Therapeutic neutralizing monoclonal antibody administration protects against lethal yellow fever virus infection

Abstract

Yellow fever virus (YFV) is a reemerging global health threat, driven by several factors, including increased spread of the mosquito vector and rapid urbanization. Although a prophylactic vaccine exists, vaccine hesitancy, supply deficits, and distribution difficulties leave specific populations at risk of severe YFV disease, as evidenced by recent outbreaks in South America. To establish a treatment for patients with severe YFV infection, we tested 37 YFV-specific monoclonal antibodies isolated from vaccinated humans and identified two capable of potently neutralizing multiple pathogenic primary YFV isolates. Using both hamster and nonhuman primate models of lethal YFV infection, we demonstrate that a single administration of either of these two potently neutralizing antibodies during acute infection fully controlled viremia and prevented severe disease and death in treated animals. Given the potential severity of YFV-induced disease, our results show that these antibodies could be effective in saving lives and fill a much-needed void in managing YFV cases during outbreaks.

Fig. 1.. Screening and selection of YFV-neutralizing mAbs.

(A) Thirty-seven mAbs were tested for neutralization of YFV-17D in a focus-forming assay, and IC₅₀ was calculated. (B) Five mAbs were tested for neutralization of YFV-DakH1279 in a focus-forming assay, and IC₅₀ was calculated.

Fig. 2.. Therapeutic mAb administration protects hamsters from pathogenic YFV infection.

(A) Kaplan-Meier survival curves of Syrian golden hamsters after challenge with YFV-Jimenez and treatment with YFV-specific or isotype control antibodies. P value determined by Mantel-Cox test with Bonferroni correction. (B) YFV-Jimenez titers in the sera of Syrian golden hamsters at 4 and 6 dpi as measured by an ex vivo infection assay to determine CCID₅₀. One hamster from the MBL-YFV-01 group had insufficient serum at 6 dpi to measure YFV-Jimenez titers. P values determined by Mann-Whitney test with Bonferroni correction. Limit of quantification (LOQ), 1.67 log₁₀. (C) Longitudinal mean weight change of each hamster treatment group after challenge with YFV-Jimenez. (D) Serum ALT levels of each hamster 6 dpi and measurements from normal controls. Two hamsters in the isotype control group and one hamster in the MBL-YFV-01 group had insufficient serum to measure ALT levels. P values determined by Mann-Whitney test with Bonferroni correction. **P < 0.01 and ***P < 0.001.

Fig. 3.. Therapeutic mAb administration protects RM from pathogenic YFV infection.

(A) Longitudinal concentration of MBL-YFV-01 and MBL-YFV-02 in the plasma of YFV-DakH1279 challenged RMs. (B) Kaplan-Meier survival curves of RMs after challenge with YFV-DakH1279 and treatment with YFV-specific antibodies. P value determined by Mantel-Cox test with Bonferroni correction. (C) Longitudinal serum YFV-DakH1279 loads in RMs, including historical controls. LOQ, 5 × 10³ copies per ml. (D) Longitudinal serum ALT levels in RMs. (E) Quantification of YFV-DakH1279 RNA in the livers of RMs at necropsy. LOQ, 1 × 10² copies per 100 ng of RNA. (F) Gross pathology of livers from YFV-DakH1279–infected RMs. Scale bars, 3 cm. (G) Hematoxylin and eosin staining of livers from YFV-DakH1279–infected RMs displaying midzonal necrosis with Councilman bodies (white arrow) in the control animals and comparably normal livers with minimal midzonal mononuclear cell infiltrates (black arrowhead) or rare midzonal Kupffer cells containing intracytoplasmic golden-tan pigment (white arrowheads; inset: scale bar, 25 μm) in the mAb-treated animals. Scale bars, 100 μm. PT, portal triad; MZ, midzonal region; CV, central vein. (H) RNAScope staining of YFV-DakH1279 RNA in the livers of YFV-DakH1279–infected RMs. DAPI, 4′,6-diamidino-2-phenylindole.