Therapeutic Efficacy of Human Monoclonal Antibodies against Andes Virus Infection in Syrian Hamsters

Establishment and optimization of a rapid and convenient viral RNA transcript copy reduction neutralization test (VcRNT) for quantification of hantaan orthohantavirus (HTNV) neutralizing antibodies

Rodent-borne orthohantavirus causes severe hemorrhagic fever worldwide, with hemorrhagic fever with renal syndrome (HFRS) in Eurasia, and hantavirus cardiopulmonary syndrome (HCPS) in the Amrerica. In East Asia, Hantaan orthohantavirus (HTNV) is the main pathogen responsible for severe HFRS, with a case fatality rate up to 10 % with no specific treatment available. The antisera or neutralizing antibody (NAb) is able to block virus infection, however, the traditional NAb titer measuring based on focus reduction neutralization test (FRNT) is quite labour-extensive and takes 7-10 days. This study aims to shorten the measuring time of NAb neutralization efficiency by 1-2 days based on quantitative RT-PCR. For this purpose, we developed an in vitro transcripted viral RNA standard and generated a viral RNA copy number standard curve. Using this standard curve, we compared the HTNV propagation kinetics between viral RNA copy numbers and secreted infectious virion. The detection limit and suitable timeframe and condition for qRT-PCR based viral RNA copy numbers measuring was also determined. In addition, when applying this method to measuring the NAb neutralization efficiency of HFRS convalescent serum samples, we could obtain the NAb neutralization efficiency within 1 or 2 days. Furthermore, this method was also nicely correlated with the FRNT - based NAb measurement. To conclude, we established a rapid and convenient viral RNA transcripts copy reduction neutralization test (VcRNT) to measure NAb neutralization efficiency that could finish within 1 or 2 days, and provided a reliable and efficient alternative for FRNT.

Standardization, validation, and comparative evaluation of a convenient surrogate recombinant vesicular stomatitis virus plaque reduction test for quantification of Hantaan orthohantavirus (HTNV) neutralizing antibodies

Hantaan orthohantavirus (HTNV) is responsible for severe hemorrhagic fever with renal syndrome (HFRS), which has a case fatality rate of 1% to 10%. Currently, the inactive vaccine licensed in endemic areas elicit low levels of neutralizing antibodies (NAbs). Early NAbs administration is helpful for patients recovery from HFRS. Therefore, measuring NAbs is crucial for evaluating the immune response following infection or vaccination. The golden standard for HTNV NAbs measurement is the focus reduction neutralization test (FRNT), which typically requires skilled technicians and is performed under high biosafety containment facility. Here, we established a surrogate NAbs titration method with replication-competent vesicular stomatitis virus (VSV) bearing HTNV glycoprotein (rVSV-HTNV-GP) based plaque reduction neutralization test (PRNT). Then compared and correlated this method with the authentic HTNV based FRNT, and applied it to measure the NAbs level in 47 serum samples from HFRS patients, healthy donors and inactive vaccine recipients. We observed positive correlations between two neutralization assays among HFRS patients and inactive vaccine recipients (R2 = 0.5994 and 0.3440, respectively) and confirmed the clear specificity with healthy donors without vaccinated and reproducibility with three more assays. Our results suggest that rVSV-HTNV-GP based PRNT is a reliable lower-biosafety level surrogate for HTNV NAbs evaluation, which is easy to perform with higher sensitivity.

Preclinical evaluation of a fully human, quadrivalent-hantavirus polyclonal antibody derived from a non-human source

Hantaviruses are rodent-borne viruses that cause severe disease in infected humans. In the New World, major hantaviruses include Andes virus (ANDV) and Sin Nombre virus (SNV) causing hantavirus pulmonary syndrome. In the Old World, major hantaviruses include Hantaan virus (HTNV) and Puumala virus (PUUV) causing hemorrhagic fever with renal syndrome. Here, we produced a pan-hantavirus therapeutic (SAB-163) comprised of fully human immunoglobulin purified from the plasma of transchromosomic bovines (TcB) vaccinated with hantavirus DNA plasmids coding for the major glycoproteins of ANDV, SNV, HTNV, and PUUV. SAB-163 has potent neutralizing antibodies (PRNT50 > 200,000) against the four targeted hantavirus and cross-neutralization against several other heterotypic hantaviruses. At a dosage of 10 mg/kg, SAB-163 is bioavailable in Syrian hamsters out to 70 days post-treatment with a half-life of 10-15 days. At this same dosage, SAB-163 administered 1 day before, or 5 days after exposure, protected all hamsters from lethal disease caused by ANDV. At a higher dose, partial but significant protection was achieved as late as day 6. SAB-163 also protected hamsters in the HTNV, PUUV, and SNV infection models when administered 1 day before or up to 3 days after challenge. This pan-hantavirus therapeutic is attractive because it is fully human, multi-targeted, safe, stable at 4°C, and effective in animal models. SAB-163 was evaluated for safety in GLP human tissue binding studies and a GLP rabbit toxicity study at 365 and 730 mg/kg and is investigational new drug enabled for phase 1 clinical trial(s).

IMPORTANCE

This candidate polyclonal human IgG product was produced using synthetic gene-based vaccines and transgenic cows. Having now gone through cGMP production, GLP safety testing, and efficacy testing in animals, SAB-163 is the world's most advanced anti-hantavirus antibody-based medical countermeasure, aside from convalescent human plasma. Importantly, SAB-163 targets the most prevalent hantaviruses on four continents.

Human-to-Human Transmission of Andes Virus Modeled in Syrian Hamsters

Several occurrences of human-to-human transmission of Andes virus, an etiological agent of hantavirus cardiopulmonary syndrome, are documented. Syrian hamsters consistently model human hantavirus cardiopulmonary syndrome, yet neither transmission nor shedding has been investigated. We demonstrate horizontal virus transmission and show that Andes virus is shed efficiently from both inoculated and contact-infected hamsters.

Hantavirus in humans: a review of clinical aspects and management

Hantavirus infections are part of the broad group of viral haemorrhagic fevers. They are also recognised as a distinct model of an emergent zoonotic infection with a global distribution. Many factors influence their epidemiology and transmission, such as climate, environment, social development, ecology of rodent hosts, and human behaviour in endemic regions. Transmission to humans occurs by exposure to infected rodents in endemic areas; however, Andes hantavirus is unique in that it can be transmitted from person to person. As hantaviruses target endothelial cells, they can affect diverse organ systems; increased vascular permeability is central to pathogenesis. The main clinical syndromes associated with hantaviruses are haemorrhagic fever with renal syndrome (HFRS), which is endemic in Europe and Asia, and hantavirus cardiopulmonary syndrome (HCPS), which is endemic in the Americas. HCPS and HFRS are separate clinical entities, but they share several features and have many overlapping symptoms, signs, and pathogenic alterations. For HCPS in particular, clinical outcomes are highly associated with early clinical suspicion, access to rapid diagnostic testing or algorithms for presumptive diagnosis, and prompt transfer to a facility with critical care units. No specific effective antiviral treatment is available.

Structural and mechanistic basis of neutralization by a pan-hantavirus protective antibody

Emerging rodent-borne hantaviruses cause severe diseases in humans with no approved vaccines or therapeutics. We recently isolated a monoclonal broadly neutralizing antibody (nAb) from a Puumala virus-experienced human donor. Here, we report its structure bound to its target, the Gn/Gc glycoprotein heterodimer comprising the viral fusion complex. The structure explains the broad activity of the nAb: It recognizes conserved Gc fusion loop sequences and the main chain of variable Gn sequences, thereby straddling the Gn/Gc heterodimer and locking it in its prefusion conformation. We show that the nAb's accelerated dissociation from the divergent Andes virus Gn/Gc at endosomal acidic pH limits its potency against this highly lethal virus and correct this liability by engineering an optimized variant that sets a benchmark as a candidate pan-hantavirus therapeutic.

Antigenic mapping and functional characterization of human New World hantavirus neutralizing antibodies

Hantaviruses are high-priority emerging pathogens carried by rodents and transmitted to humans by aerosolized excreta or, in rare cases, person-to-person contact. While infections in humans are relatively rare, mortality rates range from 1 to 40% depending on the hantavirus species. There are currently no FDA-approved vaccines or therapeutics for hantaviruses, and the only treatment for infection is supportive care for respiratory or kidney failure. Additionally, the human humoral immune response to hantavirus infection is incompletely understood, especially the location of major antigenic sites on the viral glycoproteins and conserved neutralizing epitopes. Here, we report antigenic mapping and functional characterization for four neutralizing hantavirus antibodies. The broadly neutralizing antibody SNV-53 targets an interface between Gn/Gc, neutralizes through fusion inhibition and cross-protects against the Old World hantavirus species Hantaan virus when administered pre- or post-exposure. Another broad antibody, SNV-24, also neutralizes through fusion inhibition but targets domain I of Gc and demonstrates weak neutralizing activity to authentic hantaviruses. ANDV-specific, neutralizing antibodies (ANDV-5 and ANDV-34) neutralize through attachment blocking and protect against hantavirus cardiopulmonary syndrome (HCPS) in animals but target two different antigenic faces on the head domain of Gn. Determining the antigenic sites for neutralizing antibodies will contribute to further therapeutic development for hantavirus-related diseases and inform the design of new broadly protective hantavirus vaccines.