Co-administration of the broad-spectrum antiviral, brincidofovir (CMX001), with smallpox vaccine does not compromise vaccine protection in mice challenged with ectromelia virus

Monkeypox infection: The past, present, and future

Monkeypox is a zoonotic illness caused by the monkeypox virus (MPXV) that has a similar etiology to smallpox. The first case of monkeypox was reported in Western and Central Africa in 1971, and in 2003, there was an outbreak of monkeypox viruses outside Africa. According to the World Health Organization (WHO) and Center for Disease Control and Prevention (CDC), monkeypox is transmitted through direct contact with infected animals or persons exposed to infectious sores, scabs, or body fluids. Also, intimate contact between people during sex, kissing, cuddling, or touching parts of the body can result in the spreading of this disease. The use of the smallpox vaccine against monkeypox has several challenges and hence anti-virals such as cidofovir, brincidofovir, and tecovirimat have been used for the symptomatic relief of patients and reversing the lesion formation on the skin. Despite the recent outbreak of monkeypox most especially in hitherto non-endemic countries, there is still a lack of definitive treatment for monkeypox. In the present review, emphasis was focused on etiopathology, transmission, currently available therapeutic agents, and future targets that could be explored to halt the progression of monkeypox. From our review we can postulate that owing to the lack of a definitive cure to this reemerging disorder, there is a need for general awareness about the transmission as well as to develop appropriate diagnostic procedures, immunizations, and antiviral medication.

Human Monkeypox: A Comprehensive Narrative Review and Analysis of the Public Health Implications

Recently, numerous cases of monkeypox were reported from several non-endemic countries in Europe, North America, and Oceania, suggesting an unusual and alarming public health issue, particularly considering that the disease is not directly related to human or animal travels. Attention is currently being drawn to this phenomenon since more than 70% of the global population is no longer vaccinated against smallpox. Indeed, the smallpox vaccination also confers some indirect degree of protection against other poxviruses, including monkeypox. We performed a narrative review to describe the existing literature with regard to monkeypox using the MEDLINE, EMBASE, and Scopus databases. This review aims to provide updated evidence of findings on the epidemiology, clinical features, diagnosis, management, and prevention of monkeypox, also considering the concurrent zoonotic pandemic caused by the COVID-19 coronavirus, SARS-CoV-2.

A human recombinant analogue to plasma-derived vaccinia immunoglobulin prophylactically and therapeutically protects against lethal orthopoxvirus challenge

Orthopoxviruses such as variola and monkeypox viruses continue to threaten the human population. Monkeypox virus is endemic in central and western Africa and outbreaks have reached as far as the U.S. Although variola virus, the etiologic agent of smallpox, has been eradicated by a successful vaccination program, official and likely clandestine stocks of the virus exist. Moreover, studies with ectromelia virus (the etiological agent of mousepox) have revealed that IL-4 recombinant viruses are significantly more virulent than wild-type viruses even in mice treated with vaccines and/or antivirals. For these reasons, it is critical that antiviral modalities are developed to treat these viruses should outbreaks, or deliberate dissemination, occur. Currently, 2 antivirals (brincidofovir and tecovirimat) are in the U.S. stockpile allowing for emergency use of the drugs to treat smallpox. Both antivirals have advantages and disadvantages in a clinical and emergency setting. Here we report on the efficacy of a recombinant immunoglobulin (rVIG) that demonstrated efficacy against several orthopoxviruses in vitro and in vivo in both a prophylactic and therapeutic fashion. A single intraperitoneal injection of rVIG significantly protected mice when given up to 14 days before or as late as 6 days post challenge. Moreover, rVIG reduced morbidity, as measured by weight-change, as well as several previously established biomarkers of disease. In rVIG treated mice, we found that vDNA levels in blood were significantly reduced, as was ALT (a marker of liver damage) and infectious virus levels in the liver. No apparent adverse events were observed in rVIG treated mice, suggesting the immunoglobulin is well tolerated. These findings suggest that recombinant immunoglobulins could be candidates for further evaluation and possible licensure under the FDA Animal Rule.

IMVAMUNE® and ACAM2000® Provide Different Protection against Disease When Administered Postexposure in an Intranasal Monkeypox Challenge Prairie Dog Model

The protection provided by smallpox vaccines when used after exposure to Orthopoxviruses is poorly understood. Postexposu re administration of 1st generation smallpox vaccines was effective during eradication. However, historical epidemiological reports and animal studies on postexposure vaccination are difficult to extrapolate to today’s populations, and 2nd and 3rd generation vaccines, developed after eradication, have not been widely tested in postexposure vaccination scenarios. In addition to concerns about preparedness for a potential malevolent reintroduction of variola virus, humans are becoming increasingly exposed to naturally occurring zoonotic orthopoxviruses and, following these exposures, disease severity is worse in individuals who never received smallpox vaccination. This study investigated whether postexposure vaccination of prairie dogs with 2nd and 3rd generation smallpox vaccines was protective against monkeypox disease in four exposure scenarios. We infected animals with monkeypox virus at doses of 10⁴ pfu (2× LD₅₀) or 10⁶ pfu (170× LD₅₀) and vaccinated the animals with IMVAMUNE^® or ACAM2000^® either 1 or 3 days after challenge. Our results indicated that postexposure vaccination protected the animals to some degree from the 2× LD₅₀, but not the 170× LD₅ challenge. In the 2× LD₅₀ challenge, we also observed that administration of vaccine at 1 day was more effective than administration at 3 days postexposure for IMVAMUNE^®, but ACAM2000^® was similarly effective at either postexposure vaccination time-point. The effects of postexposure vaccination and correlations with survival of total and neutralizing antibody responses, protein targets, take formation, weight loss, rash burden, and viral DNA are also presented.

Antivirals in medical biodefense

The viruses historically implicated or currently considered as candidates for misuse in bioterrorist events are poxviruses, filoviruses, bunyaviruses, orthomyxoviruses, paramyxoviruses and a number of arboviruses causing encephalitis, including alpha- and flaviviruses. All these viruses are of concern for public health services when they occur in natural outbreaks or emerge in unvaccinated populations. Recent events and intelligence reports point to a growing risk of dangerous biological agents being used for nefarious purposes. Public health responses effective in natural outbreaks of infectious disease may not be sufficient to deal with the severe consequences of a deliberate release of such agents. One important aspect of countermeasures against viral biothreat agents are the antiviral treatment options available for use in post-exposure prophylaxis. These issues were adressed by the organizers of the 16th Medical Biodefense Conference, held in Munich in 2018, in a special session on the development of drugs to treat infections with viruses currently perceived as a threat to societies or associated with a potential for misuse as biothreat agents. This review will outline the state-of-the-art methods in antivirals research discussed and provide an overview of antiviral compounds in the pipeline that are already approved for use or still under development.

Post-exposure prophylactic vaccine candidates for the treatment of human Risk Group 4 pathogen infections

Introduction: The development of therapeutics and vaccines to combat Risk Group 4 pathogens, which are associated with high case-fatality rates, is a high priority. Postexposure prophylactic vaccines have the potential to bridge classical therapeutic and vaccine applications, but little progress has been reported to date.Areas covered: This review provides an overview of postexposure prophylactic vaccine candidates against Risk Group 4 pathogens.Expert opinion: A few candidate postexposure prophylactic vaccines protect experimental animals infected with a few Risk Group 4 pathogens, such as filoviruses or hantaviruses, but the efficacy of candidate vaccines has not been similarly reported for most other high-consequence pathogens. A major drawback for the further development of existing candidates is the lack of understanding of their mechanisms of action, knowledge of which could help to identify focused paths forward in vaccine development and licensure. These drawbacks to further development ultimately slow progress toward postexposure prophylactic vaccine licensure.

Identifying and Tracking Low-Frequency Virus-Specific TCR Clonotypes Using High-Throughput Sequencing

Tracking antigen-specific T cell responses over time within individuals is difficult because of lack of knowledge of antigen-specific TCR sequences, limitations in sample size, and assay sensitivities. We hypothesized that analyses of high-throughput sequencing of TCR clonotypes could provide functional readouts of individuals' immunological histories. Using high-throughput TCR sequencing, we develop a database of TCRβ sequences from large cohorts of mice before (naive) and after smallpox vaccination. We computationally identify 315 vaccine-associated TCR sequences (VATS) that are used to train a diagnostic classifier that distinguishes naive from vaccinated samples in mice up to 9 months post-vaccination with >99% accuracy. We determine that the VATS library contains virus-responsive TCRs by in vitro expansion assays and virus-specific tetramer sorting. These data outline a platform for advancing our capabilities to identify pathogen-specific TCR sequences, which can be used to identify and quantitate low-frequency pathogen-specific TCR sequences in circulation over time with exceptional sensitivity.

Challenges and Achievements in Prevention and Treatment of Smallpox

Declaration of smallpox eradication by the WHO in 1980 led to discontinuation of the worldwide vaccination campaign. The increasing percentage of unvaccinated individuals, the existence of its causative infectious agent variola virus (VARV), and the recent synthetic achievements increase the threat of intentional or accidental release and reemergence of smallpox. Control of smallpox would require an emergency vaccination campaign, as no other protective measure has been approved to achieve eradication and ensure worldwide protection. Experimental data in surrogate animal models support the assumption, based on anecdotal, uncontrolled historical data, that vaccination up to 4 days postexposure confers effective protection. The long incubation period, and the uncertainty of the exposure status in the surrounding population, call for the development and evaluation of safe and effective methods enabling extension of the therapeutic window, and to reduce the disease manifestations and vaccine adverse reactions. To achieve these goals, we need to evaluate the efficacy of novel and already licensed vaccines as a sole treatment, or in conjunction with immune modulators and antiviral drugs. In this review, we address the available data, recent achievements, and open questions.

Multiplex PCR system for the rapid diagnosis of respiratory virus infection: systematic review and meta-analysis

OBJECTIVES

To provide a summary of evidence for the diagnostic accuracies of three multiplex PCR systems (mPCRs)-BioFire FilmArray RP (FilmArray), Nanosphere Verigene RV+ test (Verigene RV+) and Hologic Gen-Probe Prodesse assays-on the detection of viral respiratory infections.

METHODS

A comprehensive search up to 1 July 2017 was conducted on Medline and Embase for studies that utilized FilmArray, Verigene RV+ and Prodesse for diagnosis of viral respiratory infections. A summary of diagnostic accuracies for the following five viruses were calculated: influenza A virus (FluA), influenza B virus, respiratory syncytial virus, human metapneumovirus and adenovirus. Hierarchical summary receiver operating curves were used for estimating the viral detection performance per assay.

RESULTS

Twenty studies of 5510 patient samples were eligible for analysis. Multiplex PCRs demonstrated high diagnostic accuracy, with area under the receiver operating characteristic curve (AUROC) equal to or more than 0.98 for all the above viruses except for adenovirus (AUROC 0.89). FilmArray, Verigene RV+ and ProFlu+ (the only Prodesse assay with enough data) demonstrated a summary sensitivity for FluA of 0.911 (95% confidence interval, 0.848-0.949), 0.949 (95% confidence interval, 0.882-0.979) and 0.954 (95% confidence interval, 0.871-0.985), respectively. The three mPCRs were comparable in terms of detection of FluA.

CONCLUSIONS

Point estimates calculated from eligible studies showed that the three mPCRs (FilmArray, Verigene RV+ and ProFlu+) are highly accurate and may provide important diagnostic information for early identification of respiratory virus infections. In patients with low pretest probability for FluA, these three mPCRs can predict a low possibility of infection and may justify withholding empirical antiviral treatments.

40 Years without Smallpox

The last case of natural smallpox was recorded in October, 1977. It took humanity almost 20 years to achieve that feat after the World Health Organization had approved the global smallpox eradication program. Vaccination against smallpox was abolished, and, during the past 40 years, the human population has managed to lose immunity not only to smallpox, but to other zoonotic orthopoxvirus infections as well. As a result, multiple outbreaks of orthopoxvirus infections in humans in several continents have been reported over the past decades. The threat of smallpox reemergence as a result of evolutionary transformations of these zoonotic orthopoxviruses exists. Modern techniques for the diagnostics, prevention, and therapy of smallpox and other orthopoxvirus infections are being developed today.

Efficacy of delayed brincidofovir treatment against a lethal rabbitpox virus challenge in New Zealand White rabbits

In the event of a bioterror attack with variola virus (smallpox), exposure may only be identified following onset of fever. To determine if antiviral therapy with brincidofovir (BCV; CMX001) initiated at, or following, onset of fever could prevent severe illness and death, a lethal rabbitpox model was used. BCV is in advanced development as an antiviral for the treatment of smallpox under the US Food and Drug Administration's 'Animal Rule'. This pivotal study assessed the efficacy of immediate versus delayed treatment with BCV following onset of symptomatic disease in New Zealand White rabbits intradermally inoculated with a lethal rabbitpox virus (RPXV), strain Utrecht. Infected rabbits with confirmed fever were randomized to blinded treatment with placebo, BCV, or BCV delayed by 24, 48, or 72 h. The primary objective evaluated the survival benefit with BCV treatment. The assessment of reduction in the severity and progression of clinical events associated with RPXV were secondary objectives. Clinically and statistically significant reductions in mortality were observed when BCV was initiated up to 48 h following the onset of fever; survival rates were 100%, 93%, and 93% in the immediate treatment, 24-h, and 48-h delayed treatment groups, respectively, versus 48% in the placebo group (p < 0.05 for each vs. placebo). Significant improvements in clinical and virologic parameters were also observed. These findings provide a scientific rationale for therapeutic intervention with BCV in the event of a smallpox outbreak when vaccination is contraindicated or when diagnosis follows the appearance of clinical signs and symptoms.

Antiviral Treatments

Most viral respiratory tract infections are caused by classic respiratory viruses, including influenza, respiratory syncytial virus, human metapneumovirus, parainfluenza, rhinovirus, and adenovirus, whereas other viruses, such as herpes simplex, cytomegalovirus, and measles virus, can opportunistically affect the respiratory tract. The M2 inhibitors, amantadine and rimantadine, were historically effective for the prevention and treatment of influenza A but all circulating strains are currently resistant to these drugs. Neuraminidase inhibitors are the sole approved class of antivirals to treat influenza. Ribavirin, especially when combined with intravenous antibody, reduces morbidity and mortality among immunosuppressed patients.

Buccal viral DNA as a trigger for brincidofovir therapy in the mousepox model of smallpox

Orthopoxviruses continue to pose a significant threat to the population as potential agents of bioterrorism. An intentional release of natural or engineered variola virus (VARV) or monkeypox viruses would cause mortality and morbidity in the target population. To address this, antivirals have been developed and evaluated in animal models of smallpox and monkeypox. One such antiviral, brincidofovir (BCV, previously CMX001), has demonstrated high levels of efficacy against orthopoxviruses in animal models and is currently under clinical evaluation for prevention and treatment of diseases caused by cytomegaloviruses and adenoviruses. In this study we use the mousepox model of smallpox to evaluate the relationship between the magnitude of the infectious virus dose and an efficacious BCV therapy outcome when treatment is initiated concomitant with detection of ectromelia virus viral DNA (vDNA) in mouse buccal swabs. We found that vDNA could be detected in buccal swabs of some, but not all infected mice over a range of challenge doses by day 3 or 4 postexposure, when initiation of BCV treatment was efficacious, suggesting that detection of vDNA in buccal swabs could be used as a trigger to initiate BCV treatment of an entire potentially exposed population. However, buccal swabs of some mice did not become positive until 5 days postexposure, when initiation of BCV therapy failed to protect mice that received high doses of virus. And finally, the data suggest that the therapeutic window for efficacious BCV treatment decreases as the virus infectious dose increases. Extrapolating these findings to VARV, the data suggest that treatment should be initiated as soon as possible after exposure and not rely on a diagnostic tool such as the measurement of vDNA in buccal cavity swabs; however, consideration should be given to the fact that the behavior/disease-course of VARV in humans is different from that of ectromelia virus in the mouse.

Ebola virus disease: societal challenges and new treatments

Ebola virus disease (EVD) is a zoonotic disease that causes severe haemorrhagic fever, with high fatality rates of up to 90% in humans. Today, there is no effective treatment available. Person-to-person transmission occurs through exposure to blood or body fluids, which can threaten other household members and first-line healthcare workers. The first cases of EVD in Guinea were identified on 22 March 2014. It was initially believed that this like previous outbreaks would be self-limiting. However, lack of public health infrastructure, delays in virus detection and late implementation of control interventions contributed to widespread transmission of EVD in a region inexperienced in dealing with the disease. Socio-cultural and economic factors probably also played a key role in the spread of the disease, resulting in the current large-scale outbreak. Some promising candidate treatments for this disease are now being developed.

The efficacy and pharmacokinetics of brincidofovir for the treatment of lethal rabbitpox virus infection: a model of smallpox disease

Brincidofovir (BCV) has broad-spectrum in vitro activity against dsDNA viruses, including smallpox, and is being developed as a treatment for smallpox as well as infections caused by other dsDNA viruses. BCV has previously been shown to be active in multiple animal models of smallpox. Here we present the results of a randomized, blinded, placebo-controlled study of the efficacy and pharmacokinetics of a novel, "humanized" regimen of BCV for treatment of New Zealand White rabbits infected with a highly lethal inoculum of rabbitpox virus, a well characterized model of smallpox. Compared with placebo, a dose-dependent increase in survival was observed in all BCV-treatment groups. Concentrations of cidofovir diphosphate (CDV-PP), the active antiviral, in rabbit peripheral blood mononuclear cells (PBMCs) were determined for comparison to those produced in humans at the dose proposed for treatment of smallpox. CDV-PP exposure in PBMCs from rabbits given BCV scaled to human exposures at the dose proposed for treatment of smallpox, which is also currently under evaluation for other indications. The results of this study demonstrate the activity of BCV in the rabbitpox model of smallpox and the feasibility of scaling doses efficacious in the model to a proposed human dose and regimen for treatment of smallpox.

Postchallenge administration of brincidofovir protects healthy and immune-deficient mice reconstituted with limited numbers of T cells from lethal challenge with IHD-J-Luc vaccinia virus

Protection from lethality by postchallenge administration of brincidofovir (BCV, CMX001) was studied in normal and immune-deficient (nude, nu/nu) BALB/c mice infected with vaccinia virus (VACV). Whole-body bioluminescence imaging was used to record total fluxes in the nasal cavity, lungs, spleen, and liver and to enumerate pox lesions on tails of mice infected via the intranasal route with 10(5) PFU of recombinant IHD-J-Luc VACV expressing luciferase. Areas under the flux curve (AUCs) were calculated for individual mice to assess viral loads. A three-dose regimen of 20 mg/kg BCV administered every 48 h starting either on day 1 or day 2 postchallenge protected 100% of mice. Initiating BCV treatment earlier was more efficient in reducing viral loads and in providing protection from pox lesion development. All BCV-treated mice that survived challenge were also protected from rechallenge with IHD-J-Luc or WRvFire VACV without additional treatment. In immune-deficient mice, BCV protected animals from lethality and reduced viral loads while animals were on the drug. Viral recrudescence occurred within 4 to 9 days, and mice succumbed ∼10 to 20 days after treatment termination. Nude mice reconstituted with 10(5) T cells prior to challenge with 10(4) PFU of IHD-J-Luc and treated with BCV postchallenge survived the infection, cleared the virus from all organs, and survived rechallenge with 10(5) PFU of IHD-J-Luc VACV without additional BCV treatment. Together, these data suggest that BCV protects immunocompetent and partially T cell-reconstituted immune-deficient mice from lethality, reduces viral dissemination in organs, prevents pox lesion development, and permits generation of VACV-specific memory.

IMPORTANCE

Mass vaccination is the primary element of the public health response to a smallpox outbreak. In addition to vaccination, however, antiviral drugs are required for individuals with uncertain exposure status to smallpox or for whom vaccination is contraindicated. Whole-body bioluminescence imaging was used to study the effect of brincidofovir (BCV) in normal and immune-deficient (nu/nu) mice infected with vaccinia virus, a model of smallpox. Postchallenge administration of 20 mg/kg BCV rescued normal and immune-deficient mice partially reconstituted with T cells from lethality and significantly reduced viral loads in organs. All BCV-treated mice that survived infection were protected from rechallenge without additional treatment. In immune-deficient mice, BCV extended survival. The data show that BCV controls viral replication at the site of challenge and reduces viral dissemination to internal organs, thus providing a shield for the developing adaptive immunity that clears the host of virus and builds virus-specific immunological memory.