The transcription factor FoxO1 sustains expression of the inhibitory receptor PD-1 and survival of antiviral CD8(+) T cells during chronic infection

Protein kinase B (also known as AKT) and the mechanistic target of rapamycin (mTOR) are central regulators of T cell differentiation, proliferation, metabolism, and survival. Here, we show that during chronic murine lymphocytic choriomeningitis virus infection, activation of AKT and mTOR are impaired in antiviral cytotoxic T lymphocytes (CTLs), resulting in enhanced activity of the transcription factor FoxO1. Blockade of inhibitory receptor programmed cell death protein 1 (PD-1) in vivo increased mTOR activity in virus-specific CTLs, and its therapeutic effects were abrogated by the mTOR inhibitor rapamycin. FoxO1 functioned as a transcriptional activator of PD-1 that promoted the differentiation of terminally exhausted CTLs. Importantly, FoxO1-null CTLs failed to persist and control chronic viral infection. Collectively, this study shows that CTLs adapt to persistent infection through a positive feedback pathway (PD-1?FoxO1?PD-1) that functions to both desensitize virus-specific CTLs to antigen and support their survival during chronic viral infection.

IL-21 Is Produced by NKT Cells and Modulates NKT Cell Activation and Cytokine Production

The common gamma-chain cytokine, IL-21, is produced by CD4(+) T cells and mediates potent effects on a variety of immune cells including NK, T, and B cells. NKT cells express the receptor for IL-21; however, the effect of this cytokine on NKT cell function has not been studied. We show that IL-21 on its own enhances survival of NKT cells in vitro, and IL-21 increases the proliferation of NKT cells in combination with IL-2 or IL-15, and particularly with the CD1d-restricted glycosphingolipid Ag alpha-galactosylceramide. Similar to its effects on NK cells, IL-21 enhances NKT cell granular morphology, including granzyme B expression, and some inhibitory NK receptors, including Ly49C/I and CD94. IL-21 also enhanced NKT cell cytokine production in response to anti-CD3/CD28 in vitro. Furthermore, NKT cells may be subject to autocrine IL-21-mediated stimulation because they are potent producers of this cytokine following in vitro stimulation via CD3 and CD28, particularly in conjunction with IL-12 or following in vivo stimulation with alpha-galactosylceramide. Indeed, NKT cells produced much higher levels of IL-21 than conventional CD4 T cells in this assay. This study demonstrates that NKT cells are potentially a major source of IL-21, and that IL-21 may be an important factor in NKT cell-mediated immune regulation, both in its effects on NK, T, and B cells, as well as direct effects on NKT cells themselves. The influence of IL-21 in NKT cell-dependent models of tumor rejection, microbial clearance, autoimmunity, and allergy should be the subject of future investigations.

Altered gene expression and function of peripheral blood natural killer cells in children with autism

Immune related abnormalities have repeatedly been reported in autism spectrum disorders (ASD), including evidence of immune dysregulation and autoimmune phenomena. NK cells may play an important role in neurodevelopmental disorders such as ASD. Here we performed a gene expression screen and cellular functional analysis on peripheral blood obtained from 52 children with ASD and 27 typically developing control children enrolled in the case-control CHARGE study. RNA expression of NK cell receptors and effector molecules were significantly upregulated in ASD. Flow cytometric analysis of NK cells demonstrated increased production of perforin, granzyme B, and interferon gamma (IFNgamma) under resting conditions in children with ASD (p<0.01). Following NK cell stimulation in the presence of K562 target cells, the cytotoxicity of NK cells was significantly reduced in ASD compared with controls (p<0.02). Furthermore, under similar stimulation conditions the presence of perforin, granzyme B, and IFNgamma in NK cells from ASD children was significantly lower compared with controls (p<0.001). These findings suggest possible dysfunction of NK cells in children with ASD. Abnormalities in NK cells may represent a susceptibility factor in ASD and may predispose to the development of autoimmunity and/or adverse neuroimmune interactions during critical periods of development.

Attenuation of CD8(+) T-cell function by CD4(+)CD25(+) regulatory T cells in B-cell non-Hodgkin's lymphoma

The underlying mechanisms by which tumor cells are resistant to CTL-mediated apoptosis are not clear. Using a human model of B-cell non-Hodgkin's lymphoma (B-cell NHL), we show that intratumoral T(reg) cells inhibit the proliferation and granule production of activated autologous infiltrating CD8(+) T cells. Our results also show that degranulation and subsequent cytotoxic activity of infiltrating CD8(+) T cells exposed to lymphoma B cells is completely attenuated by the presence of intratumoral T(reg) cells. Furthermore, we show that increased numbers of intratumoral T(reg) cells correlates with the number of CD8(+) T cells in biopsy specimens from patients with B-cell NHL, supporting the in vitro findings that intratumoral T(reg) cells inhibit proliferation of infiltrating CD8(+) T cells. Taken together, these data indicate that human lymphoma B cells are sensitive to autologous CTL-mediated cell death but are protected by the inhibitory function of intratumoral T(reg) cells.

Distinct profiles of cytotoxic granules in memory CD8 T cells correlate with function, differentiation stage, and antigen exposure

Cytotoxic CD8 T cells exert their antiviral and antitumor activity primarily through the secretion of cytotoxic granules. Degranulation activity and cytotoxic granules (perforin plus granzymes) generally define CD8 T cells with cytotoxic function. In this study, we have investigated the expression of granzyme K (GrmK) in comparison to that of GrmA, GrmB, and perforin. The expression of the cytotoxic granules was assessed in virus-specific CD8 T cells specific to influenza virus, Epstein-Barr virus (EBV), cytomegalovirus (CMV), or human immunodeficiency virus type 1 (HIV-1). We observed a dichotomy between GrmK and perforin expression in virus-specific CD8 T cells. The profile in influenza virus-specific CD8 T cells was perforin(-) GrmB(-) GrmA(+/-) GrmK(+); in CMV-specific cells, it was perforin(+) GrmB(+) GrmA(+) GrmK(-/+); and in EBV- and HIV-1-specific cells, it was perforin(-/+) GrmB(+) GrmA(+) GrmK(+). On the basis of the delineation of memory and effector CD8 T cells with CD45RA and CD127, the GrmK(+) profile was associated with early-stage memory CD8 T-cell differentiation, the perforin(+) GrmB(+) GrmA(+) profile with advanced-stage differentiation, and the GrmB(+) GrmA(+) Grmk(+) profile with intermediate-stage differentiation. Furthermore, perforin and GrmB but not GrmA and GrmK correlated with cytotoxic activity. Finally, changes in antigen exposure in vitro and in vivo during primary HIV-1 infection and vaccination modulated cytotoxic granule profiles. These results advance our understanding of the relationship between distinct profiles of cytotoxic granules in memory CD8 T cells and function, differentiation stage, and antigen exposure.

Inflammatory response in human tick-borne encephalitis: analysis of postmortem brain tissue

In Central European tick-borne encephalitis (TBE) mechanisms of tissue destruction are poorly understood. To evaluate the contribution of immunological mechanisms to tissue injury, the authors immunohistochemically analyzed paraffin-embedded autoptic brain tissue of 26 human TBE cases. In the parenchymal compartment, there was a predominance of macrophages/microglia and cytotoxic T cells. In addition, it was found that granzyme B-expressing lymphocytes were in close contact with TBE-expressing neurons up-regulating caspase-3. These findings indicate that cellular and humoral pathways of the immune system, especially granzyme B-releasing cytotoxic T cells and macrophages/microglia, mainly contribute to tissue destruction in TBE.

Human mast cells produce and release the cytotoxic lymphocyte associated protease granzyme B upon activation

Mast cells are widely distributed throughout the body and express effector functions in allergic reactions, inflammatory diseases, and host defense. Activation of mast cells results in exocytosis of preformed chemical mediators and leads to novel synthesis and secretion of lipid mediators and cytokines. Here, we show that human mast cells also express and release the cytotoxic lymphocyte-associated protease, granzyme B. Granzyme B was active and localized in cytoplasmic granules, morphologically resembling those present in cytotoxic lymphocytes. Expression and release of granzyme B by mast cell-lines HMC-1 and LAD 2 and by cord blood- and mature skin-derived human mast cells depended on the mode of activation of these cells. In mast cell lines and cord blood-derived mast cells, granzyme B expression was mainly induced by non-physiological stimuli (A23187/PMA, Compound 48/80) and substance P. In contrast, mature skin-derived mast cells only produced granzyme B upon IgE-dependent stimulation. We conclude that granzyme B is expressed and released by human mast cells upon physiologic stimulation. This suggests a role for granzyme B as a novel mediator in mast cell biology.

Susceptibility of CCR5-deficient mice to genital herpes simplex virus type 2 is linked to NK cell mobilization

Following genital herpes simplex virus type 2 (HSV-2) exposure, NK cells and T cells are mobilized to sites of infection to control viral replication and spread. The present investigation sought to determine the role of the chemokine receptor CCR5 in this process. Mice deficient in CCR5 (CCR5-/-) displayed a significant reduction in cumulative survival following infection in comparison to wild-type, HSV-2-infected controls. Associated with decreased resistance to viral infection, CCR5-/- mice yielded significantly more virus and expressed higher levels of tumor necrosis factor alpha, CXCL1, CCL2, CCL3, and CCL5 in the vagina, spinal cord, and/or brain stem than did wild-type mice. Whereas there was no difference in absolute number of leukocytes (CD45high), CD4 T cells, or CD8 T cells residing in the draining lymph nodes, spleen, spinal cord, or brain stem comparing HSV-2-infected wild-type to CCR5-/- mice prior to or after infection, there were significantly more NK cells (NK1.1+ CD3-) residing in the brain stem and spleen of infected wild-type mice. Functionally, NK activity from cells isolated from the brain stem of HSV-2-infected wild-type mice was greater than that from HSV-2-infected CCR5-/- mice. In addition, antibody-mediated depletion of NK cells resulted in an increase in HSV-2 levels in the vaginal, spinal cord, and brain stem tissue of wild-type but not CCR5-/- mice. Collectively, the absence of CCR5 expression significantly impacts the ability of the host to control genital HSV-2 infection, inflammation, and spread associated with a specific reduction in NK cell expansion, infiltration, and activity in the nervous system.

Brain microenvironment promotes the final functional maturation of tumor-specific effector CD8+ T cells

During the priming phase of an antitumor immune response, CD8(+) T cells undergo a program of differentiation driven by professional APCs in secondary lymphoid organs. This leads to clonal expansion and acquisition both of effector functions and a specific adhesion molecule pattern. Whether this program can be reshaped during the effector phase to adapt to the effector site microenvironment is unknown. We investigated this in murine brain tumor models using adoptive transfer of tumor-specific CD8(+) T cells, and in spontaneous immune responses of patients with malignant glioma. Our data show proliferation of Ag-experienced tumor-specific T cells within the brain parenchyma. Moreover, CD8(+) T cells further differentiated in the brain, exhibiting enhanced IFN-gamma and granzyme B expression and induction of alpha(E)(CD103)beta(7) integrin. This unexpected integrin expression identified a subpopulation of CD8(+) T cells conditioned by the brain microenvironment and also had functional consequences: alpha(E)(CD103)beta(7)-expressing CD8(+) T cells had enhanced retention in the brain. These findings were further investigated for CD8(+) T cells infiltrating human malignant glioma; CD8(+) T cells expressed alpha(E)(CD103)beta(7) integrin and granzyme B as in the murine models. Overall, our data indicate that the effector site plays an active role in shaping the effector phase of tumor immunity. The potential for local expansion and functional reprogramming should be considered when optimizing future immunotherapies for regional tumor control.

Maintenance of intestinal Th17 cells and reduced microbial translocation in SIV-infected rhesus macaques treated with interleukin (IL)-21

In pathogenic HIV and SIV infections of humans and rhesus macaques (RMs), preferential depletion of CD4⁺ Th17 cells correlates with mucosal immune dysfunction and disease progression. Interleukin (IL)-21 promotes differentiation of Th17 cells, long-term maintenance of functional CD8⁺ T cells, and differentiation of memory B cells and antibody-secreting plasma cells. We hypothesized that administration of IL-21 will improve mucosal function in the context of pathogenic HIV/SIV infections. To test this hypothesis, we infected 12 RMs with SIV(mac239) and at day 14 post-infection treated six of them with rhesus rIL-21-IgFc. IL-21-treatment was safe and did not increase plasma viral load or systemic immune activation. Compared to untreated animals, IL-21-treated RMs showed (i) higher expression of perforin and granzyme B in total and SIV-specific CD8⁺ T cells and (ii) higher levels of intestinal Th17 cells. Remarkably, increased levels of Th17 cells were associated with reduced levels of intestinal T cell proliferation, microbial translocation and systemic activation/inflammation in the chronic infection. In conclusion, IL-21-treatment in SIV-infected RMs improved mucosal immune function through enhanced preservation of Th17 cells. Further preclinical studies of IL-21 may be warranted to test its potential use during chronic infection in conjunction with antiretroviral therapy.

Lung cancer is associated with decreased expression of perforin, granzyme B and interferon (IFN)-γ by infiltrating lung tissue T cells, natural killer (NK) T-like and NK cells

There is a limited understanding how of lung cancer cells evade cytotoxic attack. Previously, we have shown reduced production of the cytotoxic mediator granzyme B by CD8(+) T cells in lung cancer tissue. We hypothesized that lung cancer would be further associated with decreased production of granzyme B, perforin and proinflammatory cytokines by other cytotoxic lymphocytes, natural killer (NK) T-like and NK cells, and that this would result from soluble mediators released by the cancer cells. Lung cancer and non-cancer tissue from five patients was identified by experienced pathologists. Tumour necrosis factor (TNF)-α, interferon (IFN)-γ, granzyme B and perforin were measured in CD4 and CD8(+) T, NK T-like cells and NK cells by flow cytometry. Correlation between cancer stage and granzyme B was analysed retrospectively for 21 patients. The effects of soluble factors released by lung cancer cells on production of cytotoxic mediators and cytokines was assessed, and the role of prostaglandin E2 (PGE)2 /COX investigated using indomethacin inhibition. There were significantly decreased percentages of T, NK T-like and NK cells expressing perforin, TNF-α and IFN-γ in cancer versus non-cancer tissue, and of CD8(+) T cells and CD8(+) NK T-like cells expressing granzyme B (e.g. NK T-like cells: non-cancer 30% ± 7 versus cancer 6% ± 2·5). Cancer cells released soluble factors that inhibited granzyme B, perforin and IFN-γ production that was partially associated with the PGE2 /COX2 pathway. Thus, lung cancer is associated with decreased expression of granzyme B, perforin and IFN-γ by infiltrating T cells, NK T-like and NK cells, possibly as a result of soluble factors produced by the cancer cells including PGE2 . This may be an important immune evasion mechanism.

Impaired expression of perforin and granulysin in CD8+ T cells at the site of infection in human chronic pulmonary tuberculosis

Protective immunity in tuberculosis is dependent on the coordinated release of cytolytic effector molecules from effector T cells and the subsequent granule-associated killing of infected target cells. In this study, we investigated the expression of cytolytic (perforin and granzyme A) and antimicrobial (granulysin) molecules at the single-cell level in cryopreserved lung tissue from patients with chronic, progressive tuberculosis disease. Quantification of protein-expressing cells was performed by in situ imaging, while mRNA levels in the infected tissue were analyzed by real-time PCR. Persistent inflammation, including excessive expression of inducible nitric oxide synthase in CD68+ macrophages and significant infiltration of CD3+, CD8+ and CD4+ T cells, was evident in tuberculosis lesions in all patients. However, despite the accumulation of CD3+ T cells, perforin- and granulysin-expressing CD3+ T cells were detected at two- to threefold-lower ratios in the tuberculosis lesions than in distal lung parenchyma and uninfected control lungs, respectively. This was evident at both the protein and mRNA levels. Moreover, perforin- and granulysin-expressing CD8+ T cells were scarce in individual granulomas within the tuberculosis lesions. In contrast, significant up-regulation of granzyme A-expressing CD3+ T cells was evident in the lesions from all patients. Confocal microscopy revealed coexpression of perforin and granulysin, primarily in CD8+ T cells; however, this expression was lower in the tuberculosis lesions. These findings suggest that symptomatic, chronic tuberculosis disease is associated with insufficient up-regulation of perforin and granulysin coexpression in CD8+ T cells at the local site of infection.

Cutting edge: migration to nonlymphoid tissues results in functional conversion of central to effector memory CD8 T cells

Memory CD8 T cells, essential for defense against intracellular pathogens, are heterogeneous with respect to phenotype and function. Constitutively lytic effector memory cells primarily reside in nonlymphoid tissues, whereas secondary lymphoid tissues contain functionally quiescent central memory cells. However, the mechanism by which functionally distinct memory populations are maintained is unknown. In this study, we show that resting CD8 memory cells modified their functional abilities upon entry into nonlymphoid tissues, as exemplified by the induction of granzyme B and lytic activity. Contemporaneously, the costimulator CD27 was down-regulated. These findings hold important implications for memory cell lineage development and tissue-specific immunity.

Foxp3(+) cell infiltration and granzyme B(+)/Foxp3(+) cell ratio are associated with outcome in neoadjuvant chemotherapy-treated ovarian carcinoma

Preoperative neoadjuvant chemotherapy (NAC) can significantly reduce tumour burden in patients with primarily unresectable chemosensitive tumours, allowing a more complete cytoreduction during debulking surgery and facilitating evaluation of tumour chemosensitivity, identification of appropriate treatment options and improvement of intervention protocols. In this study, we investigate, using immunohistochemistry, the impact of platinum/taxane-based NAC (NAC) on tumour-infiltrating lymphocytes (TILs) in advanced epithelial ovarian cancer (EOC) and their relationship with clinical outcome. All patients had clinical response, as shown by ascites volume and CA125 levels compared to pre-treatment findings. NAC intervention significantly increased CD4(+), CD8(+) and granzyme B(+) infiltration while Foxp3(+) accumulation remained unaffected. TILs were prognostically neutral for both progression-free survival (PFS) and overall survival (OS) before NAC. In contrast, after NAC, elevated granzyme B(+) infiltration displayed a tendency for improved PFS (log-rank 0.064). Further, low Foxp3(+) cell density was associated with longer PFS, as compared with strong Foxp3(+) infiltration (median 20.94 vs. 11.24 months; log-rank 0.0001) and with improved OS (median 30.75 vs. 16.04 months, respectively; log-rank 0.056), demonstrating clear prognostic significance for PFS. In addition, high granzyme B(+)/Foxp3(+) ratio post-NAC strongly correlated with improved PFS compared to low granzyme B(+)/Foxp3(+) cell ratio (median 17.88 vs. 11.24 months, respectively), and showed to be a favourable prognostic factor for PFS (log-rank 0.014). Our findings indicate that NAC elicited an immunologic profile in which low immunosuppressive Foxp3(+) infiltration and elevated numbers of activated granzyme B(+) cells were significantly associated with EOC-specific PFS, suggesting a contribution of immunologic effects to improved clinical outcome.

Plasmodium falciparum-infected erythrocytes induce granzyme B by NK cells through expression of host-Hsp70

In the early immune response to Plasmodium falciparum-infected erythrocytes (iRBC), Natural Killer (NK) cells are activated, which suggests an important role in innate anti-parasitic immunity. However, it is not well understood whether NK cells directly recognize iRBC or whether stimulation of NK cells depends mainly on activating signals from accessory cells through cell-to-cell contact or soluble factors. In the present study, we investigated the influence of membrane-bound host Heat shock protein (Hsp) 70 in triggering cytotoxicity of NK cells from malaria-naïve donors or the cell line NK92 against iRBC. Hsp70 and HLA-E membrane expression on iRBC and potential activatory NK cell receptors (NKG2C, CD94) were assessed by flow cytometry and immunoblot. Upon contact with iRBC, Granzyme B (GzmB) production and release was initiated by unstimulated and Hsp70-peptide (TKD) pre-stimulated NK cells, as determined by Western blot, RT-PCR and ELISPOT analysis. Eryptosis of iRBC was determined by Annexin V-staining. Our results suggest that presence of Hsp70 and absence of HLA-E on the membrane of iRBC prompt the infected host cells to become targets for NK cell-mediated cytotoxicity, as evidenced by impaired parasite development. Contact of iRBC with NK cells induced release of GzmB. We propose that following GzmB uptake, iRBC undergo eryptosis via a perforin-independent, GzmB-mediated mechanism. Since NK activity toward iRBC could be specifically enhanced by TKD peptide and abrogated to baseline levels by blocking Hsp70 exposure, we propose TKD as an innovative immunostimulatory agent to be tested as an adjunct to anti-parasitic treatments in vivo.

Granzyme B production distinguishes recently activated CD8(+) memory cells from resting memory cells

For immune diagnostic purposes it would be critical to be able to distinguish between ongoing immune processes, such as active infections, and long-term immune memory, for example imprinted by infections that have been cleared a long time ago or by vaccinations. We tested the hypothesis that the secretion of granzyme B, as detected in ex vivo ELISPOT assays, permits this distinction. We studied EBV-, flu- and CMV-specific CD8(+) cells in healthy individuals, Vaccinia virus-reactive CD8(+) cells in the course of vaccination, and HIV-specific CD8(+) cells in HIV-infected individuals. Antigen-specific ex vivo GzB production was detected only transiently after Vaccinia immunization, and in HIV-infected individuals. Our data suggest that ex vivo ELISPOT measurements of granzyme B permit the identification of actively ongoing CD8(+) cell responses-a notion that is pertinent to the immune diagnostic of infections, transplantation, allergies, autoimmune diseases, tumors and vaccine development.

Mesenchymal stem cells suppress CD8+ T cell-mediated activation by suppressing natural killer group 2, member D protein receptor expression and secretion of prostaglandin E2, indoleamine 2, 3-dioxygenase and transforming growth factor-β

Bone marrow mesenchymal stem cells (BMSCs) inhibit immune cell responsiveness, and especially of T lymphocytes. We showed that BMSCs markedly inhibited the proliferation and cytokine production by CD8(+) T cells by a cell-to-cell contact phenomenon and secretion of soluble factors. BMSCs down-regulate the expression of natural killer group 2, member D protein (NKG2D) receptors on CD8(+) T cells when co-cultured with them. Moreover, CD8(+) T cells that express low levels of NKG2D had impaired proliferation after triggering by a mitogen. The major histocompatibility complex (MHC) class I chain-related (MIC) A/B molecule, which is a typical ligand for NKG2D, was expressed on BMSCs, and caused dampening of cell proliferation. Monoclonal antibody blocking experiments targeted to MIC A/B impaired CD8(+) T cell function, as evaluated by proliferation and cytokine production. In addition, the production of prostaglandin E2 (PGE2 ), indoleamine 2, 3-dioxygenase (IDO) and transforming growth factor (TGF)-β1 were increased when BMSCs were co-cultured with CD8(+) T cells. The addition of specific inhibitors against PGE2 , IDO and TGF-β partially restored the proliferation of CD8(+) T cells. Our results suggest that BMSCs suppress CD8(+) T cell-mediated activation by suppressing NKG2D expression and secretion of PGE2, IDO and TGF-β. Our observations further confirm the feasibility of BMSCs as a potential adoptive cellular therapy in immune-mediated diseases such as graft-versus-host disease (GVHD).

UVA induces granzyme B in human keratinocytes through MIF: implication in extracellular matrix remodeling

In a previous study, we have described that UVB induces granzyme B (GrB) in human keratinocyte cells, and that confers potent cellular cytotoxicity against various cellular models, including immune cells (Hernandez-Pigeon, H., Jean, C., Charruyer, A., Haure, M. J., Titeux, M., Tonasso, L., Quillet-Mary, A., Baudouin, C., Charveron, M., and Laurent, G. (2006) J. Biol. Chem. 281, 13525-13532). Herein, we have found that, in contrast to UVB, UVA failed to enhance keratinocyte cellular cytotoxicity but was still able to trigger GrB production. We show that GrB is accumulated through a p38 MAPK-dependent transcriptional mechanism stimulated by redox-dependent migration inhibitory factor release. Moreover, GrB purified from UVA-treated cellular extracts was found to degrade fibronectin in vitro. Treatment with antisense oligonucleotide directed against GrB resulted in the inhibition of UVA-induced cell detachment and cell death and facilitated cell migration through fibronectin and vitronectin matrix upon UVA exposure. Altogether, these results suggest another function for GrB in the context of the UV response. Indeed, combined with our previous study, it appears that, whereas this enzyme mediates keratinocyte cellular cytotoxicity following UVB irradiation, GrB supports the capacity of keratinocyte to degrade extracellular matrix components following UVA irradiation. UV-mediated GrB production may thus have important consequences in photoaging and photocarcinogenesis.

Maintenance of T cell function in the face of chronic antigen stimulation and repeated reactivation for a latent virus infection

Persisting infections are often associated with chronic T cell activation. For certain pathogens, this can lead to T cell exhaustion and survival of what is otherwise a cleared infection. In contrast, for herpesviruses, T cells never eliminate infection once it is established. Instead, effective immunity appears to maintain these pathogens in a state of latency. We used infection with HSV to examine whether effector-type T cells undergoing chronic stimulation retained functional and proliferative capacity during latency and subsequent reactivation. We found that latency-associated T cells exhibited a polyfunctional phenotype and could secrete a range of effector cytokines. These T cells were also capable of mounting a recall proliferative response on HSV reactivation and could do so repeatedly. Thus, for this latent infection, T cells subjected to chronic Ag stimulation and periodic reactivation retain the ability to respond to local virus challenge.

Increased granzyme A expression in type II pneumocytes of patients with severe chronic obstructive pulmonary disease

RATIONALE

Chronic obstructive pulmonary disease (COPD) is associated with increased numbers of CD8(+) cytotoxic T lymphocytes (CTLs) in the lung, but the functional activity of CTLs remains unknown. Granzyme A (GrA) and B (GrB) are serine proteases considered to be important effector molecules of CTLs and natural killer cells.

OBJECTIVE

To investigate protein and mRNA expression of GrA and GrB in peripheral lung tissue from patients with COPD and control subjects with normal lung function.

METHODS

Paraffin-embedded sections of surgical lung specimens from 22 patients with COPD (FEV(1), 22% predicted; GOLD stage 4) and 15 control subjects (FEV(1), 108% predicted) were immunostained for GrA and GrB, and semiquantified on a 3-point scale. Messenger RNA expression in total lung, specific cell types enriched for by laser capture microdissection, and freshly isolated primary cells were determined by reverse transcriptase-polymerase chain reaction.

MEASUREMENTS AND MAIN RESULTS

GrA and GrB immunoreactivity was observed in CD8(+) CTLs and CD57(+) natural killer cells, but also in type II pneumocytes and alveolar macrophages in both groups. Bronchiolar epithelium stained positive for GrA, but negative for GrB. These observations were confirmed by reverse transcriptase-polymerase chain reaction on total lung, laser capture microdissection-enriched specific cell types and freshly isolated primary type II pneumocytes. The scores of GrA-expressing type II pneumocytes were significantly higher in patients with COPD versus control subjects.

CONCLUSIONS

GrA and GrB mRNA and protein are detectable in human lung tissue. GrA expression is increased in type II pneumocytes of patients with very severe COPD. These results indicate that GrA may be important in the development of COPD.

Combination of IL-21 and IL-15 enhances tumour-specific cytotoxicity and cytokine production of TCR-transduced primary T cells

IL-21, and to a lesser extent IL-15, inhibits differentiation of antigen-primed CD8 T cells and promotes their homeostasis and anti-tumour activity. Here, we investigated molecular mechanisms behind tumour-specific responses of primary murine T lymphocytes engineered to express a TCR directed against human gp100/HLA-A2 following short-term exposure to IL-15 and/or IL-21. We demonstrated that IL-15 + IL-21, and to a lesser extent IL-21, enhanced antigen-specific T-cell cytotoxicity, which was related to enhanced expression of granzymes A and B, and perforin 1. Furthermore, IL-15 + IL-21 synergistically enhanced release levels and kinetics of T-cell IFNgamma and IL-2, but not IL-10. Enhanced secretion of IFNgamma was accompanied by increased gene expression and cytosolic protein content, and was restricted to effector memory T cells. To summarize, we show that IL-15 + IL-21 improves antigen-specific responses of TCR-transduced effector T cells at multiple levels, which provides a rationale to treat T cells with a combination of these cytokines prior to their use in adoptive TCR gene therapy.

Bcl6 controls granzyme B expression in effector CD8+ T cells

Bcl6, a sequence-specific transcriptional repressor, is important for generation and maintenance of memory CD8(+) T cells. Although memory CD8(+) T cells are generated from effector CD8(+) T cells, a role for Bcl6 in effector CD8(+) T cells is largely unknown. We show here that Bcl6 expression was transiently induced in activated CD8(+) T cells and continuously up-regulated in effector CD8(+) T cells. The amount of granzyme B mRNA among effector molecules produced by effector CD8(+) T cells inversely correlated with the amount of Bcl6 mRNA in CD8(+) T cells. Overexpression of Bcl6 in CD8(+) T cells resulted in lower killing activity at their effector phase, supporting the reduction of granzyme B expression in effector CD8(+) T cells by Bcl6. We identified a putative Bcl6-binding DNA sequence in the promoter region of the granzyme B gene. Binding of Bcl6 to the Bcl6-binding sequence was detected in naive CD8(+) T cells but not in activated CD8(+) T cells by chromatin immunoprecipitation assay. Furthermore, the Bcl6-binding sequence was required for Bcl6 to repress the luciferase reporter gene expression controlled by the granzyme B promoter. Thus, the granzyme B gene is a molecular target of Bcl6 in effector CD8(+) T cells.

Altered circadian expression of cytokines and cytolytic factors in splenic natural killer cells of Per1(-/-) mutant mice

Circadian systems regulate the immune system by various molecular and physiological pathways. Disruption to the circadian temporality of these pathways is associated with disease formation and progression. Circadian clock genes have been shown to regulate pathways involved in cellular proliferation, apoptosis, and DNA damage response, as aberrant rhythms in these genes are associated with various diseases. However, there is growing evidence that specific circadian genes differentially regulate functional pathways of immunocompetent cells. To extend our previous findings of the role of Period 2 in regulating splenocyte rhythms, we report that mice carrying a mutation in the Period 1 gene (Per1(-/-) mice), involved in the negative limb of the molecular clock, display significantly altered rhythms of cytokine (eg, interferon-γ) and cytolytic factors (eg, perforin and granzyme B) in splenic natural killer (NK) cells. Altered rhythms of NK cell immune factors were accompanied by changes in circadian expression of circadian clock genes, Bmal1 and Per2. In addition, Per1(-/-) circadian running-wheel activity rhythms remained rhythmic during constant darkness, although with a shortened free-running circadian period, suggesting primary involvement of peripheral molecular clocks. These findings indicate that the Per1 gene through NK cellular clocks modulates immune pathways.

Enhancement of natural killer cell effector functions against selected lymphoma and leukemia cell lines by dasatinib

As NK cell immunotherapy is still poorly successful, combinations with drugs enhancing NK cell activity are of major interest. NK large granular lymphocyte expansions associated with improved survival have been described under monotherapy with the Bcr-Abl/Src inhibitor dasatinib, which inhibits NK cell functions in vitro. As Src kinases play a major role in inhibitory and activating signaling pathways of NK cells, both outcomes appear plausible. To clarify these contradictory observations and potentially enable the use of dasatinib as adjuvant, we analyzed how clinically relevant doses promote NK cell effector functions. Polyclonal human NK cells were studied ex vivo. Functional outcomes assessed included conjugate formation, calcium flux, receptor regulation, cytokine production, degranulation, cytotoxicity, apoptosis induction and signal transduction. While dasatinib inhibits NK cell effector functions during functional assays, 24 hr pretreatment of NK cells followed by washout of dasatinib, led to dose-dependent enhancement of cytokine production, degranulation marker expression and cytotoxicity against selected lymphoma and leukemia cell lines. Mechanistically, this was neither due to an altered viability of NK cells nor increased NKG2D, LFA-1 or conjugate formation with target cells. Receptor proximal signaling events were inhibited. However, a slight time dependent enhancement of Vav phosphorylation was observed under certain circumstances. The shift in Vav phosphorylation level may be one major mechanism for NK cell activity enhancement induced by dasatinib. Our findings argue for a careful timing and dosing of dasatinib application during leukemia/lymphoma treatment to enhance NK cell immunotherapeutic efforts.

Tregs Modulate Lymphocyte Proliferation, Activation, and Resident-Memory T-Cell Accumulation within the Brain during MCMV Infection

Accumulation and retention of regulatory T-cells (Tregs) has been reported within post viral-encephalitic brains, however, the full extent to which these cells modulate neuroinflammation is yet to be elucidated. Here, we used Foxp3-DTR (diphtheria toxin receptor) knock-in transgenic mice, which upon administration of low dose diphtheria toxin (DTx) results in specific deletion of Tregs. We investigated the proliferation status of various immune cell subtypes within inflamed central nervous system (CNS) tissue. Depletion of Tregs resulted in increased proliferation of both CD8⁺ and CD4⁺ T-cell subsets within the brain at 14 d post infection (dpi) when compared to Treg-sufficient animals. At 30 dpi, while proliferation of CD8⁺ T-cells was controlled within brains of both Treg-depleted and undepleted mice, proliferation of CD4⁺ T-cells remained significantly enhanced with DTx-treatment. Previous studies have demonstrated that Treg numbers within the brain rebound following DTx treatment to even higher numbers than in untreated animals. Despite this rebound, CD8⁺ and CD4⁺ T-cells proliferated at a higher rate when compared to that of Treg-sufficient mice, thus maintaining sustained neuroinflammation. Furthermore, at 30 dpi we found the majority of CD8⁺ T-cells were CD127^hi KLRG1^- indicating that the cells were long lived memory precursor cells. These cells showed marked elevation of CD103 expression, a marker of tissue resident-memory T-cells (T_RM) in the CNS, in untreated animals when compared to DTx-treated animals suggesting that generation of T_RM is impaired upon Treg depletion. Moreover, the effector function of T_RM as indicated by granzyme B production in response to peptide re-stimulation was found to be more potent in Treg-sufficient animals. Taken together, our findings demonstrate that Tregs limit neuroinflammatory responses to viral infection by controlling cell proliferation and may direct a larger proportion of lymphocytes within the brain to be maintained as T_RM cells.