Systemic Immune Bias Delineates Malignant Astrocytoma Survival Cohorts.

Patients with grade III anaplastic astrocytomas (AA) separate into survival cohorts based on the presence or absence of mutations in isocitrate dehydrogenase (IDH). Progression to glioblastoma (GBM), morphologically distinguishable by elevated microvascular proliferation, necrosis, and cell division in tumor tissues, is considerably more rapid in IDH wild-type tumors such that their diagnosis as AA is relatively rare. More often initially presenting as GBM, these contain higher numbers of tumor-associated macrophages (TAMs) than most AA, and GBM patients also have higher levels of circulating M2 monocytes. TAM and M2 monocytes share functional properties inhibitory for antitumor immunity. Yet, although there is a wealth of data implicating TAM in tumor-immune evasion, there has been limited analysis of the impact of the circulating M2 monocytes. In the current study, immune parameters in sera, circulating cells, and tumor tissues from patients with primary gliomas morphologically diagnosed as AA were assessed. Profound differences in serum cytokines, glioma extracellular vesicle cross-reactive Abs, and gene expression by circulating cells identified two distinct patient cohorts. Evidence of type 2-immune bias was most often seen in patients with IDH wild-type AA, whereas a type 1 bias was common in patients with tumors expressing the IDH1R132H mutation. Nevertheless, a patient's immune profile was better correlated with the extent of tumor vascular enhancement on magnetic resonance imaging than IDH mutational status. Regardless of IDH genotype, AA progression appears to be associated with a switch in systemic immune bias from type 1 to type 2 and the loss of tumor vasculature integrity.

Clearance of attenuated rabies virus from brain tissues is required for long-term protection against CNS challenge with a pathogenic variant.

Rabies virus is a neurotropic lyssavirus which is 100% fatal in its pathogenic form when reaching unprotected CNS tissues. Death can be prevented by mechanisms delivering appropriate immune effectors across the blood-brain barrier which normally remains intact during pathogenic rabies virus infection. One therapeutic approach is to superinfect CNS tissues with attenuated rabies virus which induces blood-brain barrier permeability and immune cell entry. Current thinking is that peripheral rabies immunization is sufficient to protect against a challenge with pathogenic rabies virus. While this is undoubtedly the case if the virus is confined to the periphery, what happens if the virus reaches the CNS is less well-understood. In the current study, we find that peripheral immunization does not fully protect mice long-term against an intranasal challenge with pathogenic rabies virus. Protection is significantly better in mice that have cleared attenuated virus from the CNS and is associated with a more robust CNS recall response evidently due to the presence in CNS tissues of elevated numbers of lymphocytes phenotypically resembling long-term resident immune cells. Adoptive transfer of cells from rabies-immune mice fails to protect against CNS challenge with pathogenic rabies virus further supporting the concept that long-term resident immune cell populations must be established in brain tissues to protect against a subsequent CNS challenge with pathogenic rabies virus.

T-bet Is Required for the Rapid Clearance of Attenuated Rabies Virus from Central Nervous System Tissue.

Much of our understanding of CNS immunity has been gained from models involving pathological inflammation. Attenuated rabies viruses (RABV) are unique tools to study CNS immunity in the absence of conventional inflammatory mechanisms, as they spread from the site of inoculation to the CNS transaxonally, thereby bypassing the blood-brain barrier (BBB), and are cleared without neutrophil or monocyte infiltration. To better understand the role of CD4 T cell subsets in the clearance of the virus from CNS tissues, we examined the development of antiviral immunity in wild-type (WT) and T-bet knockout mice (T-bet(-/-)), which lack Th1 cells. Early control of RABV replication in the CNS tissues of WT mice is associated with the production of IFN-γ, with antiviral effects likely mediated through the enhanced expression of type I IFNs. Of interest, IFN-α and -γ are overexpressed in the infected T-bet(-/-) by comparison with WT CNS tissues, and the initial control of RABV infection is similar. Ultimately, attenuated RABV are cleared from the CNS tissues of WT mice by Ab locally produced by the activities of infiltrating T and B cells. Although T and B cell infiltration into the CNS of infected T-bet(-/-) mice is comparable, their activities are not, the consequence being delayed, low-level Ab production and prolonged RABV replication. More importantly, neither T-bet(-/-) mice immunized with an attenuated virus, nor WT mice with Th2 RABV-specific immunity induced by immunization with inactivated virus, are protected in the long term against challenge with a pathogenic RABV.

Intramuscular inoculation of mice with the live-attenuated recombinant rabies virus TriGAS results in a transient infection of the draining lymph nodes and a robust, long-lasting protective immune response against rabies.

A single intramuscular application of the live but not UV-inactivated recombinant rabies virus (RABV) variant TriGAS in mice induces the robust and sustained production of RABV-neutralizing antibodies that correlate with long-term protection against challenge with an otherwise lethal dose of the wild-type RABV. To obtain insight into the mechanism by which live TriGAS induces long-lasting protective immunity, quantitative PCR (qPCR) analysis of muscle tissue, draining lymph nodes, spleen, spinal cord, and brain at different times after TriGAS inoculation revealed the presence of significant copy numbers of RABV-specific RNA in muscle, lymph node, and to a lesser extent, spleen for several days postinfection. Notably, no significant amounts of RABV RNA were detected in brain or spinal cord at any time after TriGAS inoculation. Differential qPCR analysis revealed that the RABV-specific RNA detected in muscle is predominantly genomic RNA, whereas RABV RNA detected in draining lymph nodes is predominantly mRNA. Comparison of genomic RNA and mRNA obtained from isolated lymph node cells showed the highest mRNA-to-genomic-RNA ratios in B cells and dendritic cells (DCs), suggesting that these cells represent the major cell population that is infected in the lymph node. Since RABV RNA declined to undetectable levels by 14 days postinoculation of TriGAS, we speculate that a transient infection of DCs with TriGAS may be highly immunostimulatory through mechanisms that enhance antigen presentation. Our results support the superior efficacy and safety of TriGAS and advocate for its utility as a vaccine.

BP1003 Decreases STAT3 Expression and Its Pro-Tumorigenic Functions in Solid Tumors and the Tumor Microenvironment.

Overexpression and aberrant activation of signal transducer and activator of transcription 3 (STAT3) contribute to tumorigenesis, drug resistance, and tumor-immune evasion, making it a potential cancer therapeutic target. BP1003 is a neutral liposome incorporated with a nuclease-resistant P-ethoxy antisense oligodeoxynucleotide (ASO) targeting the STAT3 mRNA. Its unique design enhances BP1003 stability, cellular uptake, and target affinity. BP1003 efficiently reduces STAT3 expression and enhances the sensitivity of breast cancer cells (HER2+, triple negative) and ovarian cancer cells (late stage, invasive ovarian cancer) to paclitaxel and 5-fluorouracil (5-FU) in both 2D and 3D cell cultures. Similarly, ex vivo and in vivo patient-derived models of pancreatic ductal adenocarcinoma (PDAC) show reduced tissue viability and tumor volume with BP1003 and gemcitabine combination treatments. In addition to directly affecting tumor cells, BP1003 can modulate the tumor microenvironment. Unlike M1 differentiation, monocyte differentiation into anti-inflammatory M2 macrophages is suppressed by BP1003, indicating its potential contribution to immunotherapy. The broad anti-tumor effect of BP1003 in numerous preclinical solid tumor models, such as breast, ovarian, and pancreatic cancer models shown in this work, makes it a promising cancer therapeutic.

Neuroendocrine gene subsets are uniquely dysregulated in prostate adenocarcinoma.

Prostate cancer has heterogeneous growth patterns, and its prognosis is the poorest when it progresses to a neuroendocrine phenotype. Using bioinformatic analysis, we evaluated RNA expression of neuroendocrine genes in a panel of five different cancer types: prostate adenocarcinoma, breast cancer, kidney chromophobe, kidney renal clear cell carcinoma and kidney renal papillary cell carcinoma. Our results show that specific neuroendocrine genes are significantly dysregulated in these tumors, suggesting that they play an active role in cancer progression. Among others, synaptophysin (SYP), a conventional neuroendocrine marker, is upregulated in prostate adenocarcinoma (PRAD) and breast cancer (BRCA). Our analysis shows that SYP is enriched in small extracellular vesicles (sEVs) derived from plasma of PRAD patients, but it is absent in sEVs derived from plasma of healthy donors. Similarly, classical sEV markers are enriched in sEVs derived from plasma of prostate cancer patients, but weakly detectable in sEVs derived from plasma of healthy donors. Overall, our results pave the way to explore new strategies to diagnose these diseases based on the neuroendocrine gene expression in patient tumors or plasma sEVs.

Effective preexposure and postexposure prophylaxis of rabies with a highly attenuated recombinant rabies virus.

Rabies remains an important public health problem with more than 95% of all human rabies cases caused by exposure to rabid dogs in areas where effective, inexpensive vaccines are unavailable. Because of their ability to induce strong innate and adaptive immune responses capable of clearing the infection from the CNS after a single immunization, live-attenuated rabies virus (RV) vaccines could be particularly useful not only for the global eradication of canine rabies but also for late-stage rabies postexposure prophylaxis of humans. To overcome concerns regarding the safety of live-attenuated RV vaccines, we developed the highly attenuated triple RV G variant, SPBAANGAS-GAS-GAS. In contrast to most attenuated recombinant RVs generated thus far, SPBAANGAS-GAS-GAS is completely nonpathogenic after intracranial infection of mice that are either developmentally immunocompromised (e.g., 5-day-old mice) or have inherited deficits in immune function (e.g., antibody production or type I IFN signaling), as well as normal adult animals. In addition, SPBAANGAS-GAS-GAS induces immune mechanisms capable of containing a CNS infection with pathogenic RV, thereby preventing lethal rabies encephalopathy. The lack of pathogenicity together with excellent immunogenicity and the capacity to deliver immune effectors to CNS tissues makes SPBAANGAS-GAS-GAS a promising vaccine candidate for both the preexposure and postexposure prophylaxis of rabies.

Blood-brain barrier changes and cell invasion differ between therapeutic immune clearance of neurotrophic virus and CNS autoimmunity.

CNS tissues are protected from circulating cells and factors by the blood-brain barrier (BBB), a specialization of the neurovasculature. Outcomes of the loss of BBB integrity and cell infiltration into CNS tissues can differ vastly. For example, elevated BBB permeability is closely associated with the development of neurological disease in experimental allergic encephalomyelitis (EAE) but not during clearance of the attenuated rabies virus CVS-F3 from the CNS tissues. To probe whether differences in the nature of BBB permeability changes may contribute to the pathogenesis of acute neuroinflammatory disease, we compared the characteristics of BBB permeability changes in mice with EAE and in mice clearing CVS-F3. BBB permeability changes are largely restricted to the cerebellum and spinal cord in both models but differ in the extent of leakage of markers of different size and in the nature of cell accumulation in the CNS tissues. The accumulation in the CNS tissues of CD4 T cells expressing mRNAs specific for IFN-gamma and IL-17 is common to both, but iNOS-positive cells invade into the CNS parenchyma only in EAE. Mice that have been immunized with myelin basic protein (MBP) and infected exhibit the features of EAE. Treatment with the peroxynitrite-dependent radical scavenger urate inhibits the invasion of iNOS-positive cells into the CNS tissues and the development of clinical signs of EAE without preventing the loss of BBB integrity in immunized/infected animals. These findings indicate that BBB permeability changes can occur in the absence of neuropathology provided that cell invasion is restricted.

Phase Ib Clinical Trial of IGV-001 for Patients with Newly Diagnosed Glioblastoma.

PURPOSE: Despite standard of care (SOC) established by Stupp, glioblastoma remains a uniformly poor prognosis. We evaluated IGV-001, which combines autologous glioblastoma tumor cells and an antisense oligonucleotide against IGF type 1 receptor (IMV-001), in newly diagnosed glioblastoma. PATIENTS AND METHODS: This open-label protocol was approved by the Institutional Review Board at Thomas Jefferson University. Tumor cells collected during resection were treated ex vivo with IMV-001, encapsulated in biodiffusion chambers with additional IMV-001, irradiated, then implanted in abdominal acceptor sites. Patients were randomized to four exposure levels, and SOC was initiated 4-6 weeks later. On the basis of clinical improvements, randomization was halted after patient 23, and subsequent patients received only the highest exposure. Safety and tumor progression were primary and secondary objectives, respectively. Time-to-event outcomes were compared with the SOC arms of published studies. RESULTS: Thirty-three patients were enrolled, and median follow-up was 3.1 years. Six patients had adverse events (grade ≤3) possibly related to IGV-001. Median progression-free survival (PFS) was 9.8 months in the intent-to-treat population (vs. SOC, 6.5 months; P = 0.0003). In IGV-001-treated patients who met Stupp-eligible criteria, PFS was 11.6 months overall (n = 22; P = 0.001) and 17.1 months at the highest exposure (n = 10; P = 0.0025). The greatest overall survival was observed in Stupp-eligible patients receiving the highest exposure (median, 38.2 months; P = 0.044). Stupp-eligible patients with methylated O6-methylguanine-DNA methyltransferase promoter (n = 10) demonstrated median PFS of 38.4 months (P = 0.0008). Evidence of immune activation was noted. CONCLUSIONS: IGV-001 was well tolerated, PFS compared favorably with SOC, and evidence suggested an immune-mediated mechanism (ClinicalTrials.gov: NCT02507583).

Brain tissue-resident immune memory cells are required for long-term protection against CNS infection with rabies virus.

Immune memory cells residing in previously infected, nonlymphoid tissues play a role in immune surveillance. In the event that circulating antibodies fail to prevent virus spread to the tissues in a secondary infection, these memory cells provide an essential defense against tissue reinfection. CNS tissues are isolated from circulating immune cells and antibodies by the blood-brain barrier, making the presence of tissue-resident immune memory cells particularly needed to combat recurrent infection by neurotropic viruses. Wild-type and laboratory-engineered rabies viruses are neurotropic, differ in pathogenicity, and have varying effects on BBB functions. These viruses have proven invaluable tools in demonstrating the importance of tissue-resident immune memory cells in the reinfection of CNS tissues. Only Type 1 immune memory is effective at therapeutically clearing a secondary infection with wild-type rabies viruses from the CNS and does so despite the maintenance of blood-brain barrier integrity.

Targeting VPAC1 Receptors for Imaging Glioblastoma.

PURPOSE: Scintigraphic imaging of malignant glioblastoma (MG) continues to be challenging. We hypothesized that VPAC1 cell surface receptors can be targeted for positron emission tomography (PET) imaging of orthotopically implanted MG in a mouse model, using a VPAC1-specific peptide [64Cu]TP3805. PROCEDURES: The expression of VPAC1 in mouse GL261 and human U87 glioma cell lines was determined by western blot. The ability of [64Cu]TP3805 to bind to GL261 and U87 cells was studied by cell-binding. Receptor-blocking studies were performed to validate receptor specificity. GL261 tumors were implanted orthotopically in syngeneic T-bet knockout C57BL/6 mouse brain (N = 15) and allowed to grow for 2-3 weeks. Mice were injected i.v., first with ~ 150 µCi of 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) then 24 h later with ~ 200 µCi of [64Cu]TP3805. In another set of tumor-bearing mice, (N = 5), ionic [64Cu]Cl2 was injected as a control. Mice were imaged at a 2-h post-injection using an Inveon micro-PET/CT, sacrificed and % ID/g of [64Cu]TP3805 and [64Cu]Cl2 were calculated in a tumor, normal brain, and other tissues. For histologic tissue examination, 3-µm thick sections of the tumors and normal brain were prepared, digital autoradiography (DAR) was performed, and then the sections were H&E stained for histologic examination. RESULTS: Western blots showed a strong signal for VPAC1 on both cell lines. [64Cu]TP3805 cell-binding was 87 ± 1.5 %. Receptor-blocking reduced cell-binding to 24.3 ± 1.5 % (P < 0.01). PET imaging revealed remarkable accumulation of [64Cu]TP3805 in GL261 MG with a negligible background in the normal brain, as compared to [18F]FDG. Micro-PET/CT image analyses and tissue distribution showed that the brain tumor uptake for [64Cu]TP3805 was 8.2 ± 1.7 % ID/g and for [64Cu]Cl2 2.1 ± 0.5 % ID/g as compared to 1.0 ± 0.3 % ID/g and 1.4 ± 0.3 % ID/g for normal mouse brains, respectively. The high tumor/normal brain ratio for [64Cu]TP3805 (8.1 ± 1.1) allowed tumors to be visualized unequivocally. Histology and [64Cu]TP3805 DAR differentiated malignant tumors from healthy brain and confirmed PET findings. CONCLUSION: Targeting VPAC1 receptors using [64Cu]TP3805 for PET imaging of MG is a promising novel approach and calls for further investigation.

A Pilot Study of Radiation Therapy in Combination With Pembrolizumab in Patients With Metastatic Renal Cell Cancer.

OBJECTIVES: There is no study published regarding the benefit of radiation therapy (RT) in combination with immune checkpoint inhibitors (ICIs) for the treatment of metastatic renal cell cancer (mRCC). This report is part of an exploratory study aiming to determine the immunomodulatory activity of RT alone or in combination with pembrolizumab in solid tumors. MATERIALS AND METHODS: mRCC patients were treated with a combination of RT (8 Gy×1 or 4 Gy×5) followed by pembrolizumab with or without lead-in dose of pembrolizumab. Treatment response was measured based on the modified Response Evaluation Criteria in Solid Tumors criteria. Adverse events were monitored and graded. Pre-RT and post-RT tumor biopsies were obtained to evaluate programmed death-ligand 1 expression. Immune markers from peripheral blood before, during, and after treatment were analyzed using flow cytometry. RESULTS: Twelve mRCC patients who progressed on prior antiangiogenic therapy were enrolled. Half had 2 lines of prior therapy. Two patients (16.7%) had partial responses and were on study for 12.4 and 14.5 months. Three patients had stable disease for a period ranging from 4.2 to 10.4 months, whereas 7 patients had progressive disease. Median progression-free survival was 8.6 months and median overall survival was 32.3 months. Three patients had grade ≥3 events (hyperglycemia, thrombocytopenia, transaminitis). Biopsied tissue programmed death-ligand 1 expression and tumor-infiltrating lymphocytes were numerically higher in responders comparing to nonresponders (Modified Proportion Score 45% vs. 30.45%; tumor-infiltrating lymphocytes odds ratio 4.92). CONCLUSION: Combining RT with pembrolizumab in pretreated mRCC is well-tolerated and appears to have comparable efficacy with single-agent nivolumab.

Early blood-brain barrier permeability in cerebella of PLSJL mice immunized with myelin basic protein.

The blood-brain barrier (BBB) is dramatically but transiently compromised in the cerebella of myelin basic protein immunized mice at least 1 week prior to the development of the paralytic phase of experimental allergic encephalomyelitis (EAE). Treatment of mice with the peroxynitrite-dependent radical scavenger uric acid (UA) during the first week after immunization blocks the early increase in cerebellar BBB permeability and the subsequent development of clinical signs of EAE. These results indicate that the early loss of BBB integrity in the cerebellum is likely to be a necessary step in the development of paralytic EAE.

Exosomal αvß6 integrin is required for monocyte M2 polarization in prostate cancer.

Therapeutic approaches aimed at curing prostate cancer are only partially successful given the occurrence of highly metastatic resistant phenotypes that frequently develop in response to therapies. Recently, we have described αvß6, a surface receptor of the integrin family as a novel therapeutic target for prostate cancer; this epithelial-specific molecule is an ideal target since, unlike other integrins, it is found in different types of cancer but not in normal tissues. We describe a novel αvß6-mediated signaling pathway that has profound effects on the microenvironment. We show that αvß6 is transferred from cancer cells to monocytes, including ß6-null monocytes, by exosomes and that monocytes from prostate cancer patients, but not from healthy volunteers, express αvß6. Cancer cell exosomes, purified via density gradients, promote M2 polarization, whereas αvß6 down-regulation in exosomes inhibits M2 polarization in recipient monocytes. Also, as evaluated by our proteomic analysis, αvß6 down-regulation causes a significant increase in donor cancer cells, and their exosomes, of two molecules that have a tumor suppressive role, STAT1 and MX1/2. Finally, using the Ptenpc-/- prostate cancer mouse model, which carries a prostate epithelial-specific Pten deletion, we demonstrate that αvß6 inhibition in vivo causes up-regulation of STAT1 in cancer cells. Our results provide evidence of a novel mechanism that regulates M2 polarization and prostate cancer progression through transfer of αvß6 from cancer cells to monocytes through exosomes.

Protection Against CNS-Targeted Rabies Virus Infection is Dependent upon Type-1 Immune Mechanisms Induced by Live-Attenuated Rabies Vaccines.

Rabies remains a major public health issue worldwide, especially in developing countries where access to medical care can represent a real challenge. While there is still no cure for rabies, it is a vaccine-preventable disease with pre- and post-exposure prophylaxis regimens approved by the World Health Organization (WHO). However, many rabies-exposed individuals have limited access to vaccines and virus-neutralizing antibodies approved for post-exposure prophylaxis. Unfortunately, any delay in the administration of these reagents can have lethal consequences. This highlights the need to develop cost-effective immunological reagents with a greater window of efficacy. Live-attenuated vaccine strains of rabies virus presents a potential treatment in filling this gap. We show here that immunization with live-attenuated vaccines provide long-lasting rabies immunity, superior to the protection induced by inactivated vaccines. In the absence of an immunostimulatory adjuvant, vaccination with multiple doses of inactivated rabies virus induces a type-2 immune response. This type of immunity is highly effective at inducing neutralizing antibody but has limited efficacy in clearing the virus from central nervous system (CNS) tissues. In contrast, a single infection with live-attenuated rabies vaccine safely drives a type-1 immune response, associated with both the production of a neutralizing antibody and the clearance of wild-type rabies virus from CNS tissues. These results indicate that live-attenuated rabies strains have the potential to be more effective in post-exposure prophylaxis than conventional inactivated vaccines.

Comparison of uric acid and ascorbic acid in protection against EAE.

Serum levels of uric acid (UA), an inhibitor of peroxynitrite- (ONOO-) related chemical reactions, became elevated approximately 30 million years ago in hominid evolution. During a similar time frame, higher mammals lost the ability to synthesize another important radical scavenger, ascorbic acid (AA), leading to the suggestion that UA may have replaced AA as an antioxidant. However, in vivo treatment with AA does not protect against the development of experimental allergic encephalomyelitis (EAE), a disease that has been associated with the activity of ONOO- and is inhibited by UA. When compared in vitro, UA and AA were found to have similar capacities to inhibit the nitrating properties of ONOO-. However UA and AA had different capacities to prevent ONOO- -mediated oxidation, especially in the presence of iron ion (Fe3+). While UA at physiological concentrations effectively blocked dihydrorhodamine-123 oxidation in the presence of Fe3+, AA did not, regardless of whether the source of ONOO- was synthetic ONOO-, SIN-1, or RAW 264.7 cells. AA also potentiated lipid peroxidation in vivo and in vitro. In conclusion, the superior protective properties of UA in EAE may be related to its ability to neutralize the oxidative properties of ONOO- in the presence of free iron ions.

ICAM-1 upregulation in the spinal cords of PLSJL mice with experimental allergic encephalomyelitis is dependent upon TNF-alpha production triggered by the loss of blood-brain barrier integrity.

Urate (UA) selectively scavenges peroxynitrite-dependent radicals and suppresses CNS inflammation through effects that are manifested at the blood-brain barrier (BBB). ICAM-1 upregulation in the spinal cord tissues of myelin basic protein (MBP) immunized mice is selectively inhibited by UA treatment. In contrast, the expression of ICAM-1 and other adhesion molecules by circulating cells is unchanged. Moreover, TNF-alpha expression in the CNS tissues of MBP-immunized mice is suppressed by UA treatment but TNF-alpha-induced ICAM-1 expression on neurovascular endothelial cells is not. Therefore the effect of UA on ICAM-1 upregulation in the CNS tissues is likely due to its known contribution to the maintenance of BBB integrity in MBP-immunized mice which in turn inhibits cell invasion into the CNS and prevents TNF-alpha production in CNS tissues.

Rabies virus clearance from the central nervous system.

Rabies, a neurological disease associated with replication in central nervous system (CNS) tissues of any of a number of rabies viruses endemic in nature, is generally fatal. Prophylactic medical intervention is immune mediated and directed at preventing the spread of the virus from a peripheral site of exposure to the CNS. While individuals rarely develop immune responses capable of clearing the virus from CNS tissues, a variety of laboratory-attenuated rabies viruses are readily cleared from the CNS tissues in animal models. By comparing immune responses to wild-type and attenuated rabies viruses in these models, we have discovered that the latter induce processes required for immune effector infiltration into CNS tissues that are absent from lethal infections. Predominant among these are activities of cells of the neurovascular unit (NVU) that promote an interaction with circulating immune cells. In the absence of this interaction, the specialized barrier function of the NVU remains intact and circulating virus-specific immune effectors are largely excluded from infected CNS tissues. Studies of mixed infections with wild-type and attenuated rabies viruses reveal that wild-type rabies viruses fail to trigger, rather than inhibit, the interactions between immune cells and the NVU required for virus clearance from the CNS. These studies provide insights into how immune effectors with the capacity to clear the virus may be delivered into CNS tissues to contain a wild-type rabies virus infection. However, to apply immunotherapeutic strategies beyond the initial stages of CNS infection, further insights into the fate of the infected cells during virus clearance are needed.

Therapeutic immune clearance of rabies virus from the CNS.

The long-held concept that rabies infection is lethal in humans once the causative rabies virus has reached the CNS has been called into question by the recent survival of a number of patients with clinical rabies. Studies in animal models provide insight into why survival from a rabies virus infection that has spread to the CNS is possible and the immune mechanisms involved. In the CNS, both innate mechanisms capable of inhibiting virus replication and the activity of infiltrating rabies virus-specific T and B cells with the capacity to clear the virus are required. Deficiencies in the induction of either aspect of rabies immunity can lead to lethal consequences but may be overcome by novel approaches to active and passive immunization.

A peroxynitrite-dependent pathway is responsible for blood-brain barrier permeability changes during a central nervous system inflammatory response: TNF-alpha is neither necessary nor sufficient.

Elevated blood-brain barrier (BBB) permeability is associated with both the protective and pathological invasion of immune and inflammatory cells into CNS tissues. Although a variety of processes have been implicated in the changes at the BBB that result in the loss of integrity, there has been no consensus as to their induction. TNF-alpha has often been proposed to be responsible for increased BBB permeability but there is accumulating evidence that peroxynitrite (ONOO(-))-dependent radicals may be the direct trigger. We demonstrate here that enhanced BBB permeability in mice, whether associated with rabies virus (RV) clearance or CNS autoimmunity, is unaltered in the absence of TNF-alpha. Moreover, the induction of TNF-alpha expression in CNS tissues by RV infection has no impact on BBB integrity in the absence of T cells. CD4 T cells are required to enhance BBB permeability in response to the CNS infection whereas CD8 T cells and B cells are not. Like CNS autoimmunity, elevated BBB permeability in response to RV infection is evidently mediated by ONOO(-). However, as opposed to the invading cells producing ONOO(-) that have been implicated in the pathogenesis of CNS inflammation, during virus clearance ONOO(-) is produced without pathological sequelae by IFN-gamma-stimulated neurovascular endothelial cells.