array of activating or inhibitory surface receptors. In humans, major activating receptors involved in target cell killing are the natural cytotoxicity receptors (NCRs) and NKG2D. Activating receptors recognize ligands that are overexpressed or expressed de novo upon cell stress, viral infection, or tumor transformation. The HLA-class I-specific inhibitory receptors, including KIRs recognizing HLA-class I allotypic determinants and CD94/NKG2A recognizing the class-Ib HLA-E, constitute a fail-safe mechanism to avoid unwanted NK-mediated damage to healthy cells. Other receptors such as PD-1, primarily expressed by activated T lymphocytes, are important inhibitory checkpoints of immune responses that ensure T-cell tolerance. PD-1 also may be expressed by NK cells in cancer patients. Since PD-1 ligand (PD-L1) may be expressed by different tumors, PD-1/PD-L1 interactions inactivate both T and NK cells. Thus, the reliable evaluation of PD-L1 expression in tumors has become a major issue to select patients who may benefit from therapy with mAbs disrupting PD-1/PD-L1 interactions. Recently, NKG2A was revealed to be an important checkpoint controlling both NK and T-cell activation. Since most tumors express HLA-E, mAbs targeting NKG2A has been used alone or in combination with other therapeutic mAbs targeting PD-1 or tumor antigens (e.g., EGFR), with encouraging results. The translational value of NK cells and their receptors is evidenced by the extraordinary therapeutic success of haploidentical HSCT to cure otherwise fatal high-risk leukemias.

The Role of Natural Killer T Cells in Cancer-A Phenotypical and Functional Approach

Natural killer T (NKT) cells are a subset of CD1d-restricted T cells at the interface between the innate and adaptive immune system. NKT cells can be subdivided into functional subsets that respond rapidly to a wide variety of glycolipids and stress-related proteins using T- or natural killer (NK) cell-like effector mechanisms. Because of their major modulating effects on immune responses via secretion of cytokines, NKT cells are also considered important players in tumor immunosurveillance. During early tumor development, T helper (T_H)1-like NKT cell subsets have the potential to rapidly stimulate tumor-specific T cells and effector NK cells that can eliminate tumor cells. In case of tumor progression, NKT cells may become overstimulated and anergic leading to deletion of a part of the NKT cell population in patients via activation-induced cell death. In addition, the remaining NKT cells become hyporesponsive, or switch to immunosuppressive T_H2-/T regulatory-like NKT cell subsets, thereby facilitating tumor progression and immune escape. In this review, we discuss this important role of NKT cells in tumor development and we conclude that there should be three important focuses of future research in cancer patients in relation with NKT cells: (1) expansion of the NKT cell population, (2) prevention and breaking of NKT cell anergy, and (3) skewing of NKT cells toward T_H1-like subsets with antitumor activity.

Markers and function of human NK cells in normal and pathological conditions

Natural killer (NK) cells, the most important effectors of the innate lymphoid cells (ILCs), play a fundamental role in tumor immune-surveillance, defense against viruses and, in general, in innate immune responses. NK cell activation is mediated by several activating receptors and co-receptors able to recognize ligands on virus-infected or tumor cells. To prevent healthy cells from auto-aggression, NK cells are provided with strong inhibitory receptors (KIRs and NKG2A) which recognize HLA class I molecules on target cells and, sensing their level of expression, allow killing of targets underexpressing HLA-class I. In vivo, NK cell-mediated anti-tumor function may be suppressed by tumor or tumor-associated cells via inhibitory soluble factors/cytokines or the engagement of the so called immune-check point molecules (e.g., PD1-PDL1). The study of these immune check-points is now offering new important opportunities for the therapy of cancer. In haemopoietic stem cell transplantation, alloreactive NK cells (i.e., those that express KIRs, which do not recognize HLA class I molecules on patient cells), derived from HSC of haploidentical donors, are able to kill leukemia blasts and patient's DC, thus preventing both tumor relapses and graft-versus-host disease. A clear correlation exists between size of the alloreactive NK cell population and clinical outcome. Thus, in view of the recent major advances in cancer therapy based on immuno-mediated mechanisms, the phenotypic analysis of cells and molecules involved in these mechanisms plays an increasingly major role. © 2017 International Clinical Cytometry Society.

The diversity of the HLA-E-restricted peptide repertoire explains the immunological impact of the Arg107Gly mismatch

Human leukocyte antigen (HLA)-E molecules are potent inhibitors of NK cell-mediated killing. Low in polymorphisms, two alleles are widely expressed among diverse populations: HLA-E*01:01 and HLA-E*01:03. Both alleles are distinguished by one SNP resulting in the substitution Arg107Gly. Both alleles present a limited set of peptides derived from class I leader sequences physiologically; however, HLA-E*01:01 presents non-canonical peptides in the absence of HLA class I molecules. To further assess the functional differences between both alleles, we analyzed the peptide repertoire of HLA-E*01:03 by applying soluble HLA technology followed by mass-spectrometric peptide sequencing. HLA-E*01:03 restricted peptides showed a length of 9-17 amino acids and differed in their biophysical properties, no overlap in the peptide repertoire of both allelic variants could be observed; however, both alleles shared marginal peptides from the same proteomic content. Artificial APCs expressing empty HLA-E*01:01 or E*01:03 molecules were generated and stabilized using cognate HLA class I-derived peptide ligands to analyze the impact of residue 107 within the HLA-E heavy chain on the NKG2/CD94 receptor engagement. Differences in peptide stabilization could be translated to the density and half-life time of peptide-HLA-E molecules on the cell surface that subsequently impacted NK cell inhibition as verified by cytotoxicity assays. Taken together, these data illustrate functional differences of HLA-E allelic variants induced by a single amino acid. Furthermore, the function of HLA-E in pathophysiologic situations when the HLA processing machinery is interrupted seems to be more emphasized than previously described, implying a crucial role for HLA-E in tumor or viral immune episodes.

Coordinated regulation of NK receptor expression in the maturing human immune system

NK cells are responsible for recognizing and killing transformed, stressed, and infected cells. They recognize a set of non-Ag-specific features termed "altered self" through combinatorial signals from activating and inhibitory receptors. These NKRs are also expressed on CD4(+) and CD8(+) T cells, B cells, and monocytes, although a comprehensive inventory of NKR expression patterns across leukocyte lineages has never been performed. Using mass cytometry, we found that NKR expression patterns distinguish cell lineages in human peripheral blood. In individuals with high levels of CD57, indicative of a mature immune repertoire, NKRs are more likely to be expressed on non-NK cells, especially CD8(+) T cells. Mature NK and CD8(+) T cell populations show increased diversity of NKR surface expression patterns, but with distinct determinants: mature NK cells acquire primarily inhibitory receptors, whereas CD8(+) T cells attain a specific subset of both activating and inhibitory receptors, potentially imbuing them with a distinct functional role. Concurrently, monocytes show decreased expression of the generalized inhibitory receptor leukocyte Ig-like receptor subfamily b member 1, consistent with an increased activation threshold. Therefore, NKR expression is coordinately regulated as the immune system matures, resulting in the transfer of "altered self" recognition potential among leukocyte lineages. This likely reduces Ag specificity in the mature human immune system, and implies that vaccines and therapeutics that engage both its innate and adaptive branches may be more effective in the settings of aging and chronic infection.

At the Bench: Preclinical rationale for exploiting NK cells and γδ T lymphocytes for the treatment of high-risk leukemias

NK cells and γδ T lymphocytes display potent cytolytic activity against leukemias and CMV-infected cells and are thus, promising immune effector cells in the context of allo-HSCT. NK cells express HLA class I-specific inhibitory receptors and preferentially kill HLA class I(low) tumors or virus-infected cells. Killing occurs upon engagement of activating NKRs with ligands that are up-regulated on tumors and infected cells. A similar activating receptor/ligand interaction strategy is used by γδ T cells, which in addition, use their TCRs for recognition of phosphorylated antigens and still largely undefined ligands on tumor cells. In the haploidentical allo-HSCT setting, alloreactive NK cells, derived from donor HSCs, can exert potent antileukemia activity and kill residual patient DCs and T cells, thus preventing GvHD and graft rejection. However, generation of KIR(+) alloreactive NK cells from HSCs requires many weeks, during which leukemia relapses, and life-threatening infections may occur. Importantly, mature NK cells and γδ T cells can control certain infectious agents efficiently, in particular, limit CMV reactivation, and infusion of such donor cells at the time of HSCT has been implemented. Development of novel, cell-based immunotherapies, allowing improved trafficking and better targeting, will endow NK cells and γδ T lymphocytes with enhanced anti-tumor activity, also making them key reagents for therapies against solid tumors. The clinical aspects of using NK cells and γδ T lymphocytes against hematological malignancies, including the allo-HSCT context, are reviewed in the related side-by-side paper by Locatelli and colleagues [1].

Multiplex and genome-wide analyses reveal distinctive properties of KIR+ and CD56+ T cells in human blood

Killer cell Ig-like receptors (KIRs) on NK cells have been linked to a wide spectrum of health conditions such as chronic infections, autoimmune diseases, pregnancy complications, cancers, and transplant failures. A small subset of effector memory T cells also expresses KIRs. In this study, we use modern analytic tools including genome-wide and multiplex molecular, phenotypic, and functional assays to characterize the KIR(+) T cells in human blood. We find that KIR(+) T cells primarily reside in the CD56(+) T population that is distinctively DNAM-1(high) with a genome-wide quiescent transcriptome, short telomere, and limited TCR excision circles. During CMV reactivation in bone marrow transplant recipients, KIR(+)CD56(+) T cells rapidly expanded in real-time but not KIR(+)CD56(-) T cells or KIR(+) NK cells. In CMV(+) asymptomatic donors, as much as 50% of CD56(+) T cells are KIR(+), and most are distinguishably KIR2DL2/3(+)NKG2C(+)CD57(+). Functionally, the KIR(+)CD56(+) T cell subset lyses cancer cells and CMVpp65-pulsed target cells in a dual KIR-dependent and TCR-dependent manner. Analysis of metabolic transcriptome confirms the immunological memory status of KIR(+)CD56(+) T cells in contrast to KIR(-)CD56(+) T cells that are more active in energy metabolism and effector differentiation. KIR(-)CD56(+) T cells have >25-fold higher level of expression of RORC than the KIR(+) counterpart and are a previously unknown producer of IL-13 rather than IL-17 in multiplex cytokine arrays. Our data provide fundamental insights into KIR(+) T cells biologically and clinically.

Natural killer cells in hepatitis C virus infection

Hepatitis C virus (HCV) infection induces the long-term risk of liver cirrhosis or hepatocellular carcinoma and in adults represents the most common cause of liver transplantation. Natural killer (NK) cells participate in innate immune responses with efficient direct antitumor and antiviral defense. Over the years, their complex interaction with downstream adaptive responses and with the regulation of immune responses has been increasingly recognized. Considerable advances have been made particularly in understanding the role of NK cells in the pathophysiology of HCV infection and their possible use as biological markers for clinical purposes. This review summarizes the available data on the role of NK cells in the natural history of HCV infection and their role in the outcome of treatment. The main objective of this review is to summarize recent advancements in the basic understanding of NK cell function highlighting their possible translational use in clinical practice. An integrated practical view on the possible use of currently available predictive immunogenetic and NK cell functional tests is provided, to support clinical management choices for optimal treatment of patients with both standard and new drug regimens.

Killer-cell immunoglobulin-like receptors and malaria caused by Plasmodium falciparum in The Gambia

The relevance of innate immune responses to Plasmodium falciparum infection, in particular the central role of natural killer (NK) cell-derived interferon gamma (IFN-γ), is becoming increasingly recognised. Recently, it has been shown that IFN-γ production in response to P. falciparum antigens is in part regulated by killer-cell immunoglobulin-like receptor (KIR) genes, and a study from malaria-exposed Melanesians suggested an association between KIR genotypes and susceptibility to infection. This prompted us to determine and compare the frequencies of 15 KIR genes in Gambian children presenting with either severe malaria (n = 133) or uncomplicated malaria (n = 188) and in cord-blood population control samples (n = 314) collected from the same area. While no significant differences were observed between severe and uncomplicated cases, proportions of individuals with KIR2DS2+C1 and KIR2DL2+C1 were significantly higher among malaria cases overall than in population control samples. In an exploratory analysis, activating KIR genes KIR2DS2, KIR3DS1 and KIR2DS5 were slightly higher in children in disease subgroups associated with the highest mortality. In addition, our data suggest that homozygosity for KIR genotype A might be associated with different malaria outcomes including protection from infection and higher blood parasitaemia levels in those that do get infected. These findings are consistent with a probable role of KIR genes in determining susceptibility to malaria, and further studies are warranted in different populations.

Killer cell immunoglobulin-like receptor (KIR) genes in 4 distinct populations and 51 families in mainland China

In this study, we investigated the killer cell immunoglobulin-like receptor (KIR) genes and HLA-C1/C2 dimorphism in 819 healthy, unrelated individuals composed of two southern Chinese Han populations (Hunan Han and Guangdong Han) and two northern Chinese populations (Inner Mongolia Han and Inner Mongolia Mongol), using polymerase chain reaction-sequence-specific priming (PCR-SSP) method. Fifty-one Chinese families were used to determine KIR haplotypic configuration. Our data showed that KIR2DL4, KIR3DL2, KIR3DL3, and KIR3DP1 genes were present in all of the 819 individuals. However, KIR2DL4 and KIR3DP1 genes were not detected in two members of a northern Chinese family. None of the KIR genes showed significant difference between the four populations. Thirty-five different KIR gene profiles were identified, one of which has not been previously reported in the Allele Frequencies KIR database. Eleven distinct KIR haplotypic configurations were determined through family analysis. Individuals with KIR2DLl and KIR2DL3 genes but lacking KIR2DSl and KIR2DS2 genes, coupled with HLA-C1 (Asn(80)) homozygosity, predominated in each population. At least one known inhibitory KIR-HLA pair was detected in each individual. The findings shown here are valuable for future studies of the potential role of KIR genes as well as KIR-HLA interaction in disease susceptibility in related ethnic groups.

Expansions of NK-like αβT cells with chronologic aging: novel lymphocyte effectors that compensate for functional deficits of conventional NK cells and T cells

As the repertoire of αβT cell receptors (TCR) contracts with advancing age, there is an associated age-dependent accumulation of oligoclonal T cells expressing of a variety of receptors (NKR), normally expressed on natural killer (NK) cells. Evidences for differential regulation of expression of particular NKRs between T cells and NK cells suggest that NKR expression on T cells is physiologically programmed rather than a random event of the aging process. Experimental studies show NKRs on aged αβT cells may function either as independent receptors, and/or as costimulatory receptors to the TCR. Considering the reported deficits of conventional αβTCR-driven activation and also functional deficits of classical NK cells, NKR(+) αβT cells likely represent novel immune effectors that are capable of combining innate and adaptive functions. Inasmuch as immunity is a determinant of individual fitness, the type and density of NKRs could be important contributing factors to the wide heterogeneity of health characteristics of older adults, ranging from institutionalized frail elders who are unable to mount immune responses to functionally independent community-dwelling elders who exhibit protective immunity. Understanding the biology of NKR(+) αβT cells could lead to new avenues for age-specific intervention to improve protective immunity.

KIR polymorphisms modulate peptide-dependent binding to an MHC class I ligand with a Bw6 motif

Molecular interactions between killer immunoglobulin-like receptors (KIRs) and their MHC class I ligands play a central role in the regulation of natural killer (NK) cell responses to viral pathogens and tumors. Here we identify Mamu-A1*00201 (Mamu-A*02), a common MHC class I molecule in the rhesus macaque with a canonical Bw6 motif, as a ligand for Mamu-KIR3DL05. Mamu-A1*00201 tetramers folded with certain SIV peptides, but not others, directly stained primary NK cells and Jurkat cells expressing multiple allotypes of Mamu-KIR3DL05. Differences in binding avidity were associated with polymorphisms in the D0 and D1 domains of Mamu-KIR3DL05, whereas differences in peptide-selectivity mapped to the D1 domain. The reciprocal exchange of the third predicted MHC class I-contact loop of the D1 domain switched the specificity of two Mamu-KIR3DL05 allotypes for different Mamu-A1*00201-peptide complexes. Consistent with the function of an inhibitory KIR, incubation of lymphocytes from Mamu-KIR3DL05(+) macaques with target cells expressing Mamu-A1*00201 suppressed the degranulation of tetramer-positive NK cells. These observations reveal a previously unappreciated role for D1 polymorphisms in determining the selectivity of KIRs for MHC class I-bound peptides, and identify the first functional KIR-MHC class I interaction in the rhesus macaque. The modulation of KIR-MHC class I interactions by viral peptides has important implications to pathogenesis, since it suggests that the immunodeficiency viruses, and potentially other types of viruses and tumors, may acquire changes in epitopes that increase the affinity of certain MHC class I ligands for inhibitory KIRs to prevent the activation of specific NK cell subsets.

CD8+ T regulatory cells express the Ly49 Class I MHC receptor and are defective in autoimmune prone B6-Yaa mice

The immune system includes a subpopulation of CD8(+) T cells equipped to inhibit the expansion of follicular T helper (T(FH)) cells, resulting in suppression of autoantibody production and associated lupus-like disease. These CD8(+) T regulatory (Treg) cells recognize Qa-1/peptide complexes on target T(FH) cells and depend on the IL-15 cytokine for development and function. Here we show that these CD8(+) Treg cells express a triad of surface receptors--CD44, CD122, and the class I MHC receptor Ly49--and account for <5% of CD8(+) T cells. Moreover, the development of systemic lupus erythematosus-like disease in B6-Yaa mutant mice is associated with a pronounced defect in CD8(+) Treg cell activity, suggesting that this regulatory subset may represent an effective therapeutic approach to systemic lupus erythematosus-like autoimmune disease.

Thymoglobulin, interferon-γ and interleukin-2 efficiently expand cytokine-induced killer (CIK) cells in clinical-grade cultures

Background

Cytokine-induced killer (CIK) cells are typically differentiated in vitro with interferon (IFN)-γ and αCD3 monoclonal antibodies (mAb), followed by the repeated provision of interleukin (IL)-2. It is presently unknown whether thymoglobulin (TG), a preparation of polyclonal rabbit γ immunoglobulins directed against human thymocytes, can improve the generation efficiency of CIK cells compared with αCD3 mAb in a clinical-grade culture protocol.

Methods

Peripheral blood mononuclear cells (PBMC) from 10 healthy donors and 4 patients with solid cancer were primed with IFN-γ on day 0 and low (50 ng/ml), intermediate (250 ng/ml) and high (500 ng/ml) concentrations of either αCD3 mAb or TG on day 1, and were fed with IL-2 every 3 days for 21 days. Aliquots of cells were harvested weekly to monitor the expression of representative members of the killer-like immunoglobulin receptor (KIR), NK inhibitory receptor, NK activating receptor and NK triggering receptor families. We also quantified the frequency of bona fide regulatory T cells (Treg), a T-cell subset implicated in the down-regulation of anti-tumor immunity, and tested the in vitro cytotoxic activity of CIK cells against NK-sensitive, chronic myeloid leukaemia K562 cells.

Results

CIK cells expanded more vigorously in cultures supplemented with intermediate and high concentrations of TG compared with 50 ng/ml αCD3 mAb. TG-driven CIK cells expressed a constellation of NK activating/inhibitory receptors, such as CD158a and CD158b, NKp46, NKG2D and NKG2A/CD94, released high quantities of IL-12p40 and efficiently lysed K562 target cells. Of interest, the frequency of Treg cells was lower at any time-point compared with PBMC cultures nurtured with αCD3 mAb. Cancer patient-derived CIK cells were also expanded after priming with TG, but they expressed lower levels of the NKp46 triggering receptor and NKG2D activating receptor, thus manifesting a reduced ability to lyse K562 cells.

Conclusions

TG fosters the generation of functional CIK cells with no concomitant expansion of tumor-suppressive Treg cells. The culture conditions described herein should be applicable to cancer-bearing individuals, although the differentiation of fully functional CIK cells may be hindered in patients with advanced malignancies.

IL-15 induces CD8+ T cells to acquire functional NK receptors capable of modulating cytotoxicity and cytokine secretion

During the last years several authors have described a small population of CD8+ T cells expressing NK receptors (NKRs). Although their origin remains largely unknown, we have recently demonstrated that IL-15 is capable of inducing NKR expression in purified human CD8+CD56- T cells. In this study we show that IL-15-driven NKR induction in CD8+ T cells was linked with CD56 de novo acquisition, consistent with an effector-memory phenotype, increased anti-apoptotic levels, high granzyme B/perforin expression and with the ability of displaying in vitro NK-like cytotoxicity. Interestingly, dissection of NKR functional outcome in IL-15-cultured CD8+ T cells revealed: (i) that NKG2D cross-linking was able per se to upregulate degranulation levels and (ii) that KIR and NKG2A cross-linking upregulated secretion of cytokines such as IFN-γ, TNF-α, IL-1β and IL-10. These results suggest that IL-15 is capable of differentiating CD8+ T cells into NK-like T cells displaying a regulatory phenotype.

The tortoise and the hare: slowly evolving T-cell responses take hastily evolving KIR

The killer cell immunoglobulin-like receptor (KIR) locus comprises a variable and rapidly evolving set of genes encoding multiple inhibitory and activating receptors. The activating receptors recently evolved from the inhibitory receptors and both bind HLA class I and probably also class I-like structures induced by viral infection. Although generally considered natural killer (NK) cell receptors, KIR are also expressed by a large fraction of effector memory T cells, which slowly accumulate during human life. These effector memory cells are functionally similar to NK cells, as they are immediate effector cells that are cytotoxic and produce IFN-γ. However, different rules apply to NK and T cells with respect to KIR expression and function. For example, KIR tend to modulate signals driven by the T-cell receptor (TCR) rather than to act independently, and use different signal transduction pathways to modulate only a subset of effector functions. The most important difference may lie in the rules governing tolerance: while NK cells with activating KIR binding self-HLA are hyporesponsive, the same is unlikely to apply to T cells. We argue that the expression of activating KIR on virus-specific T cells carrying TCR that weakly cross-react with autoantigens can unleash the autoreactive potential of these cells. This may be the case in rheumatoid arthritis, where cytomegalovirus-specific KIR2DS2(+) T cells might cause vasculitis. Thus, the rapid evolution of activating KIR may have allowed for efficient NK-cell control of viruses, but may also have increased the risk that slowly evolving T-cell responses to persistent pathogens derail into autoimmunity.

The emerging role of HLA-E-restricted CD8+ T lymphocytes in the adaptive immune response to pathogens and tumors

Human leukocyte antigen (HLA)-E is a nonclassical major histocompatibility complex (MHC) class I molecule of limited sequence variability that is expressed by most tissues albeit at low levels. HLA-E has been first described as the ligand of CD94/NKG2 receptors expressed mainly by natural killer (NK) cells, thus confining its role to the regulation of NK-cell function. However, recent evidences obtained by our and other groups indicate that HLA-E complexed with peptides can interact with alphabeta T-cell receptor (TCR) expressed on CD8(+) T cells. Although, HLA-E displays a selective preference for nonameric peptides, derived from the leader sequence of various HLA class I alleles, several reports indicate that it can present also "noncanonical" peptides derived from both stress-related and pathogen-associated proteins. Because HLA-E displays binding specificity for innate CD94/NKG2 receptors, as well as all the features of an antigen-presenting molecule, its role in both natural and acquired immune responses has recently been re-evaluated.

CD94/NKG2C is a killer effector molecule in patients with Stevens-Johnson syndrome and toxic epidermal necrolysis

BACKGROUND

Toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS) are severe, bullous cutaneous diseases with uncertain pathogenesis, although cytotoxic T cells seem to be involved. Natural killer (NK)-like activity has been found in blister infiltrates. Cytotoxic T lymphocytes (CTLs) with NK-like activity (NK-CTLs) have been shown to express T-cell receptors restricted by the HLA-Ib molecule HLA-E. Alternatively, the HLA-E-specific activating receptor CD94/NKG2C can trigger T-cell receptor-independent cytotoxicity in CTLs.

OBJECTIVE

Our aim was to test whether HLA-E expression sensitizes keratinocytes to killing by CTLs with NK-like activity and to explore the expression of activating receptors specific for HLA-E in blister cytotoxic lymphocytes.

METHODS

We used flow cytometry and immunohistochemistry to analyze HLA-E expression in keratinocytes from affected skin in patients with SJS, TEN, and other less severe drug-induced exanthemas. The expression of CD94/NKG2C was analyzed by means of flow cytometry in PBMCs and blister cells from patients. PBMCs and blister cells were analyzed for their ability to kill HLA-E-expressing cells. Involvement of CD94/NKG2C in triggering degranulation of cytolytic cells was explored by means of CD107a mobilization assays and standard cytotoxicity chromium release assays.

RESULTS

We found that keratinocytes from affected skin expressed HLA-E and that cell-surface HLA-E sensitizes keratinocytes to killing by CD94/NKG2C(+) CTLs. Frequencies of CD94/NKG2C(+) peripheral blood T and NK cells were increased in patients with SJS and TEN during the acute phase. Moreover, activated blister T and NK lymphocytes expressed CD94/NKG2C and were able to degranulate in response to HLA-E(+) cells in an NKG2C-dependent manner.

CONCLUSION

CD94/NKG2C might be involved in triggering cytotoxic lymphocytes in patients with SJS and TEN.

Expression of the HLA-C2-specific activating killer-cell Ig-like receptor KIR2DS1 on NK and T cells

Killer Ig-like receptors (KIRs) are MHC class I-specific receptors expressed by Natural Killer (NK) and T cell subsets. KIRs either inhibit (KIR-L) or activate (KIR-S) lymphocyte functions. Inhibitory KIR2DL1 and activating KIR2DS1 share ligand specificity for the HLA-C2 group, consistent with their almost identical extracytoplasmic domain. This homology hampered the distinction between KIR2DL1 and KIR2DS1. We report here the characterization of the KIR2DS1(+) subsets among primary human NK and T cells. Regardless of the host HLA-C genotype, around 10% of circulating NK cells expressed KIR2DS1 in absence of KIR2DL1. In HLA-C2 individuals, KIR2DS1 was not able to induce NK cell education (i.e., the acquisition of NK cell competence) nor to interfere with KIR2DL1-induced NK cell education. KIR2DS1 was also present on rare oligoclonal TCRalphabeta(+)CD8alpha(+) and TCRalphabeta(+)CD4(-)CD8(-) subsets. As KIR2DS1 has been associated with autoimmunity and hematopoietic stem cell transplantation, these results pave the way to dissect the function of KIR2DS1 in these clinical conditions.

Expression of NK cell receptors on decidual T cells in human pregnancy

Specific receptors enable NK cells to discriminate between cells with normal expression of MHC class I and cells that have low or absent expression of MHC class I molecules. In addition to NK cells, these receptors can be expressed on T cell subsets, mainly on CD8+ T cells but also on gammadeltaTCR+ T cells and CD4+ T cells. Although the function of NK cell receptor expression on T cells is not completely understood, various studies have shown that they are involved in down regulation of T cell receptor (TCR)-mediated activation and influence effector functions, like cytotoxicity and cytokine production. The aim of this study was to analyze expression of NK cell receptors on peripheral blood and decidual T cells during human pregnancy using flow cytometry. We demonstrate that a proportion of decidual T cells express HLA-C specific killer immunoglobulin-like receptors (KIRs). Furthermore, a small proportion of decidual T cells express the HLA-E specific CD94-NKG2A inhibitory and CD94-NKG2C activating receptors. Decidual KIR+ and CD94-NKG2+ T cells mainly display a CD3+CD4-CD8- phenotype. However, decidual tissue also contains higher percentages of KIR and CD94-NKG2 expressing CD4+ and CD8+ T cells compared to peripheral blood. So far, the functional capacities of decidual T cells expressing the NK cell receptors are unknown but NK cell receptor expression on decidual T cells may provide an alternative means by which decidual T cells distinguish self (maternal) cells from allogeneic fetal cells, and act to modulate the decidual immune response.

Immunophenotypic attributes of benign peripheral blood gammadelta T cells and conditions associated with their increase

CONTEXT

In comparison to alphabeta T cells, little is known about the immunophenotype of healthy peripheral blood gammadelta T cells or about conditions associated with expansion of this usually minor T-cell subset.

OBJECTIVE

To study the immunophenotype of increased nonneoplastic peripheral blood gammadelta T cells and to determine clinical conditions associated with this laboratory finding.

DESIGN

Flow cytometric T-cell phenotyping studies performed on 352 consecutive peripheral blood specimens were reviewed, and 62 cases (18%) in which gammadelta T cells comprised either more than 5% of the total lymphocytes or had an absolute count of more than 200 cells per muL or both, were studied further. Clinical data were available from 36 cases.

RESULTS

The gammadelta T cells often had an immunophenotype distinct from the alphabeta T cells, with differences in CD5 expression as the most common (n = 17), followed by differences in CD3 (n = 6) and CD7 (n = 3). CD16 coexpression by the gammadelta T cells was also frequent (n = 20). In 28 (78%) of 36 cases, there were one or more associated conditions: infection/inflammatory disease (n = 18), autoimmune disease (n = 9), lymphoproliferative disorder (n = 6), and splenectomy (n = 3).

CONCLUSIONS

Circulating gammadelta T cells are immunophenotypically distinct from alphabeta T cells, and mild increases in these cells are not uncommon and may be associated with immune system activation and splenectomy. Recognition of this phenomenon is important because reactive gammadelta T cells can exhibit distinctive immunophenotypic features that are also encountered in neoplastic conditions, such as T-cell large granular lymphocytic leukemia.

Clinical improvement by farnesyltransferase inhibition in NK large granular lymphocyte leukemia associated with imbalanced NK receptor signaling

Large granular lymphocyte (LGL) leukemia is commonly associated with poor hematopoiesis. The first case of pulmonary artery hypertension (PAH) was observed in a 57-year-old woman with natural killer (NK)-LGL leukemia and transfusion-dependent anemia. Using a genetic approach, we demonstrated that killing of pulmonary endothelial cells by patient NK cells was mediated by dysregulated balance in activating and inhibitory NK-receptor signaling. Elevated pulmonary artery pressure and erythroid differentiation improved after disrupting the NK-receptor signaling pathway with 4 courses of a farnesyltransferase inhibitor, tipifarnib. Coincidental association between PAH and LGL leukemia suggest a causal relationship between the expanded lymphocyte population and these clinical manifestations. This trial is registered at www.ClinicalTrials.gov as NCI 6823.

Two opposite signaling outputs are driven by the KIR2DL1 receptor in human CD4+ T cells

Inhibitory killer Ig-like receptors (KIR), expressed by human natural killer cells and effector memory CD8(+) T-cell subsets, bind HLA-C molecules and suppress cell activation through recruitment of the Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1). To further analyze the still largely unclear role of inhibitory KIR receptors on CD4(+) T cells, KIR2DL1 transfectants were obtained from a CD4(+) T-cell line and primary cells. Transfection of CD4(+) T cells with KIR2DL1 dramatically increased the T-cell receptor (TCR)-induced production of interleukin-2 independently of ligand binding but inhibited TCR-induced activation after ligation. KIR-mediated costimulation of TCR activation involves intact KIR2DL1-ITIM phosphorylation, SHP-2 recruitment, and PKC- phosphorylation. Synapses leading to activation were characterized by an increase in the recruitment of p-Tyr, SHP-2, and p-PKC-, but not of SHP-1. Interaction of KIR2DL1 with its ligand led to a strong synaptic accumulation of KIR2DL1 and the recruitment of SHP-1/2, inhibiting TCR-induced interleukin-2 production. KIR2DL1 may induce 2 opposite signaling outputs in CD4(+) T cells, depending on whether the KIR receptor is bound to its ligand. These data highlight unexpected aspects of the regulation of T cells by KIR2DL1 receptors, the therapeutic manipulation of which is currently being evaluated.

CD158k/KIR3DL2 is a useful marker for identifying neoplastic T-cells in Sézary syndrome by flow cytometry

Enumeration of neoplastic T-cells in peripheral blood specimens is necessary for the diagnosis of Sézary syndrome (SS) and monitoring treatment responses. Because neoplastic T-cells in SS can be difficult to identify by morphology alone, flow cytometry immunophenotyping is often utilized. However, the reported immunophenotypic criteria for identifying neoplastic T-cells in SS are variable, not present in all cases, or sometimes found in reactive T-cell populations. Peripheral blood lymphocytes from 33 cases of SS were evaluated for the expression of pan-T cell antigens and killer cell immunoglobulin-like MHC receptors (KIR) CD158a, CD158b, CD158e, CD158i, and CD158k by multiparameter flow cytometry using monoclonal antibodies EB6, GL183, FES172, Z27, and Q66. A variety of abnormalities related to expression of pan-T-cell antigens typical of neoplastic T-cells were observed. Expression of CD158k was observed in 32/33 cases and restricted to the phenotypically abnormal T-cell populations, while expression of other KIR was mostly negative. Our findings confirm and extend recent reports by one group that CD158k is expressed by most SS cases. Moreover, our observation that CD4 positive, CD7 negative T-cells are mostly CD158k negative further suggests that CD158k may be able to help identify and enumerate neoplastic T-cells in SS even when present at low levels.

Human cytomegalovirus infection induces a rapid and sustained change in the expression of NK cell receptors on CD8+ T cells

The CD8(+) T cell compartment of human CMV-seropositive individuals characteristically contains a high proportion of cells that express NK cell receptors (NKRs) which may contribute to the surveillance of virus-infected cells. To test whether this enhanced expression is a direct and immediate result of CMV infection, we used DNA microarrays to analyze putative changes in the RNA expression level of 39 NKRs in CMV-specific CD8(+) T cells of renal transplant recipients experiencing primary CMV infection. Already in the acute phase of infection 29 NKRs were induced, of which 19 remained high 1 year after cessation of viral replication. Activating and inhibitory NKRs were induced to a similar extent. Detailed longitudinal flow cytometric analyses confirmed NKR changes at the protein level. Strikingly, a strong induction of CD94 on CD3(+) T cells was observed with surface expression of activating CD94(dim) NKG2C dimers appearing before inhibitory CD94(bright) NKG2A ones. After the acute phase of infection, the balance between inhibitory and activating receptors did not change. Thus, CMV infection induces a rapid and lasting change in the expression of NKRs on human CD8(+) T cells.

CD8alpha+beta(low) effector T cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder characterized by the loss of self-tolerance to nuclear antigens. Aberrant T-cell function plays a central role in lupus pathogenesis. We and others previously demonstrated that peripheral TCRalphabeta+CD3+ T cells express CD8beta either at a high (CD8beta(high)) or low density (CD8beta(low)), thereby defining two functionally distinct subsets. CD8beta(low) T cells express predominantly CD8alphaalpha and less CD8alphabeta as a coreceptor, display a differentiated phenotype and exert effector function. CD8beta(high) T cells appear to be the precursors expressing predominantly the heterodimeric efficient CD8alphabeta coreceptor, exhibiting a naïve phenotype and high proliferative capacity. In the present study, the distribution and functional properties of CD8beta(high) and CD8beta(low) T cells of SLE patients were compared (n = 20) with those of healthy subjects (n = 16). It was found that expansion of CD8beta(low) T-cell subset correlated with disease activity indicating chronic antigenic stimulation leading to a major lack of naïve CD8beta(high) precursor T cells in SLE. Functional characteristics of CD8beta(low) T cells including production of cytokines and cytotoxic granules were not significantly different between patients with SLE and healthy individuals. We speculate that unbalanced CD8beta(high)/CD8beta(low) T-cell relation reflects a skewed homeostasis within the CD8+ T-cell compartment towards fully differentiated effector T cells possibly due to persistent antigen stimulation in SLE.

Antiviral NK cell responses in HIV infection: II. viral strategies for evasion and lessons for immunotherapy and vaccination

As is the case in other viral infections, humans respond to HIV infection by activating their NK cells. However, the virus uses several strategies to neutralize and evade the host's NK cell responses. Consequently, it is not surprising that NK cell functions become compromised in HIV-infected individuals in early stages of the infection. The compromised NK cell functions also adversely affect several aspects of the host's antiviral adaptive immune responses. Researchers have made significant progress in understanding how HIV counters NK cell responses of the host. This knowledge has opened new avenues for immunotherapy and vaccination against this infection. In the first part of this review article, we gave an overview of our current knowledge of NK cell biology and discussed how the genes encoding NK cell receptors and their ligands determine innate genetic resistance/susceptibilty of humans against HIV infections and AIDS. In this second part, we discuss NK cell responses, viral strategies to counter these responses, and finally, their implications for anti-HIV immunotherapy and vaccination.

Lineage-specific transition of histone signatures in the killer cell Ig-like receptor locus from hematopoietic progenitor to NK cells

The clonal distribution and stable expression of killer cell Ig-like receptor (KIR) genes is epigenetically regulated. To assess the epigenetic changes that occur during hemopoietic development we examined DNA methylation and chromatin structure of the KIR locus in early hemopoietic progenitor cells and major lymphocyte lineages. In hemopoietic progenitor cells, KIR genes exhibited the major hallmarks of epigenetic repression, which are dense DNA methylation, inaccessibility of chromatin to Micrococcus nuclease digest, and a repressive histone signature, characterized by strong H3K9 dimethylation and reduced H4K8 acetylation. In contrast, KIR genes of NK cells showed active histone signatures characterized by absence of H3K9 dimethylation and presence of H4K8 acetylation. Histone modifications correlated well with the competence of different lymphocyte lineages to express KIR; whereas H4K8 acetylation was high in NK and CD8+ T cells, it was almost absent in CD4+ T cells and B cells and, in the latter case, replaced by H3K9 dimethylation. In KIR-competent lineages, active histone signatures were also observed in silent KIR genes and in this case found in combination with dense DNA methylation of the promoter and nearby regions. The study suggests a two-step model of epigenetic regulation in which lineage-specific acquisition of euchromatic histone marks is a prerequisite for subsequent gene-specific DNA demethylation and expression of KIR genes.

Amino-acid sequence motifs for PKC-mediated membrane trafficking of the inhibitory killer Ig-like receptor

Activation-induced upregulation of inhibitory killer Ig-like receptor (KIR) is regulated by protein kinase Cs (PKCs). Conventional PKCs increase KIR expression on the post-transcriptional level by increasing the recycling of surface molecules and endoplasmic reticulum (ER)-Golgi processing. PKCdelta plays a role in the secretion of cytoplasmic KIR through lytic granules. In this study, we identified amino acid sequence motifs associated with PKC-mediated KIR membrane trafficking by systematic mutagenesis. Mutations of Y(398) and HLWC(364) completely inhibited the PMA-induced increase of KIR molecules at surface as well as total protein levels, indicating that these are associated with ER-Golgi processing and sorting to plasma membrane through lytic granules. Mutations of Y-based motif, including Y(398), acidic region (PE(394)), dileucine motif-like region (IL(423)) and PKC-phosphorylatable S(415) caused a blockade of surface KIR endocytosis after PKC stimulation. Mutation of T(145) caused an accumulation of mutant proteins in late endosomes and lysosomes after PKC activation, suggesting that T(145) might be related to the recovery of endocytosed KIR to the surface membrane. We also demonstrated that PKCs could directly phosphorylate the KIR cytoplasmic tail by means of western blot and in vitro kinase assay, implying that phosphorylation status of KIR cytoplasmic tail can direct the fate of surface KIR molecules. Taken together, various sequence motifs are implicated in the PKC-mediated post-transcriptional upregulation of KIR, and each of these motifs work in different steps after PKC activation.

Influence of KIR gene diversity on the course of HSV-1 infection: resistance to the disease is associated with the absence of KIR2DL2 and KIR2DS2

Herpes simplex virus type 1 (HSV-1) causes lifelong latent infections in most humans. Periodical virus reactivations from latency in the neurons of sensitive ganglia lead to transport to mucocutaneous regions and productive replication, which results in recurrent inflammatory herpetic lesions or in asymptomatic virus shedding. The medical consequences of such lesions and the frequency of recurrences vary greatly in different subjects. Furthermore, many infected individuals never suffer manifestations of the disease, even when exposed to stimuli that trigger clinical recurrences in other humans. The origin of the variability in the clinical course of HSV-1 infection remains unexplained. Herpesviruses and other pathogens sabotage the expression of major histocompatibility complex class I molecules by infected cells, thus subverting T-cell-mediated immunity. Subversion of antigen presentation is counteracted by natural killer cells, which survey the human leukocyte antigen (HLA) expression by specific receptors. These include the killer cell immunoglobulin-like receptors (KIRs), which are encoded by a complex of extremely diverse and rapidly evolving genes. Here, we analyze the contribution of KIR gene diversity to the variable clinical course of HSV-1 infection by comparing the distribution of these genes in humans with clinical manifestations of the disease with that in asymptomatically infected donors. This study provides preliminary evidence that the receptors KIR2DL2 and KIR2DS2 predispose to symptomatic HSV-1 infection and favor the frequently recurring forms of the disease. Possible contribution of the 'HLA-C1' ligand to HSV-1 disease was not statistically supported. Because of an absolute genetic linkage between KIR2DL2 and KIR2DS2, we could not determine which receptor was primarily responsible for the observed association, but our results suggest that presence in the genome of KIR2DL2 and KIR2DS2 hinders an effective cellular response to HSV-1.

Expansion of natural killer cell receptor (CD94/NKG2A)-expressing cytolytic CD8 T cells and CD4+CD25+ regulatory T cells from the same cord blood unit

OBJECTIVE

Cord blood contains a significant number of precursor cells that differentiate to cytotoxic effector cells and immunoregulatory cells. We tried to expand inhibitory natural killer cell receptor CD94-expressing CD8 T cells with cytolytic activity and CD4(+)CD25(+) regulatory T cells from the same cord cell unit.

METHODS

Cytotoxic CD94-expressing CD8 T cells were expanded from CD4-depleted cord blood using an immobilized anti-CD3 monoclonal antibody and a cytokine and also CD4(+)CD25(+) regulatory T cells were expanded from a CD4-enriched fraction derived from the same cord blood unit using anti-CD3/CD28 monoclonal antibody-coated Dynabeads and cytokines.

RESULTS

We were able to obtain a more than 1000-fold expansion of CD94-expressing CD8 T cells and a more than 50-fold expansion of CD4(+)CD25(+) cells from the same cord blood unit. These expanded CD4(+)CD25(+) cells expressed FoxP3 mRNA at a level about 100-fold higher than that in isolated CD25(-) cells and could suppress allogeneic mixed lymphocyte culture by >80% (effector cells: CD4(+)CD25(+) cells = 2:1). Cytolytic activities of purified CD94-expressing cells detected by a 4-hour (51)Cr release assay against K562 were >60%. Coculture of CD94-expressing cells with expanded CD4(+)CD25(+) cells did not have any effect on cytolytic activities of purified CD94-expressing cells against K562 cells.

CONCLUSION

These expanded cytolytic CD94-expressing CD8 cells might be able to induce a graft-vs-leukemia effect without enhancing graft-vs-host disease, and CD4(+)CD25(+) cells might be able to suppress allogeneic responses, including graft-vs-host disease and graft rejection after cord blood transplantation.

Chain-terminating natural mutations affect the function of activating KIR receptors 3DS1 and 2DS3

To determine the nucleotide polymorphism of activating killer-cell immunoglobulin-like receptors (aKIR) 3DS1 and 2DS3, we developed a novel direct-sequencing method and analyzed DNA samples of 175 KIR3DS1(+) individuals and 72 KIR2DS3(+) individuals from the white population. The putative ligand-binding extracellular immunoglobulin (Ig)-like domains of these aKIR receptors are highly conserved, a scenario contrary to inhibitory KIRs that recognize polymorphic human leukocyte antigen (HLA) class I molecules. Null alleles 3DS1*049N and 2DS3*003N that do not express cell-surface receptors were discovered, and they occur commonly in whites (3DS1*049N = 2%; 2DS3*003N = 0.8%). Sequence-specific polymerase chain reaction (PCR) detecting these null alleles is negative with DNA from nonwhite subjects, suggesting that these null alleles are specific to whites and probably originated after the colonization of modern humans in Europe.

Human CD8+intraepithelial lymphocytes: a unique model to study the regulation of effector cytotoxic T lymphocytes in tissue

The epithelium of the human small intestine contains a large population of intraepithelial cytolytic alphabeta T-cell receptor (TCR) CD8 alpha beta T lymphocytes (IE-CTLs), whose main role is to sustain epithelial integrity by rapidly eliminating infected and damaged cells. In mouse, the recognition of inducible/modified self-molecules, i.e. non-classical major histocompatibility complex (MHC) class I molecules, is mediated by the TCR and natural killer receptors (NKRs) co-expressed on the cell surface of a non-conventional autoreactive CD8 alpha alpha alpha beta TCR cell subset. In contrast, in humans, the recognition of non-classical MHC class I molecules induced by stress and inflammation on intestinal epithelial cells (IECs) is principally mediated by NKRs expressed on conventional CD8 alpha beta alpha beta TCR cells. By sensing microenvironmental signals of inflammation and stress through NKRs, IE-CTLs fine tune their TCR activation threshold. Furthermore, IE-CTLs under particular conditions, involving interleukin-15 upregulation, acquire the capacity to kill distressed intestinal epithelial cells in an antigen non-specific manner. Adaptive IE-CTLs appear hence to have autoreactive properties and modulate their immune response based on innate signals, reflecting the fitness of the tissue.