small molecules

2026-08-17 | Lassa fever and Argentine hemorrhagic fever treatment in guinea pigs using broad-spectrum cap-dependent endonuclease inhibitors.

The class Bunyaviricetes encompasses several highly pathogenic viruses that cause lethal hemorrhagic fevers. Due to their limited prevention and treatment options and high pathogenicity, these viruses require handling in biosafety level-4 facilities. Within the bunyaviruses, arenaviruses are particularly notable for their pathogenicity and ability to cause severe hemorrhagic disease in humans. The cap-dependent endonuclease (CEN) is a unique and crucial enzyme involved in the replication cycle of these viruses. As humans do not possess a similar enzyme, CEN represents an ideal target for antiviral drug development with reduced risk of side effects. Recently, we identified a promising CEN inhibitor (CENi) demonstrating potent inhibition of virus replication. In this manuscript, we demonstrate the successful therapeutic efficacy of CENis against Lassa fever and Argentine hemorrhagic fever virus infections in guinea pig models of lethal hemorrhagic fever. In addition, we identified several CENis with antiviral activity against other highly pathogenic arenaviruses. These findings further support the potential of CENis as therapeutic agents for arenavirus infections that cause severe and often lethal hemorrhagic fever. Collectively, our results suggest that CENis are promising candidates for pan-arenavirus therapy and may also have broader utility against other CEN-containing viruses for which no approved antiviral treatments currently exist.IMPORTANCEArenaviruses, such as Lassa virus and Junin virus, cause severe hemorrhagic fevers in humans and are associated with high mortality rates and limited treatment options. Because of their pathogenicity and potential for outbreaks, these viruses represent an important global health threat. The viral cap-dependent endonuclease (CEN) plays a critical role in arenavirus replication by enabling the cap-snatching process required for viral mRNA synthesis. Notably, mammalian cells lack a comparable enzyme, making CEN an attractive target for antiviral drug development. In this study, we demonstrate that inhibitors targeting the arenavirus CEN effectively suppress viral replication and provide therapeutic protection in animal models of lethal Lassa virus and Junin virus infections. We also identify compounds with antiviral activity against multiple highly pathogenic arenaviruses. These findings establish CEN inhibition as a promising strategy for the development of broad-spectrum antivirals against arenaviruses that cause life-threatening hemorrhagic fevers.

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2026-06-26 | Missed Opportunities for Timely Diagnosis and Effective Therapeutic Management of Prolonged Fever: A Case Study of Confirmed Lassa Fever in N'Zérékoré, Guinea, 2022.

Lassa fever is a potentially fatal viral hemorrhagic disease caused by a ribonucleic acid (RNA) virus of the Arenaviridae family, endemic in West Africa. It is highly virulent and contagious in several countries, with a nonspecific clinical presentation that poses a major public health challenge. An in-depth investigative survey was conducted in N'Zérékoré to identify the transmission chain of a confirmed case of Lassa fever. This study reports a confirmed case of Lassa fever diagnosed 13 days after the onset of persistent fever. The disease was suspected at the regional hospital of N'Zérékoré following the worsening of the initial clinical picture, characterized by the onset of hemorrhagic manifestations and failure of antibiotic therapy. Confirmation of Lassa virus infection by reverse transcriptase-polymerase chain reaction (RT-PCR) on a blood sample was obtained a day prior to the patient's death. The patient did not receive ribavirin treatment and remained on the same antibiotic regimen (ceftriaxone) from the onset of fever, combined with dexamethasone, omeprazole, and a unit of blood transfusion. The therapeutic pathway of this confirmed Lassa fever case in N'Zérékoré highlights the need for improved management of viral hemorrhagic fevers and consideration of differential diagnoses when broad-spectrum antibiotic therapy fails.

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2026-06-13 | In silico prioritization and cheminformatics identify structurally diverse small-molecule inhibitors of Lassa virus glycoprotein-mediated membrane fusion.

Lassa virus (LASV) is a hemorrhagic fever arenavirus of significant public health concern, infecting millions of people per year in Africa. Here, we developed a computational strategy to identify specific inhibitors of LASV glycoprotein-mediated virus cell entry, leveraging a previous screen of 297,156 small molecules from the MLPCN library, with the results deposited in the PubChem database. Data mining methods were developed to efficiently select small molecules prioritized for both potency and specificity in inhibiting Lassa virus infection. Cheminformatics classification then identified diverse chemical scaffolds that had not been previously reported. Representatives were evaluated against authentic LASV infection, yielding potencies as low as 10 nM. Investigation of the target mechanism compared vesicular stomatitis virus bearing the GPs of LASV, the distantly related Junín virus, and unrelated Ebola virus. The results identified three distinct chemical scaffolds that demonstrated strong LASV selectivity, each acting at the membrane fusion stage of virus cell entry. Sensitivity was mapped to regions of GP2 known to coordinate pH-triggered conformational rearrangements needed for membrane fusion. Time-of-addition experiments demonstrated loss of activity coincident with endosomal escape, and cell-cell fusion assays confirmed direct inhibition of GP-mediated syncytia formation. Together, these findings characterize each scaffold as an effective LASV fusion inhibitor and highlight the effectiveness of our combined computational and experimental approaches in identifying mechanistically informative antiviral scaffolds.

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2026-06-08 | Ending Lassa neglect: the urgent case for a licensed vaccine.

Lassa fever is an endemic viral hemorrhagic disease in West Africa with significant morbidity and mortality, yet it remains inadequately addressed in global health priorities. First identified in Nigeria in 1969, the disease continues to affect an estimated 100 000-300 000 individuals annually, with high case fatality rates among hospitalized patients and vulnerable populations. Despite its substantial burden and recurrent seasonal outbreaks, particularly in Nigeria, major gaps persist in both prevention and treatment strategies. Notably, there is no licensed vaccine available more than five decades after its discovery, and current therapeutic practices rely heavily on ribavirin, a drug supported by limited and methodologically weak evidence. Recent years have witnessed encouraging developments, including early-phase vaccine trials and large-scale epidemiological initiatives such as the ENABLE study, alongside coordinated efforts to establish adaptive clinical trial platforms. However, these advancements remain insufficient without sustained funding, robust clinical trial infrastructure, and policy-level commitment. This letter highlights the urgent need to accelerate vaccine development, reassess existing treatment guidelines, and strengthen outbreak preparedness in endemic regions. Addressing these gaps is critical to transitioning from reactive outbreak response to proactive and evidence-based disease control, ultimately reducing the burden of Lassa fever and improving global health equity.

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2026-05-16 | Favipiravir for Lassa fever: an open-label, randomized controlled phase 2 trial.

Lassa fever (LF) is a viral hemorrhagic fever endemic to West Africa, with high case fatality in hospitalized patients and limited treatment options, including ribavirin. Preclinical evidence suggests high-dose favipiravir is a promising antiviral treatment alternative. We conducted a randomized controlled open-label phase 2 clinical trial at two reference hospitals in Nigeria to evaluate favipiravir in the treatment of LF. Primary endpoints were the description of classic pharmacokinetic parameters (maximum plasma concentration, time to reach maximum plasma concentration, area under the curve (AUC), half-life and volume of distribution) as well as the safety and tolerability of favipiravir compared with ribavirin in the treatment of acute LF. Hospitalized adult patients with mild-to-moderate RT-PCR-confirmed LF were eligible to participate. In total, 41 patients were randomized (ribavirin n = 21; favipiravir n = 20), and 36 completed the 10-day follow-up period. A total of 19 (46.3%) participants were female, and the median age was 37 years. The primary endpoints were met. Pharmacokinetic analysis of favipiravir in a one-compartment model indicated reliable exposure with maximum plasma concentration of 50.9 (IQR 42.1 to 75.1) mg l-1 in steady state, half-life of 10.9 (IQR 8.2 to 17.1) h and AUC (0-240 h) of 9,275 (IQR 7,139.4 to 15,794.8) mg l-1 h-1. The 30 drug-related treatment-emergent adverse events were evenly distributed between the treatment arms; 16 (53.5%) events occurred in the favipiravir group, and none of these were classified as severe or serious. Anemia was the most frequently observed adverse event in the ribavirin arm and vomiting in the favipiravir arm. All study participants survived and were successfully discharged from the isolation ward. This trial indicates favipiravir's potential as a safe and well-tolerated alternative treatment regimen for LF and pharmacokinetic data suggest an optimized favipiravir regimen for future clinical evaluation. Clinicaltrials.gov: NCT04907682 .

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antibodies

2026-04-30 | Evaluation of candidate reference materials for the harmonization of Lassa fever serology.

Lassa fever is a zoonotic disease endemic to several West African countries, with seasonal outbreaks and potential to cause future epidemics. Vaccines and other medical countermeasures are in development, requiring reliable assays for evaluation. A WHO International Standard (IS) for anti-Lassa virus (LASV) antibodies can support harmonization of serological assay results, aiding vaccine and therapeutic assessment, surrogates of protection identification, and improving epidemiological understanding. In this study, a pooled plasma sample from Lassa fever survivors was evaluated in a multi-centre collaborative study involving 17 laboratories for its suitability as a reference material for detecting anti-LASV antibodies. Additionally, two well-characterized monoclonal antibody (mAb) cocktails were assessed as potential alternatives to convalescent plasma. Expressing the antibody titre of the collaborative study panel samples relative to the convalescent plasma pool (NIBSC 20/202) or the mAb cocktails harmonized the results from the participants reducing the inter-laboratory variation. However, while the candidate IS 20/202 performed consistently across all assays, the mAb cocktails were not detected by a few binding antibody methods. These findings support the use of mAb cocktails as reference material for evaluating humoral responses within a laboratory or network using common assays; however, for an IS, applicable globally across methods, convalescent serum or plasma remains the most suitable material.

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2026-04-29 | Contact Networks of Small Mammals Highlight Potential Transmission Foci of Mammarenavirus lassaense.

Lassa fever (LASV; Mammarenavirus lassaense) is an endemic zoonosis in West Africa. Human infections arise from rodent-to-human transmission, primarily from the synanthropic reservoir Mastomys natalensis (M. natalensis). In Sierra Leone, small-mammal communities vary across land-use gradients, shaping LASV transmission risk. How anthropogenic environments facilitate the rodent-rodent interactions remains poorly understood. Small mammals were sampled over 43,266 trap nights in Sierra Leone's LASV-endemic Eastern Province, detecting 684 rodents and shrews. To assess potential transmission, space-sharing networks were constructed from co-trapping events within species-specific home range radii. Shared space use was approximated in these networks, enabling the comparison of encounter patterns across habitats. Network topology varied significantly by land use. Village networks were the most connected (highest average degree), whereas agricultural communities supported the most species (higher rarefied richness) and were the most fragmented (higher modularity). Notably, the probability of intraspecific space sharing among M. natalensis was highest in agricultural settings, suggesting that land use modulates key intraspecific transmission pathways. Lassa fever seroprevalence was 5.7% community-wide, with antibodies detected in nine species. No statistically significant association was found between overall seroprevalence and land use or aggregate network structure (mean degree). However, predictive modeling for M. natalensis indicated that a higher individual degree is associated with seropositivity, suggesting complex, scale-dependent relationships. These findings reveal that simple ecological drivers do not fully explain LASV exposure, highlighting the importance of species-specific behaviors (i.e., M. natalensis clustering in agriculture) and the multihost serological landscape in assessing transmission risk.

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2026-03-26 | Serologic Evidence of Hemorrhagic Fever Virus Spillover in Rural Liberia.

Outbreaks of zoonotic emerging infectious diseases, including viral hemorrhagic fevers, are increasing in frequency. Clinical detection remains challenging due to the lack of pathognomonic signs or symptoms and limited access to diagnostics. To better understand the prevalence of prior exposure to viral hemorrhagic fever viruses, serum from community participants in rural Liberia was tested for immunoglobulin G antibodies. Serum collected from individuals enrolled in the ENABLE study, an observational study of Lassa fever virus incidence and seroprevalence, were analyzed for immunoglobulin G against Ebola virus, Marburg virus, Lassa virus, Rift Valley Fever virus, Crimean-Congo hemorrhagic fever virus, pan-alphavirus, and pan-flavivirus by MAGPIX, a multiplex immune assay. Associations with seropositivity were evaluated using questionnaires that included demographic, animal, and environmental exposure information. Eighty-eight percent of samples from 456 participants tested positive for ≥1 of the viral antibodies with a majority (63%) having antibodies to ≥2 viruses. Seropositivity was highest for Lassa virus (67%) followed by pan-flavivirus (51%), pan-alphavirus (35%), Crimean-Congo hemorrhagic fever virus (24%), Ebolavirus (13%), Rift Valley Fever virus (9%), and Marburg virus (8%). Older age, sex (variable by pathogen), and exposure to cats and rats were associated with seropositivity. These findings demonstrate a significant spillover of filoviruses, bunyaviruses, flaviviruses, and alphaviruses in rural Liberia in contrast with an absence of detected outbreaks. These data support the need for enhanced surveillance and understanding of the ecological and behavioral risk factors for zoonotic spillover events, across a spectrum of disease presentation, given their potential and ongoing threat to global public health.

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2026-02-09 | Acute febrile illness surveillance using TaqMan Array Cards in two urban health facilities, Monrovia, Liberia, December 2018-March 2020.

Fever is a common symptom of infectious diseases including for those with epidemic potential. Beyond malaria, the causes of undifferentiated (i.e., non-respiratory, non-diarrheal) acute febrile illnesses are not well characterized in Liberia. From December 2018 through March 2020, we established two acute febrile illness (AFI) sentinel surveillance sites in urban Monrovia at Redemption Hospital and Star of the Sea Health Centre, health facilities that were among the first to have Ebola cases during the 2014-2015 West Africa epidemic. Enrolled AFI patients were two (2) years of age or greater, had a measured fever of ≥37.5oC or history of fever within the past week, and without a known cause of fever. A standardized survey was administered to collect demographic, clinical characteristics, and risk factors. Whole blood was taken, nucleic acid material was extracted and ran on TaqMan Array Cards (TAC), a real-time polymerase chain reaction (RT-PCR) testing platform for 28 pathogens. Data were analyzed using descriptive statistics, and multivariate regression models of any TAC detections stratified by site and age. We enrolled 1506 AFI patients, 1206 (80%) from Redemption Hospital and 300 (20%) from Star of the Sea. AFI patients were predominantly female (69%) and had a median (interquartile range) age of 18 (7-27) years. Among the 699 (46%) that were TAC positive, 627 were detected from Redemption Hospital and 72 were detected from Star of the Sea Health Centre. Overall Plasmodium spp. (malaria) (96%) were the majority of detections followed by dengue virus (2%), Streptococcus pneumoniae (2%), and Rickettsia spp. (1%). We detected 19 co-infections [malaria co-infections (84%) being the most common]. Two pathogens with epidemic potential, Neisseria meningitidis (detected at Star of the Sea Health Centre) and Lassa virus (detected at Redemption Hospital), were also found. Patients with non-malaria TAC detections (n = 29) were higher at Star of the Sea Health Centre than Redemption Hospital (4% versus 1% respectively, p < 0.05). In multivariate regression for those ages 15 years and older at Redemption Hospital (adjusting for sex, age, pregnancy status, education, occupation, any medication use, measured fever at enrollment, headache, abdominal pain, vomiting/nausea and joint pain), any medication use (aOR=0.6, 95% CI = 0.4-0.9), measured fever at enrollment (aOR=3.5, 95% CI = 1.1-12.0), headache (aOR=1.7, 95% CI = 1.1-2.6 were statistically significant with any TAC detection. In multivariate regression for those ages 2-14 years at Redemption Hospital (adjusting for sex, age, abdominal pain, cough, vomiting/nausea, runny nose, and any animal exposure), having abdominal pain (aOR=1.9, 95% CI = 1.3-2.8), vomiting/nausea (aOR=0.6, 95% CI = 0.4-1.0), and any animal exposure (aOR=1.5, 95% CI = 1.0-2.3) were statistically significant with any TAC detection. This is the first laboratory evidence of dengue and rickettsial disease in humans in Liberia. Liberia's incipient AFI platform was successful exploring causes of fever in emerging infections and detected circulating pathogens beyond malaria. AFI surveillance data can assist in the prioritization of public health diagnostic and clinical capabilities to prevent, detect, and respond to emerging infectious disease threats in Liberia.

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2026-01-11 | Lassa fever symptomatology, viral dynamics, and host immune response (PREPARE): a prospective, observational cohort study in Liberia.

Lassa virus (LASV) is a persistent threat to public health in west Africa and beyond. LASV is endemic in west Africa and each year it is responsible for an estimated 2·7 million infections, 23 700 hospitalisations, and 5000 deaths. With over 32 reported cases of Lassa fever imported into non-endemic countries-one-third of which were fatal-the importance of enhanced detection and management of Lassa fever extends beyond west Africa. The prevalence, pathogenesis, and persistence (PREPARE) study was a prospective cohort study among patients admitted to two hospitals in a hyperendemic area of Liberia. Any patients aged 5 years or older with a febrile illness were eligible to enrol and be tested for Lassa fever. The study aimed to measure the prevalence of LASV infection and assess the signs and symptoms, LASV viral replication kinetics, and LASV-specific IgM and IgG responses longitudinally among adults and children with laboratory-confirmed Lassa fever. From July 10, 2018, to Aug 12, 2024, a total of 435 participants were enrolled, including 362 admitted with a febrile illness and 73 who were directly admitted with clinical suspicion for Lassa fever. Lassa fever was diagnosed by plasma LASV RT-PCR in 41 (11%) of 362 febrile participants and 47 (64%) of 73 participants directly admitted with suspected Lassa fever, resulting in a total of 88 cases of confirmed Lassa fever. At entry, anorexia (71 [81%] of 88 vs 178 [51%] of 347), severe fatigue or weakness (63 [72%] vs 178 [51%]), and nausea or vomiting (39 [44%] vs 95 [27%]) were more likely to be reported by participants with Lassa fever than by participants who tested LASV RNA negative. Among the participants with Lassa fever, 11 (13%) of 88 died after admission. Mental status changes, seizures, acute kidney failure, hyperkalaemia, and metabolic acidosis were more frequent in patients with Lassa fever who died than in patients who survived. Median cycle threshold values at study entry for glycoprotein complex gene (GPC) or polymerase gene (L) were lower in those who died (GPC cycle threshold 22·4 [IQR 20·0-27·9]; L cycle threshold 21·7 [19·0-27·7]) than in those who survived (GPC cycle threshold 31·5 [28·0-33·9]; L cycle threshold 32·3 [28·0-33·9]). Among the 70 participants with Lassa fever who consented to longitudinal follow-up through their hospitalisation, seven died and these participants tended to have lower cycle threshold values and lower IgM and IgG LASV responses compared with survivors. In a region of Liberia where it is endemic, Lassa fever is a prevalent cause of morbidity and mortality. Several symptoms were more likely in those with Lassa fever but overlap with those caused by other common infectious diseases. Compared with survivors, those who died during hospitalisation for Lassa fever tended to have evidence of organ dysfunction along with higher viral loads at study entry and during follow-up and lower antibody levels during their illness, suggesting a muted humoral immune response might be a factor in the development of severe Lassa fever. US National Institute of Allergy and Infectious Diseases and National Institutes of Health.

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vaccines

2026-07-25 | Computational Design of a Broad-Spectrum Multi-Epitope mRNA Vaccine Candidate for Mammarenaviruses.

Mammarenaviruses cause serious diseases such as Lassa fever and Argentine hemorrhagic fever that threaten global public health; however, vaccines and therapeutic options remain limited. Therefore, developing a broadly effective vaccine against mammarenaviruses is a priority. In this study, we systematically analyzed the main structural protein sequences of ten mammarenaviruses. We combined antigenic epitopes from the Immune Epitope Database (IEDB) and used inverse vaccination and immunoinformatics methods to screen for highly conserved B- and T-cell epitopes with strong immunogenicity. We then added tissue plasminogen activator (tPA), which is the most effective vaccine against these pathogens. To construct a broad-spectrum multi-epitope fusion mRNA vaccine candidate, we included a tPA signal peptide, PADRE adjuvant, and linkers. The mRNA sequences were algorithm-optimized. We assessed the structural stability and immunogenicity of the candidate vaccine using molecular docking, molecular dynamics (MD) simulation, and immunosimulation. The designed vaccine had good antigenicity and structural stability, forming stable complexes with a variety of intrinsic immunoreceptors and triggering a strong, sustained, and comprehensive immune response during immunosimulation. Our study findings posit the designed vaccine as a potential broad-spectrum multi-epitope vaccine candidate against mammarenaviruses. Further real-world studies are required to validate these results.

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2026-06-27 | Evaluating vectors for the design of a spillover-disrupting Lassa virus transmissible vaccine.

Lassa fever is a viral zoonotic disease that sickens tens of thousands of people each year when it spills over from its rodent reservoir throughout West Africa. Despite the burden this persistent spillover places on public health, stopping it has proven to be an intractable challenge despite decades of investment and effort. A revolutionary solution is the development of a transmissible vaccine that can spread through the rodent population resulting in immune coverage sufficient to eliminate Lassa virus transmission. Here, we evaluate the feasibility of a transmissible vaccine constructed from native cytomegaloviruses (CMVs) previously isolated from the natural reservoir of Lassa virus, Mastomys natalensis. Using a combination of field sampling, large-scale CMV genome characterization, and mathematical models parameterized using Bayesian methods, we quantified transmission rates and interactions among viruses in northern Sierra Leone. The results demonstrate that two of the three previously isolated CMVs co-infect freely and have R0 values consistent with autonomous elimination of Lassa virus from its rodent reservoir. These results set the stage for the development of a CMV vectored transmissible vaccine that could stop the spillover of Lassa virus throughout West Africa.

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2026-06-10 | Adjuvanted inactivated rabies virus-vectored Lassa virus vaccine in healthy adults: a phase 1 trial.

Lassa fever causes substantial morbidity and mortality in West Africa, and no licensed vaccine is available. We evaluated LASSARAB, an inactivated rabies virus-vectored Lassa virus (Josiah strain) glycoprotein complex vaccine. We conducted a randomized, controlled, dose-escalation phase 1 trial. Participants (total n = 54) received two intramuscular doses of LASSARAB containing 700 (n = 15), 1,400 (n = 15) or 2,800 (n = 14) relative units of antigen formulated with the TLR-4 agonist 3D-6-acyl PHAD-SE adjuvant, or licensed rabies vaccine control (n = 10), administered 28 days apart. This protocol-defined interim analysis reports the primary safety evaluation and secondary immunogenicity assessments through day 61. There were no prespecified hypotheses or formal power calculations. All primary safety end points demonstrated an acceptable safety profile. After dose 1, local solicited adverse events occurred in 86.7-100.0% of LASSARAB groups and 80% of controls; systemic events in 33.3-71.4% and 60.0% of controls. After dose 2, local solicited adverse events occurred in 66.7-86.7% of LASSARAB groups and 55.6% of controls; systemic events in 53.3-71.4% of LASSARAB groups and 55.6% of controls. Events were predominantly mild and self-limited. Unsolicited adverse events occurred in 28.6-60.0% of LASSARAB groups and 20.0% of controls. No serious adverse event, immune-mediated condition or sensorineural hearing loss occurred. Safety laboratory abnormalities occurred in 13.3-66.7% of LASSARAB groups and 30.0% of controls (14 mild, 6 moderate and none severe). After two doses, Lassa virus GPC IgG ELISA seroconversion (≥fourfold rise) was achieved in 100.0% (44 of 44) of LASSARAB recipients and 0.0% (0 of 10) of controls. Rabies glycoprotein IgG ELISA seroconversion (≥fourfold rise) and neutralizing antibody by rapid fluorescent focus inhibition test (RFFIT) seroprotection (≥0.5 IU ml-1) were also 100% across all groups, including controls. LASSARAB + 3D-6-acyl phosphorylated hexaacyl disaccharide (PHAD)-SE demonstrated a favorable safety profile and immunogenicity against Lassa and rabies viruses. The per-protocol final study report will include safety and durability through day 394. ClinicalTrials.gov identifier NCT06546709 .

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2026-05-21 | Decoding the human CD4+ T cell epitope repertoire for Lassa fever virus reveals T cell-based pan-mammarenavirus vaccine candidates.

Mammarenaviruses are classified into Old World and New World viruses (Old World arenaviruses [OWAs] and New World arenaviruses [NWAs]). Characterization of antigens recognized by human T cells is essential for identifying immunodominant targets, informing vaccine design, and performing immunological assessments. Here, we select the Lassa virus (LASV) as a prototype OWA to map the human CD4 T cell epitope repertoire. We then calculate conservation in different LASV lineages and other representative OWAs and NWAs and define conserved T cell epitope regions (CTERs) using Lassa as the OWA prototype and Junin as the NWA prototype. We show that these CTERs are able to broadly cross-recognize other OWA or NWA sequences. We validate our findings in humans immunized with an experimental glycoprotein complex (GPC) LASV vaccine or infected with lymphocytic choriomeningitis mammarenavirus (LCMV), as well as in the mouse model immunized with a stabilized GPC vaccine candidate. Our results on mammarenavirus-specific T cell immunity contribute to guiding the development of next-generation mammarenavirus vaccines.

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2026-04-07 | B cell immunity to the Lassa virus glycoprotein is a correlate of vaccination-induced virus control in mice.

Lassa fever, a viral hemorrhagic fever caused by the arenavirus Lassa virus (LASV), affects thousands of individuals annually, highlighting the need for a vaccine. Yet, immunological correlates of viral load control remain poorly defined. Here we study vaccination-induced immunity in a surrogate LASV challenge model in mice. We find that LASV-cross-reactive B cell immunity induced by the glycoprotein of distantly related arenaviruses, such as lymphocytic choriomeningitis virus (LCMV), provides significant viral load control. Counter to common concepts, suppression of viremia is observed in the absence of CD8 T cells or neutralizing antibodies but correlates with non-neutralizing glycoprotein-specific antibody responses. Adoptive cell transfer experiments with monoclonal LCMV-specific B cells demonstrates that these cells suppress viral loads when previously activated by a heterologous cross-reactive glycoprotein and diversified by somatic hypermutation. These findings establish vaccination-induced B cell immunity to the LASV glycoprotein as a correlate of viral load control, independently of virus-neutralizing antibody titers at the time of challenge.

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gene therapies

2026-03-14 | Development of a Conditional Replication System Using a Lassa Virus Glycoprotein Complex-Encoding Retroviral Vector for Isolating Resistant Variants to Inhibitors in BSL-2.

A high-risk infectious disease or a Category A pathogen, Lassa virus (LASV), requires strict containment, classified as biosafety level 4 (BSL-4) conditions, which restricts research on the virus due to the scarcity of BSL-4 facilities. Thus, replication-defective pseudotyped retroviral vectors have been widely used as safe materials for neutralizing activity assays of drugs and antibodies in BSL-2. Here, we established a novel retroviral vector system encoding LASV glycoprotein complex (GPC) that can exclusively replicate in cells expressing the Gag-Pol protein of murine leukemia virus (MLV) under BSL-2 conditions. Using this conditional replication system, we successfully isolated LASV GPC variants resistant to either an anti-LASV compound, lamellarin α 20-sulfate, or a neutralizing antibody derived from a Lassa fever survivor. In the lamellarin α 20-sulfate-resistant variants, K125E and H13R amino acid substitutions cooperatively conferred resistance. The K125E enhanced infectivity and simultaneously conferred a lethal effect on cells in the conditional replication system, while the H13R mitigated the latter effect, thereby enabling stable expression of LASV GPC in cells. In the neutralizing antibody-resistant variants, I403T substitution was responsible for the resistance by impairing antibody binding. This study provides a valuable BSL-2-based platform for isolating LASV GPC variants resistant to inhibitors and characterizing their mutations.

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2023-12-16 | Plasmid-Based Lassa Virus Reverse Genetics.

Several mammarenaviruses cause hemorrhagic fever (HF) disease in humans and pose a significant public health problem in their endemic regions. The Old World (OW) mammarenavirus Lassa virus (LASV) is estimated to infect several hundred thousand people yearly in West Africa, resulting in high numbers of Lassa fever (LF) cases, a disease associated with high morbidity and mortality. No licensed vaccines are available to combat LASV infection, and anti-LASV drug therapy is limited to the off-label use of ribavirin whose efficacy remains controversial. The development of reverse genetics approaches has provided investigators with a powerful approach for the investigation of the molecular, cell biology and pathogenesis of mammarenaviruses. The use of cell-based minigenome systems has allowed examining the cis- and trans-acting factors involved in viral genome replication and gene transcription, assembly, and budding, which has facilitated the identification of several anti-mammarenavirus candidate drugs. Likewise, it is possible now to rescue infectious recombinant mammarenaviruses from cloned cDNAs containing predetermined mutations in their genomes to investigate virus-host interactions and mechanisms of viral pathogenesis. Reverse genetics have also allowed the generation of mammarenaviruses expressing foreign genes to facilitate virus detection, to identify antiviral drugs, and to generate live-attenuated vaccine (LAV) candidates. Likewise, reverse genetics techniques have allowed the generation of single-cycle infectious, reporter-expressing mammarenaviruses to study some aspects of the biology of HF-causing human mammarenavirus without the need of high security biocontainment laboratories. In this chapter, we describe the experimental procedures to generate recombinant (r)LASV using state-of-the-art plasmid-based reverse genetics.

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2023-02-06 | Molecular Engineering of a Mammarenavirus with Unbreachable Attenuation.

Several mammarenaviruses cause severe hemorrhagic fever (HF) disease in humans and pose important public health problems in their regions of endemicity. There are no United States (US) Food and Drug Administration (FDA)-approved mammarenavirus vaccines, and current anti-mammarenavirus therapy is limited to an off-label use of ribavirin that has limited efficacy. Mammarenaviruses are enveloped viruses with a bi-segmented negative-strand RNA genome. Each genome segment contains two open reading frames (ORF) separated by a noncoding intergenic region (IGR). The large (L) segment encodes the RNA dependent RNA polymerase, L protein, and the Z matrix protein, whereas the small (S) segment encodes the surface glycoprotein precursor (GPC) and nucleoprotein (NP). In the present study, we document the generation of a recombinant form of the prototypic mammarenavirus lymphocytic choriomeningitis virus (LCMV) expressing a codon deoptimized (CD) GPC and containing the IGR of the S segment in both the S and L segments (rLCMV/IGR-CD). We show that rLCMV/IGR-CD is fully attenuated in C57BL/6 (B6) mice but able to provide complete protection upon a single administration against a lethal challenge with LCMV. Importantly, rLCMV/IGR-CD exhibited an unbreachable attenuation for its safe implementation as a live-attenuated vaccine (LAV). IMPORTANCE Several mammarenaviruses cause severe disease in humans and pose important public health problems in their regions of endemicity. Currently, no FDA-licensed mammarenavirus vaccines are available, and anti-mammarenaviral therapy is limited to an off-label use of ribavirin whose efficacy is controversial. Here, we describe the generation of recombinant version of the prototypic mammarenavirus lymphocytic choriomeningitis virus (rLCMV) combining the features of a codon deoptimized (CD) GPC and the noncoding intergenic region (IGR) of the S segment in both S and L genome segments, called rLCMV/IGR-CD. We present evidence that rLCMV/IGR-CD has excellent safety and protective efficacy features as live-attenuated vaccine (LAV). Importantly, rLCMV/IGR-CD prevents, in coinfected mice, the generation of LCMV reassortants with increased virulence. Our findings document a well-defined molecular strategy for the generation of mammarenavirus LAV candidates able to trigger long-term protective immunity, upon a single immunization, while exhibiting unique enhanced safety features, including unbreachable attenuation.

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2021-03-01 | Lassa virus: characterization of infectious agent, biological models for pathogenesis studies and variants of vaccine

Lassa virus (LASV) is classified into genus Mammarenavirus of Arenaviridae family. This virus is etiological agent of Lassa fever (LF) which is widespread in Africa. On average, in four out of five infected people, LF occurs without symptoms. The annual incidence ranges from 100,000 to 500,000 registered clinical cases, at a mortality rate of 1-2%. Among hospitalized patients with severe symptoms of hemorrhagic fever, this figure may be from 14 to 89.5%. Signs of an adverse outcome in LF are open bleeding and disorders of CNS (convulsions, tremor, disorientation and coma). Death occurs from multiple organ failure. Severely ill people recover slowly and may have relapses and complications such as pneumonia, myocarditis, psychosis, and hearing loss. Transmission of the virus in endemic territories occurs by alimentary way, air-dust and airborne droplets from a zoonotic source – rodents of the species African multimammate rat (Mastomys natalensis), by accidental contacts of people with their secretions (urine, feces, saliva) as well as when butchering carcasses and eating rodents. These animals are characterized by asymptomatic carrier and life-long persistence of the virus. Cases of transmission of the virus from person to person through the blood or other body fluids of patients are described. A sick person is contagious for two months, because the virus circulates in the blood despite high levels of antibodies. Infection of medical staff occurs during emergency surgical operations, or when the rules of contact precautions are not observed. Currently, with the ongoing LF outbreak in Nigeria, since 2016, hospitals have registered mortality rates of 22 and 8% for patients and health workers, respectively. During 1969-2016, 33 imported cases of this disease were described from West Africa to non-endemic territories (in the USA, Canada, Great Britain, the Netherlands, Germany, Israel and Japan). The mortality rate among these patients was 39%. The lack of prophylactic vaccines and specific therapeutic drugs is the major challenge for the prevention of LF. Thus, this review considers biological models (cell cultures and animals) that are suitable for studying the pathogenesis of this disease, preclinical studies of the specific activity and harmlessness of candidate vaccines, as well as options for these developments based on the platforms such as inactivated LASV and its DNA, the reassortant of Mopeia arenavirus, and measles virus attenuated strains, recombinant and replication-defective viruses (smallpox vaccine, Venezuelan equine encephalitis, bovine vesicular stomatitis, adenovirus of chimpanzee) and virus-like particles.

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2020-01-01 | Development of rationally designed live attenuated vaccines for Lassa fever and Venezuelan equine encephalitis.

Lassa Virus (LASV) and Venezuelan Equine Encephalitis Virus (VEEV) are two single stranded RNA viruses belonging to the Arenavirus and Alphavirus families, respectively. Both are emerging pathogens without approved vaccines or treatments. VEEV is an important biothreat pathogen because it has been weaponized and is extremely infectious as an aerosol. VEEV causes biphasic febrile illness that can progress to a viral encephalitis with low mortality, but high morbidity. LASV causes a viral hemorrhagic fever, Lassa Fever (LF), which is endemic in West Africa, and responsible for between 100-500k annual infections with a 1-2% overall mortality rate. ML29 and VEEV TC-83 are well-described live attenuated vaccines based on LASV and VEEV, respectively. This work describes strategies to further attenuate and enhance the safety of ML29 and TC-83, an important step in preclinical development. VEEV V4020 was designed based on the stabilization of an E2 mutation, and rearrangement of the structural genes of TC-83. Here, VEEV V4020 is shown to be more attenuated than TC-83 based on IC inoculation in mice, and more phenotypically stable, in terms of pathogenicity, during serial passaging. ML29 is a reassortant virus combining the immune dominant glycoprotein (GPC) and nucleoprotein (NP) of LASV with the replicative machinery of to Mopeia virus (MOPV), a nonpathogenic relative of LASV. We provide evidence ML29 is safer and more immunogenic than MOPV in STAT-1 deficient (STAT-1-/-) mice and Hartley guinea pigs. Additionally, Defective Interfering Particles (DIPs) from ML29 enhance vaccine immunity and attenuation in STAT-1-/- mice, and in intracranial inoculations of CBA/J mice. A potential mechanism of attenuation for ML29 is presented based on small RNAs detected from the ML29 L-segment by Northern Blot (NB). Furthermore, a unique RNA band was associated with DIP enriched ML29 was detected. A L-segment based Minigenome System (MG) for arenaviruses is described, which can be used for future analysis of the mechanism of replication for reassortant arenaviruses. The advanced safety data for both ML29 and VEEV V4020, described in this dissertation, combined with non-human primate efficacy studies described elsewhere, supports the advancement of both of these experimental vaccines to human clinical trials.

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2026-04-27 | Griffithsin-mediated inhibition of cellular entry of hemorrhagic fever viruses and insights into its mechanisms.

Griffithsin (GRFT), a lectin derived from the red algae Griffithsia, is known as an antiviral agent that binds to high-mannose glycans on viral envelope glycoproteins (GPs). In this study, we evaluated the antiviral activity of GRFT against Ebola virus (EBOV), Marburg virus (MARV), Lassa virus (LASV), Lujo virus (LUJV), and Crimean-Congo hemorrhagic fever virus (CCHFV), all of which cause severe and often fatal hemorrhagic fevers in humans. GRFT effectively blocked the entry of these viruses into cells, with stronger inhibition observed against LASV, LUJV, and CCHFV than against EBOV and MARV. This inhibitory effect depended on the lectin activity of GRFT, as its mutant lacking glycan-binding function completely lost the ability to inhibit the entry of these viruses into cells. We found that GRFT induced aggregation of virus-like particles (VLPs) derived from EBOV and MARV, whereas this activity was not observed with LASV- and LUJV-derived VLPs. Most of the escape mutants of LASV and LUJV GPs exhibited amino acid substitutions that likely disrupted GRFT binding by removing glycosylation sites at positions 79 and 73, respectively. Interestingly, other substitutions close to these positions, although unrelated to glycosylation, also contributed to reduced inhibitory activity of GRFT, suggesting a unique recognition mode in which both sugar chains and adjacent amino acid residues constitute the binding site structure for GRFT. Overall, our results provide insights into mechanisms underlying the antiviral effects of GRFT and highlight lectin-related activities as a key feature for broad-spectrum antiviral agents targeting highly glycosylated envelope GPs. Emerging and re-emerging infectious diseases, including viral hemorrhagic fevers, pose a major global health threat due to their potential for widespread outbreaks. Currently, treatment options for such diseases are limited and often ineffective against newly emerging viruses. Here, we demonstrate that Griffithsin (GRFT), a naturally derived lectin from red algae, inhibits the entry of multiple hemorrhagic fever viruses into host cells. By blocking key processes of the viral entry mediated by envelope glycoproteins, lectins such as GRFT can exhibit broad antiviral activity that could potentially overcome the limitations of existing treatments against emerging viruses. Our findings emphasize that targeting sugar chains and adjacent structures on viral glycoproteins with GRFT could provide a therapeutic strategy against diverse viral species. Such an approach is particularly valuable for newly emerging viruses for which specific countermeasures have not yet been established.

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2026-04-11 | QStrain: an interactive platform for viral genome analysis and nucleic acid therapeutic design.

BACKGROUND: QStrain is an integrated resource platform designed to facilitate viral genome analysis and the rational design of nucleic acid therapeutics. RESULTS: The system integrates reference-guided multiple sequence alignment of high-risk viral pathogens, including Severe Acute Respiratory Syndrome Coronavirus 2, Lassa virus, Severe Fever with Thrombocytopenia Syndrome virus, Middle East Respiratory Syndrome Coronavirus, Influenza A virus subtype H5N1 and H7N9, Nipah virus, Respiratory Syncytial Virus, and Dengue virus, with a growing database of viral genomes. QStrain provides versatile visualization modules such as frequency profiles, conservation scores, RNA expression patterns, and phylogenetic trees to enhance the interpretation of viral sequence variation. By identifying highly conserved genomic regions, QStrain supports the prediction of candidate therapeutic targets and enables the automated design of small interfering RNA (siRNA) and antisense oligonucleotides (ASOs). Additional features include off-target searching and 2D structure viewing for comprehensive assessment of therapeutic potential. CONCLUSIONS: Ultimately, QStrain ( https://qstrain.sookmyung.ac.kr ) provides a critical, user-friendly framework to accelerate the design pipeline of nucleic acid-based therapies, enhancing preparedness against current and future viral outbreaks.

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2026-03-20 | Design of a global population-covering multi-epitope mRNA vaccine against Lassa virus using immunoinformatics.

The Lassa virus (LV) is a hemorrhagic virus that causes Lassa fever (LF). Despite its high mortality rate in Africa, no FDA-approved mRNA vaccine currently exists. Considering its epidemic potential, a new multi-epitope mRNA vaccine (LF-mVax) candidate is designed by immunoinformatics, targeting the GP, NP, and ZP through CD8+, CD4+, and B cell epitopes. LF-mVax was introduced with antigenic, non-allergic, and non-toxic epitopes that were derived from consensus sequences. The combined CD8 + and CD4 + epitopes provided 99.98% coverage of the global population, with robust immunity. Additionally, the selected epitopes were attached to adjuvants and linkers to make a stable, immunogenic vaccine against LV with favourable biophysical features. The analyses of the secondary and tertiary structures exhibit excellent quality (Ramachandran 82.4%, Z-score − 6.39), and the docking results show strong TLR-2 and TLR-4 binding (-1048.9 and − 1099.9 kJ/mol). The results were validated by MM-GBSA, MD simulation, PCA, and DCCM analysis. LF-mVax was cloned in E. coli (GC 45.83%, CAI 0.9962), and immune simulations predicted strong innate and adaptive responses with IL-2 and IFN-γ activation. The mRNA showed stability during entry, transcription, and expression in the host. Nevertheless, laboratory and animal studies are needed to establish the safety and potency of the LF-mVax. The online version contains supplementary material available at 10.1038/s41598-026-36965-6.

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2025-11-10 | Safety, tolerability, and immunogenicity of INO-4500, a synthetic DNA-based vaccine against Lassa virus, in a phase 1b clinical trial in healthy Ghanaian adults.

Lassa fever (LF) is an acute viral hemorrhagic illness endemic to West Africa, with no licensed vaccines or targeted treatments available, highlighting a critical gap in global health preparedness. T cell-mediated immunity plays a central role in viral control and survival. Synthetic DNA vaccines offer a promising strategy to induce both humoral and cellular immunity against LF. A Phase 1b, randomized, double-blind, placebo-controlled trial was conducted to assess the safety, tolerability, and immunogenicity of INO-4500, a DNA vaccine encoding the Lassa virus (Josiah strain) glycoprotein precursor (GPC). A total of 220 healthy adults were randomized to receive either 1 mg or 2 mg of INO-4500 (intervention), or placebo, administered intradermally (ID) followed by electroporation (EP) at Day 0 and Week 4. Safety was evaluated through Week 48. Primary immunogenicity endpoints included humoral and cellular immune responses at multiple timepoints post-vaccination. INO-4500 was well tolerated, with no Grade 3 or higher treatment-emergent adverse events (TEAEs) deemed to be related to the intervention; 88.6% of all TEAEs were Grade 1. No cases of attributable hearing loss were reported. INO-4500 groups demonstrated statistically significant increases in Lassa virus GPC-specific binding antibodies at Weeks 6 and 12 compared to placebo, with the 2 mg group eliciting the strongest responses. T cell responses remained elevated above baseline through Week 48 in both INO-4500 groups, indicating durable cellular immunity. DNA vaccine INO-4500 was well tolerated and elicited durable humoral and cellular immune responses in healthy adults. These findings support further clinical development of INO-4500 as a potential preventive vaccine to reduce LF-associated morbidity and mortality in endemic regions. https://clinicaltrials.gov, identifier NCT04093076.

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2025-08-01 | Design and in-silico evaluation of a novel multiepitope-based recombinant DNA vaccine candidate against Lassa hemorrhagic fever

Introduction Emerging and re-emerging infectious pathogens are major threats to global public health. With the continued rise in the number of annual reported cases in Nigeria, the genomic diversity of the virus, as well as the expanding geography and species distribution of its reservoir hosts, Lassa fever has become a foremost endemic neglected zoonosis in Nigeria, with no available vaccine for its prevention globally. The present study aimed to develop a cross protective, multiepitope-based recombinant DNA Vaccine against Lassa Virus strains circulating in Nigeria. Methods Several Multiple humoral and cell-mediated epitopes were mapped from each consensus sequences of a total of 69 glycoprotein and 67 nucleoprotein sequences of the Lassa virus (LASV) strains across lineage I, II, III and VI circulating in Nigeria and characterized using high-throughput in silico bioinformatics tools to construct a putative LASV vaccine candidate, and the constructed candidate was evaluated in silico for its structural and physicochemical properties. Results A total of 4, 10 and 3 CTL, HTL and linear B-cell non-toxic, non-allergenic and highly antigenic epitopes, respectively, were mapped and used for the construction of the vaccine candidate. The chimeric LASV vaccine had good expression levels in procaryotic and eucaryotic cells, was thermostable, hydrophobic, non-allergenic, non-toxigenic and highly antigenic. Also, the putative candidate elicited both humoral and cell-mediated immune response, in addition to its induction of interferon gamma after a prime and boost dose-regime. Furthermore, the putative vaccine candidate was able to adapt to the codon usage of E. coli and Cavia porcellus (Guinea Pig), and successfully cloned in pVAX1 vector. Conclusion This study was able to design and construct a high quality LASV vaccine candidate from the circulating strains in Nigeria, preparatory to further downstream in vitro and in vivo validations and Proof of Concept experiments.

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