Analysis of West Nile disease convalescents identifies human monoclonal antibodies protective against West Nile and related orthoflaviviruses
Tomás Cervantes Rincón, Tereza Frckova, Zaria I. Contejean, Jasmine Cantergiani, Kevin Groen, Benedetta Cena, Simone G. Moro, Filippo Bianchini, Luca Simonelli, David Jarrossay, Silvia Tosolini, Roger Kuratli, Anna R.E. Robinson, Monika Cizkova, Emily G. Niejadlik, Jacques Moritz, Roshan Thakur, Zuzana Krátka, Dragana Mijatović, Jasmina Grujić, Jiri Holoubek, Zorana Budakov-Obradović, Jiri Salat, Václav Hönig, Marija Vraneš, Zvezdana Lojpur, Dajana Lendak, Siniša Sević, Monika Bajči, Lidija Popović-Dragonjić, Biljana Popovska Jovičić, Jagoda Gavrilović, Tania Kapoor, Margaret R. MacDonald, Stylianos Bournazos, Luca Varani, Martin Palus, Benjamin G. Hale, Pavle Banović, Daniel Ruzek, Christopher O. Barnes and Davide F. Robbiani
One antibody protected mice even when treatment was delayed for several days, while another neutralized five mosquito-borne orthoflaviviruses. The findings are promising but remain preclinical.
Researchers have identified two human antibodies that could provide starting points for new treatments against West Nile virus and several related mosquito-borne pathogens. The study, published in Immunity, describes an exceptionally potent antibody called W010 and a broader antibody, W014, that recognizes a conserved viral target shared across multiple orthoflaviviruses.
The findings address a persistent medical gap. West Nile virus can invade the central nervous system and cause meningitis, encephalitis, paralysis and death, particularly among older adults and immunocompromised people. Yet there is currently no licensed human vaccine or virus-specific medicine; treatment is largely supportive.
Mining the immune response of West Nile survivors
The researchers recruited 72 people hospitalized with suspected West Nile disease or West Nile fever in Serbia during the 2022 and 2023 transmission seasons. They measured the participants’ antibody responses against domain III of the viral envelope protein, or EDIII, a region involved in attachment to host cells and a major target of virus-neutralizing antibodies.
Antibody activity differed considerably between participants. The team selected three convalescent individuals whose blood strongly neutralized the virus and isolated memory B cells carrying antibodies directed against EDIII. From 107 paired antibody gene sequences, the researchers produced and tested 44 recombinant human IgG antibodies. Fifteen displayed strong neutralizing activity, but W010 and W014 stood out for different reasons.
W010 delivered the greatest potency. In tests using authentic West Nile virus, it neutralized both major disease-associated viral lineages at concentrations of approximately four nanograms per millilitre. W014 was less potent against West Nile virus itself, but its unusual breadth made it scientifically important.
Protection after infection
To test W010 as a potential treatment rather than merely a preventive antibody, the researchers challenged mice with a lethal dose of West Nile virus lineage II. A single 30-microgram dose of W010 protected all treated animals when administered one day before infection or one or three days afterward. Treatment begun five days after infection still produced a statistically significant survival benefit, although protection was less complete at this later stage. The principal experiment was replicated twice, with a combined total of 12 mice in each treatment group.
That delayed-treatment result is potentially important because patients with West Nile disease are unlikely to receive therapy immediately after a mosquito bite. In practice, infection is often recognized only after fever or neurological symptoms emerge.
However, the timing cannot be translated directly from mice to humans. Viral replication, immune responses and disease progression occur on different timescales in the two species. The experiment therefore demonstrates a post-exposure therapeutic effect in an animal model, not a five-day treatment window for patients.
W010 also remained protective in a more immunologically vulnerable mouse model in which type I interferon signalling was blocked. All control animals died, whereas W010 produced 58% survival when administered on the day of infection and 100% survival when given one day later.
A broader antibody with lower potency
W014 presented a different therapeutic profile. In reporter-virus assays, the antibody neutralized:
West Nile virus
Japanese encephalitis virus
Murray Valley encephalitis virus
Saint Louis encephalitis virus
Usutu virus
These viruses belong to the Japanese encephalitis serocomplex and can cause febrile or neurological disease in humans. Structural analysis indicated that W014 binds amino acids that are highly conserved among these viruses, explaining its cross-reactivity.
The breadth came with a trade-off. W014 generally required higher concentrations than W010, particularly in experiments involving authentic rather than reporter viruses. Its target also appears to be partly hidden within the mature viral particle, suggesting that the envelope protein must temporarily shift or “breathe” before the antibody can gain access.
Preventive administration of W014 reduced mortality in West Nile-infected mice. That experiment was smaller, 10 antibody-treated animals and five controls, and the researchers did not demonstrate animal protection against Japanese encephalitis, Murray Valley encephalitis, Saint Louis encephalitis or Usutu viruses. For those pathogens, the evidence currently consists primarily of laboratory neutralization tests.
Taken together, W010 and W014 illustrate a common challenge in antibody development: potency and breadth do not always coincide. W010 was extremely potent against West Nile virus but comparatively narrow, whereas W014 recognized a more conserved target across several viruses but neutralized them less efficiently.
Interferon autoantibodies did not prevent antiviral antibody formation
The study also investigated autoantibodies that interfere with type I interferons, proteins that coordinate the body’s early antiviral defence. Such autoantibodies have previously been associated with an elevated risk of severe viral disease.
Among 39 participants tested, 10 had antibodies targeting interferon-α2, interferon-ω or both. Seven participants, 18% of the tested group, had autoantibodies capable of neutralizing low concentrations of these interferons. All seven were men, with an average age of approximately 65 years.
Importantly, interferon autoantibodies did not prevent participants from developing West Nile-neutralizing serum activity. People with the autoantibodies had higher levels of antibodies binding EDIII, but their overall virus-neutralizing activity was similar to that of participants without them. The authors proposed that impaired early interferon defence might allow greater viral replication and therefore expose the immune system to more antigen, although the study did not directly test this explanation.
Structural maps may guide future vaccines and antibody combinations
By solving crystal structures of four antibodies bound to West Nile EDIII, the team mapped the precise viral surfaces recognized by each antibody. W010 attacks a relatively accessible region and uses a binding orientation distinct from several previously described West Nile antibodies. W014 reaches a more concealed but highly conserved region.
These structural maps could support two parallel development strategies. One would optimize W010-like antibodies as rapid treatments for West Nile disease. The other would use the conserved W014 epitope to design broader antibodies or vaccines intended to protect against several related viruses. A combination containing antibodies that recognize non-overlapping sites might also reduce the risk of viral escape.
That risk is not merely theoretical. During cell-culture experiments, the researchers selected a West Nile variant carrying an N368T substitution in EDIII. The change reduced W010 neutralization by roughly 100-fold. Whether the same mutation would emerge during infection in an animal or patient is unknown.
Promising candidates, not yet medicines
The study should be viewed as an antibody-discovery and proof-of-concept investigation, not evidence that an approved West Nile treatment is imminent. W010 and W014 have not been tested for safety, dosage or clinical efficacy in humans. The antibodies were recovered from only three selected convalescent donors, and the therapeutic experiments were conducted in mouse models.
Additional limitations include the absence of in-vivo protection studies for W014 against viruses other than West Nile and the possibility of resistance to W010. The researchers also did not determine participants’ CCR5 genotypes, which may affect susceptibility to neuroinvasive West Nile disease. The Institute for Research in Biomedicine has filed a provisional patent covering findings from the work.
Before either antibody could enter clinical practice, researchers would need to refine its pharmaceutical properties, establish manufacturing procedures, test toxicity and dosing, evaluate antibody combinations and complete phased human trials. For W014, animal challenge studies against the additional orthoflaviviruses will be especially important.
Nevertheless, the study provides two complementary leads: a highly potent West Nile-specific candidate capable of working after infection in mice, and a broader antibody directed at a conserved vulnerability shared by several medically important viruses. Together, they offer a potential foundation for both targeted West Nile therapy and longer-term development of broad-spectrum countermeasures against mosquito-borne encephalitis viruses.
Study reference: Cervantes Rincón T. and colleagues, “Analysis of West Nile disease convalescents identifies human monoclonal antibodies protective against West Nile and related orthoflaviviruses,” Immunity, 2026; 59:1–15. DOI: 10.1016/j.immuni.2026.05.013
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