Immunotherapy of malignant gliomas using autologous and allogeneic tissue cells.

Immunotherapy of brain tumors is rapidly emerging as a potential clinical option [1-3]. The quality and magnitude of immune responses evoked by the new generation anti-tumor vaccines is in general highly dependent on the source or choice of peptide antigens, and as well, a suitable immunopotentiator. Poorly immunogenic antigens, such as those present in tumor cell lysates, may not reliably provide stimulation like recombinant or DNA-encoded protein antigens might be expected to. In addition, the efficacy of the vaccine may depend on inherent counteracting measures of the tumor which dampen immune surveillance and immune effector activity triggered by immunization [4]. Our body has many means of limiting an immune response to our own (self) proteins. In particular, patients with gliomas exhibit a broad suppression of cell-mediated immunity [5-8]. Unfortunately, for most tumor vaccines the induction of local or systemic immune effector cells does not necessarily translate into objective clinical responses or increased survival [9]. Here we review immunotherapeutic approaches against gliomas and recent pre-clinical and clinical initiatives based on cellular or active immunization of the patient's immune system using autologous and allogeneic tissues or cultured cells. Available evidence shows that single modality cancer therapies likely remain suboptimal. Combination regimens targeting the immune system at multiple coordinated levels must be developed, and possibly combined with strategies to inhibit immune suppressive factors if significant clinical benefit is to be achieved.

T cell expansion is regulated by activated Gr-1+ splenocytes.

CD4+ T cell proliferation depends on the balance between NO and extra-cellular superoxide (O2-). By reducing NO bio-availability, O2- promotes splenic T cell proliferation and immune response intensity. Here, we show that spleen cells from naïve mice produced neither NO nor O2- during T cell activation, but Gr-1+ splenocytes from primed mice regulated Ag-specific T cell expansion via production of both molecules. Purified splenic Gr-1+ cells included mostly granulocytes at various stages of maturation, as well as monocytes. Activation or recruitment of regulatory Gr-1+ cells was dependent on immunization with CFA. Importantly, these regulatory cells were not detected in draining lymph nodes. These data suggest that innate Gr-1+ splenic cells regulate adaptive immunity.

Cell cycle phase-specific survival of CD95 ligand-challenged Jurkat cells: upregulation of heat-shock response.

An important means of regulating T-cell function occurs via physical deletion (cytolysis) of unnecessary/unwanted T cells. Among cytolytic pathways, CD95 (Fas)-based killing plays a prominent role. Although activation of T cells results in rapid upregulation of surface CD95 expression, sensitivity to CD95-based killing lags behind. To assess determinants of resistance to CD95-based killing, we used Jurkat cells as a model. Analysis of the 10% survivors of a LD(90) dose of CD95 ligand (CD95L) at 24 h demonstrated them to arise preferentially from the S + G2/M phases of the cell cycle and to remain clustered in S + G2/M without undergoing cell division. Protein immunoblot, immunocytochemistry, and RT-PCR analyses demonstrated that hsp72 was markedly upregulated in CD95L survivors within hours of CD95L challenge, indicative of a heat-shock response. Indeed, exposure of Jurkat cells to bona fide heat shock did markedly upregulate hsp72 and, upon subsequent CD95L challenge, did greatly enhance cell survival with persistent clustering to S + G2/M. These findings collectively suggest that in response to a CD95L insult, development of a heat-shock response above some critical threshold level can protect against lethality. This raises the possibility that exaggerated and/or protracted heat-shock responses under in vivo conditions may favor the survival of T cells (including autoaggressive T cells) that otherwise would be destined to die via a CD95-based pathway.

Endothelin-1 and monocyte chemoattractant protein-1 modulation in ischemia and human brain-derived endothelial cell cultures.

Brain tissue damage due to ischemia/reperfusion has been shown to be caused, in part, by activated macrophages infiltrating into the post-ischemic brain. Using the Middle Cerebral Artery Occlusion (MCAO) mouse model, this study demonstrated that, in vivo, both endothelin-1 (Et-1), a potent vasoconstrictor, and the macrophage chemokine, monocyte chemoattractant factor-1 (MCP-1) are induced in ischemia. Further studies, using human brain-derived endothelial cells (CNS-EC), showed that in vitro, Et-1 can directly stimulate MCP-1 mRNA expression and MCP-1 protein; and this Et-1-induced MCP-1 production is mediated by the ET(A) receptor. Inflammatory cytokines, tumor necrosis factor alpha and interleukin-1beta, functioned additively and synergistically, respectively, with Et-1 to increase this MCP-1 production. Partial elucidation of the signal transduction pathways involved in Et-1-induced MCP-1 production demonstrated that protein kinase C-, but not cAMP-dependent pathways are involved. These data demonstrate that Et-1, functioning as an inflammatory peptide, increased levels of MCP-1, suggesting a mechanism for chemokine regulation during ischemia/reperfusion injury.

Superoxide prevents nitric oxide-mediated suppression of helper T lymphocytes: decreased autoimmune encephalomyelitis in nicotinamide adenine dinucleotide phosphate oxidase knockout mice.

NO, which suppresses T cell proliferation, may be inactivated by superoxide (O2-) due to their strong mutual affinity. To examine this possibility, preactivated Th clones were cocultured with stimulated macrophages. PMA neutralized the inhibitory activity of NO, which was dependent on extracellular O2- production. In contrast, macrophages from p47phox -/- (pKO) mice, which lack functional NADPH oxidase, retained their NO-dependent inhibition of T cell proliferation upon stimulation with PMA, indicating that NADPH oxidase is the major source of NO-inactivating O2- in this system. To examine the NO-O2- interaction in vivo, the role of NADPH oxidase in experimental autoimmune encephalomyelitis was studied in pKO mice. No clinical or histological signs were observed in the pKO mice. Neither a bias in Th subsets nor a reduced intensity of T cell responses could account for the disease resistance. Although spleen cells from pKO mice proliferated poorly in response to the immunogen, inhibition of NO synthase uncovered a normal proliferative response. These results indicate that NO activity may play a critical role in T cell responses in pKO mice and that in normal spleens inhibition of T cell proliferation by NO may be prevented by simultaneous NADPH oxidase activity.

Virus-induced neuronal apoptosis blocked by the herpes simplex virus latency-associated transcript.

Latent infections with periodic reactivation are a common outcome after acute infection with many viruses. The latency-associated transcript (LAT) gene is required for wild-type reactivation of herpes simplex virus (HSV). However, the underlying mechanisms remain unclear. In rabbit trigeminal ganglia, extensive apoptosis occurred with LAT(-) virus but not with LAT(+) viruses. In addition, a plasmid expressing LAT blocked apoptosis in cultured cells. Thus, LAT promotes neuronal survival after HSV-1 infection by reducing apoptosis.

Antigen presentation to Th1 but not Th2 cells by macrophages results in nitric oxide production and inhibition of T cell proliferation: interferon-gamma is essential but insufficient.

The induction and role of nitric oxide (NO) during antigen presentation by macrophages to T helper (Th) cell subsets was examined. When cultured with Th1 clones, macrophage APC produced NO only in the presence of cognate Ag, which in turn suppressed T cell proliferation. IFN-gamma production by the activated Th1 cells was essential for the induction of NO. Th2 cells presented with the same cognate Ag did not induce NO production and proliferated uninhibited. Coactivation of Th1 and Th2 cells specific for the same Ag indicated that Th2 cells did not inhibit NO production, but were sensitive to NO induced by stimulated Th1 cells. Antigenic activation of Th2 cells in the presence of rIFN-gamma resulted in NO-mediated inhibition of proliferation. Th2 cells provided only a cell-associated cofactor, whereas Th1 cells secreted a soluble cofactor for IFN-gamma as well, i.e., TNF-alpha. Finally, a role for IFN-gamma and NO during immune responses was studied in spleen cells obtained from immunized IFN-gamma(-/-) mice. NO production and subsequent inhibition of Ag-specific proliferation ex vivo was observed only after the addition of rIFN-gamma. These studies suggest an IFN-gamma-dependent regulatory role for NO during Ag-specific Th cell activation involving macrophages, with obvious implications for Th subset-dependent immune responses in general.

Corneal macrophage infiltrates following ocular herpes simplex virus type 1 challenge vary in BALB/c mice vaccinated with different vaccines.

Macrophage cell infiltrates in the cornea were examined following ocular herpes simplex virus type 1 (HSV-1) challenge of vaccinated BALB/c mice. Mice were vaccinated with individual HSV-1 glycoproteins, cocktails of different HSV-1 glycoproteins, or live avirulent HSV-1 (strain KOS). Cryostat sections of cornea were taken at different times after challenge and reacted with M1/70, F4/80, BM8, or MOMA-1 monoclonal antibodies. The pattern of macrophage responses in the cornea differed depending on the vaccine that was given prior to HSV-1 ocular challenge. No macrophage response was detected in mice vaccinated with the highly protective 5gPs consisting of the five glycoproteins gB, gC, gD, gE, and gI. In contrast, mock vaccinated mice and mice vaccinated with gK, which is known to exacerbate HSV-1 induced eye disease, had high sustained macrophage responses. Mice vaccinated with 7gPs (5gPs+gG and gH) had moderate levels of macrophages. It appeared that (1) the most effective vaccines induced no detectable infiltrating macrophages in the eyes, while the least efficacious vaccines had very high levels of infiltrating macrophages; (2) presence of CD11b(+) cells in the cornea appeared to correlate with enhanced blepharitis, but did not appear to affect corneal scarring; and (3) presence of F4/80(+) cells in the cornea tended to correlate with increased corneal scarring.

Endothelin-1-induced interleukin-8 production in human brain-derived endothelial cells is mediated by the protein kinase C and protein tyrosine kinase pathways.

We have previously demonstrated that endothelin-1 (Et-1) induces human central nervous system-derived endothelial cells (CNS-EC) to produce and secrete the chemokine interleukin 8 (IL-8). In the present study, we use specific inhibitors and activators to elucidate the signal transduction pathways involved in this process. Et-1-induced IL-8 production was blocked by ET(A) receptor antagonist BQ610, but not by ET(B) receptor antagonist BQ788, demonstrating that CNS-EC activation is initiated by Et-1 binding to the ET(A) receptor. IL-8 mRNA expression is blocked by the protein kinase C inhibitor bisindolylmaleimide or protein tyrosine kinase inhibitors, genestein and geldanamycin, establishing the involvement of the protein kinase C and protein tyrosine kinase pathways in the activation process. The transcription factor, NF-kappaB, is involved in Et-1 activation as determined by specific inhibitors of translocation and direct analysis of DNA-binding proteins. Neither inhibition nor activation of cAMP-dependent protein kinase affected IL-8 production in the absence or presence of Et-1. Similarly, no effect was observed upon inhibition of protein phosphatases by okadaic acid. Thus, the signal transduction process induced by Et-1 in CNS-EC, leading to increased mRNA IL-8 expression, is initiated by Et-1 binding to ET(A) receptor followed by subsequent activation of protein kinase C, protein tyrosine kinase, and NF-kappaB. Because increased expression of Et-1 is associated with hypertension and stroke and IL-8 is likely to be involved in the accumulation of neutrophils causing tissue damage in ischemic/reperfusion injury, identification of the mechanism involved in the Et-1-induced increase in IL-8 production may have significant therapeutic value.

Vaccination with different HSV-1 glycoproteins induces different patterns of ocular cytokine responses following HSV-1 challenge of vaccinated mice.

We previously reported that vaccination of BALB/c mice with different baculovirus expressed HSV-1 glycoproteins induced varying degrees of protection against HSV-1 ocular challenge, ranging from complete protection to no protection, to exacerbation of eye disease. To correlate specific local immune responses with protection and exacerbation of corneal scarring, we examined immune cell infiltrates in the cornea after ocular HSV-1 challenge of vaccinated mice. Mice were vaccinated with gD, which completely protects against corneal scarring, gG, which produces no protection against corneal scarring, or gK, which exacerbates corneal scarring. Cryostat sections of cornea were taken at different times after challenge and examined for infiltrating cells containing IL-2, IL-4, IFN-gamma, IL-6, or TNF-alpha. No corneal infiltrates were seen before challenge or 1 day after ocular challenge in any groups. By days 3-7, many cells containing IL-4 and IFN-gamma, but few cells containing IL-2, had infiltrated into the corneas of gG or mock vaccinated mice. At the same times, many cells containing IL-2, but few cells containing IL-4 or IFN-gamma, were seen in the corneas of gD vaccinated mice. In contrast, the corneas of mice vaccinated with gK contained large amounts of IL-2, IFN-gamma, and IL-4. Our results suggest that: (1) corneas from gD vaccinated mice had no corneal disease and developed a response highly biased toward IL-2 responses; (2) corneas from gG or mock vaccinated eyes had significant corneal disease and developed a mostly IL-4 and IFN-gamma cytokine response; and (3) corneas from gK vaccinated mice had exacerbated corneal disease and developed strong IL-2, IL-4 and IFN-gamma cytokine responses.

Endothelin-1 enhances plasminogen activator inhibitor-1 production by human brain endothelial cells via protein kinase C-dependent pathway.

The effects of endothelin-1 (ET-1) on the production of plasminogen activator inhibitor 1 (PAI-1) and tissue plasminogen activator (t-PA) by human brain-derived endothelial cells in culture were studied. At 100 nmol/L, ET-1 increased PAI-1 production by 88+/-6% within 72 hours, and increased PAI-1 mRNA expression within 1 hour of stimulation; there was no significant effect on t-PA production. PAI-1 activity was also examined and found to increase with ET-1 treatment. Suboptimal concentrations of ET-1 and tumor necrosis factor-alpha (TNF-alpha) acted synergistically to increase PAI-1 production. ET-1 activated protein kinase C and cAMP-dependent protein kinase pathways within 3 to 5 minutes of treatment, with the peak at 10 minutes. Activation of protein kinase C by phorbol-12-myristate-13-acetate (PMA) resulted in increased PAI-1 production, whereas activation of the cAMP-dependent protein kinase by forskolin or dibutyryl cAMP (dBu-cAMP) significantly decreased PAI-1 production. However, simultaneous activation of protein kinase C by PMA and cAMP-dependent protein kinase by dBu-cAMP only slightly attenuated PMA-induced PAI-1 increase. Inhibition of protein kinase C by GF-109213X abolished the effects of ET-1. These results demonstrate that ET-1 and TNF-alpha function synergistically to induce procoagulant activity of brain endothelial cells in a process that involves a protein kinase C-dependent pathway.

HIV-1 tat protein induces the production of interleukin-8 by human brain-derived endothelial cells.

This study focused on the role of the HIV-derived viral protein, tat, in activating central nervous system (CNS)-derived endothelial cells (EC) to produce interleukin-8 (IL-8), a stimulator and chemoattractant for neutrophils and lymphocytes. Human CNS-EC treated with tat (100 ng/ml) demonstrated a 2 to 3 fold upregulation in IL-8 mRNA and protein. Tumor necrosis factor-alpha (TNF) and tat were found to act additively in upregulating IL-8 production. In contrast, transforming growth factor beta (TGF beta), appeared to down modulate tat-induced IL-8 production. These data suggest that extracellular tat, especially in the presence of TNF, may be responsible for the local production of IL-8.

Specific and nonspecific immune stimulation of MHC-II-deficient mice results in chronic HSV-1 infection of the trigeminal ganglia following ocular challenge.

Ocular herpes simplex virus type 1 (HSV-1) infection of MHC-II-deficient mice (AO/Obeta mice) or their parental C57BL/6J wild-type mice resulted in the establishment of typical HSV-1 latent infections in the trigeminal ganglia (TG) of the surviving mice by day 28 postinfection. Latency was characterized by the complete absence of infectious virus in TG extracts, the ability to recover latent virus only following prolonged tissue culture cultivation of explanted TG, and the presence of HSV-1 DNA in TG extracts. When mice were vaccinated prior to ocular HSV-1 challenge, latency appeared unaltered in the C57BL/6J wild-type mice. However, in AO/Obeta mice, clearance of virus from the TG appeared to be seriously impaired, resulting in a chronic productive infection, rather than a latent infection. Infectious virus was readily detected in TG extracts of vaccinated AO/Obeta mice until at least 63 days postinfection. Glycoprotein B mRNA was also readily detected, confirming continued viral transcription. These chronic infections occurred regardless of whether the AO/Obeta mice were vaccinated with HSV-1-specific antigens (i.e., live HSV-1 strain KOS, recombinantly expressed HSV-1 glycoprotein D plus Freund's adjuvant, or a mixture of seven recombinantly expressed HSV-1 glycoproteins plus adjuvant) or non-HSV-1-specific antigens (i.e., tissue culture medium plus 5% fetal bovine serum, the expression vector plus adjuvant, or adjuvant alone). Passive transfer of HSV-1 neutralizing antibody to vaccinated AO/Obeta mice between days 0 and 28 post-ocular challenge did not clear infectious virus from the TG. Passive transfer of anti-HSV-1 antibody or purified naive mouse serum to unvaccinated AO/Obeta mice on days 3 or 6 post-HSV-1 ocular challenge also resulted in chronic, rather than latent, infection of the TG. Passive transfer of naive sera from B-cell-deficient mice or injection of keyhole limpet hemocyanin or purified IgG, but not PBS or dextran, 3 days after HSV-1 challenge also resulted in chronic infection of the TG.

Nicotine increases plasminogen activator inhibitor-1 production by human brain endothelial cells via protein kinase C-associated pathway.

BACKGROUND AND PURPOSE: Smoking both increases stroke risk and reduces the risk of thrombolysis-associated intracerebral hemorrhage. Plasminogen activator inhibitor-1 (PAI-1) is a major regulator of fibrinolysis; elevation of PAI-1 is associated with an increased risk of thrombotic disorders. We studied the effect of nicotine, an important constituent of cigarette smoke, on PAI-1 production by human brain endothelial cells. METHODS: Adult human central nervous system endothelial cells (CNS-EC) were used for tissue culture experiments. We analyzed culture supernatant for PAI-1 protein and measured PAI-1 mRNA (by Northern blot analysis) and protein kinase C (PK-C) activity. RESULTS: Nicotine at 100 nmol/L increased PAI-1 protein production and mRNA expression by CNS-EC. After 72 hours of exposure to nicotine, the concentration of secreted PAI-1 in the cell supernatant was increased 1.90+/-0.2 fold compared with untreated cells. PAI-1 mRNA also increased approximately twofold. Inhibition of PK-C completely abolished this effect. Nicotine had no effect on the concentration of tissue plasminogen activator. CONCLUSIONS: Nicotine increases brain endothelial cell PAI-1 mRNA expression and protein production via PK-C-dependent pathway. These findings provide new insights into why smoking may be associated with predisposition to thrombosis and inversely associated with intracerebral hemorrhage after therapeutic tissue plasminogen activator therapy.

The role of neutralizing antibody and T-helper subtypes in protection and pathogenesis of vaccinated mice following ocular HSV-1 challenge.

In order to determine the possible correlation of specific immune responses with protection against mortality and ocular disease following ocular herpes simplex virus type 1 (HSV-1) challenge, BALB/c mice were vaccinated with different doses and regimens of baculovirus-expressed gD. Neutralizing antibody, virus titres in the eyes, corneal scarring, and survival were measured. In addition, infiltration into the cornea of CD4+ T cells and cells containing the lymphokines interleukin-2 (IL-2), IL-4, IL-6 and tumour necrosis factor-alpha (TNF-alpha) were monitored on days 3, 7, 10, 14 and 21 post-challenge by immunocytochemistry. The vaccination regimens used induced varying degrees of immune responses and protection upon ocular challenge with HSV-1. Our results suggest that neutralizing antibody was the most important immune response in protecting mice against lethal ocular challenge and corneal scarring. TNF-alpha and IL-2 were not crucial in terms of survival and corneal scarring, since gD1 (one vaccination with 1 microg of gD) and gD0.1 (one vaccination with 0.1 microg of gD), both of which provided high levels of protection, showed no TNF-alpha or IL-2 expression. However, TNF-alpha and IL-2 were crucial in terms of virus clearance from the eyes, since gD3 (three vaccinations with 1 microg of gD), which had less virus in their eyes, had high numbers of TNF-alpha and IL-2 infiltrates. Finally, mock-vaccinated mice were not protected from death and corneal disease following HSV-1 challenge. Eyes of mock-vaccinated mice had little or no TNF-alpha or IL-2 responses and the strongest IL-4 and IL-6 responses.

Endothelin-1 induces production of the neutrophil chemotactic factor interleukin-8 by human brain-derived endothelial cells.

Increased levels of endothelin-1 (Et-1), a potent vasoconstrictor, have been correlated with hypertension and neuronal damage in ischemic/reperfusion injury. The presence of polymorphonuclear cells (PMNs) in the brain has been shown to be directly responsible for this observed pathology. To address the question of whether Et-1 plays a role in this process, human brain-derived endothelial cells (CNS-ECs) were cultured with Et-1. The results demonstrate that Et-1 induces production of the neutrophil chemoattractant interleukin-8 (IL-8) twofold to threefold after 72 hours; mRNA was maximal after 1 hour of stimulation. Conditioned culture medium derived from Et-1-stimulated CNS-ECs induced a chemotactic response in the PMN migration assay. The inflammatory cytokines tumor necrosis factor-alpha (TNF) and IL-1beta functioned additively with Et-1 in increasing IL-8 production. In contrast, transforming growth factor-beta (TGF-beta), but not IL-10, completely abolished the effect of Et-1 on IL-8 production. However, Et-1 did not modulate intercellular adhesion molecule-1 (ICAM-1) expression. These data demonstrate that Et-1 may be a risk factor in ischemic/reperfusion injury by inducing increased levels of the neutrophil chemoattractant IL-8.

Up-regulation of the cAMP/PKA pathway inhibits proliferation, induces differentiation, and leads to apoptosis in malignant gliomas.

Manipulation of signal transduction pathways has been increasingly used to modulate tumor growth. We have investigated the effects of up-regulation of the cAMP/protein kinase A (PKA) pathway in cell lines and primary cultures of malignant gliomas. The malignant glioma cell line A-172 was treated with agonistic cAMP analogs dibutyryl cyclic AMP (dcAMP) and 8-bromo-cyclic AMP (8-Br-cAMP), an adenylate cyclase activator (forskolin), and a phosphodiesterase inhibitor (3-isobutyl-1-methyl-xanthene [IBMX]). Proliferation was determined by 3H-thymidine assay. Differentiation was measured by morphologic changes, glial fibrillary acidic protein (GFAP) content, and invasion potential. Apoptosis was measured quantitatively by the TUNEL method, which labels DNA fragments using terminal transferase. Agonistic cAMP analogs, forskolin, and IBMX were found to decrease proliferation in A-172 cells after 24 hours. Treatment with 8-Br-cAMP for 24 hours caused an increase in GFAP and decrease in invasion. Apoptosis was induced after 48 hours in the presence of synergistic cAMP analogs for the Type II PKA isozyme, but not Type I PKA isozyme. Activation of PKA by increasing cAMP levels (forskolin, IBMX) or directly by cAMP analogs correlated with decreased proliferation, increased differentiation, and induction of apoptosis in A-172 cells. Modulation of the cAMP/PKA pathway may thus represent a possible target site for treating malignant gliomas.

Circulating antibody against tumor necrosis factor-alpha protects rat brain from reperfusion injury.

The role of tumor necrosis factor-alpha (TNF alpha) in brain injury is controversial. We studied the effect of anti-TNF-alpha antibody in a rat model of reversible middle cerebral artery occlusion. During focal ischemia and early reperfusion, TNF-alpha was rapidly and transiently released into circulation. Pretreatment with intravenous anti-TNF-alpha antibody reduced cortical (71%, P < 0.015) and subcortical (58%, P < 0.007) injury, enhanced the cerebral blood flow during reperfusion, and improved the neurologic outcome. This further supports the contention that TNF-alpha is a deleterious cytokine in stroke, whereas circulating antibody against TNF-alpha may protect brain from reperfusion injury.

Extensive peroxynitrite activity during progressive stages of central nervous system inflammation.

Nitric oxide (NO) production has been associated with disease activity in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). This free radical can be transformed by superoxide to peroxynitrite, an extremely toxic oxidant which causes lipid peroxidation. In addition, peroxynitrite nitrates tyrosine residues, resulting in nitrotyrosine, which can be identified immunohistochemically. The results of this study indicate that peroxynitrite is formed very early during EAE development, correlating with clinical disease activity. Nitrotyrosine-positive cells display a widespread distribution in brain and spinal cord during severe disease and are associated with both perivascular infiltrates and parenchymal sites. Double-staining procedures demonstrated that a subpopulation of CD11b-positive cells (macrophages/microglia) reacted with nitrotyrosine antibodies. Immunostaining for inducible NO synthase demonstrated a similar distribution as nitrotyrosine staining. These experiments indicate that peroxynitrite is formed during progressive stages of disease activity.

Soluble TNF-alpha receptors are constitutively shed and downregulate adhesion molecule expression in malignant gliomas.

The regulation of adhesion molecule expression in malignant gliomas by tumor necrosis factor-alpha (TNF) and soluble TNF receptors (TNFR) was examined in the malignant glioma cell line A-172 and in 2 primary glioblastoma cell cultures (LA-492 and LA-567). A-172 cells expressed only the p55 TNF receptor transcripts and protein. The 2 primary cell cultures expressed both the p55 and p75 TNF receptors. In A-172 cells and in 1 of 2 primary glioma cell cultures, TNF upregulated the expression of ICAM-1 and VCAM-1, A-172 and both primary glioma cultures also shed their TNF receptors in the absence of activation by stimulating agents. Soluble p55 (sp55) receptors, but not soluble p75 (sp75) receptors, were found to reduce the TNF induced VCAM-1 and ICAM-1 expression in both the glioma cell line and the primary cell culture. Immunostaining of malignant glioma sections confirmed the presence of soluble TNFR and adhesion molecule expression in glioma cells in situ. These data suggest that soluble TNF receptors may play a role in the mechanism by which malignant gliomas downregulate the effects of infiltrating immune-competent cells.