Expression of HLA class I-specific inhibitory receptors in human cytolytic T lymphocytes: a regulated mechanism that controls T-cell activation and function

Divide, Conquer, and Sense: CD8+CD28- T Cells in Perspective

Understanding the rationale for the generation of a pool of highly differentiated effector memory CD8⁺ T cells displaying a weakened capacity to scrutinize for peptides complexed with major histocompatibility class I molecules via their T cell receptor, lacking the “signal 2” CD28 receptor, and yet expressing a highly diverse array of innate receptors, from natural killer receptors, interleukin receptors, and damage-associated molecular pattern receptors, among others, is one of the most challenging issues in contemporary human immunology. The prevalence of these differentiated CD8⁺ T cells, also known as CD8⁺CD28⁻, CD8⁺KIR⁺, NK-like CD8⁺ T cells, or innate CD8⁺ T cells, in non-lymphoid organs and tissues, in peripheral blood of healthy elderly, namely centenarians, but also in stressful and chronic inflammatory conditions suggests that they are not merely end-of-the-line dysfunctional cells. These experienced CD8⁺ T cells are highly diverse and capable of sensing a variety of TCR-independent signals, which enables them to respond and fine-tune tissue homeostasis.

Squamous tissue lymphocytes in the esophagus of controls and patients with reflux esophagitis and Barrett's esophagus are characterized by a non-inflammatory phenotype

BACKGROUND AND OBJECTIVE

Reflux esophagitis (RE) is characterized by inflammation of the squamous epithelium (SQ) of the esophagus and may progress to Barrett's esophagus (BE) characterized by intestinal metaplasia. The role of inflammation in this transition has been postulated but lacks experimental evidence. Here, the inflammatory responses in the esophagus of these patients were investigated.

PATIENTS AND METHODS

Fifty-one esophageal biopsies from with patients BE (n = 19), RE (n = 8) and controls (n = 23) were analyzed. T-cells were analyzed before and after ex vivo expansion (14 days) by multicolor flow cytometric analysis. The following markers were studied: CD3, CD4, CD8 (T-cell markers), Granzyme B (marker of cytotoxicity), CD103 (αE/epithelial integrin) and NKg2a (inhibitory receptor on T-cells and NK-cells).

RESULTS

Analysis of ex vivo cultures from normal looking SQ from controls, RE patients, and BE patients revealed no significant differences in the number and phenotypes of T-cells. In contrast, tissue from RE was different to normal SQ in four aspects: 1) higher percentages of CD3+ CD4+-cells (72±7% vs 48±6%, p = 0.01) and 2) CD8+ GranzymeB+-cells (53±11% vs 26±4%, p<0.05), while 3) lower percentages of CD4+ CD103+-cells (45±19% vs 80±3%, p = 0.02) and 4) CD8+ NKg2a+-cells (31±12% vs 44±5%).

CONCLUSION

Despite the fact that both tissues are exposed to the same reflux associated inflammatory triggers, the immune response observed in RE is clearly distinct from that in SQ of BE. The differences in immune responses in BE tissue might contribute to its susceptibility for transformation into intestinal metaplasia.

Protective genotypes in HIV infection reflect superior function of KIR3DS1+ over KIR3DL1+ CD8+ T cells

Certain human class I histocompatibility-linked leukocyte antigen (HLA)/killer cell immunoglobulin-like receptor (KIR) genotypic combinations confer more favourable prognoses upon exposure to human immunodeficiency virus (HIV). These combinations influence natural killer (NK) cell function, thereby implicating NK cells in protection from HIV infection or disease progression. Because CD8(+) T cells restrict HIV replication, depend upon HLA class I antigen presentation and can also express KIR molecules, we investigated how these HLA/KIR combinations relate to the phenotype and function of CD8(+) T cells from uninfected controls and individuals with chronic HIV infection. CD8(+) T cells from KIR3DL1 and KIR3DS1 homozygous individuals, and expressing the corresponding KIR, were enumerated and phenotyped for CD127, CD57 and CD45RA expression. Ex vivo and in vitro responsiveness to antigen-specific and polyclonal stimulation was compared between KIR-expressing and non-expressing CD8(+) T cells by interferon-γ production. There were higher numbers and fractions of KIR3DL1-expressing CD8(+) T cells in HIV-infected individuals independent of HLA-Bw4 co-expression, whereas expansion of KIR3DS1-expressing CD8(+) T cells reflected HLA-Bw4*80I co-expression. KIR3DL1(+) and S1(+) CD8(+) T cells were predominantly CD127(-)CD57(+)CD45RA(+). KIR3DL1-expressing CD8(+) T cells were insensitive to ex vivo stimulation with peptides from HIV or common viruses, but responded to anti-CD3 and recovered responsiveness to common viruses in vitro. Ex vivo non-responsiveness of KIR3DL1-expressing CD8(+) T cells was also independent of HLA-Bw4. KIR3DS1-expressing T cells responded normally to ex vivo antigenic stimulation, illustrating functional superiority over KIR3DL1(+) CD8(+) T cells.

Polymorphisms of killer immunoglobulin-like receptors (KIRs) and HLA ligands in northeastern Thais

Killer cell immunoglobulin-like receptors (KIRs) are cell surface receptors on natural killer (NK) cells and subsets of T cells. The functions of NK cells are partly regulated by interactions between KIRs and HLA ligands on target cells. In this study, the presence or absence of 17 KIR genes and their known HLA ligands have been investigated in 235 unrelated individuals living in northeastern Thailand (NET). Subtypes of KIR2DS4 including full length (KIR2DS4F) and deleted forms (KIR2DS4D) have also been determined. Framework genes (KIR2DL4, 3DL2, 3DL3, and 3DP1) were found in all individuals and KIR genes belonging to the A haplotype (KIR2DL1, 2DL3, 3DL1, and 2DS4) were present in more than 90% of NET. KIR2DS4D (61.7%) was more common than KIR2DS4F (52.8%). A total of 33 different KIR genotypes were observed. Of these, three new genotypes were identified. The most common genotype (AA) was observed in 35.7% of NET, and HLA-C alleles bearing the C1 epitope (HLA-C1) had the highest frequency (97%). All individuals had at least one inhibitory KIR and its corresponding HLA ligand; 40.9% of NET had three pairs of receptor-ligand combinations, and 18.3% had all three receptor-ligand combinations of KIR2DL3+C1, 3DL1+Bw4, and 3DL2+A11. Surprisingly, the patterns of KIR gene frequencies in NET are more similar to those of Caucasians than Japanese, Korean, and Chinese. This is the first report on complete analysis of KIR and known HLA ligands in Thais. These data provide basic knowledge on KIR for further studies on disease associations and transplantation in northeastern Thais.

CD8⁺ T cells with an intraepithelial phenotype upregulate cytotoxic function upon influenza infection in human lung

The human lung T cell compartment contains many CD8⁺ T cells specific for respiratory viruses, suggesting that the lung is protected from recurring respiratory infections by a resident T cell pool. The entry site for respiratory viruses is the epithelium, in which a subset of lung CD8⁺ T cells expressing CD103 (αE integrin) resides. Here, we determined the specificity and function of CD103⁺CD8⁺ T cells in protecting human lung against viral infection. Mononuclear cells were isolated from human blood and lung resection samples. Variable numbers of CD103⁺CD8⁺ T cells were retrieved from the lung tissue. Interestingly, expression of CD103 was seen only in lung CD8⁺ T cells specific for influenza but not in those specific for EBV or CMV. CD103⁺ and influenza-reactive cells preferentially expressed NKG2A, an inhibitor of CD8⁺ T cell cytotoxic function. In contrast to CD103⁻CD8⁺ T cells, most CD103⁺CD8⁺ cells did not contain perforin or granzyme B. However, they could quickly upregulate these cytotoxic mediators when exposed to a type I IFN milieu or via contact with their specific antigen. This mechanism may provide a rapid and efficient response to influenza infection, without inducing cytotoxic damage to the delicate epithelial barrier.

Low numbers and altered phenotype of invariant natural killer T cells in recurrent varicella zoster virus infection

Invariant natural killer T (iNKT) cells play an important role in the immune response against various infectious agents. In this study we investigated their role in human defense against the varicella zoster virus. We observed decreased numbers of iNKT cells in patients who failed to control latent varicella zoster virus infection, e.g. underwent several reactivations of the virus. The residual population of iNKT cells expressed significantly higher levels of inhibitory receptor CD158a that was further up-regulated in the course of acute viral infection. Both of these abnormalities might contribute to impaired control of varicella zoster virus in human.

Killer Ig–like receptor-mediated control of natural killer cell alloreactivity in haploidentical hematopoietic stem cell transplantation

Natural killer (NK) cells are key members of the innate immune system. In a self-environment, they sense and kill target cells lacking major histocompatibility complex class I molecules and release various cytokines on activation. The discovery of human leukocyte antigen (HLA) class I specific inhibitory receptors (including the allotype-specific killer immunoglobulin-like receptors), and of various activating receptors and their ligands, provided the basis for understanding the molecular mechanism of NK-cell activation and function, mainly resulting from the balance between activating and inhibitory signals. In an allogeneic setting, such as T cell–depleted haploidentical hematopoietic stem cell transplantation, NK cells may express inhibitory killer immunoglobulin-like receptors that are not engaged by any of the HLA class I alleles present on allogeneic cells. Such “alloreactive” NK cells greatly contribute both to eradication of leukemia blasts escaping the preparative regimen and to clearance of residual host dendritic cells and T lymphocytes (thus preventing graft-versus-host disease and graft rejection, respectively). Improved prevention of graft-versus-host disease might be achieved by redirecting to lymph nodes adoptively transferred, alloreactive NK cells by inducing CCR7-uptake in vitro. Recent studies suggested that, after immune-suppressive therapy, alloreactive NK cells from an HLA-haploidentical donor may prevent leukemia recurrence also in patients who have not received allogeneic hematopoietic stem cell transplantation.

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.

Natural killer alloeffector responses in haploidentical hemopoietic stem cell transplantation to treat high-risk leukemias

Natural killer (NK) cells, a major cell type of the innate immunity, express surface receptors that regulate potent effector functions such as cytolytic activity and release of cytokines playing a central role in inflammatory response and immunoregulation. In this contribution, we briefly outline the major steps from the discovery of human leukocyte antigen (HLA)-class I-specific inhibitory receptors in humans to recent successful clinical applications in the cure of high-risk leukemias both in adults and in pediatric patients. A central role is played by 'alloreactive' NK cells originated from donor's CD 34(+) cells in eradicating leukemic cells in the setting of T-cell-depleted haploidentical hemopoietic stem cell transplantation. Because alloreactive NK cells play a central role also in preventing graft rejection and graft-vs-host disease, they may represent an ideal tool to treat patients affected by acute high-risk leukemias.

Comparative analysis of transcriptional profiling of CD3+, CD4+ and CD8+ T cells identifies novel immune response players in T-cell activation

Background

T-cell activation is an essential step of the immune response and relies on the tightly controlled orchestration of hundreds of genes/proteins, yet the cellular and molecular events underlying this complex process are not fully understood, especially at the genome-scale. Significantly, a comparative genome-scale transcriptional analysis of two T-cell subsets (CD4+ and CD8+) against each other and against the naturally mixed population (CD3+ cells) remains unexplored.

Results

Comparison of the microarray-based gene expression patterns between CD3+ T cells, and the CD4+ and CD8+ subsets revealed largely conserved, but not identical, transcriptional patterns. We employed a Gene-Ontology-driven transcriptional analysis coupled with protein abundance assays in order to identify novel T-cell activation genes and cell-type-specific genes associated with the immune response. We identified potential genes involved in the communication between the two subsets (including IL23A, NR4A2, CD83, PSMB2, -8, MIF, IFI16, TNFAIP1, POU2AF1, and OTUB1) and would-be effector-function-specific genes (XCL2, SLAMF7, TNFSF4, -5, -9, CSF3, CD48 and CD244). Chemokines induced during T-cell activation, but not previously identified in T cells, include CCL20, CXCL9, -10, -11 (in all three populations), and XCL2 (preferentially in CD8+ T cells). Increased expression of other unexpected cytokines (GPI, OSM and MIF) suggests their involvement in T-cell activation with their functions yet to be examined. Differential expression of many receptors, not previously reported in the context of T-cell activation, including CCR5, CCR7, IL1R2, IL1RAP, IL6R, TNFRSF25 and TNFRSF1A, suggests their role in this immune process. Several receptors involved in TCR activation (CD3D, CD3G, TRAT1, ITGAL, ITGB1, ITGB2, CD8A and B (CD8+ T-cell specific) along with LCK, ZAP70 and TYROBP were synchronously downregulated. Members of cell-surface receptors (HLA-Ds and KLRs), none previously identified in the context of T-cell activation, were also downregulated.

Conclusion

This comparative genome-scale, transcriptional analysis of T-cell activation in the CD4+ and CD8+ subsets and the mixed CD3+ populations made possible the identification of many immune-response genes not previously identified in the context of T-cell activation. Significantly, it made possible to identify the temporal patterns of many previously known T-cell activation genes, and also identify genes implicated in effector functions of and communication between CD4+ and CD8+ T cells.

Positive psychosocial factors and NKT cells in ovarian cancer patients

Psychosocial factors are known to be associated with properties of both NK cells and T cells in cancer patients. Less is known about the relationship between psychosocial factors and NKT cells, a rare group of lymphocytes that have known relevance for tumor control. We examined four psychosocial factors and percentage and number of CD3+CD56+ NKT cells, CD3-CD56+ NK cells, and CD3+CD56- T cells in peripheral blood lymphocytes (PBL), ascites, and tumor of 35 ovarian cancer patients and 28 patients with benign pelvic masses. Patients awaiting surgery for a suspected cancerous mass completed questionnaires and gave a pre-surgical blood sample. Ascites and tumor were taken during surgery. After lymphocyte isolation, subpopulations were analyzed by flow cytometry. Benign and cancer patients did not differ on PBL subpopulations. Among cancer patients, NKT cell percentage was significantly higher in tumor and ascites than in PBL; T cell percentage was significantly higher in PBL than tumor. NKT, NK, and T cell number were significantly higher in peripheral blood than in ascites. Positive reframing was related to significantly higher NKT cell percentage and number in PBL. Social support was related to significantly higher NKT cell percentage in tumor. Vigor was related to significantly higher NKT cell percentage in PBL. Total mood disturbance was not related to NKT cell percentage or number. No significant relationships were found between psychosocial factors and NK cell percentage and number and T cell percentage and number. Given the anti-tumor activity of CD3+CD56+ cells, these relationships may have relevance for cancer control.

Unusual expression of CD94 on CD8+ TCR-alpha beta T cells in infectious mononucleosis

Infectious mononucleosis, caused by primary Epstein-Barr virus (EBV) infection, is usually a benign, self-limited lymphoproliferative disorder. We report a case of a 21-year-old woman who presented with fever, sore throat, severe neutropenia, and absolute lymphocytosis with atypical lymphocytes. In situ hybridization for EBV-encoded small RNA performed on the marrow aspirate clot specimen demonstrated scattered positive cells. EBV serology was compatible with primary infection. Flow cytometry immunophenotypic studies performed on aspirate material revealed a profoundly expanded population of CD8+ T-cell receptor (TCR)-alphabeta T cells with uniform expression of CD94. No evidence of a monoclonal T-cell population was found as assessed by V(beta) use with flow cytometry and by TCR gamma-chain gene rearrangement using a polymerase chain reaction method. Uniform expression of CD94 in an exuberant reactive proliferation of CD8+ TCR-alphabeta T cells in infectious mononucleosis has not been reported previously, and combined with atypical morphology might be misinterpreted as a malignant neoplasm.

Lymphocyte activation in response to melanoma: interaction of NK-associated receptors and their ligands

In recent years, studies on the molecular and cellular mechanisms of immune responses against melanoma have contributed to a better understanding of how these tumours can be recognised by cytotoxic cells and the mechanisms they have developed to escape from innate and adaptive immunity. Lysis of melanoma cells by natural killer (NK) cells and cytolytic T cells is the result of a fine balance between signals transmitted by activating and inhibitory receptors. In addition to the T cell receptor, these were initially described as NK cell-associated receptors (NKRs) and were later also found on subsets of T lymphocytes, particularly effector-memory and terminally differentiated CD8 T cells. An increase of NKR(+)CD8(+) T cells has been found in melanoma patients, correlating with the expansion of differentiated effector CD8(+)CD28(null) CD27(null) T cells. NKRs can regulate the lysis of target cells expressing appropriate ligands. Activating receptors recognise ligands on tumours whereas inhibitory receptors are specific for MHC class I antigens and sense missing self. Altered expression of MHC class I antigens is frequently found on melanoma cells, preventing recognition by specific cytolytic T cells but favouring NK cell recognition. Changes in the expression of NKR-ligands in melanoma contribute in explaining the differences in the capacity of cytotoxic immune cells to control melanoma growth and dissemination.

Increased Frequency of CD4+ Cells Expressing CD161 in Cancer Patients

PURPOSE

Although the function of natural killer receptors on T cells infiltrating tumors and their potential effect on antitumor immunity has been investigated, little is known about T cells expressing NKR-P1A (CD161) in cancer patients. In the present study, we examined T cells expressing CD161 in the peripheral blood, the tumor tissue and in malignant effusions of patients with several types of malignancies.

EXPERIMENTAL DESIGN

Expression of CD161 in CD4(+) or CD8(+) (lacking CD56) T cells isolated from peripheral blood (n = 61), tumor specimens (n = 8), and malignant effusions (n = 37) of cancer patients was examined using four-color flow cytometry. Proliferative capacity and cytokine production of purified CD4(+)CD161(+)CD56(-) cells were studied after weak or strong stimulation, with or without costimulation, in the presence or absence of interleukin 2. The possible regulatory function of activated CD4(+)CD161(+)CD56(-) cells on T-cell alloresponses was also investigated.

RESULTS

CD4(+) cells expressing CD161 were increased in cancer patients, compared with healthy individuals. This increase in the peripheral blood of cancer patients positively correlated with disease stage and was augmented at the tumor site. Phenotypic analysis revealed that CD4(+)CD161(+) cells are memory T cells, with low expression of activation markers. CD4(+)CD161(+) cells play an immunoregulatory role through cytokine production, because upon receiving costimulatory signals via CD28, they exert suppressive activity on autologous peripheral blood mononuclear cell alloresponses.

CONCLUSIONS

CD4(+)CD161(+)CD56(-) cells represent a distinct memory T-cell population significantly increased in cancer patients. Depending on the type of signals provided by the tumor microenvironment, CD4(+)CD161(+) cells may regulate the immune response.

CD8 T cells expressing NK associated receptors are increased in melanoma patients and display an effector phenotype

CD8+ T cells can express NK-associated receptors (NKRs) that may regulate their cytolytic function. We have characterized the expression of several NKRs on peripheral blood CD8+ T cells from melanoma patients and compared them to age-matched healthy donors. The analysis performed includes HLA class I specific receptors (KIRs, LILRB1 and CD94/NKG2) and other NK receptors like CD57, CD56 and CD16. Melanoma patients showed a higher variability in the expression of NKRs on circulating CD8+ T cells than age-matched healthy donors. NKR expression on CD8+ T cells from melanoma patients showed a significant increase of KIR2DL2/L3/S2 (mAb gl183), CD244, CD57, CD56 and CD16. We have also found an increase of CD8+ CD28- CD27- T cells in melanoma patients. This subset represents terminally differentiated effector cells expressing CD244 and high levels of perforin. The expression of NKRs was also mainly restricted to this T cell subset. Altogether, circulating CD8+ T cells from melanoma patients display a distinct phenotype characterized by downregulation of costimulatory molecules and higher expression of NKRs. We suggest that the increased expression of NKRs on T cells may contribute to the final outcome of the immune response against melanoma both stimulating or inhibiting activation and differentiation to effector cells. Blocking inhibitory receptor function and enhancing activating receptors may represent new strategies with therapeutic potential against melanoma.

Expression of Leukocyte Immunoglobulin-Like Receptors and Natural Killer Receptors on Virus-Specific CD8+T Cells during the Evolution of Epstein-Barr Virus-Specific Immune Responsesin Vivo

Antigen-primed cytotoxic T lymphocytes (CTL) may express leukocyte immunoglobulin-like receptors (LILRs) and natural killer receptors (NKRs). Published work suggests that expression of some of these receptors confers survival advantage, leading to the idea that cells expressing such receptors may accumulate as an antigen-specific response evolves. Here we tested this hypothesis by analyzing expression of CD85j (also known as LILRB1 or ILT2), KIRs, CD94, and CD161 by Epstein- Barr virus (EBV)-specific CTL during the primary and persistent phases of EBV infection in humans. During primary infection, few EBV-specific CTL expressed these receptors and this proportion was equally low in early persistent infection. Thus, expression of these molecules does not influence capacity to survive downregulation of the primary response. However, in donors persistently infected with EBV for many years, a significantly higher proportion of EBV-specific CTL expressed CD85j and NKRs, suggesting that cells expressing these receptors can accumulate with time. Using FACS analysis, we confirmed, at a single cell level, that expression of CD85j, defined by staining with the antibody VMP55, was associated with reduced capacity of EBV-specific CD8+ T cells to respond to antigen. Thus, in the later stages of persistent infection, protective immunity to EBV may be reduced due to the preferential accumulation of hyporesponsive EBV-specific CD8+ T cells.

Up-regulation of inhibitory natural killer receptors CD94/NKG2A with suppressed intracellular perforin expression of tumor-infiltrating CD8+ T lymphocytes in human cervical carcinoma

Inhibitory signals that govern the cytolytic functions of CD8(+) T lymphocytes have been linked to the expression of natural killer cell receptors (NKRs) on CTLs. There is limited knowledge about the induction of inhibitory NKR (iNKR) expression in vivo. Up-regulation of iNKRs has been linked to the modulation of the virus- and/or tumor-specific immune responses in animal models. In the present study, we directly examined the expression of various NKRs on tumor-infiltrating lymphocytes (TILs) derived from human cervical cancer. We found that in human cervical cancer, the percentage expression of immunoglobulin-like NKR(+)CD8(+) T lymphocytes were similar in gated CD8(+)-autologous TILs and peripheral blood mononuclear cells. On the contrary, cervical cancer-infiltrating CD8(+) T lymphocytes expressed up-regulated C-type lectin NKRs CD94/NKG2A compared with either peripheral blood CD8(+) T cells or normal cervix-infiltrating CD8(+) T lymphocytes. Dual NKR coexpression analyses showed that CD94 and NKG2A were mainly expressed on CD56(-)CD161(-)CD8(+) TILs within the cancer milieu. Immunohistochemical study showed that cervical cancer cells expressed abundant interleukin 15 (IL-15) and transforming growth factor-beta (TGF-beta). In kinetic coculture assay, cervical cancer cells can promote the expression of CD94/NKG2A on CD8(+) T lymphocytes. The cancer-derived effects can be reversed by addition of rIL-15Ralpha/Fc and anti-TGF-beta antibody. Functional analyses illustrated that intracellular perforin expression of CD8(+) T cells was minimal upon up-regulation of CD94/NKG2A. Kinetic cytotoxicity assays showed that up-regulated expressions of CD94/NKG2A restrain CD8(+) T lymphocyte cytotoxicity. Our study strongly indicated that cervical cancer cells could promote the expression of iNKRs via an IL-15- and possibly TGF-beta-mediated mechanism and abrogate the antitumor cytotoxicity of TILs.

Comparative analysis of NK- or NK-CTL-mediated lysis of immature or mature autologous dendritic cells

Natural killer (NK) cells have been shown to kill efficiently autologous immature dendritic cells (iDC), while sparing those undergone maturation. In this study we investigated the effect of the interaction between autologous DC and NK-cytolytic T lymphocytes (NK-CTL), a subset of HLA-E-restricted CD8(+) T cells that express HLA class I-specific inhibitory NK receptors. Although these cells share with NK cells various phenotypic and functional features (such as the capacity to lyse most allogeneic, NK-susceptible tumor cell lines), different from NK cells, NK-CTL failed to lyse autologous DC. However, after pulsing DC with a cytomegalovirus-derived, HLA-E-binding peptide recognized by NK-CTL, both iDC and mature DC became highly susceptible to lysis. On the other hand,the addition of the peptide resulted in the down-regulation of the NK-mediated lysis of the same autologous iDC. The capability of killing autologous DC, presenting a non-self, HLA-E-binding peptide, may represent a feedback mechanism by which NK-CTL down-regulate HLA-E-restricted responses to certain pathogens.

Efficient tumor cell lysis by autologous, tumor-resident T lymphocytes in primary ovarian cancer samples by an EP-CAM-/CD3-bispecific antibody

The epithelial cell adhesion molecule (Ep-CAM) is expressed on the surface of most human carcinomas, including ovarian, breast, lung, prostate and colorectal carcinoma. Ep-CAM was shown to be a valid target for monoclonal antibody-based therapies. We have investigated whether an Ep-CAM-/CD3-bispecific single-chain antibody called bscEp-CAM x CD3 is effective in tumor cell elimination within the cellular microenvironment of primary ovarian cancer tissue. The ex vivo elimination of ovarian cancer cells in tumor preparations from 21 patients was monitored by flow cytometry using Ep-CAM/CA-125 double-labeling or Ep-CAM single-labeling combined with propidium iodide uptake of cells. Methodology was established by the ovarian cancer cell line OvCAR. A total of 17 (81%) patient samples showed a dose-dependent tumor cell elimination by bscEp-CAM x CD3. High and specific tumor cell lysis was seen at bscEp-CAM x CD3 concentrations as low as 1 ng/ml, at very low effector:target ratios and in the absence of T cell costimulation. The high efficacy of the bispecific antibody may be due to the non-restricted activation of tumor-resident cytotoxic T lymphocytes. In clinical trials, the ex vivo data with the T cell-recruiting bispecific antibody bscEp-CAM x CD3 may translate into a high response rate and efficacy of tumor cell elimination.

Demonstration of aberrant T-cell and natural killer-cell antigen expression in all cases of granular lymphocytic leukaemia

The diagnosis of granular lymphocytic leukaemia (GLL) requires the presence of an immunophenotypically distinct T-cell (T-GLL) or natural killer-cell (NK-GLL) population. Flow cytometric immunophenotyping was performed on 21 T-GLL patients, 11 NK-GLL patients and 20 normal control subjects using antibodies to T and NK cell-associated antigens in order to accurately identify the distinguishing features of T-GLL and NK-GLL. The NK antigens evaluated included: CD16, CD57, CD94, CD161, and the killing inhibitory receptors (KIRs) CD158a, CD158b and CD158e (p70). Abnormal T-antigen expression was present in all T-GLL patients. CD57 was frequently expressed in T-GLL, however, one-third of patients showed partial CD57 expression similar to that seen in T cells from normal control subjects. Ten T-GLL were KIR positive; all expressed a single KIR isoform. All NK-GLL showed a distinctive, abnormal immunophenotype. Four NK-GLL expressed a single KIR isoform; the remaining seven patients lacked all tested KIRs, which is also a distinct, abnormal finding. Immunoperoxidase staining of bone marrow biopsy specimens from NK-GLL patients with antibodies to CD8, TIA-1 and granzyme B revealed the disease-specific distinctive staining patterns previously found in T-GLL. These studies delineate the unique immunophenotypic features diagnostic of T-GLL and provide strong evidence that NK-GLL, like T-GLL, represents a clonal lymphoproliferative disorder.

Alloreactive killer cells: hindrance and help for haematopoietic transplants

Haematopoietic-cell transplantation is a treatment for leukaemia and lymphoma. To reduce the incidence of graft-versus-host disease (GVHD) caused by transplanted T cells, donors and recipients are HLA matched. For patients for whom a matched donor is not available, one option is transplantation from an HLA-mismatched relative who shares one HLA haplotype. This procedure is distinguished by the use of a stronger conditioning regimen for the patient and of a T-cell-depleted graft containing numerous stem cells. After transplantation, natural killer cells are prevalent, and they can include alloreactive cells that kill tumour cells and prevent GVHD. The alloreactions seem to be determined by the mismatched HLA class I ligands and their killer-cell immunoglobulin-like receptors.

HLA genes associated with autoimmunity and progression to disease in type 1 diabetes

Insulin dependent diabetes mellitus (type I DM) is caused by an autoimmune process which culminates in destruction of pancreatic beta cells with resultant loss of insulin production. Preceding the clinical diagnosis of type I DM is a preclinical stage characterized by autoantibodies to insulin, glutamic acid decarboxylase (GAD) and a tyrosine phosphatase-like molecule (IA-2). We have studied both HLA class I and class 2 allele distributions in diabetic probands and autoantibody positive individuals in members of 452 families recruited for the Australian type I diabetes DNA repository. The results demonstrate that progression to autoimmunity as measured by the appearance of autoantibodies is strongly associated with the class 2 alleles DRB1*03 and DRB*04 and with DRB1*03/04 heterozygosity. In contrast, the progression to clinical disease appears associated with class I alleles A24, A30 and B18 while A1, A28, B14 and B56 appear negatively associated. The class 2 alleles appear to have a minimal role in the progression from autoantibody positivity to clinical disease. These results are consistent with the view that CD4+ T cells responding to peptides in the context of class 2 molecules are responsible for initiating autoantibody production, while the destruction of islet cells leading to clinical expression of the disease is the function of CD8+ T cells recognizing relevant peptides in the context of class I molecules.

Engagement of the inhibitory receptor CD158a interrupts TCR signaling, preventing dynamic membrane reorganization in CTL/tumor cell interaction

Renal cell carcinoma (RCC) infiltrating lymphocytes (TILs) express killer cell immunoglobulinlike receptors (KIRs) that inhibit the antitumor CD8(+) T-cell lysis. In the present study, to better examine the functional consequences of KIR engagement on cytotoxic T lymphocyte (CTL)/tumor interaction, we have investigated the influence of KIR CD158a on early steps of T-cell activation. We show that coengagement of T-cell receptor (TCR) and CD158a by tumor cells inhibited tyrosine phosphorylation of early signaling proteins ZAP-70 and LAT, lipid raft coalescence, and TCR/CD3 accumulation at the CTL/tumor cell interface. In addition, the guanine exchange factor Vav was not phosphorylated, and no actin cytoskeleton rearrangement was observed. Our data indicate a role of KIR CD158a in the dynamic events induced by TCR triggering, preventing CTL membrane reorganization, and subsequent completion of CTL activation program. Accordingly, the expression of CD158 by TILs may favor tumor cell escape to the immune response.

Tumor escape from killing: role of killer inhibitory receptors and acquisition of tumor resistance to cell death

Immunotherapy of cancer has always been a very attractive fourth-modality therapeutic approach. Over the past few years, advances in the identification of tumor antigens have offered new perspectives and provided new opportunities for more accurate immunotherapy for cancer. However, when applied to patients with established tumors, it rarely leads to an objective response. This is partly due to the fact that tumors evade host immunity at both the induction and effector phases. Thus, understanding tumor escape mechanisms may be the key to successful immunotherapy for cancer. In the present review, we will focus on how the expression of killer Ig receptors (KIR) on tumor infiltrating lymphocytes can compromise their function and how tumors evade apoptotic death - two additional mechanisms of tumor escape.

Avoiding the kiss of death: how HIV and other chronic viruses survive

Virus-specific CD8 T cells during chronic infection often exceed in numbers virus-replicating infected cells. Why then do antiviral CD8 T cells not do a better job of controlling infection? Although viral strategies for immune evasion are well known, this review will focus on changes in the CD8 T cell that interfere with cytolytic function. Most antiviral CD8 T cells in chronic infection do not express perforin, a molecule that is required for cytolysis. IL-2 and other costimulatory signals can restore cytotoxicity that has been impaired, suggesting a role for CD4 T cell anergy. The chance to eradicate an infection by T cell mediated lysis is undermined after an infection becomes established, in part because the effector immune response is impaired in the setting of chronic antigen.

A novel mechanism of antitumor response involving the expansion of CD3+/CD56+ large granular lymphocytes triggered by a tumor-expressed activating ligand

We describe a patient with acute myeloid leukemia (AML) who developed polyclonal large granular lymphocyte (LGL) proliferation. The reciprocal evolution of AML and LGLs suggested that these LGLs had an anti-tumor activity. The patient's LGLs killed autologous leukemia cells in a different way to classical T lymphocyte-mediated cytotoxicity since it did not rely on the recognition of target antigens presented by major histocompatibility complex (MHC) class I molecules by the CD3/TcRalphabeta complex. This killing was also different from natural killer (NK)-mediated cytotoxicity, which depends on the absence of MHC class I molecule recognition by NK inhibitory receptors. The LGLs were polyclonal, had a CD3+/CD8+/CD56+ phenotype, and did not express the natural killer cell receptors (NKRs) for MHC class I molecules. The LGLs did not express the NK-specific activating natural cytotoxicity receptors but expressed the 2B4 non-MHC restricted triggering receptor, whose ligand CD48 was expressed by leukemic cells and normal bone marrow cells. The 2B4 receptor participated in the ability of LGLs to lyse patient's leukemia. This represents a novel function for 2B4 in man, since this molecule, at variance with the murine system, was considered not to have direct effects on CD8+ T cell-mediated cytotoxicity. This case report allowed us to describe a novel T lymphocyte-mediated anti-tumor mechanism which relied on (1) the abnormal expansion of the rare 2B4-positive CD3+/CD8+/CD56+ T lymphocyte subset, (2) an as yet undescribed cytotoxicity mechanism in man which depended on 2B4 molecule. The relevance of this observation in human cancer immunotherapy has to be further investigated.

Differential expression of inhibitory or activating CD94/NKG2 subtypes on MART-1-reactive T cells in vitiligo versus melanoma: a case report

Selection and activation of T cells is tightly regulated by both antigen-specific receptors and co-receptors to ensure that responses to self antigens are largely avoided. By T cell receptor clonotypic mapping and staining with tetrameric HLA-peptide complexes, we demonstrate the presence of melanocyte differentiation antigen MART-1 specific T cells in the areas of destruction of both neoplastic and normal melanocytic cells in a case of a primary melanoma and its associated hypopigmentation. These self reactive T cells expressed CD94/NKG2 major histocompatibility complex class I specific C-type lectin-like receptors. This family of receptors includes both activating and inhibitory isoforms. Thus, we performed a detailed analysis that revealed the exclusive presence of inhibitory NKG2-A/B receptors in the vitiligo-like leukoderma, whereas both the inhibitory receptors and the activating NKG2-C/E isoforms were present within the tumor. Our data suggest the differential expression of killer inhibitory receptors as a possible mechanism to regulate T cell responses to self antigens.

Immunity to polyoma virus infection and tumorigenesis

Because oncogenic DNA viruses establish persistent infections in humans, continuous immunosurveillance for neoplastic cells is required to prevent virus-induced tumors. Antigen-specific CD8+ T lymphocytes are critical in vivo effectors for eliminating virus-infected and virus-transformed cells. Investigation into the induction, regulation, and maintenance of CD8+ T cells specific for these viruses is hindered by the lack of tractable animal models that mimic natural infection. Resistance to tumors induced by polyoma virus, a persistent natural mouse DNA virus, is mediated by polyoma-specific CD8+ T cells. Mice susceptible to polyoma virus tumorigenesis mount a smaller, albeit still considerable, expansion of anti-polyoma CD8+ T cells; importantly, these antiviral CD8+ T cells lack cytotoxic activity while retaining the phenotype of cytotoxic T lymphocyte (CTL) effectors. In this review, we will discuss potential in vivo mechanisms that regulate the functional competence of anti-polyoma CD8+ T cells, particularly in the context of chronic antigenic stimulation provided by persistent viral infections and tumors.

NK-associated receptors on CD8 T cells from treatment-naive HIV-infected individuals: defective expression of CD56

OBJECTIVES

This study addresses the detailed expression of natural killer (NK)- associated receptors on CD8 T lymphocytes in treatment-naive HIV-infected individuals.

DESIGN

Experimental study analysing the expression of NK-associated receptors on peripheral blood T lymphocytes from HIV-infected individuals compared with healthy controls.

METHODS

Flow cytometry was used to analyse the expression of CD56, CD16, CD94, NKG2A, NKB1, CD161, CD244, and perforin, according to the CD28 phenotype, on CD8(bright) T cells obtained from treatment-naive HIV-infected individuals and from healthy controls.

RESULTS

The results showed that CD8(bright) T cells from treatment-naive HIV-infected individuals had a decreased expression of CD56 and that CD8(bright)CD56 cell numbers correlated with CD4 cell counts. NK-associated markers were preferentially expressed on CD8(bright)CD28 negative T cells, both in healthy controls and HIV-infected individuals. An increased expression of CD94, CD244, and perforin, which was the consequence of the expansion of the CD8(bright)CD28 negative T-cell subset, was also observed in HIV infection.

CONCLUSIONS

As the CD8(bright)CD56 T cells are the mature cytolytic effector cells, the defective expression of CD56 on CD8(bright) T cells shown in HIV-infected individuals could be involved in the decreased peripheral blood T-cell cytotoxicity found in HIV infection.

Allogeneic MHC class I ligands and their role in positive and negative regulation of human cytotoxic effector cells

The allogeneic mixed lymphocyte culture (MLC) has served as an important experimental system for elucidating the cellular and molecular basis of human lymphocyte responses. Complex mixtures of lymphocytes are stimulated by disparate alloantigens, inducing cellular activation and generating a cytokine milieu that is an excellent breeding ground for the proliferation and differentiation of many distinct lymphocyte subsets. Cloning of individual lymphocytes following alloactivation has allowed various cytotoxic lymphocytes to be isolated and characterized with respect to phenotype and specificity. These analyses have revealed that all types of cytotoxic effector cells are regulated by interactions with MHC-peptide ligands, however, the consequences of these interactions can result in opposite functional outcomes. In this review we summarize how allogeneic MHC class I-peptide ligands positively or negatively regulate the activities of four distinct groups of cytotoxic lymphocytes and how this information might be transferred into clinical use.

Expression of inhibitory receptors in natural killer (CD3(-)CD56(+)) cells and CD3(+)CD56(+) cells in the peripheral blood lymphocytes and tumor infiltrating lymphocytes in patients with primary hepatocellular carcinoma

The cytolytic responses of NK (CD3(-)CD56(+)) and CD3(+)CD56(+) cells are inhibited by the engagement of the killer inhibitory receptors (p58.1, p58.2, and CD94) with respective ligands on the target cell. The expression of these receptors in peripheral blood lymphocytes (PBLs) (n = 18) and tumor infiltrating lymphocytes (TILs) (n = 7) was examined in patients with primary hepatocellular carcinoma (HCC). There were no differences in the expression of the three inhibitory receptors by both NK and CD3(+)CD56(+) PBLs in patients with HCC compared to that of control NK and CD3(+)CD56(+) PBLs, respectively (all P = NS). However, the expression of p58.1 by NK TILs and by CD3(+)CD56(+) TILs in patients with HCC was significantly decreased compared to that of hepatic lymphocytes of the control subjects (8.9% vs 37.85%, P = 0.047; 4.1% vs 25.2%, P = 0.049, respectively). The expression of p58.2 by CD3(+)CD56(+) TILs and CD94 by NK TILs was also decreased compared to that of hepatic lymphocytes of the control subjects (16.9% vs 73.1%, P = 0.047; 21% vs 49.95%, P = 0.037, respectively). These changes were limited to hepatic TILs, and this observation may reflect an adaptive anti-tumor phenomenon occurring in the microenvironment of HCC.

Induction of a TRAIL-mediated suicide program by interferon alpha in primary effusion lymphoma

Gammaherpes viruses are often detected in lymphomas arising in immunocompromised patients. We have found that Azidothymidine (AZT) alone induces apoptosis in Epstein Barr Virus (EBV) positive Burkitt's lymphoma (BL) cells but requires interferon alpha (IFN-alpha) to induce apoptosis in Human Herpes Virus Type 8 (HHV-8) positive Primary Effusion Lymphomas (PEL). Our analysis of a series of AIDS lymphomas revealed that IFN-alpha selectively induced very high levels of the Death Receptor (DR) tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in HHV-8 positive PEL lines and primary tumor cells whereas little or no induction was observed in primary EBV+ AIDS lymphomas and EBV-Burkitt's lines. AZT and IFN-alpha mediated apoptosis in PEL was blocked by stable overexpression of dominant negative Fas Associated Death Domain (FADD), decoy receptor 2 (DcR2), soluble TRAIL receptor fusion proteins (DR-4 and DR-5) and thymidine. Trimeric TRAIL (in place of IFN-alpha) similarly synergized with AZT to induce apoptosis in HHV-8 positive PEL cells. This is the first demonstration that IFN-alpha induces functional TRAIL in a malignancy that can be exploited to effect a suicide program. This novel antiviral approach to Primary Effusion lymphomas is targeted and may represent a highly effective and relatively non-toxic therapy.

Distinct mRNA microarray profiles of tolerogenic dendritic cells

Dendritic cells are crucial to the activation as well as suppression of the immune response. Previous reports have illustrated that APC interacting with antigen-specific T suppressor cells become tolerogenic, inducing T helper anergy. To characterize the molecular changes occurring in tolerogenic APC, the mRNA profile of KG-1 dendritic cells exposed to allospecific T helper and T suppressor cells were analyzed. This study now provides evidence that immature dendritic cells stimulated by T suppressor cells differentiate into mature dendritic cells with a distinct phenotype. The identification of Ts induced pathways of dendritic cell differentiation is critical to the development of new therapeutic strategies.

Dressed to kill? A review of why antiviral CD8 T lymphocytes fail to prevent progressive immunodeficiency in HIV-1 infection

CD8 T cells play an important role in protection and control of HIV-1 by direct cytolysis of infected cells and by suppression of viral replication by secreted factors. However, although HIV-1-infected individuals have a high frequency of HIV-1-specific CD8 T cells, viral reservoirs persist and progressive immunodeficiency generally ensues in the absence of continuous potent antiviral drugs. Freshly isolated HIV-specific CD8 T cells are often unable to lyse HIV-1-infected cells. Maturation into competent cytotoxic T lymphocytes may be blocked during the initial encounter with antigen because of defects in antigen presentation by interdigitating dendritic cells or HIV-infected macrophages. The molecular basis for impaired function is multifactorial, due to incomplete T-cell signaling and activation (in part related to CD3zeta and CD28 down-modulation), reduced perforin expression, and inefficient trafficking of HIV-specific CD8 T cells to lymphoid sites of infection. CD8 T-cell dysfunction can partially be corrected in vitro with short-term exposure to interleukin 2, suggesting that impaired HIV-specific CD4 T helper function may play a significant causal or exacerbating role. Functional defects are qualitatively different and more severe with advanced disease, when interferon gamma production also becomes compromised.

Regulation of the natural killer cell receptor repertoire

Natural killer cells express inhibitory receptors specific for MHC class I proteins and stimulatory receptors with diverse specificities. The MHC-specific receptors discriminate among different MHC class I alleles and are expressed in a variegated, overlapping fashion, such that each NK cell expresses several inhibitory and stimulatory receptors. Evidence suggests that individual developing NK cells initiate expression of inhibitory receptor genes in a sequential, cumulative, and stochastic fashion. Superimposed on the receptor acquisition process are multiple education mechanisms, which act to coordinate the stimulatory and inhibitory specificities of developing NK cells. One process influences the complement of receptors expressed by individual NK cells. Other mechanisms may prevent NK cell autoaggression even when the developing NK cell fails to express self-MHC-specific inhibitory receptors. Together, these mechanisms ensure a self-tolerant and maximally discriminating NK cell population. Like NK cells, a fraction of memory phenotype CD8(+) T cells, as well as other T cell subsets, express inhibitory class I--specific receptors in a variegated, overlapping fashion. The characteristics of these cells suggest that inhibitory receptor expression may be a response to prior antigenic stimulation as well as to poorly defined additional signals. A unifying hypothesis is that both NK cells and certain T cell subsets initiate expression of inhibitory receptors in response to stimulation.

Expression and function of NK cell receptors in CD8+ T cells

A wide variety of inhibitory and stimulatory NK cell receptors are expressed by some CD8+ cytotoxic T lymphocytes in mice and humans. Recent data address the induction of these receptors on activated or memory CD8+ T cells and have led to hypotheses addressing their function in the CD8+ T cell response.

[HLA molecules, immunity and gestation]

During pregnancy, the fetus develops particularly efficient molecular regulatory mechanisms to prevent possible maternal anti-paternal alloimmune response and avoid viral spreading from maternal tissue. Among the different mechanisms, there has been noted a selective expression of HLA molecules on trophoblast cells: the absence of HLA class II and of polymorphic HLA-A and HLA-B expression but presence of both non polymorphic HLA-G and HLA-E class Ib as well as of HLA-C class Ia. The functional consequences of such a particular pattern of HLA expression in gestation are examined here.

Non-MHC-restricted CD4+ T lymphocytes are regulated by HLA-Cw7-mediated inhibition

Natural killer cells (NK cells) represent an important component of innate immunity with the capacity to kill many tumor and virus-infected cells. The discovery of several classes of killer cell inhibitory receptors expressed by NK cells that bind specific MHC class I ligands on target cells provides detailed insight into the regulation of NK cells. Inhibitory receptors deliver negative signals following MHC ligand binding that abrogate cytotoxicity and, thus, determine the specificity of NK effector cell function. Here, we describe a novel subset of human memory CD4(+) T lymphocytes that display an NK-like pattern of regulation. These CD4(+) T cells display non-MHC-restricted cytotoxicity that is governed by HLA-Cw7 mediated inhibition. In NK cells, such specificity is associated with expression of the inhibitory receptor p58.2. In contrast, neither p58.2 nor other known inhibitory receptors were detected on these non-MHC-restricted CD4(+) T cells. This suggests that these cells are regulated by a hitherto unknown inhibitory receptor. The finding that interactions with MHC molecules downregulate the function of these CD4(+) T cells suggests that these non-MHC-restricted T cells may function to detect and eliminate cells with aberrant MHC expression.