Therapeutic immune clearance of rabies virus from the CNS

Characterisation of a Live-Attenuated Rabies Virus Expressing a Secreted scFv for the Treatment of Rabies

Rabies virus (RABV) causes possibly the oldest disease and is responsible for an estimated >59,000 human fatalities/year. Post exposure prophylaxis (PEP), the administration of vaccine and rabies immunoglobulin, is a highly effective tool which is frequently unavailable in RABV endemic areas. Furthermore, due to the constraints of the blood-brain barrier, current PEP regimes are ineffective after the onset of clinical symptoms which invariably result in death. To circumvent this barrier, a live-attenuated recombinant RABV expressing a highly RABV-neutralising scFv antibody (62-71-3) linked to the fluorescent marker mCherry was designed. Once rescued, the resulting construct (named RABV-62scFv) was grown to high titres, its growth and cellular dissemination kinetics characterised, and the functionality of the recombinant 62-71-3 scFv assessed. Encouraging scFv production and subsequent virus neutralisation results demonstrate the potential for development of a therapeutic live-attenuated virus-based post-infection treatment (PIT) for RABV infection.

Overcoming the blood–brain barrier for the therapy of malignant brain tumor: current status and prospects of drug delivery approaches

Besides the broad development of nanotechnological approaches for cancer diagnosis and therapy, currently, there is no significant progress in the treatment of different types of brain tumors. Therapeutic molecules crossing the blood–brain barrier (BBB) and reaching an appropriate targeting ability remain the key challenges. Many invasive and non-invasive methods, and various types of nanocarriers and their hybrids have been widely explored for brain tumor treatment. However, unfortunately, no crucial clinical translations were observed to date. In particular, chemotherapy and surgery remain the main methods for the therapy of brain tumors. Exploring the mechanisms of the BBB penetration in detail and investigating advanced drug delivery platforms are the key factors that could bring us closer to understanding the development of effective therapy against brain tumors. In this review, we discuss the most relevant aspects of the BBB penetration mechanisms, observing both invasive and non-invasive methods of drug delivery. We also review the recent progress in the development of functional drug delivery platforms, from viruses to cell-based vehicles, for brain tumor therapy. The destructive potential of chemotherapeutic drugs delivered to the brain tumor is also considered. This review then summarizes the existing challenges and future prospects in the use of drug delivery platforms for the treatment of brain tumors.

Challenges of Rabies Serology: Defining Context of Interpretation

The case fatality rate of rabies, nearly 100%, is one of the most unique characteristic of this ancient virus infection. The crucial role rabies virus neutralizing antibody plays in protection is both well established and explanation of why rabies serology is important. Various laboratory methods can and have been used but serum neutralization methods have long been the gold standard due to the ability to measure function (neutralization), however these methods can be difficult to perform for several reasons. Assays such as enzyme linked absorbance assays (ELISA), indirect fluorescence antibody (IFA) and more recently lateral flow methods are in use. Interpretation of results can be problematic, not only between methods but also due to modifications of the same method that can lead to misinterpretations. A common assumption in review of laboratory test results is that different methods for the same component produce comparable results under all conditions or circumstances. Assumptions and misinterpretations provide the potential for detrimental decisions, ranging from regulatory to clinically related, and most importantly what 'level' is protective. Review of the common challenges in performance and interpretation of rabies serology and specific examples illuminate critical issues to consider when reviewing and applying results of rabies serological testing.

Neurological recovery with serological response in a rabies survivor on long-term follow-up

An 18-year-old girl presented with headache, vomiting, dysarthria, diplopia and ataxia following a stray dog bite 20 days prior to presentation. The dog was killed by her neighbours. She received three doses of anti-rabies vaccine and one dose of rabies immunoglobulin (RVIG) before presentation. Diagnosis of rabies was confirmed based on four-fold rise in serum and CSF rabies virus neutralizing antibodies (RVNA) by rapid fluorescent focus inhibition test (RFFIT) titres coupled with history of dog-bite and a normal MRI. With supportive care and empirical administration of IVIG her condition improved over months and at her final visit to hospital at five years, she was physically independent with mild persistent dysarthria. Ours is one of the longest followed cases of rabies survivor in whom we had used IVIG empirically and could demonstrate the decline in the RVNA level in CSF and verify the steady neurological recovery over five years.

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.

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

Rabies

Rabies is a life-threatening neglected tropical disease: tens of thousands of cases are reported annually in endemic countries (mainly in Africa and Asia), although the actual numbers are most likely underestimated. Rabies is a zoonotic disease that is caused by infection with viruses of the Lyssavirus genus, which are transmitted via the saliva of an infected animal. Dogs are the most important reservoir for rabies viruses, and dog bites account for >99% of human cases. The virus first infects peripheral motor neurons, and symptoms occur after the virus reaches the central nervous system. Once clinical disease develops, it is almost certainly fatal. Primary prevention involves dog vaccination campaigns to reduce the virus reservoir. If exposure occurs, timely post-exposure prophylaxis can prevent the progression to clinical disease and involves appropriate wound care, the administration of rabies immunoglobulin and vaccination. A multifaceted approach for human rabies eradication that involves government support, disease awareness, vaccination of at-risk human populations and, most importantly, dog rabies control is necessary to achieve the WHO goal of reducing the number of cases of dog-mediated human rabies to zero by 2030.

Dogs that develop rabies post-vaccination usually manifest the paralytic subtype

Rabies infection can manifest as either encephalitic (furious) or paralytic (dumb) types, with a ratio of approximately 2:1 in dogs. The clinical type of rabies that develops post-vaccination has only been reported in studies from one country, all with similar findings. We report a study of 36 rabid dogs with obtainable vaccination history, presenting to The Queen Saovabha Memorial Institute, Bangkok, Thailand during 2002-2008. Dogs were classified into encephalitic or paralytic types. Of 22 non-vaccinated dogs, 16 (73%) had the encephalitic type. In contrast, of the 14 vaccinated dogs, 10 (71%) had the paralytic type, a difference that was significant (p=0.016). Recent studies on canine brains have shown that lymphocyte response is more pronounced in paralytic rabies at the brainstem level, whereas viral burden is greater in the encephalitic form. We postulate partial immune response in the vaccinated dogs might influence rabies to manifest as the paralytic type. These results can serve as a natural experiment that can help explain the basis for the differences between the paralytic and encephalitic forms of canine rabies.

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.

Factors Impacting the Control of Rabies

Rabies is a classical zoonosis that has been known to man for ages. The disease can be caused by several viral species in the Lyssavirus genus, but the type species, rabies virus (RABV), is by far the most important from a zoonosis perspective. The extreme neurotropism of RABV and the evolutionarily conserved elements and structures of the mammalian brain suggest that this virus evolved an ultimate niche for replication, simultaneously exploiting classical social behavior of a wide diversity of hosts among the chiropters and carnivores. There is substantial evidence that RABV originated in bats and later switched hosts to yield globally disseminated canine rabies. Following the revolutionary work of Louis Pasteur, control and elimination of dog rabies was achieved in Europe, but widespread colonial introduction of European strains of dog RABV to other parts of the world occurred. Thus, dog rabies spread rapidly in the 1900s, and today the vast majority of the tens of thousands of annual human rabies cases stem from dog rabies, which has become endemic in the entire developing world. The fact that human rabies is preventable, through control in the dog reservoir on one hand and through effective prophylaxis in cases of exposure on the other hand, is an indictment of public health strategies and practices. This article discusses some of the drivers that have contributed to the recurrent neglect of rabies in the modern world, as well as evolving One Health-based rabies control partnerships and initiatives that have been progressive, productive, and promising of true global benefits.

Novel Approaches to the Prevention and Treatment of Rabies

Rabies is a highly lethal disease caused by the neurotropic rabies virus (RABV), and it remains an important public health problem globally. Effective vaccines have been developed for pre- and post-exposure prophylaxis (PEP). PEP is only effective if it is initiated promptly after recognizing exposure. Once neurological symptoms develop, however, it is widely accepted that there is no effective treatment available. Recent studies indicate that the presence of RABV-specific immunity (i.e. Virus neutralizing antibodies, VNA) and the transient enhancement of the BBB permeability are absolutely required for effective virus clearance from the CNS. In principle, it has been shown in mice using various live-attenuated RABVs or recombinant RABVs expressing three copies of the G or expressing chemokine/cytokines, which can induce high levels of VNA in the serum and also capable of transiently enhancing the BBB permeability that it is possible to clear the virus from CNS. Also, it has been demonstrated that, intravenous administration of VNA together with MCP-1 (shown to transiently open up BBB) can clear RABV from the CNS in both immunocompetent and immunocompromised mice, as late as 5 days after lethal challenge. Novel therapeutic approaches aimed at allowing the peripheral VNA to cross the BBB by administration of the VNA in combination with biological or chemical agents that can transiently open up the BBB would be useful to establish an effective therapy for rabies in humans. In this review, we focus on the some of the approaches that can be used to meet the challenges in the field of rabies treatment.

Cellular immune response following pre-exposure and postexposure rabies vaccination by intradermal and intramuscular routes

Purpose

Immunization against rabies in humans induces protective neutralizing antibodies; however, the induction of type 1 or type 2 cytokine mediated cellular immune responses following rabies vaccination is not understood. Hence, the present study investigated cellular cytokine responses in vaccinated individuals.

Materials and Methods

The study groups included healthy rabies antigen naive controls (n=10), individuals who received intradermal primary (n=10) or booster pre-exposure vaccination (n=20) and subjects who received postexposure rabies vaccination either by intradermal (n=18) or intramuscular (n=20) routes. The antigen specific cellular responses were analyzed by stimulating peripheral blood mononuclear cells with a rabies vaccine antigen in the interferon-γ (IFN-γ) and interleukin-4 (IL-4) enzyme-linked immunospot (ELISpot) assay. These responses were compared to the rabies virus neutralizing antibody (RVNA) titers that were measured by rapid fluorescent focus inhibition test.

Results

We observed that cellular and humoral immune responses to primary intradermal rabies vaccination could be greatly enhanced by a booster vaccine; and both type 1 and type 2 cytokine responses were significantly elevated. The magnitude of type 1 and type 2 cytokine responses did not differ significantly among the intramuscular and intradermal routes of postexposure vaccination. The number of cells producing IFN-γ and IL-4 correlated significantly with the levels of RVNA.

Conclusion

Both type 1 and type 2 cellular cytokine responses are strongly induced after rabies vaccination and directly correlate with levels of RVNA titers. The neutralizing antibody as well as the type 1 and type 2 cytokine responses may be important for vaccine induced protective responses against rabies.

Pre- and post-exposure safety and efficacy of attenuated rabies virus vaccines are enhanced by their expression of IFNγ

Consistent with evidence of a strong correlation between interferon gamma (IFNγ) production and rabies virus (RABV) clearance from the CNS, we recently demonstrated that engineering a pathogenic RABV to express IFNγ highly attenuates the virus. Reasoning that IFNγ expression by RABV vaccines would enhance their safety and efficacy, we reverse-engineered two proven vaccine vectors, GAS and GASGAS, to express murine IFNγ. Mortality and morbidity were monitored during suckling mice infection, immunize/challenge experiments and mixed intracranial infections. We demonstrate that GASγ and GASγGAS are significantly attenuated in suckling mice compared to the GASGAS vaccine. GASγ better protects mice from lethal DRV4 RABV infection in both pre- and post-exposure experiments compared to GASGAS. Finally, GASγGAS reduces post-infection neurological sequelae, compared to control, during mixed intracranial infection with DRV4. These data show IFNγ expression by a vaccine vector can enhance its safety while increasing its efficacy as pre- and post-exposure treatment.

Survival from rabies encephalitis

Rabies is a major public health problem in Asia and Africa, with nearly 60,000 deaths every year, and represents a substantial economic burden. Neurologists frequently encounter atypical cases, and need to make informed decisions regarding diagnosis and management. No therapy has been shown to unequivocally improve survival in rabies till date. Despite the overwhelmingly fatal nature of this disease, a small number of patients have been reported to survive acute rabies encephalitis with varying degrees of neurological sequelae. This paper presents the eleventh documented case of survival from rabies, which developed after being bitten by a stray dog, albeit with severe neurological residua. Similar to patients in previous reports, this man demonstrated a robust immune response as indicated by peripheral viral clearance and very high serum and cerebrospinal fluid antibody titres. Immunologically-mediated virus clearance therefore appears to be a prerequisite for survival. A detailed review of previously reported survivors, as well as descriptions of the host response and viral clearance in human rabies, current therapy for this disease and future directions in improving the currently dismal prognosis are provided.

Intrathecal humoral immunity to encephalitic RNA viruses

The nervous system is the target for acute encephalitic viral infections, as well as a reservoir for persisting viruses. Intrathecal antibody (Ab) synthesis is well documented in humans afflicted by infections associated with neurological complications, as well as the demyelinating disease, multiple sclerosis. This review focuses on the origin, recruitment, maintenance, and biological relevance of Ab-secreting cells (ASC) found in the central nervous system (CNS) following experimental neurotropic RNA virus infections. We will summarize evidence for a highly dynamic, evolving humoral response characterized by temporal alterations in B cell subsets, proliferation, and differentiation. Overall local Ab plays a beneficial role via complement-independent control of virus replication, although cross or self-reactive Ab to CNS antigens may contribute to immune-mediated pathogenesis during some infections. Importantly, protective Ab exert anti-viral activity not only by direct neutralization, but also by binding to cell surface-expressed viral glycoproteins. Ab engagement of viral glycoproteins blocks budding and mediates intracellular signaling leading to restored homeostatic and innate functions. The sustained Ab production by local ASC, as well as chemokines and cytokines associated with ASC recruitment and retention, are highlighted as critical components of immune control.

Emergency vaccination alleviates highly pathogenic porcine reproductive and respiratory syndrome virus infection after contact exposure

Background

To assess the effectiveness of emergency vaccination for reducing the contact-induced infection and pathological damage caused by the highly pathogenic porcine reproductive and respiratory syndrome virus (HPPRRSV), Twenty pigs were equally divided into four groups. Groups 1, 2 and 3 were housed in one unit, whereas Group 4 was separately housed. Group 1 was challenged with HPPRRSV on day 0. Group 2 and 4 did not receive treatment and were used as the contact-infected and uninfected controls, respectively. Group 3 was treated with the attenuated vaccine at 0 days post-inoculation. The rectal temperatures, clinical signs, pathologic lesions and viraemia of the piglets were detected and evaluated.

Results

The vaccinated pigs in Group 3 showed less clinical morbidity, viraemia, temperature fluctuations and lung lesions at 14 days post-inoculation, as compared with the contact-infected (Group 2) and experimentally infected (Group 1) pigs. Higher serum IFN-γ levels were detected among the pigs that received emergency immunisation. Thus, IFN-γ may be involved in immunity against HPPRRSV infection.

Conclusions

These results indicated that emergency vaccination could effectively alleviate HPPRRSV infection during experimental contact exposure. Our findings provide a novel and useful strategy for controlling clinical HPPRRSV.

Rabies: still a uniformly fatal disease? Historical occurrence, epidemiological trends, and paradigm shifts

Rabies has the highest case fatality of any infectious disease. Pathobiological and clinical insights have questioned the assertion that death is inevitable after onset of acute encephalomyelitis. Relying upon national laboratory-based surveillance, we reviewed records of human rabies acquired in the United States during 1960-2009. Changes in the epidemiology of human rabies were notable, due to improved animal management, safer and more efficacious biologics, and revisions in prevention guidelines. Historically, domestic animals were the most important source of infection. Since the 1990s, more human cases were associated with rabid bats. Prior to 1980, postexposure prophylaxis failures were reported. After development of modern rabies immune globulin and vaccines, none occurred. Of 75 human cases identified, only four patients survived. Rabies remains an extremely high consequence zoonosis, but the disease is not uniformly fatal, per se. Rabies is essentially preventable when primary exposures are averted, or appropriate prophylaxis occurs before illness.