Heat shock protein 70 is able to prevent heat shock-induced resistance of target cells to CTL

Rationale of hyperthermia for radio(chemo)therapy and immune responses in patients with bladder cancer: Biological concepts, clinical data, interdisciplinary treatment decisions and biological tumour imaging

Bladder cancer, the most common tumour of the urinary tract, ranks fifth among all tumour entities. While local treatment or intravesical instillation of bacillus Calmette-Guerin (BCG) provides a treatment option for non-muscle invasive bladder cancer of low grade, surgery or radio(chemo)therapy (RT) are frequently applied in high grade tumours. It remains a matter of debate whether surgery or RT is superior with respect to clinical outcome and quality of life. Surgical resection of bladder cancer can be limited by acute side effects, whereas, RT, which offers a non-invasive treatment option with organ- and functional conservation, can cause long-term side effects. Bladder toxicity by RT mainly depends on the total irradiation dose, fraction size and tumour volume. Therefore, novel approaches are needed to improve clinical outcome. Local tumour hyperthermia is currently used either as an ablation therapy or in combination with RT to enhance anti-tumour effects. In combination with RT an increase of the temperature in the bladder stimulates the local blood flow and as a result can improve the oxygenation state of the tumour, which in turn enhances radiation-induced DNA damage and drug toxicity. Hyperthermia at high temperatures can also directly kill cells, particularly in tumour areas which are poorly perfused, hypoxic or have a low tissue pH. This review summarises current knowledge relating to the role of hyperthermia in RT to treat bladder cancer, the induction and manifestation of immunological responses induced by hyperthermia, and the utilisation of the stress proteins as tumour-specific targets for tumour detection and monitoring of therapeutic outcome.

Glucocorticoids attenuate acute graft-versus-host disease by suppressing the cytotoxic capacity of CD8(+) T cells

Glucocorticoids (GCs) are released from the adrenal gland during inflammation and help to keep immune responses at bay. Owing to their potent anti-inflammatory activity, GCs also play a key role in controlling acute graft-versus-host disease (aGvHD). Here we demonstrate that mice lacking the glucocorticoid receptor (GR) in T cells develop fulminant disease after allogeneic bone marrow transplantation. In a fully MHC-mismatched model, transfer of GR-deficient T cells resulted in severe aGvHD symptoms and strongly decreased survival times. Histopathological features were aggravated and infiltration of CD8(+) T cells into the jejunum was increased when the GR was not expressed. Furthermore, serum levels of IL-2, IFNγ, and IL-17 were elevated and the cytotoxicity of CD8(+) T cells was enhanced after transfer of GR-deficient T cells. Short-term treatment with dexamethasone reduced cytokine secretion but neither impacted disease severity nor the CTLs' cytolytic capacity. Importantly, in an aGvHD model in which disease development exclusively depends on the presence of CD8(+) T cells in the transplant, transfer of GR-deficient T cells aggravated clinical symptoms and reduced survival times as well. Taken together, our findings highlight that suppression of CD8(+) T-cell function is a crucial mechanism in the control of aGvHD by endogenous GCs.

The hedgehog receptor patched1 in T cells is dispensable for adaptive immunity in mice

Hedgehog (Hh) signaling modulates T cell development and function but its exact role remains a matter of debate. To further address this issue we made use of conditional knock-out mice in which the Hh receptor Patched1 (Ptch) is inactivated in the T cell lineage. Thymocyte development was moderately compromised by the deletion of Ptch as characterized by reduced numbers of CD4 and CD8 single-positive cells. In contrast, peripheral T cells were not affected. Proliferation and IFNγ secretion by Ptch-deficient T cells were indistinguishable from controls irrespectively of whether we used strong or suboptimal conditions for stimulation. Analysis of CTL and T_reg cell functions did not reveal any differences between both genotypes, and T cell apoptosis induced by glucocorticoids or γ-irradiation was also similar. Surprisingly, absence of Ptch did not lead to an activation of canonic Hh signaling in peripheral T cells as indicated by unaltered expression levels of Gli1 and Gli2. To test whether we could uncover any role of Ptch in T cells in vivo we subjected the mutant mice to three different disease models, namely allogeneic bone marrow transplantation mimicking graft-versus-host disease, allergic airway inflammation as a model of asthma and growth of adoptively transferred melanoma cells as a means to test tumor surveillance by the immune system. Nonetheless, we were neither able to demonstrate any difference in the disease courses nor in any pathogenic parameter in these three models of adaptive immunity. We therefore conclude that the Hh receptor Ptch is dispensable for T cell function in vitro as well as in vivo.

Response of preosteoblasts to thermal stress conditioning and osteoinductive growth factors

Conditioning protocols involving mechanical stress independently or with chemical cues such as growth factors (GFs) possess significant potential to enhance bone regeneration. However, utilization of thermal stress conditioning alone or with GFs for bone therapy has been under-investigated. In this study, a preosteoblast cell line (MC3T3-E1) was exposed to treatment with water bath heating (44°C, 4 and 8 min) and osteoinductive GFs (bone morphogenetic protein-2 and transforming growth factor-β1) individually or in combination to investigate whether these stimuli could promote induction of bone-related markers, an angiogenic factor, and heat shock proteins (HSPs). Cells remained viable when heating durations were less than 20 min at 40ºC, 16 min at 42ºC, and 10 min at 44ºC. Increasing heating duration at 44°C, promoted gene expression of HSPs, osteocalcin (OCN), and osteopontin (OPN) at 8 h post-heating (PH). Heating in combination with GFs caused the greatest gene induction of osteoprotegerin (OPG; 6.9- and 1.6-fold induction compared to sham-treated and GF only treated groups, respectively) and vascular endothelial growth factor (VEGF; 16.0- and 1.6-fold compared to sham and GF-only treated groups, respectively) at 8 h PH. Both heating and GFs independently suppressed the matrix metalloproteinase-9 (MMP-9) gene. GF treatment caused a more significant decrease in MMP-9 protein secretion to non-detectable levels compared to heating alone at 72 h PH. Secretion of OCN, OPN, and OPG increased with the addition of GFs but diminished with heating as measured by ELISA at 72 h PH. These results suggest that conditioning protocols utilizing heating and GFs individually or in combination can induce HSPs, bone-related proteins, and VEGF while also causing downregulation of osteoclastic activity, potentially providing a promising bone therapeutic strategy.

The endogenous danger signals HSP70 and MICA cooperate in the activation of cytotoxic effector functions of NK cells

Although natural killer (NK) cells are often described as first line defence against infected or malignant cells which act without the need of prior activation, it is known now that the NK cell activity is tightly regulated by other cells and soluble factors. We show here that the stress-inducible heat shock protein (HSP) 70 activates human NK cells to kill target cells expressing major histocompatibility complex class I chain-related molecule A (MICA) in a natural killer group 2 member D (NKG2D-) dependent manner. The HSP70-derived peptide TKD (TKDNNLLGRFELSG) was able to replace the full-length HSP70 and to exert the same function. Interestingly, the expression of the cytotoxic effector protease granzyme B in NK cells was increased after TKD stimulation. When MICA and MICB expression was induced in human tumour cells by a histone deacetylase inhibitor and NK cells were activated by HSP70 or TKD, both treatments jointly improved the killing of the tumour cells. Thus, the synergistic activity of two stress-inducible immunological danger signals, HSP70 and MICA/B, leads to activation and enhanced cytotoxicity of human NK cells against tumour cells.

The endogenous danger signals HSP70 and MICA cooperate in the activation of cytotoxic effector functions of NK cells

Although natural killer (NK) cells are often described as first line defence against infected or malignant cells which act without the need of prior activation, it is known now that the NK cell activity is tightly regulated by other cells and soluble factors. We show here that the stress-inducible heat shock protein (HSP) 70 activates human NK cells to kill target cells expressing major histocompatibility complex class I chain-related molecule A (MICA) in a natural killer group 2 member D (NKG2D-) dependent manner. The HSP70-derived peptide TKD (TKDNNLLGRFELSG) was able to replace the full-length HSP70 and to exert the same function. Interestingly, the expression of the cytotoxic effector protease granzyme B in NK cells was increased after TKD stimulation. When MICA and MICB expression was induced in human tumour cells by a histone deacetylase inhibitor and NK cells were activated by HSP70 or TKD, both treatments jointly improved the killing of the tumour cells. Thus, the synergistic activity of two stress-inducible immunological danger signals, HSP70 and MICA/B, leads to activation and enhanced cytotoxicity of human NK cells against tumour cells.

Tumour infiltrating host cells and their significance for hyperthermia

Much information can be gained by investigating the consequences of hyperthermia on individual cell populations in vitro, however the precise effects of such a therapeutic modality in vivo depend on the tumour microenvironment and the cellular composition therein. Although the direct cytotoxic effects of hyperthermia on tumour tissue can lead to an immediate reduction in tumour volume, long-term benefits to local and distal tumour recurrence will very much depend on the induction of immunity and the capacity of effector cells to traffic to tumours and elicit their cytotoxic functions. The immunological sequelae to hyperthermia are even more important in those instances when large tumour volumes preclude the delivery of appropriate thermal damage. The development of protective anti-tumour immunity requires a plethora of interactions and responses, the vast majority of which can be influenced by temperatures that are consistent with fever-like temperatures (39 degrees -40 degrees C), as well as hyperthermia treatment (<41 degrees C). This article reviews current knowledge relating to the effects of hyperthermia treatment on aspects of the induction and manifestation of immunological responses that are most pertinent to the development and maintenance of protective anti-tumour immunity.

The exocytosis of lytic granules is impaired in Vti1b- or Vamp8-deficient CTL leading to a reduced cytotoxic activity following antigen-specific activation

The exocytosis of cytotoxic proteins stored in lytic granules of activated CTL is a key event during killing of target cells. Membrane fusion events that are mediated by soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE) proteins are crucial, as demonstrated by patients with familial hemophagocytic lymphohistocytosis type 4 who have mutations in the SNARE protein syntaxin-11 that result in an impaired degranulation of cytotoxic cells. We found an increased mRNA expression of the SNARE protein genes Vti1b and Vamp8 during Ag-specific activation of CTL from TCR-transgenic OT-I mice. Therefore, we investigated the cytolytic activity of CTL from TCR-transgenic Vti1b and Vamp8 knockout mice. At 3 d as well as at 4 d of Ag-specific stimulation, the degranulation of CTL was significantly reduced in Vti1b and Vamp8 knockout mice, as determined by cell surface expression of the degranulation marker CD107a. After 3 d of Ag-specific stimulation, the cytolytic activity of Vti1b- and Vamp8-deficient CTL was reduced to approximately 50% compared with heterozygous controls. However, 4 d after stimulation, the cytotoxic activity of Vti1b- as well as Vamp8-deficient CTL was not impaired anymore. The capacity of Vti1b- and Vamp8-deficient dendritic cells to process Ags and to stimulate the proliferation of CTL was not reduced, arguing against an indirect effect on the activation of CTL. These findings suggest a role of the SNARE proteins vti1b and vesicle-associated membrane protein 8 in the degranulation of CTL. However, a deficiency can apparently be compensated and affects only transiently the cytotoxic activity of CTL during their development to armed effector cells.

Multipotent adult germ-line stem cells, like other pluripotent stem cells, can be killed by cytotoxic T lymphocytes despite low expression of major histocompatibility complex class I molecules

Background

Multipotent adult germ-line stem cells (maGSCs) represent a new pluripotent cell type that can be derived without genetic manipulation from spermatogonial stem cells (SSCs) present in adult testis. Similarly to induced pluripotent stem cells (iPSCs), they could provide a source of cellular grafts for new transplantation therapies of a broad variety of diseases. To test whether these stem cells can be rejected by the recipients, we have analyzed whether maGSCs and iPSCs can become targets for cytotoxic T lymphocytes (CTL) or whether they are protected, as previously proposed for embryonic stem cells (ESCs).

Results

We have observed that maGSCs can be maintained in prolonged culture with or without leukemia inhibitory factor and/or feeder cells and still retain the capacity to form teratomas in immunodeficient recipients. They were, however, rejected in immunocompetent allogeneic recipients, and the immune response controlled teratoma growth. We analyzed the susceptibility of three maGSC lines to CTL in comparison to ESCs, iPSCs, and F9 teratocarcinoma cells. Major histocompatibility complex (MHC) class I molecules were not detectable by flow cytometry on these stem cell lines, apart from low levels on one maGSC line (maGSC Stra8 SSC5). However, using a quantitative real time PCR analysis H2K and B2m transcripts were detected in all pluripotent stem cell lines. All pluripotent stem cell lines were killed in a peptide-dependent manner by activated CTLs derived from T cell receptor transgenic OT-I mice after pulsing of the targets with the SIINFEKL peptide.

Conclusion

Pluripotent stem cells, including maGSCs, ESCs, and iPSCs can become targets for CTLs, even if the expression level of MHC class I molecules is below the detection limit of flow cytometry. Thus they are not protected against CTL-mediated cytotoxicity. Therefore, pluripotent cells might be rejected after transplantation by this mechanism if specific antigens are presented and if specific activated CTLs are present. Our results show that the adaptive immune system has in principle the capacity to kill pluripotent and teratoma forming stem cells. This finding might help to develop new strategies to increase the safety of future transplantations of in vitro differentiated cells by exploiting a selective immune response against contaminating undifferentiated cells.

Reviewers

This article was reviewed by Bhagirath Singh, Etienne Joly and Lutz Walter.

Internalization of annexin A5-functionalized iron oxide particles by apoptotic Jurkat cells

Apoptosis plays an important role in the etiology of various diseases. Several studies have reported on the use of annexin A5-functionalized iron oxide particles for the detection of apoptosis with MRI, both in vitro and in vivo. The protein annexin A5 binds with high affinity to the phospholipid phosphatidylserine, which is exposed in the outer leaflet of the apoptotic cell membrane. When co-exposed to apoptotic stimuli, this protein was shown to internalize into endocytic vesicles. Therefore in the present study we investigated the possible internalization of commercially available annexin A5-functionalized iron oxide particles (r1 = 34.0 +/- 2.1 and r2 = 205.0 +/- 10.4 mm(-1) s(-1) at 20 MHz), and the effects of their spatial distribution on relaxation rates R2*, R2 and R1. Two different incubation procedures were performed, where (1) Jurkat cells were either incubated with the contrast agent after induction of apoptosis or (2) Jurkat cells were simultaneously incubated with the apoptotic stimulus and the contrast agent. Transmission electron microscopy images and relaxation rates showed that the first incubation strategy mainly resulted in binding of the annexin A5-iron oxide particles to the cell membrane, whereas the second procedure allowed extensive membrane-association as well as a small amount of internalization. Owing to the small extent of internalization, only minor differences were observed between the DeltaR2*/DeltaR2 and DeltaR2/DeltaR1 ratios of cell pellets with membrane-associated or internalized annexin A5 particles. Only the increase in R1 (DeltaR1) appeared to be diminished by the internalization. Internalization of annexin A5-iron oxide particles is also expected to occur in vivo, where the apoptotic stimulus and the contrast agent are simultaneously present. Where the extent of internalization in vivo is similar to that observed in the present study, both T2- and T2*-weighted MR sequences are considered suitable for the detection of these particles in vivo.

Thymic alterations in mice deficient for the SNARE protein VAMP8/endobrevin

SNARE (soluble-N-ethylmaleimide-sensitive factor attachment receptor) proteins mediate the recognition and fusion of transport vesicles in eukaryotic cells. The SNARE protein VAMP8 (also called endobrevin) is involved in the fusion of late endosomes and in some pathways of regulated exocytosis. In a subset of mice deficient for the SNARE protein VAMP8, a severe alteration of the thymus and in T lymphocyte development was observed and characterized. The size of the thymus and the number of thymocytes were dramatically reduced compared with those in heterozygous littermates. Further, the compartmentalization into cortex and medulla and the organization of the thymus epithelium were disturbed. The numbers of all thymocyte subpopulations were reduced, with the CD4 and CD8 double-positive thymocytes being most severely affected. The proportion of proliferating thymocytes was reduced, and the staining of apoptotic cells in situ and ex vivo indicated an increased number of apoptotic cells. Isolated thymocytes of Vamp8^−/− mice were more susceptible to various apoptotic stimuli including glucocorticoids, FAS receptor, and CD3/CD28-mediated signaling in vitro, even before an increased number of apoptotic cells was detectable in situ. However, bone marrow of phenotypically affected Vamp8^−/− mice was readily able to repopulate immunodeficient hosts suggesting that the SNARE protein VAMP8 has a specific function in the thymic stroma affecting the proliferation and apoptosis of T lymphocytes during maturation in the thymus.

The tumorigenicity of mouse embryonic stem cells and in vitro differentiated neuronal cells is controlled by the recipients' immune response

Embryonic stem (ES) cells have the potential to differentiate into all cell types and are considered as a valuable source of cells for transplantation therapies. A critical issue, however, is the risk of teratoma formation after transplantation. The effect of the immune response on the tumorigenicity of transplanted cells is poorly understood. We have systematically compared the tumorigenicity of mouse ES cells and in vitro differentiated neuronal cells in various recipients. Subcutaneous injection of 1×10⁶ ES or differentiated cells into syngeneic or allogeneic immunodeficient mice resulted in teratomas in about 95% of the recipients. Both cell types did not give rise to tumors in immunocompetent allogeneic mice or xenogeneic rats. However, in 61% of cyclosporine A-treated rats teratomas developed after injection of differentiated cells. Undifferentiated ES cells did not give rise to tumors in these rats. ES cells turned out to be highly susceptible to killing by rat natural killer (NK) cells due to the expression of ligands of the activating NK receptor NKG2D on ES cells. These ligands were down-regulated on differentiated cells. The activity of NK cells which is not suppressed by cyclosporine A might contribute to the prevention of teratomas after injection of ES cells but not after inoculation of differentiated cells. These findings clearly point to the importance of the immune response in this process. Interestingly, the differentiated cells must contain a tumorigenic cell population that is not present among ES cells and which might be resistant to NK cell-mediated killing.

The heat shock protein HSP70 promotes mouse NK cell activity against tumors that express inducible NKG2D ligands

The stress-inducible heat shock protein (HSP) 70 is known to function as an endogenous danger signal that can increase the immunogenicity of tumors and induce CTL responses. We show in this study that HSP70 also activates mouse NK cells that recognize stress-inducible NKG2D ligands on tumor cells. Tumor size and the rate of metastases derived from HSP70-overexpressing human melanoma cells were found to be reduced in T and B cell-deficient SCID mice, but not in SCID/beige mice that lack additionally functional NK cells. In the SCID mice with HSP70-overexpressing tumors, NK cells were activated so that they killed ex vivo tumor cells that expressed NKG2D ligands. In the tumors, the MHC class I chain-related (MIC) A and B molecules were found to be expressed. Interestingly, a counter selection was observed against the expression of MICA/B in HSP70-overexpressing tumors compared with control tumors in SCID, but not in SCID/beige mice, suggesting a functional relevance of MICA/B expression. The melanoma cells were found to release exosomes. HSP70-positive exosomes from the HSP70-overexpressing cells, in contrast to HSP70-negative exosomes from the control cells, were able to activate mouse NK cells in vitro to kill YAC-1 cells, which express NKG2D ligands constitutively, or the human melanoma cells, in which MICA/B expression was induced. Thus, HSP70 and inducible NKG2D ligands synergistically promote the activation of mouse NK cells resulting in a reduced tumor growth and suppression of metastatic disease.

Cytotoxic T lymphocytes carrying a pattern recognition protein Tag7 can detect evasive, HLA-negative but Hsp70-exposing tumor cells, thereby ensuring FasL/Fas-mediated contact killing

Within the broad problem of host immune surveillance versus tumor immune evasion, a most intriguing question is how the cellular immunity can cope with cancerous cells that have gotten rid of the classical antigen-presenting machinery. One such option stems from (1) the fact that HLA loss is often attended with expression of Hsp70 on the tumor cell surface, and (2) our findings that human lymphocytes express a protein Tag7 (also known as PGRP-S) capable of tight and specific interaction with cognate Hsp70. Here we show that a subpopulation of human CD4(+)CD25(+) lymphocytes, obtained either in culture as lymphokine-activated killers or directly from healthy donors, carry Tag7 and FasL on their surface and can indeed kill the HLA-negative tumor-derived cells K562 and MOLT-4 that expose Hsp70 and Fas. The primary binding of lymphocyte Tag7 to target-cell Hsp70 is very specific (eg, it is blocked by preincubating either cell with minimal peptides from the "partner" protein), and secures cell contact indispensable for subsequent FasL/Fas-triggered apoptosis. Unrelated to natural killer cell action or the putative role of Hsp as an antigen-presenting substitute, this novel mechanism is rather a backup analog of orthodox (CD8(+)) target recognition (Tag7 acting as built-in T-cell receptor and Hsp70 itself as ligand).

Effects of thermal stress on tumor antigenicity and recognition by immune effector cells

The primary rationale for the application of clinical hyperthermia in the therapy of cancer is based on the direct cytotoxic effect of heat and the radio-chemosensitization of tumor cells. More recently, additional attention is given to the observation that heat and heat-shock proteins can activate the host's immune system. The expression of heat-shock genes and proteins provides an adaptive mechanism for stress tolerance, allowing cells to survive non-physiologic conditions. However, the same adaptive mechanism can ultimately favor malignant transformation by interfering with pathways that regulate cell growth and apoptosis. Cytoprotection and thermotolerance raised the concern that heat-treated tumor cells might also be resistant to attack by immune effector mechanisms. Many studies, including those from our group, address this concern and document that heat-exposure, although transiently modulating sensitivity to CTL, do not hinder CTL attack. Moreover, there are promising reports of heat-related upregulation of NK-activating ligands, rendering those tumors which have lost MHC class I molecules target for NK cell attack. Heat-induced cytoprotection, therefore, does not necessarily extend protection from cytotoxic immune mechanisms. When interpreting the effects of heat, it is important to keep in mind that thermal effects on cell physiology are strongly dependent on the thermal dose, which is a function of the magnitude of change in temperature and the duration of heat exposure. The thermal dose required to induce cell death in vitro strongly varies from cell type to cell type and depends on microenvironmental factors (Dewey 1994). Therefore, to dissect the immunological behaviour of a given tumor and its micro-environment at different thermal doses, it is essential to characterize the thermosensitivity of every single tumor type and assess the proportion of cells surviving a given heat treatment. In this review, we summarize the pleiotropic effects that heat exposure has on tumor cells. In particular, we focus on the effects of heat on the antigen presentation of tumor cells and their susceptibility to immune effector mechanisms. We emphasize that the response to thermal stress is not a one-time point event, but rather a time period starting with the heat exposure and extending over several days of recovery. In addition, the response of tumor cells and their susceptibility to immune effector cells is strongly dependent on the model system, on the magnitude and duration of the thermal stress and on the time of recovery after heat exposure. Consideration of these aspects might help to explain some of the conflicting results that are reported in the field of thermal stress response.

Effect of neutrophil apoptosis on monocytic cytokine response to Porphyromonas gingivalis lipopolysaccharide

BACKGROUND

Neutrophil apoptosis may play a critical role in the resolution of inflammation by stimulating anti-inflammatory cytokine generation from monocytes. In this study, we investigated the effect of apoptotic neutrophils on interleukin (IL)-10 and IL-1beta production from monocytes in response to Porphyromonas gingivalis lipopolysaccharide.

METHODS

Peripheral blood neutrophils from healthy individuals were isolated by sodium diatrizoate density gradient centrifugation. In order to induce apoptosis, neutrophils were cultured for 24 hours in modified Dulbecco's medium supplemented with 10% autologous serum. Cell apoptosis was quantified by Annexin V positivity and loss of CD16 expression on the cell surface. Peripheral blood mononuclear cells were isolated from the same subjects; monocytes were purified by magnetic cell sorting and cultured with or without apoptotic or fresh neutrophils. Lipopolysaccharide from Porphyromonas gingivalis was used for cell stimulation. IL-1beta and IL-10 levels in supernatants were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

IL-10 generation was significantly increased in monocytes cultured with apoptotic neutrophils compared to monocytes alone or cocultured with fresh neutrophils (P <0.05). IL-1beta was suppressed both in resting and lipopolysaccharide-stimulated monocytes in the presence of apoptotic neutrophils compared to monocytes alone or monocytes cultured with fresh neutrophils at all time points (P <0.05).

CONCLUSION

Neutrophil apoptosis provides a signal to monocytes, changing the phenotype of the monocyte resulting in the production of anti-inflammatory cytokines and suppression of proinflammatory cytokines in response to lipopolysaccharide.

Cancer immunotherapy and heat-shock proteins: promises and challenges

Recent mechanistic studies on the role of heat-shock proteins (HSPs) to induce innate and adaptive immune responses have resulted in conflicting reports. Whereas some groups reported that HSPs have direct immunological function, others emphasised the endotoxin contamination of HSP preparations and questioned the antigen-specificity of HSP vaccines. The present review will discuss these issues and suggest that HSPs have diverse and distinct immunological functions that could be superimposed on effects resulting from endotoxin contamination or misunderstood by using experimental procedures with inadequate controls. To understand the actual function of HSPs in their interaction with the immune system, methods and procedures need to be optimised and appropriate controls need to be used. These points should also clarify the conflicting findings about HSPs and promote our knowledge about other immuologically important components that may be present in HSP preparations.

"The stress of dying": the role of heat shock proteins in the regulation of apoptosis

Heat shock proteins (Hsps) are a family of highly homologous chaperone proteins that are induced in response to environmental, physical and chemical stresses and that limit the consequences of damage and facilitate cellular recovery. The underlying ability of Hsps to maintain cell survival correlates with an inhibition of caspase activation and apoptosis that can, but does not always, depend upon their chaperoning activities. Several mechanisms proposed to account for these observations impact on both the "intrinsic", mitochondria-dependent and the "extrinsic", death-receptor-mediated pathways to apoptosis. Hsps can inhibit the activity of pro-apoptotic Bcl-2 proteins to prevent permeabilization of the outer mitochondrial membrane and release of apoptogenic factors. The disruption of apoptosome formation represents another mechanism by which Hsps can prevent caspase activation and induction of apoptosis. Several signaling cascades involved in the regulation of key elements within the apoptotic cascade are also subject to modulation by Hsps, including those involving JNK, NF-kappaB and AKT. The coordinated activities of the Hsps thus modulate multiple events within apoptotic pathways to help sustain cell survival following damaging stimuli.

Granzyme-mediated cytotoxicity does not involve the mannose 6-phosphate receptors on target cells

Cytotoxic T lymphocytes (CTL) and natural killer cells secrete granzymes to kill infected or transformed cells. The mannose 6-phosphate receptor (Mpr) 300 on target cells has been reported to function as receptor for secreted granzyme B. Using lymphoblasts and mouse embryonal fibroblast lines from Mpr300 and Mpr46 knockout mice, we show here that both receptors are not essential for CTL-induced apoptosis. Similarly, cells exposed to either monomeric granzyme B or granzyme B-serglycin complexes readily internalize the granzyme and undergo apoptosis in the absence of Mpr300 and Mpr46. Further, no colocalization of granzyme B and Mpr300 could be observed in target cells after internalization. In conclusion, these results strongly argue against an Mpr300- or Mpr46-dependent pathway of granzyme-mediated killing and provide new insight in the internalization of monomeric and complexed granzyme B.

Peptidoglycan recognition protein tag7 forms a cytotoxic complex with heat shock protein 70 in solution and in lymphocytes

The peptidoglycan recognition protein Tag7 is shown to form a stable 1:1 complex with the major stress protein Hsp70. Neither protein is cytotoxic by itself, but their complex induces apoptotic death in several tumor-derived cell lines even at subnanomolar concentrations. The minimal part of Hsp70 needed to evoke cytotoxicity is residues 450-463 of its peptide-binding domain, but full cytotoxicity requires its ATPase activity; remarkably, Tag7 liberated from the complex at high ATP is not cytotoxic. The Tag7-Hsp70 complex is produced by tag7-transfected cells and by lymphokine-activated killers, being assembled within the cell and released into the medium through the Golgi apparatus by a mechanism different from the commonly known granule exocytosis. Thus, we demonstrate how a heat shock protein may perform functions clearly distinct from chaperoning or cell rescue and how peptidoglycan recognition proteins may be involved in innate immunity and anti-cancer defense.

Heat shock protein 70 (Hsp70) membrane expression on head-and-neck cancer biopsy-a target for natural killer (NK) cells

PURPOSE

Heat shock protein 70 (Hsp70) was detected on the cell membrane of human tumor cell lines, but not on normal cells. Here we studied Hsp70 membrane expression as a target for natural killer (NK) cells on tumor material and control tissues of head-and-neck cancer patients.

METHODS AND MATERIALS

Membrane-bound Hsp70 was determined by flow cytometry on single-cell suspensions of tumors and the corresponding normal tissues of head-and-neck cancer patients. The cytolytic activity of NK cells against Hsp70-positive tumor cells was measured in a standard cytotoxicity assay.

RESULTS

In total, 54 of 74 primary tumors were found to be Hsp70 membrane-positive (73%); tongue/mouth, 21 of 24 (88%); oropharynx, 13 of 20 (65%); hypopharynx, 3 of 6 (50%); larynx, 8 of 11 (73%); trachea 1 of 2 (50%); esophagus, 4 of 5 (80%); lymph node metastases, 4 of 6 (67%). The corresponding control tissue was negative for membrane-bound Hsp70. Biopsies (6 of 6) of patients after in vivo gamma-irradiation (fractionated 5 x 2 Gy) were strongly Hsp70 membrane-positive. Irradiated, Hsp70-positive tumor cells are targets for Hsp70-peptide stimulated NK cells.

CONCLUSION

An irradiation-inducible, tumor-selective Hsp70 membrane localization provides a target structure for Hsp70-peptide stimulated human NK cells.

Inhibition of tumor growth in mice with severe combined immunodeficiency is mediated by heat shock protein 70 (Hsp70)-peptide-activated, CD94 positive natural killer cells

Previously, we reported that the major stress-inducible heat shock protein 70 (Hsp70) acts as a recognition structure for natural killer (NK) cells, if localized on the cell surface of tumor cells. Incubation of purified NK cells with low-dose interleukin (IL)-2 (100 IU/mL) plus recombinant Hsp70-protein or the immunogenic 14-mer Hsp70-peptide TKDNNLLGRFELSG450-463, termed TKD (2 microg/mL), enhances the cytolytic activity against Hsp70 membrane-positive (CX+) but not against Hsp70-negative (CX-) tumor cells. Here, we show that the cytolytic activity against Hsp70-positive tumor cells is inducible by incubation of unseparated peripheral blood mononuclear cells (PBMNC) with low-dose IL-2 plus TKD. Cell sorting experiments revealed that within the PBMNC population CD94(+)/CD3(-) NK cells, and not CD94(-)/CD3(+) T cells, mediate the cytotoxic activity against Hsp70-positive tumor cells. The antitumoral effect of PBMNC stimulated either with IL-2 plus TKD or with IL-2 alone was assessed in tumor-bearing severe combined immunodeficiency/beige mice. A single intravenous (iv) injection of 40 x 10(6) IL-2 plus TKD-stimulated PBMNC (containing 5.2 x 10(6) NK cells) on day 4 results in a 60% reduction in tumor size, from 3.89 g to 1.56 g. In contrast, the adoptive transfer of the identical amount PBMNC stimulated with low-dose IL-2 only (containing 4.4 x 10(8) NK cells) reduces the tumor size only less than 10% (3.64 g). A phenotypic characterization of the excised tumors revealed that predominantly Hsp70-positive tumor cells were eliminated by TKD-activated PBMNC. Kinetic studies demonstrate that the in vivo cytolytic capacity of TKD-stimulated PBMNC is dependent on the effector to target cell ratio. An iv injection of effector cells on day 1 or 2 after tumor cell inoculation results in significantly smaller tumors (0.77 g or 0.89 g) on day 21 as compared with mice that were immunoreconstituted on day 4 or 8 (1.39 g or 2.23 g). The tumor size of nonimmunoreconstituted control animals was 3.55 g.