Increased expression of CD80, CD86 and CD70 on T cells from HIV-infected individuals upon activation in vitro: regulation by CD4+ T cells

Multidomain peptide hydrogel adjuvants elicit strong bias towards humoral immunity

Adjuvants play a critical role in enhancing vaccine efficacy; however, there is a need to develop new immunomodulatory compounds to address emerging pathogens and to expand the use of immunotherapies. Multidomain peptides (MDPs) are materials composed of canonical amino acids that form injectable supramolecular hydrogels under physiological salt and pH conditions. MDP hydrogels are rapidly infiltrated by immune cells in vivo and have previously been shown to influence cytokine production. Therefore, we hypothesized that these immunostimulatory characteristics would allow MDPs to function as vaccine adjuvants. Herein, we demonstrate that loading antigen into MDP hydrogels does not interfere with their rheological properties and that positively charged MDPs can act as antigen depots, as demonstrated by their ability to release ovalbumin (OVA) over a period of 7-9 days in vivo. Mice vaccinated with MDP-adjuvanted antigen generated significantly higher IgG titers than mice treated with the unadjuvanted control, suggesting that these hydrogels potentiate humoral immunity. Interestingly, MDP hydrogels did not elicit a robust cellular immune response, as indicated by the lower production of IgG2c and smaller populations of tetramer-positive CD8+ T splenocytes compared to mice vaccinated alum-adjuvanted OVA. Together, the data suggest that MDP hydrogel adjuvants strongly bias the immune response towards humoral immunity while evoking a very limited cellular immune response. As a result, MDPs may have the potential to serve as adjuvants for applications that benefit exclusively from humoral immunity.

Altered type 1 interferon responses in alloimmunized and nonalloimmunized patients with sickle cell disease

Patients with sickle cell disease (SCD) have a high prevalence of RBC alloimmunization. However, underlying mechanisms are poorly understood. Given that proinflammatory type 1 interferons (IFNα/β) and interferon stimulated genes (ISGs) promote alloimmunization in mice, we hypothesized that IFNα/β may contribute to the increased frequency of alloimmunization in patients with SCD. To investigate this, expression of ISGs in blood leukocytes and peripheral blood mononuclear cells (PBMCs) of previously transfused SCD patients with or without alloimmunization and race-matched healthy controls were quantified, and IFNα/β gene scores were calculated. IFNα/β gene scores of SCD leukocytes and plasma cytokines were elevated, compared to controls (gene score, p < 0.01). Upon stimulation with IFNβ, isolated PBMCs from patients with SCD had elevated ISGs and IFNα/β gene scores (p < 0.05), compared to stimulated PBMCs from controls. However, IFNβ-stimulated and unstimulated ISG expression did not significantly differ between alloimmunized and non-alloimmunized patients. These findings indicate that patients with SCD express an IFNα/β gene signature, and larger studies are needed to fully determine its role in alloimmunization. Further, illustration of altered IFNα/β responses in SCD has potential implications for IFNα/β-mediated viral immunity, responses to IFNα/β-based therapies, and other sequelae of SCD.

The role of CD27 in anti-viral T-cell immunity

CD27 is a co-stimulatory immune-checkpoint receptor, constitutively expressed on a broad range of T-cells (αβ and γδ), NK-cells and B-cells. Ligation of CD27 with CD70 results in potent co-stimulatory effects. In mice, co-stimulation of CD8⁺ T-cells through CD27 promotes immune activation and enhances primary, secondary, memory and recall responses towards viral infections. Limited in vitro human studies support mouse experiments and show that CD27 co-stimulation enhances antiviral T-cell immunity. Given the potent co-stimulatory effects of CD27, manipulating CD27 signalling is of interest for viral, autoimmune and anti-tumour immunotherapies. This review focuses on the role of CD27 co-stimulation in anti-viral T-cell immunity and discusses clinical studies utilising the CD27 co-stimulation pathway for anti-viral, anti-tumour and autoimmune immunotherapy.

Tetherin/BST-2: Restriction Factor or Immunomodulator?

BACKGROUND

Cell-mediated immune (CMI) responses are critical for the control of HIV-1 infection and their importance was highlighted by the existence of viral proteins, particularly Vpu and Nef, that antagonize these responses. Pandemic HIV-1 Vpu counteracts Tetherin/BST-2, a host factor that could prevent the release of HIV-1 virions by tethering virions on the cell surface, but a link between Tetherin and HIV-1 CMI responses has not yet been demonstrated in vivo. In vitro, the virological and immunological impact of Tetherin-mediated accumulation of virions ranged from enhanced or diminished cell-to-cell spread to enhanced recognition by virus-specific antibodies for natural killer cellmediated lysis. However, Tetherin-restricted virions could be internalized through an endocytosis motif in the Tetherin cytoplasmic tail.

METHODS

Given the uncertainties on which in vitro results manifest in vivo and the dearth of knowledge on how Tetherin influences retroviral immunity, in vivo retrovirus infections in mice encoding wild-type, null and endocytosis-defective Tetherin were performed. Here, we review and highlight the results from these in vivo studies.

RESULTS

Current data suggests that endocytosis-defective Tetherin functions as a potent innate restriction factor. By contrast, endocytosis-competent Tetherin, the form found in most mammals including humans and the form counteracted by HIV-1 Vpu, was linked to stronger CMI responses in mice.

CONCLUSION

We propose that the main role of endocytosis-competent Tetherin is not to directly restrict retroviral replication, but to promote a more effective CMI response against retroviruses.

Molecular Profile of Tumor-Specific CD8+ T Cell Hypofunction in a Transplantable Murine Cancer Model

Mechanisms of self-tolerance often result in CD8(+) tumor-infiltrating lymphocytes (TIL) with a hypofunctional phenotype incapable of tumor clearance. Using a transplantable colon carcinoma model, we found that CD8(+) T cells became tolerized in <24 h in an established tumor environment. To define the collective impact of pathways suppressing TIL function, we compared genome-wide mRNA expression of tumor-specific CD8(+) T cells from the tumor and periphery. Notably, gene expression induced during TIL hypofunction more closely resembled self-tolerance than viral exhaustion. Differential gene expression was refined to identify a core set of genes that defined hypofunctional TIL; these data comprise the first molecular profile of tumor-specific TIL that are naturally responding and represent a polyclonal repertoire. The molecular profile of TIL was further dissected to determine the extent of overlap and distinction between pathways that collectively restrict T cell functions. As suggested by the molecular profile of TIL, protein expression of inhibitory receptor LAG-3 was differentially regulated throughout prolonged late-G1/early-S phase of the cell cycle. Our data may accelerate efficient identification of combination therapies to boost anti-tumor function of TIL specifically against tumor cells.

Abatacept (CTLA-4Ig) treatment reduces T cell apoptosis and regulatory T cell suppression in patients with rheumatoid arthritis

OBJECTIVE

Abatacept (CTLA-4Ig) blocks CD28-mediated T cell activation by binding to the costimulatory B7 ligands CD80/CD86 on antigen presenting cells. Costimulatory molecules, however, can also be expressed on T cells upon activation. Therefore, the aim of our study was to investigate direct effects of CTLA-4Ig on distinct T cell subsets in RA patients.

METHODS

Phenotypic and functional analyses of CD4(+) T cells, including CD4(+) FoxP3(+) CD25(+) regulatory T cells (Treg), from RA patients were performed before and during CTLA-4Ig therapy. In addition T cells from healthy volunteers were analysed on in vitro culture with CTLA-4Ig or anti-CD80 and anti-CD86 antibodies. Apoptotic DNA fragmentation in CD4(+) and CD4(+) FoxP3(+) T cells was measured by TUNEL staining.

RESULTS

We observed an increase in T cells, including Treg cells, after initiation of CTLA-4Ig therapy, which was linked to a downregulation of activation-associated marker molecules and CD95 on CD4(+) T cells and Treg cells. CTLA-4Ig decreased CD95-mediated cell death in vitro in a dose-dependent manner. Functional analysis of isolated Treg cells from RA patients further revealed a diminished suppression of responder T cell proliferation. This was found to be due to CTLA-4Ig-mediated blocking of CD80 and CD86 on responder T cells that led to a diminished susceptibility for Treg cell suppression.

CONCLUSION

CTLA-4Ig therapy in RA patients exerts effects beyond the suppression of T cell activation, which has to be taken into account as an additional mechanism of CTLA-4Ig treatment.

TNFRs and Control of Chronic LCMV Infection: Implications for Therapy

The control of persistent viral infections requires the immune system to limit the spread of the virus while avoiding immunopathology. Recent studies have revealed that members of the tumor necrosis factor receptor (TNFR) superfamily play unique and pivotal roles in control of chronic lymphocytic choriomeningitis virus (LCMV) infection and in some settings can tip the balance between immune control and immune pathology. We review these findings and discuss how our understanding of the role of TNFRs in the immune response to chronic LCMV infection may shed light on what happens during HIV infection in humans. We discuss preclinical models of TNF/TNFR family-targeted immunotherapy of chronic LCMV infection and evaluate which TNFRs present the most promising targets for immune intervention.

Association between co-stimulatory molecule gene polymorphism and acute rejection of allograft

Co-stimulatory molecules play important roles in T cell-mediated immune response and transplantation. Numerous epidemiological studies have evaluated the association between CD28, CTLA-4 gene variant and allograft rejection. However, the results of these studies on the association remain conflicting. The main purpose of this study was to integrate previous results and explore whether the CD28 IVS3 +17T/C variant, CTLA-4, CD86 and PDCD1 gene polymorphisms were associated with allograft rejection susceptibility. PubMed and Embase (before 2014-3-25), were searched for studies on the relationship of CD28, CTLA-4, CD86 and PDCD1 gene polymorphisms and the incidence of allograft rejection susceptibility. Eligible articles were included for data extraction. The main outcome was the frequency of co-stimulate molecule gene polymorphisms between rejection and non-rejection populations. Comparison of the distribution of SNP was mainly performed using Review Manager 5.0. The odds ratio (OR) and its 95% confidence interval (95% CI) were used to assess the strength of association. Significant associations of the CD28 IVS3 +17T/C variant with acute allograft rejection susceptibility were found (CC +CT/TT OR, 1.45; 95% CI, 1.08-1.94; P=0.01). Also we found an association of the CD28 IVS3 +17T/C variant with kidney allograft rejection cases (CC +CT/TT OR, 1.72; 95% CI, 1.19-2.49; P=0.004) and (C allele OR, 1.74; 95% CI, 1.11-2.75; P=0.02), but not established for liver allograft rejection cases (CC +CT/TT OR, 1.19; 95% CI, 0.47-2.98; P=0.72) and (C allele OR, 0.96; 95% CI, 0.67-1.39; P=0.84). And we found an association of the CD86 +1057G/A variant with non-allograft rejection cases (AA +AG/GG OR, 0.35; 95% CI, 0.14-0.85; P=0.02). This meta-analysis demonstrates that the CD28 IVS3 +17T/C variant might increase acute allograft rejection risk in kidney transplant but not in liver transplant, and there was an association between CD86 +1057G/A variant and reduced acute rejection risk. Further studies will be needed to confirm our findings.

A consensus surface activation marker signature is partially dependent on human immunodeficiency virus type 1 Nef expression within productively infected macrophages

Background

The high prevalence of HIV-associated comorbidities including neurocognitive disorder, high levels of residual inflammatory mediators in the plasma and cerebrospinal fluid and the resurgence of HIV replication upon interruption of antiviral treatment in HIV-1 infected individuals, strongly suggests that despite therapy HIV persists in its cellular targets which include T-lymphocytes and cells of the myeloid lineage. These reservoirs present a major barrier against eradication efforts. Knowledge of the molecular mechanisms used by HIV to modulate innate macrophage immune responses and impair viral clearance is quite limited. To explore the role of HIV in potentially modulating macrophage function through changes in protein expression, we used single-cell analyses with flow cytometry to determine whether, in unpolarized cultures, macrophage surface marker phenotype was altered by HIV infection in a manner that was independent of host genetic background.

Results

These analyses revealed that at several time points post-infection, GFP + HIV-infected macrophages were significantly enriched in the CD14+ fraction (3 to 5-fold, p = .0001) compared to bystander, or uninfected cells in the same culture. However, the enrichment and higher levels of CD14 on HIV expressing macrophages did not depend on the production of HIV Nef. Sixty to eighty percent of macrophages productively infected with HIV after day 28 post-infection were also enriched in the population of cells expressing the activation markers CD69 (2 to 4-fold, p < .0001) and CD86 (2 to 4-fold, p < .0001 ) but suppressed amounts of CD68 (3 to 10-fold, p < .0001) compared to bystander cells. Interestingly, there was no enrichment of CD69 on the surface of HIV producing cells that lacked Nef or expressed a variant of Nef mutated in its SH3-binding domain.

Conclusions

These findings suggest that HIV actively regulates the expression of a subset of surface molecules involved in innate and inflammatory immune signaling in primary human macrophages through Nef-dependent and Nef-independent mechanisms acting within productively infected cells.

Impairment of B-cell functions during HIV-1 infection

A variety of B-cell dysfunctions are manifested during HIV-1 infection, as reported early during the HIV-1 epidemic. It is not unusual that the pathogenic mechanisms presented to elucidate impairment of B-cell responses during HIV-1 infection focus on the impact of reduced T-cell numbers and functions, and lack of germinal center formation in lymphoid tissues. To our understanding, however, perturbation of B-cell phenotype and function during HIV-1 infection may begin at several different B-cell developmental stages. These impairments can be mediated by intrinsic B-cell defects as well as by the lack of proper T-cell help. In this review, we will highlight some of the pathways and molecular interactions leading to B-cell impairment prior to germinal center formation and B-cell activation mediated through the B-cell receptor in response to HIV-1 antigens. Recent studies indicate a regulatory role for B cells on T-cell biology and immune responses. We will discuss some of these novel findings and how these regulatory mechanisms could potentially be affected by the intrinsic defects of B cells taking place during HIV-1 infection.

CD70 deficiency impairs effector CD8 T cell generation and viral clearance but is dispensable for the recall response to lymphocytic choriomeningitis virus

CD27 interactions with its ligand, CD70, are thought to be necessary for optimal primary and memory adaptive immune responses to a variety of pathogens. Thus far, all studies addressing the function of the CD27-CD70 axis have been performed in mice lacking CD27, in those overexpressing CD70, or in those in which these molecules were blocked or mimicked by Abs or recombinant soluble CD70. Because these methods have in some cases led to divergent results, we generated CD70-deficient mice to directly assess its role in vivo. We find that lack of CD70-mediated stimulation during primary responses to lymphocytic choriomeningitis virus lowered the magnitude of CD8 Ag-specific T cell response, resulting in impaired viral clearance, without affecting CD4 T cell responses. Unexpectedly, CD70-CD27 costimulation was not needed for memory CD8 T cell generation or the ability to mount a recall response to lymphocytic choriomeningitis virus. Adoptive transfers of wild-type memory T cells into CD70(-/-) or wild-type hosts also showed no need for CD70-mediated stimulation during the course of the recall response. Moreover, CD70 expression by CD8 T cells could not rescue endogenous CD70(-/-) cells from defective expansion, arguing against a role for CD70-mediated T:T help in this model. Therefore, CD70 appears to be an important factor in the initiation of a robust and effective primary response but dispensable for CD8 T cell memory responses.

Distinctive features of the differentiated phenotype and infiltration of tumor-reactive lymphocytes in clear cell renal cell carcinoma

Clear cell renal cell carcinoma (RCC) is considered an immunogenic tumor, but it has been difficult to identify tumor-infiltrating lymphocytes (TIL) that show in vitro tumor recognition. We compared the characteristics of fresh RCC TIL to peripheral blood lymphocytes (PBL) or melanoma TIL. Our results showed that RCC TIL contained fewer CD27(+) T cells, and fewer naïve and central memory (CM) T cells, but more effector memory (EM) T cells than melanoma TIL or renal PBL. We hypothesized that factors in the RCC microenvironment were skewing TIL phenotype toward EM. One possibility was the expression of CD70 on nearly all human RCCs, but not melanomas. Differentiation of naïve T cells to EM cells only occurred from CD70 costimulation in concert with T-cell receptor (TCR) stimulation (signal one), suggesting that EM TIL responding to CD70 would be enriched for T cells reactive with local antigens, including those associated with RCC. Clonotypic analysis of TCRs in fresh RCCs showed that EM T cells were more clonally expanded than CM or naïve T cells, and the clonal expansion occurred at the tumor site as oligoclonal TCRs were distinct from PBL TCRs from the same patient. In addition, we found that 2 TCRs from the highly represented EM TIL clones, when reexpressed in fresh PBL, recognized an MHC-class II or MHC-class I-restricted antigens shared by multiple RCC lines. Our results suggest that RCC-reactive TIL do exist in situ, but may be difficult to recover and study because of proliferative exhaustion, driven by tumor-expressed CD70.

Enhanced costimulation by CD70+ B cells aggravates experimental autoimmune encephalomyelitis in autoimmune mice

OBJECTIVE

Assess whether CD70+ B cells contribute to EAE.

MATERIALS AND METHODS

MOG-specific TCR transgenic mice (2D2) were crossed with mice with constitutive CD70 expression on B cells. The development of EAE and the phenotype of B-T lymphocytes were studied in 2D2xCD70 animals.

RESULTS

Spontaneous EAE developed in 20% of 2D2xCD70 and 3% of 2D2 mice. EAE was also more severe in 2D2xCD70 versus 2D2 animals upon MOG immunization. The susceptibility of 2D2xCD70 to EAE was associated with fewer FoxP3+ T cells.

CONCLUSIONS

Expression of CD70 by B cells aggravates EAE possibly by reducing the number of regulatory T cells.

Altered T cell differentiation associated with loss of CD27 and CD28 in HIV infected Indian individuals

BACKGROUND

HIV-1 infection is associated with depletion of naïve T cell subsets and skewed T cell differentiation and maturation, leading to accumulation of T cells at intermediate and end stages of differentiation. CD27 and CD28 expression have been utilized in assessing these population subsets.

METHODS

We characterized T cell subsets based on expression of CD45RA, CCR7, CD27, and CD28 and compared these subsets in HIV-1 infected Indian subjects and uninfected controls.

RESULTS

HIV-1 infection was associated with an increase in effector and memory T cell subsets and a concomitant decrease in naïve T cells. HIV-1 infected subjects showed accumulation of intermediate CD8 T cell (CD27+CD28-) differentiation subsets, whereas CD4 T cells progressed to late stage differentiation (CD27-CD28-). These subsets were negatively associated with CD4 T cell counts and positively associated with plasma viremia. CD57, an immunosenescence marker, was also increased on T cell subsets from HIV-1 infected individuals. Antiretroviral therapy resulted in partial restoration of differentiation status.

CONCLUSION

Persistent HIV-1 replication and chronic immune activation, along with altered cytokine secretion profile, lead to impaired T cell differentiation and maturation. Detailed understanding of factors associated with differentiation defects in HIV-1 infected Indian individuals will strongly assist in Indian HIV-1 vaccine efforts and add to our knowledge of HIV-1 subtype C pathogenesis.

Opposing effects of CD70 costimulation during acute and chronic lymphocytic choriomeningitis virus infection of mice

T cell costimulation is important for T cell activation. The CD27/CD70 pathway contributes to effector and memory T cell development and is involved in T cell and B cell activation. CD27/CD70 is known for having opposing roles during different models of antigenic challenges. During primary T cell responses to influenza virus infection or during tumor challenges, CD27/CD70 costimulation has a positive role on T cell responses. However, during some chronic infections, constitutive triggering of this signaling pathway has a negative role on T cell responses. It is currently unclear what specific characteristic of an antigen determines the outcome of CD27/CD70 costimulation. We investigated the effect of a transient CD70 blockade during an acute or a chronic lymphocytic choriomeningitis virus (LCMV) infection in mice. Blockade of this pathway during acute LCMV infection (Armstrong strain) resulted in delayed T cell responses and decreased CD127 (interleukin-7 receptor α [IL-7Rα] chain) conversion. Upregulation of CD127 is an important event in T cell differentiation that heralds the passage of an effector T cell to a long-lived memory T cell. In contrast to the reduced CD8 T cell responses after CD70 blockade during acute infection, CD70 blockade during chronic LCMV infection resulted in increased CD8 T cell responses. Our data show the dual roles of this costimulatory pathway in acute versus persistent antigen challenge. Our findings suggest that antigen persistence may determine the effect of CD27/CD70 signaling on CD8 T cell responses. Tailored triggering or blockade of this costimulatory pathway may be important in vaccination regimens against acute or chronic pathogens.

Chronic myelogenous leukemia maintains specific CD8(+) T cells through IL-7 signaling

Chronic myelogenous leukemia (CML) is a malignant myeloproliferative disease of hematopoietic stem cells. The disease progresses after several years from an initial chronic phase to a blast phase. Leukemia-specific T cells are regularly detected in CML patients and may be involved in the immunological control of the disease. Here, we analyzed the role of leukemia-specific CD8(+) T cells in CML disease control and the mechanism that maintains CD8(+) T-cell immunosurveillance in a retroviral-induced murine CML model. To study antigen-specific immune responses, the glycoprotein of the lymphocytic choriomeningitis virus was used as model leukemia antigen. Leukemia-specific CTL activity was detectable in vivo in CML mice and depletion of CD8(+) T cells rapidly led to disease progression. CML-specific CTL were characterized by the expression of the IL-7 receptor α-chain. In addition, leukemia cells produced IL-7 that was crucial for the maintenance of leukemia-specific CTL and for disease control. Therefore, CML cells maintain the specific CD8(+) T-cell-mediated immune control by IL-7 secretion. This results in prolonged control of disease and probably contributes to the characteristic chronic phase of the disease.

Role of CD4+ cytotoxic T lymphocytes in the control of viral diseases and cancer

Our knowledge on the physiological role of CD4(+) T lymphocytes has improved in the last decade: available data convincingly demonstrate that, besides the 'helper' activity, CD4(+) T cells may be also endowed with lytic properties. The cytotoxic function of these effector cells has a relevant role in the control of pathogenic infections and in mediating antitumor immune responses. On these bases, several immunotherapeutic approaches exploiting the cytotoxic properties of CD4(+) T cells are under investigation. This review summarizes available data supporting the functional and therapeutic relevance of cytotoxic CD4(+) T cells, with a particular focus on Epstein-Barr virus (EBV)-related disorders.

Role of CD27/CD70 pathway of activation in immunity and tolerance

The CD70/CD27 axis has gained increasing interest among the immunologists, because of its capacity to regulate immunity versus tolerance. Recent studies clearly show that expression of CD70 may prevent tolerance induced by antigen presentation in the steady-state, i.e., by nonactivated DCs. In addition, CD27 signaling appears critical for T cell expansion and survival and therefore, induction of long-term memory. It contributes to germinal center formation, B cell activation, and production of neutralizing antibodies but can also be subverted by viruses, in particular, during chronic infections. The potential role of the CD27/CD70 pathway in the course of inflammatory diseases, as in EAE, arthritis, and inflammatory bowel disease models, suggests that CD70 may be a target for immune intervention. Conversely, the potency of costimulation through CD27 suggests that the CD27/CD70 axis could be exploited for the design of anti-cancer vaccines.

Timing and tuning of CD27-CD70 interactions: the impact of signal strength in setting the balance between adaptive responses and immunopathology

SUMMARY

After binding its natural ligand cluster of differentiation 70 (CD70), CD27, a tumor necrosis factor receptor (TNFR)-associated factor-binding member of the TNFR family, regulates cellular activity in subsets of T, B, and natural killer cells as well as hematopoietic progenitor cells. In normal immune responses, CD27 signaling appears to be limited predominantly by the restricted expression of CD70, which is only transiently expressed by cells of the immune system upon activation. Studies performed in CD27-deficient and CD70-transgenic mice have defined a non-redundant role of this receptor-ligand pair in shaping adaptive T-cell responses. Moreover, adjuvant properties of CD70 have been exploited for the design of anti-cancer vaccines. However, continuous CD27-CD70 interactions may cause immune dysregulation and immunopathology in conditions of chronic immune activation such as during persistent virus infection and autoimmune disease. We conclude that optimal tuning of CD27-CD70 interaction is crucial for the regulation of the cellular immune response. We provide a detailed comparison of costimulation through CD27 with its closely related family members 4-1BB (CD137), CD30, herpes virus entry mediator, OX40 (CD134), and glucocorticoid-induced TNFR family-related gene, and we argue that these receptors do not have a unique function per se but that rather the timing, context, and intensity of these costimulatory signals determine the functional consequence of their activity.

Protective CD8 T cell memory is impaired during chronic CD70-driven costimulation

Chronic infection results in continuous formation and exhaustion of effector CD8 T cells and in failure of memory CD8 T cell development. Expression of CD70 and other molecules that provide costimulation to T cells is maintained during chronic infection. To analyze the impact of constitutive CD70-driven costimulation, we generated transgenic mice expressing CD70 specifically on T cells. We show that CD70 promoted accumulation of CD8 T cells with characteristics strikingly similar to exhausted effector CD8 T cells found during chronic infection. CD70 on T cells provided costimulation that enhanced primary CD8 T cell responses against influenza. In contrast, memory CD8 T cell maintenance and protection against secondary challenge with influenza was impaired. Interestingly, we found no effect on the formation of either effector or memory CD4 T cells. We conclude that constitutive expression of CD70 is sufficient to deregulate the CD8 T cell differentiation pathway of acute infection reminiscent of events in chronic infection.

Chronic lymphocytic leukemia (CLL) cells genetically modified to express B7-1, ICAM-1, and LFA-3 confer APC capacity to T cells from CLL patients

In chronic lymphocytic leukemia (CLL), malignant B cells and nonmalignant T cells exhibit dysfunction. We previously demonstrated that infection of CLL cells with modified vaccinia Ankara (MVA) expressing the costimulatory molecules B7-1, ICAM-1, and LFA-3 (designated TRICOM) increased expression of these costimulatory molecules on the surface of CLL cells and thus augmented their antigen-presenting capability. Here, we evaluate the effect of MVA-TRICOM-modified CLL cells on T cells. Following incubation with irradiated MVA-TRICOM-modified CLL cells, allogeneic and autologous CD4(+) and CD8(+) T cells expressed significantly higher levels of B7-1, ICAM-1, and LFA-3. We show that this increase was the result of physical acquisition from the antigen-presenting cells (APCs), and that purified T cells that acquired costimulatory molecules from MVA-TRICOM-modified CLL cells were able to stimulate the proliferation of untreated T cells. These results demonstrate for the first time that T cells from CLL patients can acquire multiple costimulatory molecules from autologous CLL cells and can then act as APCs themselves. Given the immunodeficiencies characteristic of CLL, enhancing the antigen-presenting function of CLL cells and T cells simultaneously could be a distinct advantage in the effort to elicit antitumor immune responses.

PDL-1 upregulation on monocytes and T cells by HIV via type I interferon: restricted expression of type I interferon receptor by CCR5-expressing leukocytes

The programmed death (PD)-1 interacts with its ligand (PDL-1) delivering a negative signal to T cells. During human immunodeficiency virus (HIV)-1 infection PD-1 and PDL-1 expressions are increased. Here we show that monocytes and CCR5(+) T cells of HIV-uninfected donors upregulated PDL-1 upon in vitro exposure to HIV. HIV-induced PDL-1 required interferon (IFN)-alpha, but not IFN-gamma, production. Inhibition of endocytosis, required for HIV-induced IFN-alpha production, prevented PDL-1 upregulation. IFN-alpha-inducing Toll-like receptor (TLR) agonists increased PDL-1 on monocytes and CCR5(+) T cells. CD80 and CD86 were also increased on monocytes and CCR5(+) T cells after HIV exposure, but only CD80 was IFN-alpha-dependent. IFN-alpha-receptor subunit 2 (IFNAR2), was expressed only by CCR5(+) T cells and monocytes, explaining why these leukocytes responded to HIV-induced IFN-alpha. Finally, T cell proliferation was improved by PDL-1 blockade in HIV-treated PBMC. In the setting of HIV infection, IFN-alpha may negatively affect T cell responses by inducing PDL-1.

The price of the CD27-CD70 costimulatory axis: you can't have it all

T cells require costimulatory signals for optimal proliferation, differentiation, and survival and thus to induce protective immune responses. Recent data, however, show that during chronic lymphocyte choriomeningitis virus (LCMV) infection, triggering of the costimulatory receptor CD27 by its ligand CD70 impedes neutralizing antibody production and leads to viral persistence. Thus, while being crucial for the induction of some adaptive effector pathways, costimulation may block the development of others. Pathogens may exploit this Achilles' heal to achieve persistence.

Evaluation of CD86 gene polymorphism at +1057 position in liver transplant recipients

BACKGROUND

Efficient T cell-APC interaction requires the participation of primary and co-stimulatory signals. The main co-stimulatory pathway involves the interaction of CD80 and CD86, expressed on the APCs, with their T cell counter-receptor, CD28 and CTLA-4. Recently, a G to A transition has been described at position +1057 of the CD86 gene, located in their cytoplasmic tail.

METHODS

CD86 polymorphism was analyzed by sequence based typing in DNA samples obtained from 205 liver transplant recipients. Acute rejection and chronic rejection were diagnosed based upon conventional clinical, biochemical and histological criteria.

RESULTS

The study of CD86 +1057 (G/A) polymorphism revealed that recipients bearing the A allele or the AA genotype have a reduced risk of acute rejection. In fact, the AA genotype was absent in the group of patients showing acute rejection episodes, whereas its frequency in those patients without acute rejection episodes was 8.8% (P=0.009, OR=0.07). This polymorphism did not reveal any association with the incidence of chronic rejection, but patients bearing the AA genotype showed a higher graft survival rate (83.3%) than those bearing the GA genotype (49.3%) or GG genotype (56.5%).

CONCLUSIONS

The results of the present report suggest that the CD86 AA genotype at +1057 position could be involved in liver transplant acceptance, given that its presence is related to a decrease of acute rejection frequency and to a graft survival increase.

Physiological relevance of antigen presentasome (APS), an acquired MHC/costimulatory complex, in the sustained activation of CD4+ T cells in the absence of APCs

T-cell interaction with antigen-presenting cells (APCs) results in activation and clonal expansion of naive T cells. CD80 expression/acquisition in T cells has been implicated in disease processes in patients with rheumatoid arthritis and multiple myeloma and patients infected with HIV. Our previous data indicate that antigen-specific activation of naive T cells results in T-cell acquisition of CD80 molecules from APCs. However, the functional relevance of the acquired CD80 by T cells in signal pathways has remained unresolved. This study aims to define for the first time the role of acquired CD80 in T-cell clonal expansion. We demonstrate the following: (1) T cells, upon CD80 acquisition, sustain their proliferative response in the absence of APCs; (2) T cells that acquire CD80 sustain the activity of transcriptional factors such as nuclear factor-κB (NFκB) and activator protein-1 (AP1) for 24 hours after separation from APCs and up-regulate signal transducer and activator of transcription-5 (Stat5) in the absence of APCs or exogenous signal 1; and (3) maintenance of these signals results in unique cytokine production. Collectively, our data support the unique concept that naive T cells sustain their activation by removing “antigen presentasome” (APS; eg, antigen-presenting complex) from APCs, thereby releasing the constraint of APC requirement for further activation. (Blood. 2005;105: 3238-3246)

CD27 expression promotes long-term survival of functional effector-memory CD8+ cytotoxic T lymphocytes in HIV-infected patients

Human immunodeficiency virus (HIV)-specific CD8(+) T cells persist in high frequencies in HIV-infected patients despite impaired CD4(+) T helper response to the virus, but, unlike other differentiated effector cytotoxic T lymphocytes, most continue to express the tumor necrosis factor receptor family member CD27. Because the ligand for CD27 (CD70) is also overexpressed in HIV-infected hosts, we examined the nature of expression and potential functional consequences of CD27 expression on HIV-specific CD8(+) T cells. Analysis of CD27(+) and CD27(-) T cells derived from the same HIV-specific clone revealed that retention of CD27 did not interfere with acquisition of effector functions, and that after T cell receptor stimulation, CD27(+) cells that concurrently were triggered via CD27 exhibited more resistance to apoptosis, interleukin 2 production, and proliferation than CD27(-) T cells. After transfer back into an HIV-infected patient, autologous HIV-specific CD27(-) T cells rapidly disappeared, but CD27(+) T cells derived from the same clone persisted at high frequency. Our findings suggest that the CD27-CD70 interaction in HIV infection may provide CD27(+) CD8(+) T cells with a survival advantage and compensate for limiting or absent CD4(+) T help to maintain the CD8 response.

HLA-DR, ICAM-1, CD40, CD40L, and CD86 are incorporated to a similar degree into clinical human immunodeficiency virus type 1 variants expanded in natural reservoirs such as peripheral blood mononuclear cells and human lymphoid tissue cultured ex vivo

To provide additional information on the acquisition of host cell membrane proteins by human immunodeficiency virus type 1 (HIV-1) produced by natural cellular reservoirs, two different field isolates were used to infect ex vivo expanded peripheral blood mononuclear cells (PBMCs) and human lymphoid tissue histocultures. The insertion of host-derived HLA-DR, intercellular adhesion molecule-1 (ICAM-1), CD40, CD40L, and CD86 within HIV-1 particles was evaluated by using specific antibodies linked to a solid matrix to capture ultrafiltrated viral progeny. Overall, our data indicate that neither the HIV-1 co-receptor usage (i.e., T-tropic or macrophage-tropic) nor the cellular source of HIV-1 has an impact on the incorporation process but it was found to be under the influence of the donor source. Given that most viral replication is thought to occur in lymphoid tissues and previous works have shown that HIV-1 life cycle is affected by several virus-anchored host proteins, our results suggest that this phenomenon is likely to contribute to the pathogenesis of this retroviral infection.

Spontaneous T cell apoptosis in feline immunodeficiency virus (FIV)-infected cats is inhibited by IL2 and anti-B7.1 antibodies

Lymph node (LN) T cells from feline immunodeficiency virus (FIV)-infected cats have an increased expression of B7 co-stimulatory molecules as well as their ligand CTLA4, resembling an activation phenotype shown to induce anergy and apoptosis in activated T cells. In addition, LN T cells from FIV-infected cats also show increased spontaneous apoptosis compared to uninfected animals. The apoptosis observed in these animals occurs primarily in T cells expressing B7 and CTLA4, suggesting a role for B7 and CTLA4 interactions in the induction of anergy/apoptosis. In order to investigate the role of B7 and CTLA4 interactions on T cell apoptosis in LN T cells from FIV-infected cats, we performed blocking experiments by measuring T cell apoptosis in LN T cell cultures treated with anti-feline B7.1, B7.2, and CTLA4 specific antibodies, as well as interleukin (IL)-2. The addition of IL2, the primary cytokine produced by B7/CD28 interactions, resulted in a significant decrease of T cell apoptosis in cultured LN cells as assessed by two-color flow cytometry and TUNEL assay. The addition of anti-B7.1 antibodies significantly inhibited T cell apoptosis in FIV-infected cats with low-level plasma viremia, while addition of anti-B7.2 and anti-CTLA4 antibodies had no affect. These results suggest a role of B7 signaling in the increased spontaneous apoptosis observed in LN T cells from FIV-infected animals.

B7+CTLA4+ T cells engage in T-T cell interactions that mediate apoptosis: a model for lentivirus-induced T cell depletion

Apoptosis in lymph node (LN) T cells of feline immunodeficiency virus (FIV)-infected cats is associated with cells co-expressing B7.1 and B7.2 costimulatory molecules, and their ligand CTLA4. To study the possibility of B7.1/B7.2-CTLA4 mediated T-T interactions and the predicted induction of T cell apoptosis in vitro, costimulatory molecules were up-regulated on CD4+ and CD8+ T cells by mitogen stimulation. B7.1 expression on in vitro stimulated CD4+ and CD8+ cells increased within 24h; B7.2 and CTLA4 expression increased after 48-72 h. Apoptosis, as analyzed by terminal deoxynucleotidyl transferase (transferase nick end labeling, TUNEL)-based staining followed by three color flow cytometric analysis, correlated to the cells expressing B7 and/or CTLA4. Blocking experiments revealed that CD4+ and CD8+ T cell apoptosis could be significantly inhibited with anti-B7 antibodies. As FIV infection results in immune activation with a T cell phenotype similar to that of the in vitro activated T cells, the data support the hypothesis that the chronic expansion of B7+CTLA4+ LN T cells in infected cats allows for T-T cell interactions resulting in T cell depletion and eventually the development of AIDS.

Feline Immunodeficiency Virus Infection Phenotypically and Functionally Activates Immunosuppressive CD4+CD25+T Regulatory Cells

Disease progression of feline immunodeficiency virus (FIV) infection is characterized by up-regulation of B7.1 and B7.2 costimulatory molecules and their ligand CTLA4 on CD4(+) and CD8(+) T cells. The CD4(+)CTLA4(+)B7(+) phenotype described in FIV(+) cats is reminiscent of CD4(+)CD25(+)CTLA4(+) cells, a phenotype described for immunosuppressive T regulatory (Treg) cells. In the present study, we describe the phenotypic and functional characteristics of CD4(+)CD25(+) T cells in PBMC and lymph nodes (LN) of FIV(+) and control cats. Similar to Treg cells, feline CD4(+)CD25(+) but not CD4(+)CD25(-) T cells directly isolated from LN of FIV(+) cats do not produce IL-2 and fail to proliferate in response to mitogen stimulation. Unstimulated CD4(+)CD25(+) T cells from FIV(+) cats significantly suppress the proliferative response and the IL-2 production of Con A-stimulated autologous CD4(+)CD25(-) T cells compared with unstimulated CD4(+)CD25(+) T cells from FIV(-) cats. Flow-cytometric analysis confirmed the apparent activation phenotype of the CD4(+)CD25(+) cells in LN of chronically FIV(+) cats, because these cells showed significant up-regulation of expression of costimulatory molecules B7.1, B7.2, and CTLA4. These FIV-activated, anergic, immunosuppressive CD25(+)CTLA4(+)B7(+)CD4(+) Treg-like cells may contribute to the progressive loss of T cell immune function that is characteristic of FIV infection.

Immune activation and CD8+ T-cell differentiation towards senescence in HIV-1 infection

Progress in the fight against the HIV/AIDS epidemic is hindered by our failure to elucidate the precise reasons for the onset of immunodeficiency in HIV-1 infection. Increasing evidence suggests that elevated immune activation is associated with poor outcome in HIV-1 pathogenesis. However, the basis of this association remains unclear. Through ex vivo analysis of virus-specific CD8(+) T-cells and the use of an in vitro model of naïve CD8(+) T-cell priming, we show that the activation level and the differentiation state of T-cells are closely related. Acute HIV-1 infection induces massive activation of CD8(+) T-cells, affecting many cell populations, not only those specific for HIV-1, which results in further differentiation of these cells. HIV disease progression correlates with increased proportions of highly differentiated CD8(+) T-cells, which exhibit characteristics of replicative senescence and probably indicate a decline in T-cell competence of the infected person. The differentiation of CD8(+) and CD4(+) T-cells towards a state of replicative senescence is a natural process. It can be driven by excessive levels of immune stimulation. This may be part of the mechanism through which HIV-1-mediated immune activation exhausts the capacity of the immune system.

Restoration of CD28 expression in CD28- CD8+ memory effector T cells reconstitutes antigen-induced IL-2 production

The control of many persistent viral infections by Ag-specific cytolytic CD8+ T cells requires a concurrent virus-specific CD4+ Th cell response. This reflects in part a requirement of activated effector CD8+ T cells for paracrine IL-2 production as a growth and survival factor. In human CMV and HIV infection, the majority of differentiated virus-specific CD8+ T cells notably lose the ability to produce IL-2 but also lose expression of CD28, a costimulatory molecule. Analysis of the fraction of memory CD8+ T cells that continue to express CD28 revealed these cells retain the ability to produce IL-2. Therefore, we examined if IL-2 production by CD28- CD8+ T cells could be restored by introduction of a constitutively expressed CD28 gene. Expression of CD28 in CD28- CD8+ CMV- and HIV-specific CD8+ T cells reconstituted the ability to produce IL-2, which could sustain an autocrine proliferative response after Ag recognition. These results suggest that the loss of CD28 expression during differentiation of memory/effector CD8+ T cells represents a decisive step in establishing regulation of responding CD8+ T cells, increasing the dependence on CD4+ Th for proliferation after target recognition, and has implications for the treatment of viral disease with adoptively transferred CD8+ T cells.

Persistent immune activation in HIV-1 infection is associated with progression to AIDS

BACKGROUND

HIV-1 infection is characterized by chronic generalized CD8 and CD4 T cell hyperactivation, the biological effect of which is not understood.

OBJECTIVE

To study the relation between chronic immune activation and CD4 T cell depletion in HIV-1 infection.

DESIGN

Prospective cohort study among participants of the Amsterdam Cohort Studies on HIV-1 infection and AIDS who have a known seroconversion date (n = 102).

METHODS

CD4 and CD8 T cell activation marker expression was analysed by FACScan before and after seroconversion (1 and 5 years after seroconversion); T cell proliferation and T cell numbers were also measured. Cox proportional hazard analyses were used to study the predictive value of these parameters for progression to AIDS.

RESULTS

Preseroconversion low CD4 T cell numbers or elevated levels of CD4 T cell activation were associated with increased risk for development of AIDS after HIV-1 seroconversion. Progression to AIDS was associated with loss of both CD4 and CD8 naive T cells. The predictive value of CD8 T cell activation was confirmed and, in addition, in the course of infection low CD4 T cell counts and increasing proportions of dividing CD4 T cells, dividing CD8 T cells or elevated CD4 T cell activation marker expression became independent predictors of progression to AIDS.

CONCLUSIONS

Increased T cell activation has predictive value for HIV-1 disease progression even before seroconversion. These data support the hypothesis that persistent hyperactivation of the immune system may lead to erosion of the naive T cell pool and CD4 T cell depletion.

Lethal T cell immunodeficiency induced by chronic costimulation via CD27-CD70 interactions

It has been proposed that HIV-1, in addition to directly infecting and killing CD4+ T cells, causes T cell dysfunction and T cell loss by chronic immune activation. We analyzed the effects of chronic immune activation in mice that constitutively expressed CD70, the ligand for the tumor necrosis factor receptor family member CD27, on B cells. CD70 transgenic (CD70 Tg) mice showed a progressive conversion of naive T cells into effector-memory cells, which culminated in the depletion of naive T cells from lymph nodes and spleen. T cell changes depended on continuous CD27-CD70 interactions and T cell antigen receptor stimulation. Despite this hyperactive immune system, CD70 Tg mice died aged 6-8 months from Pneumocystis carinii infection, a hallmark of T cell immunodeficiency. Thus, persistent delivery of costimulatory signals via CD27-CD70 interactions, as may occur during chronic active viral infections, can exhaust the T cell pool and is sufficient to induce lethal immunodeficiency.

Premature ageing of the immune system: the cause of AIDS?

The reasons for the failure of the immune system to control HIV-1 infection, and the resulting immunodeficiency, remain unclear. HIV-1 persists in its host despite vigorous immune responses, including a strong, and probably functional, HIV-specific cytotoxic T-lymphocyte response. Interestingly the immunological features of HIV-1-infected individuals show many similarities to those seen in elderly people without HIV infection. We propose that, through a process of continuous immune activation, HIV-1 infection leads to an acceleration of the adaptive immune system ageing process, resulting in premature exhaustion of immune resources, which participates in the onset of immunodeficiency. This hypothesis might shed new light on HIV-1 pathogenesis and could suggest the need to reconsider current immunotherapeutic strategies to fight the virus.

Acquisition of CD80 by human T cells at early stages of activation: functional involvement of CD80 acquisition in T cell to T cell interaction

The interaction between CD28 on T cells and CD80 on APCs intensifies the linkage between TCR and MHC at the site of contact between T cells and APCs. In this study, we demonstrate that during human T cell/human APC interaction, the autologous or allogeneic human CD4(+) T cells become positive for the detection of CD80 at an early stage of activation (24 h). This detection of CD80 is attributable to the acquisition of CD80 from APCs, as opposed to the up-regulation of endogenous CD80, as demonstrated by CD4(+) T cells treated with cyclohexamide. Furthermore, no CD80 mRNA could be detected at 24 h in T cells that had acquired CD80 from APCs. CD80 acquisition by T cells from APCs was enhanced upon TCR engagement. The amount of CD80 acquisition by CD4(+) T cells was shown to be related to the expression of CD80 on APCs. Using soluble fusion proteins (soluble CTLA-4, CD28, and CD80) to block either CD28 on the surface of T cells or CD80 on the surface of APCs, it was demonstrated that CD80 acquisition by T cells is mediated through its receptors, possibly CD28 interaction. Moreover, we demonstrate that T cells that have acquired CD80 have the ability to stimulate other T cells. These data thus suggest that CD80 acquisition by human T cells might play a role in the immunoregulation of T cell responses.

The innate immune response to tumors and its role in the induction of T-cell immunity

Recent genetic studies have resurrected the concept that the adaptive and innate immune systems play roles in tumor surveillance. Natural killer (NK) cells recognize many tumor cells but not normal self cells, and they are thought to aid in the elimination of nascent tumors. Two main strategies are employed by NK cells to recognize tumor targets. Many tumor cells down-regulate class I major histocompatibility complex (MHC) molecules, thus releasing the NK cell from the inhibition provided by class I MHC-specific inhibitory receptors ('missing self recognition'). More recently, it has become clear that a stimulatory receptor expressed by NK cells, T cells and macrophages (NKG2D) recognizes ligands (MHC class I chain related [MIC], H6O, retinoic acid early inducible [Rae1] and UL16 binding proteins [ULBP]) that are up-regulated on tumor cells and virally infected cells but are not expressed well by normal cells. Ectopic expression of these ligands on tumor cells leads to the potent rejection of the tumors in vivo. Importantly, mice that previously rejected the ligand+ tumor cells develop T-cell immunity to the parental (ligand-) tumor cells. The recognition of induced-self ligands as a strategy to recognize abnormal self sets a precedent for a new immune recognition strategy of the innate immune system.

New insights into the functionality of a virion-anchored host cell membrane protein: CD28 versus HIV type 1

It is now well established that the HIV type 1 (HIV-1) incorporates a vast array of host-encoded molecules in its envelope during the budding process. Interestingly, it was demonstrated that the attachment process is accentuated by supplementary interactions between virion-anchored host molecules and their cognate ligands. Such an enhancement of the viral attachment process was found to result in an increase of infectivity for both T and macrophage-tropic strains of HIV-1. Given that previous work indicates that HIV-1 is budding at the site of cell-to-cell contact, a location rich in the costimulatory CD28 glycoprotein, we investigated whether CD28 could be efficiently acquired by HIV-1. We have been able to generate progeny viruses bearing or not bearing on their surfaces host-derived CD28 using our previously described transient transfection and expression system. The physical presence of CD28 was found to markedly increase virus infectivity in a CD28/B7-dependent manner following infection of two human lymphoid cell lines expressing high levels of surface B7-1/B7-2, two natural ligands of CD28. The physiological significance of CD28 incorporation was provided by the observation that an anti-CD28 Ab decreased replication in primary human mononuclear cells of clinical isolates of HIV-1 propagated in such cells. A virus precipitation assay revealed that M-, T-, and dual-tropic clinical strains of HIV-1 produced in primary human mononuclear cells do indeed incorporate CD28. These results show for the first time that HIV-1 can incorporate CD28 and the acquisition of this specific host surface glycoprotein modulates the virus life cycle.

Characterization of CD4(+) CTLs ex vivo

The cytotoxic potential of CD8(+) T cells and NK cells plays a crucial role in the immune response to pathogens. Although in vitro studies have reported that CD4(+) T cells are also able to mediate perforin-mediated killing, the in vivo existence and relevance of cytotoxic CD4(+) T cells have been the subject of debate. Here we show that a population of CD4(+) perforin(+) T cells is present in the circulation at low numbers in healthy donors and is markedly expanded in donors with chronic viral infections, in particular HIV infection, at all stages of the disease, including early primary infection. Ex vivo analysis shows that these cells have cytotoxic potential mediated through the release of perforin. In comparison with more classical CD4(+) T cells, this subset displays a distinct surface phenotype and functional profile most consistent with end-stage differentiated T cells and include Ag experienced CD4(+) T cells. The existence of CD4(+) cytotoxic T cells in vivo at relatively high levels in chronic viral infection suggests a role in the immune response.

Dynamics of T cell responses in HIV infection

Cytotoxic CD8(+) T cells play a major role in the immune response against viruses. However, the dynamics of CD8(+) T cell responses during the course of a human infection are not well understood. Using tetrameric complexes in combination with a range of intracellular and extracellular markers, we present a detailed analysis of the changes in activation and differentiation undergone by Ag-specific CD8(+) T cells, in relation to Ag-specific CD4(+) T cell responses, in the context of a human infection: HIV-1. During primary HIV-1 infection, the initial population of HIV-specific CD8(+) T cells is highly activated and prone to apoptosis. The Ag-specific cells differentiate rapidly from naive to cells at a perforin low intermediate stage of differentiation, later forming a stable pool of resting cells as viral load decreases during chronic infection. These observations have significant implications for our understanding of T cell responses in human viral infections in general and indicate that the definition of effector and memory subsets in humans may need revision.

Plasma levels of soluble CD27: a simple marker to monitor immune activation during potent antiretroviral therapy in HIV-1-infected subjects

Plasma levels of soluble CD27 (sCD27) are elevated in diseases characterized by T cell activation and are used as a marker of immune activation. We assessed the usefulness of determining plasma sCD27 as a marker for monitoring immune activation in HIV-1-infected patients treated with highly active antiretroviral therapy (HAART). A first cross-sectional examination of 68 HIV-1-infected and 18 normal subjects showed high levels of sCD27 in HIV-1 infection; plasma sCD27 was correlated to HIV-1 viraemia and inversely correlated to CD4+ T cell count. Twenty-six HIV-1-infected patients undergoing HAART were studied at baseline and after 6, 12, 18 and 24 months of therapy. Seven additional patients under HAART were analysed at baseline, during and after interruption of therapy. In the total population, HAART induced a significant and progressive reduction, but not a normalization, of plasma levels of sCD27 after 24 months. A full normalization of plasma sCD27 was observed in the virological responders (undetectable HIV-1 RNA at months 18 and 24) and also in patients with moderate immunodeficiency at baseline (CD4+ T cell count >200 cells/mm3). Changes in plasma neopterin paralleled the changes in sCD27 but only baseline sCD27 levels were predictive of a greater increase in CD4+ T cell count during the follow-up. Discontinuation of therapy resulted in a rapid increase of sCD27 plasma levels associated with viraemia rebound and drop in CD4+ T cell count. Our findings suggest that plasma sCD27 may represent an alternative and simple marker to monitor immune activation during potent antiretroviral therapy. HIV-1-induced immune activation can be normalized by HAART in successfully treated patients where the disease is not advanced.

Human CD8+ CTL recognition and in vitro lysis of herpes simplex virus-infected cells by a non-MHC restricted mechanism

Cytotoxic T lymphocytes (CTL) are important for the recognition and lysis of virally infected cells, but their effectiveness can be limited by viral immune evasion mechanisms. We investigated the immunophenotype and function of human CD8+ T cells raised in response to herpes simplex virus (HSV). The expanded population contained cells of an activated and mature phenotype, as determined by the expressions of CD25, CD45RO, CD57, CD95 and HLA-DR. Cultured cells also expressed CD45RA. These cells lysed autologous and allogeneic HSV-infected lymphoblastoid cell line (LCL) targets via a non-major histocompatibility complex (MHC) restricted recognition pathway. Inhibition assays showed the mechanism of cytotoxicity to be calcium-dependent, granule exocytosis pathway, rather than the internal disintegration pathway. Cold target competition assays indicated that a common CTL population contributed to the recognition of autologous and allogeneic-infected targets. These effectors showed recognition of infected targets which was distinct from that of K562 cells. Non-MHC restricted lysis-associated molecule 2B4 (CD244) was upregulated on culturing and made a significant contribution to lysis of FcgammaR-bearing targets in a redirected killing assay. These findings suggest that CTL can recognize virally infected cells through a combination of non-MHC restricted mechanisms and may result in more efficient lysis than classical CD8+ T cells.

Induction of tumor-specific T cell memory by NK cell-mediated tumor rejection

Natural killer (NK) cells may modulate the development of adaptive immune responses, but until now there has been little evidence to support this hypothesis. We investigated the primary and secondary immunity elicited by various tumor cell lines that express CD70 and interact with CD70 ligand (CD27), which is constitutively expressed on NK cells. CD70 expression enhanced primary tumor rejection in vivo as well as T cell immunity against secondary tumor challenge. Primary rejection of major histocompatibility complex (MHC) class I-deficient RMA-S.CD70 tumor cells was mediated by NK cells and perforin- and interferon-gamma-dependent mechanisms. This NK cell-mediated process also efficiently evoked the subsequent development of tumor-specific cytotoxic and T helper type 1 responses to the parental, MHC class I-sufficient, RMA tumor cells. Thus CD27-CD70 interactions provide a key link between innate NK cell responses and adaptive T cell immunity.