The 5'-flanking region of the human CGL-1/granzyme B gene targets expression of a reporter gene to activated T-lymphocytes in transgenic mice

Longitudinal, noninvasive imaging of T-cell effector function and proliferation in living subjects

Adoptive immunotherapy is evolving to assume an increasing role in treating cancer. Most imaging studies in adoptive immunotherapy to date have focused primarily on locating tumor-specific T cells rather than understanding their effector functions. In this study, we report the development of a noninvasive imaging strategy to monitor T-cell activation in living subjects by linking a reporter gene to the Granzyme B promoter (pGB), whose transcriptional activity is known to increase during T-cell activation. Because pGB is relatively weak and does not lead to sufficient reporter gene expression for noninvasive imaging, we specifically employed 2 signal amplification strategies, namely the Two Step Transcription Amplification (TSTA) strategy and the cytomegalovirus enhancer (CMVe) strategy, to maximize firefly luciferase reporter gene expression. Although both amplification strategies were capable of increasing pGB activity in activated primary murine splenocytes, only the level of bioluminescence activity achieved with the CMVe strategy was adequate for noninvasive imaging in mice. Using T cells transduced with a reporter vector containing the hybrid pGB-CMVe promoter, we were able to optically image T-cell effector function longitudinally in response to tumor antigens in living mice. This methodology has the potential to accelerate the study of adoptive immunotherapy in preclinical cancer models.

T-cell activation promotes tumorigenesis in inflammation-associated cancer

Chronic inflammation has long been associated with a wide range of malignancies, is now widely accepted as a risk factor for development of cancer, and has been implicated as a promoter of a variety of cancers including hematopoietic malignancies. We have described a mouse model uniquely suited to examine the link between inflammation and lymphoma in which the Tax oncogene, expressed in activated T and NK cells, perpetuates chronic inflammation that begins as microscopic intraepithelial lesions and develops into inflammatory nodules, subcutaneous tumors, and large granular lymphocytic leukemia. The use of bioluminescent imaging in these mice has expanded our ability to interrogate aspects of inflammation and tumorigenesis non-invasively. Here we demonstrate that bioluminescence induction in these mice correlated with inflammation resulting from wounding, T cell activation, and exposure to chemical agents. In experiments in which long-term effects of inflammation on disease outcome were monitored, the development of lymphoma was promoted by an inflammatory stimulus. Finally we demonstrated that activation of T-cells in T-cell receptor (TCR) transgenic TAX-LUC animals dramatically exacerbated the development of subcutaneous TCR^- CD16⁺ LGL tumors. The role of activated T-cells and acquired immunity in inflammation-associated cancers is broadly applicable to hematopoietic malignancies, and we propose these mice will be of use in dissecting mechanisms by which activated T-cells promote lymphomagenesis in vivo.

Secondary replicative function of CD8+ T cells that had developed an effector phenotype

Models of the differentiation of memory CD8+ T cells that replicate during secondary infections differ over whether such cells had acquired effector function during primary infections. We created a transgenic mouse line that permits mapping of the fate of granzyme B (gzmB)-expressing CD8+ T cells and their progeny by indelibly marking them with enhanced yellow fluorescent protein (EYFP). Virus-specific CD8+ T cells express gzmB within the first 2 days of a primary response to infection with influenza, without impairment of continued primary clonal expansion. On secondary infection, virus-specific CD8+ T cells that became EYFP+ during a primary infection clonally expand as well as all virus-specific CD8+ T cells. Thus, CD8+ T cells that have acquired an effector phenotype during primary infection may function as memory cells with replicative function.

Imaging spontaneous tumorigenesis: inflammation precedes development of peripheral NK tumors

Early events in tumor development are spontaneous, microscopic, and affected by the microenvironment. We developed a mouse model of spontaneous lymphoma in which malignant transformation is coupled with light emission that can be detected noninvasively using bioluminescent imaging. The human T-cell leukemia virus (HTLV) type 1 transcriptional transactivator Tax is an oncogene sufficient to produce lymphoma in transgenic animal models. Using the granzyme B promoter to restrict Tax expression to the mature natural killer (NK)/T-cell compartment, we have reproduced many elements of HTLV-associated adult T-cell leukemia/lymphoma. Tax activates signaling cascades associated with transformation, inflammation, and tumorigenesis. Here, we report that Tax-mediated activation of luciferase in long terminal repeat-luciferase (LTR-LUC) mice serves as a reporter for imaging these processes in vivo. Using bioluminescent imaging (BLI), we discovered that microscopic intraepithelial lesions precede the onset of peripheral subcutaneous tumors, tumorigenesis progresses through early reversible stages, and Tax is sufficient for inducing tumors. Based on these findings, we propose that Tax expression in activated lymphocytes initiates a cascade of events that leads to NK/T cell recruitment, activation, and transformation. The use of BLI expands our ability to interrogate the role of Tax in tumorigenesis in vivo and has made the association of inflammation with tumor initiation amenable for study.

Differential microenvironment localization of effector and memory CD8 T cells

CD8 T cells are critical for the clearance of intracellular pathogens. Upon infection, naive CD8 T cells differentiate into effector cells that target and eliminate infected cells. Following clearance of the pathogen, most effector cells die, although a small fraction survives to establish a memory population. Subsequent exposure to the same pathogen induces a rapid response of memory T cells and efficient elimination of the pathogen. Although much is known about the CD8 T cell response, the precise microenvironment location of effector and memory CD8 T cells in secondary lymphoid organs is not well characterized. In this study, we present an in situ analysis of the localization of effector and memory CD8 T cells during the murine immune response to lymphocytic choriomenginits virus. We identified the location of these cells using a transgenic mouse model system in which CD8 T cells are irreversibly tagged with yellow fluorescent protein (YFP) after activation. After infection, YFP+ CD8 T cells were initially observed within T cell zones. Later, these cells were found in the red pulp and a disruption of all CD8 T cell zones was observed. After resolution of the immune response, YFP+ memory CD8 T cells were observed primarily in T cells zones. Thus, in the spleens of mice, effector CD8 T cells localize to the red pulp and memory CD8 T cells localize to the T cell zones. Upon rechallenge, memory CD8 T cells rapidly proliferate and the secondary effector CD8 T cells are found in the red pulp.

Contribution of TIA-1+ and granzyme B+ cytotoxic T lymphocytes to cryptal apoptosis and ulceration in active inflammatory bowel disease

In spite of the clinicopathological differences between Crohn's disease (CD) and ulcerative colitis (UC), they share the fundamental feature of destructive inflammatory processes involving the intestinal wall. The aim of the present study was to investigate the contribution of cell-mediated cytotoxicity to mucosal damage in CD and UC. Colonic mucosal biopsy specimens from patients with active CD (n=25) and UC (n=26) and normal controls (n=12) were immunohistochemically analyzed for the expression of CD3, CD4, CD8, and T cell-restricted intracellular antigen (TIA)-1, which promotes apoptosis by alternative splicing of pre-messenger RNA of the Fas receptor, and granzyme B (GrB), which leads to apoptosis through induction of perforin. Histological scores for cryptal apoptosis and ulceration were assessed in hematoxylin- and eosin-stained sections. In patients with CD and UC, CD3+(P<0.001), CD4+(P<0.001), CD8+(P<0.01), TIA-1+(CD, P<0.01; UC, P<0.001), and GrB+(CD, P<0.01; UC, P<0.001) intraepithelial lymphocytes (IELs) were significantly increased as compared with controls. Positive relationships were found between the histological scores for apoptosis or ulceration and the numbers of CD8+or TIA-1+IELs. In conclusion, cytotoxic T lymphocytes are present in increased numbers in the mucosa of patients with active CD and UC, and local activation of IELs may contribute to mucosal damage with these diseases.

Molecular characterization and expression of a granzyme of an ectothermic vertebrate with chymase-like activity expressed in the cytotoxic cells of Nile tilapia (Oreochromis niloticus)

We have identified the gene coding for a novel serine protease with close similarities to mammalian granzymes from nonspecific cytotoxic cells of a teleost fish Oreochromis niloticus. The genomic organization of tilapia granzyme-1 (TLGR-1) has the signature five-exon-four-intron structure shared by all granzymes and similar hematopoietic Ser proteases. Molecular modeling studies suggested a granzyme-like structure for this protein with four disulfide linkages and two additional Cys residues. The expression of this gene is found to be restricted to cytotoxic cell populations with a low level of constitutive expression when compared to similar granzymes in other teleost species. High levels of transcriptional activation of TLGR-1 with different stimuli suggested that this gene is highly induced during immune reactions. Triplet residues around the active site Ser of TLGR, which determines the primary substrate specificity of granzymes, differ significantly from that of other granzymes. Recombinant TLGR-1 was expressed in the mature and proenzyme forms using pPICZ-alpha vector in the Pichia pastoris expression system. Recombinant TLGR-1 was used to determine the primary substrate specificity of this protease using various synthetic thiobenzyl ester substrates. In vitro enzyme kinetics assays suggested a preference for residues with bulky side chains at the P1 site, indicating a chymase-like activity for this protease. These results indicate the presence of novel granzymes in cytotoxic cells from ectothermic vertebrates.

A class I transgene reveals regulatory events on chromosome 1 marking peripheral T cell differentiation and memory

T cells respond to external signals by altering patterns of gene expression. Our characterization of a transgenic mouse revealed a genetic locus that is specifically regulated in T cells. Elucidation of the factors controlling the expression of the marker transgene may reveal basic regulatory mechanisms used by T cells as they differentiate from naive to primed/memory T cells. Although endogenous MHC class I K(q) expression is normal in these animals, expression of the K(b) transgene differentiates naive from primed/memory T cells. K(bHigh) T cells bear the phenotypic and functional properties of primed/memory T cells, while K(bLow) T cells have naive phenotypes. The transition from K(bLow) to K(bHigh) appears to involve signals resulting from engagement of the TCR. We show that transgene integration has occurred on chromosome 1, between D1Mit365 and D1Mit191. The gene regulatory mechanisms directing expression of the locus marked by the transgene are distinct from those controlling other known T cell-related genes within this locus. Stimulation of K(bHigh) T cells results in the up-regulation of both the endogenous K(q) gene and the K(b) transgene. However, the same stimuli induce increased expression of only K(q) on K(bLow) T cells. This indicates that even though the transcription factors necessary for class I expression are present in K(bLow) T cells, the K(b) gene appears not to be accessible to these factors. These findings suggest a change in chromatin structure at the transgene integration site as cells progress from a naive to a primed/memory differentiation state.

Human T Regulatory Cells Can Use the Perforin Pathway to Cause Autologous Target Cell Death

Cytotoxic T lymphocytes and natural killer cells use the perforin/granzyme pathway to kill virally infected cells and tumor cells. Mutations in genes important for this pathway are associated with several human diseases. CD4(+) T regulatory (Treg) cells have emerged as important in the control of immunopathological processes. We have previously shown that human adaptive Treg cells preferentially express granzyme B and can kill allogeneic target cells in a perforin-dependent manner. Here, we demonstrate that activated human CD4(+)CD25(+) natural Treg cells express granzyme A but very little granzyme B. Furthermore, both Treg subtypes display perforin-dependent cytotoxicity against autologous target cells, including activated CD4(+) and CD8(+) T cells, CD14(+) monocytes, and both immature and mature dendritic cells. This cytotoxicity is dependent on CD18 adhesive interactions but is independent of Fas/FasL. Our findings suggest that the perforin/granzyme pathway is one of the mechanisms that Treg cells can use to control immune responses.

A transgenic mouse model genetically tags all activated CD8 T cells

Identifying and characterizing Ag-specific CD8+ T cells are central to the study of immunological memory. Although powerful strategies such as MHC tetramers and peptide-induced cytokine production assays exist for identifying Ag-specific CD8+ T cells, alternate strategies that are not dependent upon a priori knowledge of the immunodominant and subdominant antigenic epitopes, as well as the MHC background of the animal are of obvious utility. In this study, we present a transgenic mouse model that uses Cre-loxP recombination to permanently mark all activated CD8+ T cells with beta-galactosidase. We used the lymphocytic choriomeningitis virus infection model to track the dynamics of the antiviral CD8+ T cell responses. We show that in this transgenic mouse model system, all of the antiviral effector and memory CD8+ T cells are contained within the beta-gal-marked CD8+ T cell population.

Quantitative morphological analysis of Langerhans cells in healthy and diseased human gingiva

Langerhans cells (LC) are implicated in the initiation and maintenance of inflammatory periodontal diseases. The purpose of this immunohistological study using morphometric and automated image analysis was to determine the morphological features of CD1a+ LC in healthy and inflammatory gingiva according to their localisation in the upper epithelium or the basal layer. The study was on gingival samples from 11 healthy controls (C), eight patients with gingivitis (G) and 12 patients with severe chronic adult periodontitis (P). The results show that in the basal layer of all experimental groups, the perimeter, surface and equivalent diameter of CD1a+ LC were significantly decreased (P<0.005) when compared with those in the upper epithelium of the same group. Furthermore, CD1a+ LC had become more rounded, reflected by a significant increase in form factor (P<0.005), when located close to the epithelial basal membrane. In the upper epithelium of group P, the perimeter, surface and equivalent diameter of CD1a+ LC were significantly decreased (P<0. 05) and the form factor significantly increased (P<0.05) when compared with the upper epithelium of group C. This work provides evidence for important morphological variations in CD1a+ LC according to their location within the epithelium and the severity of the periodontal disease. The observed morphological changes may reflect a cellular adaptation during the epithelial transmigration and could eventually be involved in immune stimulation during periodontitis.

Immunohistological and morphometric analysis of intra-epithelial lymphocytes and Langerhans cells in healthy and diseased human gingival tissues

Periodontal diseases are histologically characterized by an infiltration of several inflammatory cell populations into the gingival epithelium and connective tissue, associated with degradation of extracellular matrix components. The purpose of this in situ study was to evaluate the inflammatory state of gingival tissues by the number of intra-epithelial lymphocyte (IEL) subsets and the area fraction (AA%) occupied by collagen fibres in the upper gingival connective tissue, and also to evaluate the number of CD1a+ Langerhans cells (LC) in order to show correlation(s), if any, between these histological findings. The gingival samples were from 10 clinically healthy controls (group C), 8 patients with gingivitis (group G) and 9 with chronic adult periodontitis (group P). A quantitative evaluation of the number of cell populations (CD1a+, CD45RB+, CD3+, CD8+, CD20+, TIA-1+ and GrB+ cells) and the area fraction (AA%) occupied by collagen fibres in the upper gingival connective tissue was made by morphometric and automated image analysis. The results showed that, compared with group C, all IEL subset numbers were significantly increased (p<0.05) in G and P groups, CD20+ excepted. In addition, there was a significant increase in the cytotoxic TIA-1+ IEL number (p<0.05) in group P when compared with group G. The study also showed a significant decrease in the number of CD1a+ LC in groups G and P (p<0.02 and p<0.001, respectively) when compared with group C. No significant difference was found in CD1a+ LC number between groups G and P. The determination of coefficients of correlation (r) with data obtained for each patient showed that in group G, CD1a+ LC number was significantly correlated with CD45RB+ (p<0.05) and CD3+ (p<0.01) IEL numbers whereas during periodontitis, CD1a+ LC number was significantly and inversely correlated with CD20+ (p<0.01), cytotoxic TIA-1+ (p<0.01) and with activated cytotoxic GrB+ (p<0.01) IEL numbers. Moreover, in group P a significant (p<0.05) positive correlation was shown between CD1a+ LC number and the AA% occupied by collagen fibres. This work demonstrates a decrease in CD1a+ LC number according to the severity of the periodontal disease estimated by the number of IEL and by the area fraction occupied by collagen fibres in human gingiva. The decrease of such cells could represent a way to avoid immune overstimulation.

Immunohistologic and morphometric analysis of cytotoxic T lymphocytes in gingivitis

BACKGROUND

Gingivitis is an inflammatory phenomenon localized in gingival tissues and histologically characterized by an infiltration of several inflammatory cell populations. The purpose of this study was to characterize, localize, and quantify in situ inflammatory and cytotoxic T lymphocytes using immunolabeled gingival tissue sections in order to specify their implication during human gingivitis, since it is well known that such cells play an important role in the defense against bacterial elements.

METHODS

Paraffin gingival tissue sections from 7 patients with gingivitis (G) and from 7 clinically and histologically healthy controls (C) were immunohistochemically stained by specific antibodies (anti-CD45, anti-CD3, anti-CD8, anti-CD20, anti-TIA-1, anti-GrB, and anti-CD68), allowing the quantification of inflammatory cells in upper gingival epithelium (Ep), in the basal epithelium layer (BEp), and in upper connective tissue (CT). Collagen fibers were stained by sirius red F3Ba in order to evaluate, by morphometric and automated image analysis, the surface occupied by collagen bundles and to histologically confirm the absence of pathology of the clinically selected healthy controls.

RESULTS

In the gingivitis group, CD45+, CD3+, CD8+, TIA-1+, and GrB+ lymphocyte numbers were significantly increased in Ep (P<0.05); and CD45+, CD3+, and TIA-I+ lymphocyte numbers were significantly increased in BEp (P <0.05) compared respectively to Ep and BEp of group C. In Ep of group G, mean CD8+/CD3+ cell ratio was significantly increased (P<0.05) compared to BEp and CT, and 25% of TIA-1+ cytotoxic cells were activated GrB+ cells.

CONCLUSIONS

The present study suggests that intraepithelial cytotoxic T lymphocytes play an important role during gingivitis and CD8 expression and that activation of TIA-1+ cytotoxic cells could be induced in Ep in response to epithelial environment. Thus, gingival epithelial tissue, which is generally only considered as a physical barrier, in fact contains numerous immune cell populations preventing the infiltration of pathogenic elements into the connective tissue. Particular clinical attention must be taken for the preservation of the epithelial tissue integrity.

Upstream elements bestow T-cell and haemopoietic progenitor-specific activity on the granzyme B promoter

Cytotoxic T cells and early haemopoietic progenitors share the expression of a number of specific genes. Of these, granzyme B has attracted particular interest because of its role in inducing apoptosis during cytotoxic T cell-mediated target cell killing, and its potential role in the mobilisation and homeostasis of haemopoietic stem cells. Studies of granzyme B regulation should therefore yield valuable information concerning the molecular control of these processes, and also identify elements capable of directing gene expression to two cell types of relevance to gene therapy. Here we show that proximal regulatory elements already known to direct promoter activity in T cells are similarly active in haemopoietic progenitors. However, this activity is not strictly specific, since the promoter regions also direct low levels of reporter gene expression in fibroblasts. More importantly, we also report the presence of two previously unidentified clusters of DNaseI hypersensitive sites upstream from the murine granzyme B gene, and show that these regions impart both increased transcriptional activity and the appropriate cell type specificity on the granzyme B promoter. These upstream regulatory regions are therefore likely to play a key role in the coordination of granzyme B expression in vivo.

Modelling T-cell memory by genetic marking of memory T cells in vivo

Immunological memory is the ability of the immune system to respond with enhanced vigour to pathogens that have been encountered in the past. Following infection or immunization, most effector T cells undergo apoptotic cell death, but a small fraction of these cells, proportional to the early antigen load and initial clonal burst size, persist in the host as a stable pool of memory T cells. The existence of immunological memory has been recognized for over 2,000 years, but our understanding of this phenomenon is limited, primarily because memory lymphocytes cannot be unequivocally identified as they lack specific, permanent markers. Here we have developed a transgenic mouse model system whereby memory T cells and their precursors can be irreversibly marked with a reporter gene and thus can be unambiguously identified. Adoptive transfer of marked CD8+ T cells specific for lymphocytic choriomeningitis virus protected naive recipients following viral challenge, demonstrating that we have marked memory T cells. We also show that cytotoxic effector lymphocytes that develop into memory T cells can be identified in the primary response.

Expression of cytotoxic proteins by neoplastic T cells in mycosis fungoides increases with progression from plaque stage to tumor stage disease

Granzyme B (GrB) and T-cell-restricted intracellular antigen (TIA-1) are cytotoxic proteins that are specifically expressed by cytotoxic CD4 or CD8 positive T cells and natural killer cells. Recent studies demonstrated frequent expression of GrB and TIA-1 by neoplastic cells in primary cutaneous CD30(+) large T-cell lymphomas and lymphomatoid papulosis but not in CD30(-) large T-cell lymphomas. In the present study, 74 biopsies from 54 patients with mycosis fungoides (MF) were investigated for the expression of GrB and TIA-1 using immunohistochemistry on paraffin sections. Staining of more than 10% of the neoplastic T cells for GrB or TIA-1 was considered positive. All but two follow-up biopsies had been obtained from patients without extracutaneous disease at the time of biopsy. Expression of TIA-1 and GrB was found in 33 (45%) and 14 (19%) of 74 MF biopsies, respectively. Comparison of biopsies from T3NoMo-stage MF (n = 27) and T2NoMo-stage MF (n = 45) showed increased expression of TIA-1 (55 versus 37%) and GrB (33 versus 9%) in T3NoMo-stage MF. Evaluation of multiple sequential biopsies from successive stages of MF also revealed an increase in the GrB/TIA-1 expression with tumor progression in five of eight cases. A clearcut relation between the expression of TIA-1 and/or GrB and the type of skin lesion biopsied was found. Considering all 74 biopsies, expression of TIA-1 and GrB was found in 18 of 50 (35%) and 5 of 50 (10%) patches or plaques, 9 of 16 (55%) and 3 of 16 (20%) tumors without blastic transformation, and 6 of 8 (75%) and 6 of 8 (75%) tumors with blastic transformation (defined as >50% blast cells). Correlation between GrB/TIA-1 expression in first diagnostic biopsies from patches or plaques from 40 patients with T2NoMo-stage MF and clinical follow-up data did not reveal differences in clinical behavior and survival between patients with (n = 14) or without (n = 26) expression of cytotoxic proteins, indicating that MF expressing cytotoxic proteins should not be considered as a separate group.

A cytotoxic phenotype does not predict clinical outcome in anaplastic large cell lymphomas

AIM

To investigate whether anaplastic large cell lymphomas (ALCL) expressing cytotoxic proteins have a relatively worse clinical outcome compared with ALCL lacking a cytotoxic phenotype.

METHODS

59 primary cases of ALCL originating from different sites were investigated by immunohistochemistry for the presence of the cytotoxic proteins T cell intracytoplasmic antigen (TIA-1) and granzyme B in the neoplastic cells. Since site of origin and expression of anaplastic lymphoma kinase (ALK) strongly influence prognosis, the presence of a cytotoxic phenotype was also investigated in relation to the primary site of origin (lymph node, gut, or skin) and ALK expression. The prognostic value was investigated by analysis of overall and relapse-free survival time, including Cox regression analysis.

RESULTS

39 of 59 ALCL (66%) appeared to have a cytotoxic phenotype as shown by expression of TIA-1 or granzyme B or both in the neoplastic cells. The presence of a cytotoxic phenotype did not have any influence on prognosis. Even when the survival data were corrected for site of origin and stage at presentation or were analysed separately for ALK positive and negative cases, no prognostic influence of a cytotoxic phenotype was observed.

CONCLUSIONS

In primary biopsies of patients with ALCL, the presence of a cytotoxic phenotype is not related to clinical outcome of the disease.

The 5′ Flanking Region of the Human Granzyme H Gene Directs Expression to T/Natural Killer Cell Progenitors and Lymphokine-Activated Killer Cells in Transgenic Mice

Human granzyme H is a neutral serine protease that is expressed predominantly in the lymphokine-activated killer (LAK)/natural killer (NK) compartment of the immune system. The gene that encodes this granzyme is located between the granzyme B and cathepsin G genes on human chromosome 14q11.2. Although the murine orthologue of human granzyme H has not yet been identified, murine granzymes C, D, E, F, and G also lie between the murine granzyme B and cathepsin G genes on murine chromosome 14; murine granzymes C, D, and F are also highly expressed in LAK cells, but minimally in cytotoxic T lymphocytes (CTL). We therefore tested whether the 5′ flanking region of human granzyme H contains the cis-acting DNA sequences necessary to target a reporter gene to the LAK/NK compartment of transgenic mice. A 1.2-kb fragment of 5′ flanking human granzyme H sequence was linked to an SV40 large T-antigen (TAg) reporter gene and used to create six transgenic founder lines. SV40 TAg was specifically expressed in the LAK cells of these mice, but not in resting T or NK cells, in CTL, or in any other tissues. Most mice eventually developed a fatal illness characterized by massive hepatosplenomegaly and disseminated organ infiltration by large malignant lymphocytes. Cell lines derived from splenic tumors were TAg+ and NK1.1+ large granular lymphocytes and displayed variable expression of CD3, CD8, and CD16. Although these cell lines contained perforin and expressed granzymes A, B, C, D, and F, they did not exhibit direct cytotoxicity. Collectively, these results suggest that the 5′ flanking sequences of the human granzyme H gene target expression to an NK/T progenitor compartment and to activated NK (LAK) cells. Mice and humans may therefore share a regulatory “program” for the transcription of NK/LAK specific granzyme genes.

The 5′ Flanking Region of the Human Granzyme H Gene Directs Expression to T/Natural Killer Cell Progenitors and Lymphokine-Activated Killer Cells in Transgenic Mice

Human granzyme H is a neutral serine protease that is expressed predominantly in the lymphokine-activated killer (LAK)/natural killer (NK) compartment of the immune system. The gene that encodes this granzyme is located between the granzyme B and cathepsin G genes on human chromosome 14q11.2. Although the murine orthologue of human granzyme H has not yet been identified, murine granzymes C, D, E, F, and G also lie between the murine granzyme B and cathepsin G genes on murine chromosome 14; murine granzymes C, D, and F are also highly expressed in LAK cells, but minimally in cytotoxic T lymphocytes (CTL). We therefore tested whether the 5′ flanking region of human granzyme H contains the cis-acting DNA sequences necessary to target a reporter gene to the LAK/NK compartment of transgenic mice. A 1.2-kb fragment of 5′ flanking human granzyme H sequence was linked to an SV40 large T-antigen (TAg) reporter gene and used to create six transgenic founder lines. SV40 TAg was specifically expressed in the LAK cells of these mice, but not in resting T or NK cells, in CTL, or in any other tissues. Most mice eventually developed a fatal illness characterized by massive hepatosplenomegaly and disseminated organ infiltration by large malignant lymphocytes. Cell lines derived from splenic tumors were TAg+ and NK1.1+ large granular lymphocytes and displayed variable expression of CD3, CD8, and CD16. Although these cell lines contained perforin and expressed granzymes A, B, C, D, and F, they did not exhibit direct cytotoxicity. Collectively, these results suggest that the 5′ flanking sequences of the human granzyme H gene target expression to an NK/T progenitor compartment and to activated NK (LAK) cells. Mice and humans may therefore share a regulatory “program” for the transcription of NK/LAK specific granzyme genes.

Dual mechanisms of apoptosis induction by cytotoxic lymphocytes

Cytotoxic T lymphocytes and natural killer cells together comprise the means by which the immune system detects and rids higher organisms of virus-infected or transformed cells. Although differing considerably in the way they detect foreign or mutated antigens, these cells utilize highly analogous mechanisms for inducing target cell death. Both types of effector lymphocytes utilize two principal contact-dependent cytolytic mechanisms. The first of these, the granule exocytosis mechanism, depends on the synergy of a calcium-dependent pore-forming protein, perforin, and a battery of proteases (granzymes), and it results in penetration by effector molecules into the target cell cytoplasm and nucleus. The second, which requires binding of FasL (CD95L) on the effector cell with trimeric Fas (CD95) molecules on receptive target cells, is calcium independent and functions by generating a death signal at the inner leaflet of the target cell membrane. Exciting recent developments have indicated that both cytolytic mechanisms impinge on an endogenous signaling pathway that is strongly conserved in species as diverse as helminths and humans and dictates the death or survival of all cells.

High proportion of granzyme B-positive (activated) intraepithelial and lamina propria lymphocytes in lymphocytic gastritis

Intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LpLs) have not been well studied in gastric mucosa, particularly in lymphocytic gastritis. Therefore, they were immunohistologically characterized with antibodies recognizing CD3, CD8, CD57, T cell-restricted intracellular antigen (TIA-1), and granzyme B (GrB). The TIA-1 labels cytotoxic granules of resting and activated T-cells, whereas GrB decorates activated cytotoxic T cells. Thirty patients with celiac disease, including 20 taking gluten and 10 on a gluten-free diet, 15 patients with nonceliac disease-associated lymphocytic gastritis, and 20 controls were studied. Stained cells were counted and results were given as IELs/100 epithelial cells or percentage of lamina propria cells. Sixty percent to 90% of CD3+ IELs and up to 12% of lamina propria cells contained TIA-1-positive cytotoxic granules. The number of GrB+ IELs and LpLs was increased in Helicobacter pylori-positive controls (p < 0.03 vs. H pylori-negative controls) and celiac disease patients taking gluten (p < 0.05 vs. controls). The highest number of GrB+ IELs and LpLs was found in nonceliac disease-associated lymphocytic gastritis (p < 0.009 vs. controls, p < 0.05 vs. celiac disease). This study shows that a high proportion of gastric IELs and LpLs is potentially cytotoxic in nature. Through stimuli not yet identified, a proportion of them becomes activated after H pylori infestation and in lymphocytic gastritis.

Switching gears during T-cell maturation: RANTES and late transcription

Although much is understood about the induction of genes expressed early (within 24 h) after T-cell activation, little is known about the regulation of expression of genes expressed 'late' (three or more days) post-stimulation. A better understanding of transcriptional regulation at this important stage of T-cell maturation may yield new insights into T-cell development and new immunotherapeutic targets.

Cytokine Expression and Tumorigenicity of Large Granular Lymphocytic Leukemia Cells From Mice Transgenic for the tax Gene of Human T-Cell Leukemia Virus Type I

The human T-cell leukemia virus type I (HTLV-I) regulatory protein, Tax, has been speculated to play a major role in HTLV-I leukemogenesis. Indeed, several studies have suggested that upregulation of various cellular oncogenes and cytokines by Tax may explain the pathogenesis observed in HTLV-I–infected individuals, as well as several Tax-transgenic animal models. We report here the analysis of cytokine expression in a Tax-transgenic animal model with large granular lymphocytic (LGL) leukemia. Two different transgenic mice showed identical expression of interleukin-1α (IL-1α), IL-1β, interferon γ (IFNγ), and granulocyte-macrophage colony-stimulating factor (GM-CSF ) in peripheral tail tumors. Interestingly, LGL cell lines derived from these same tumors expressed high levels of both IFNγ and GM-CSF, which correlated with the level of Tax expression. These same LGL cell lines also expressed high levels of lymphocyte function-associated antigen-1 (LFA-1) and intracellular adhesion molecule-1 (ICAM-1). Engraftment of these LGL cell lines into severe combined immunodeficient (SCID) mice led to the development of leukemia and lymphomas. Examination of these SCID mice showed that their pathology was nearly identical to that observed in the original Tax-transgenic mouse model. Both the Tax-transgenic and engrafted SCID mouse models allow for the analysis of cellular events that are required for tumor development associated with HTLV infection and suggest that Tax expression may be responsible for the upregulation of certain cytokines and adhesion molecules that affect the infiltrating capabilities of HTLV-I–infected cells.

Cytokine Expression and Tumorigenicity of Large Granular Lymphocytic Leukemia Cells From Mice Transgenic for the tax Gene of Human T-Cell Leukemia Virus Type I

The human T-cell leukemia virus type I (HTLV-I) regulatory protein, Tax, has been speculated to play a major role in HTLV-I leukemogenesis. Indeed, several studies have suggested that upregulation of various cellular oncogenes and cytokines by Tax may explain the pathogenesis observed in HTLV-I–infected individuals, as well as several Tax-transgenic animal models. We report here the analysis of cytokine expression in a Tax-transgenic animal model with large granular lymphocytic (LGL) leukemia. Two different transgenic mice showed identical expression of interleukin-1α (IL-1α), IL-1β, interferon γ (IFNγ), and granulocyte-macrophage colony-stimulating factor (GM-CSF ) in peripheral tail tumors. Interestingly, LGL cell lines derived from these same tumors expressed high levels of both IFNγ and GM-CSF, which correlated with the level of Tax expression. These same LGL cell lines also expressed high levels of lymphocyte function-associated antigen-1 (LFA-1) and intracellular adhesion molecule-1 (ICAM-1). Engraftment of these LGL cell lines into severe combined immunodeficient (SCID) mice led to the development of leukemia and lymphomas. Examination of these SCID mice showed that their pathology was nearly identical to that observed in the original Tax-transgenic mouse model. Both the Tax-transgenic and engrafted SCID mouse models allow for the analysis of cellular events that are required for tumor development associated with HTLV infection and suggest that Tax expression may be responsible for the upregulation of certain cytokines and adhesion molecules that affect the infiltrating capabilities of HTLV-I–infected cells.

T-cell receptor ligation by peptide/MHC induces activation of a caspase in immature thymocytes: the molecular basis of negative selection

T-cell receptors (TCRs) are created by a stochastic gene rearrangement process during thymocyte development, generating thymocytes bearing useful, as well as unwanted, specificities. Within the latter group, autoreactive thymocytes arise which are subsequently eliminated via a thymocyte-specific apoptotic mechanism, termed negative selection. The molecular basis of this deletion is unknown. Here, we show that TCR triggering by peptide/MHC ligands activates a caspase in double-positive (DP) CD4+ CD8+ thymocytes, resulting in their death. Inhibition of this enzymatic activity prevents antigen-induced death of DP thymocytes in fetal thymic organ culture (FTOC) from TCR transgenic mice as well as apoptosis induced by anti-CD3epsilon monoclonal antibody and corticosteroids in FTOC of normal C57BL/6 mice. Hence, a common caspase mediates immature thymocyte susceptibility to cell death.

Transgenic mouse models for HTLV-I infection

Human T-cell leukemia virus type I (HTLV-I) was the first human retrovirus isolated and is responsible for at least one form of human leukemia. The pathogenic mechanism(s) whereby HTLV transforms T lymphocytes in vivo is(are) obscure due to its long-term latency and the lack of practical representative animal models. The tax gene of HTLV-I has been implicated in this transformation process because of its ability to transactivate several cellular genes associated with T-cell replication and activation. Here, transgenic mouse models are discussed that express the Tax protein of HTLV-I and provide insights into its role in the cellular transformation process.

Cytotoxic lymphocytes require granzyme B for the rapid induction of DNA fragmentation and apoptosis in allogeneic target cells

We have generated H-2b mice with a homozygous null mutation in the granzyme (gzm) B gene. Gzm B is a neutral serine protease with Aspase activity that is found only in the granules of activated cytolytic T cells, natural killer cells, and lymphokine-activated killer cells. Gzm B-/- mice develop normally and have normal hematopoiesis and lymphopoiesis. In vitro, cytotoxic T lymphocytes (CTL) derived from gzm B-/- animals are able to induce 51Cr release from allotarget cells, but with reduced efficiency. However, gzm B-/- CTL have a profound defect in their ability to induce rapid DNA fragmentation and apoptosis in allogeneic target cells. This defect is kinetic since DNA fragmentation is partially compensated and 51Cr release is completely rescued with long incubation times. We conclude that gzm B serves a critical and nonredundant role for the rapid induction of target cell DNA fragmentation and apoptosis by alloreactive cytotoxic T lymphocytes.

A promoter element of the human serine esterase granzyme B gene controls specific transcription in activated T cells

The human granzyme B gene encodes a serine protease expressed specifically in cytoplasmic granules of cytotoxic T lymphocytes, released upon effector-target cell interaction. Previous studies have shown that granzyme B mRNA was induced in T lymphocytes after antigenic or mitogenic stimulation. To study the regulation of human granzyme B gene expression during lymphocyte activation we analyzed its 5' flanking region using chloramphenicol acetyl transferase (CAT) reporter gene constructs. We show that a 208-bp fragment (-148 to +60) containing an NF-AT (nuclear factor of activated T cells)-binding site promotes CAT expression in phytohemagglutinin-activated T lymphocytes, in immobilized monoclonal anti-CD3 antibody-activated Jurkat T cell line while it is inactive in unstimulated PEER and Jurkat T cells lines or B Epstein-Barr virus-transformed cell lines.