Passive protection assay of monoclonal antibodies against dengue virus in suckling mice

Structure and function analysis of therapeutic monoclonal antibodies against dengue virus type 2

Dengue virus (DENV) is the most prevalent insect-transmitted viral disease in humans globally, and currently no specific therapy or vaccine is available. Protection against DENV and other related flaviviruses is associated with the development of antibodies against the viral envelope (E) protein. Although prior studies have characterized the neutralizing activity of monoclonal antibodies (MAbs) against DENV type 2 (DENV-2), none have compared simultaneously the inhibitory activity against a genetically diverse range of strains in vitro, the protective capacity in animals, and the localization of epitopes. Here, with the goal of identifying MAbs that can serve as postexposure therapy, we investigated in detail the functional activity of a large panel of new anti-DENV-2 mouse MAbs. Binding sites were mapped by yeast surface display and neutralization escape, cell culture inhibition assays were performed with homologous and heterologous strains, and prophylactic and therapeutic activity was evaluated with two mouse models. Protective MAbs localized to epitopes on the lateral ridge of domain I (DI), the dimer interface, lateral ridge, and fusion loop of DII, and the lateral ridge, C-C' loop, and A strand of DIII. Several MAbs inefficiently inhibited at least one DENV-2 strain of a distinct genotype, suggesting that recognition of neutralizing epitopes varies with strain diversity. Moreover, antibody potency generally correlated with a narrowed genotype and serotype specificity. Five MAbs functioned efficiently as postexposure therapy when administered as a single dose, even 3 days after intracranial infection of BALB/c mice. Overall, these studies define the structural and functional complexity of antibodies against DENV-2 with protective potential.

The development of therapeutic antibodies that neutralize homologous and heterologous genotypes of dengue virus type 1

Antibody protection against flaviviruses is associated with the development of neutralizing antibodies against the viral envelope (E) protein. Prior studies with West Nile virus (WNV) identified therapeutic mouse and human monoclonal antibodies (MAbs) that recognized epitopes on domain III (DIII) of the E protein. To identify an analogous panel of neutralizing antibodies against DENV type-1 (DENV-1), we immunized mice with a genotype 2 strain of DENV-1 virus and generated 79 new MAbs, 16 of which strongly inhibited infection by the homologous virus and localized to DIII. Surprisingly, only two MAbs, DENV1-E105 and DENV1-E106, retained strong binding and neutralizing activity against all five DENV-1 genotypes. In an immunocompromised mouse model of infection, DENV1-E105 and DENV1-E106 exhibited therapeutic activity even when administered as a single dose four days after inoculation with a heterologous genotype 4 strain of DENV-1. Using epitope mapping and X-ray crystallographic analyses, we localized the neutralizing determinants for the strongly inhibitory MAbs to distinct regions on DIII. Interestingly, sequence variation in DIII alone failed to explain disparities in neutralizing potential of MAbs among different genotypes. Overall, our experiments define a complex structural epitope on DIII of DENV-1 that can be recognized by protective antibodies with therapeutic potential.

Dengue virus (DENV) is a mosquito-transmitted virus that infects 25 to 100 million humans annually and can progress to a life-threatening hemorrhagic fever and shock syndrome. Currently, no vaccines or specific therapies are available. Prior studies identified a highly neutralizing monoclonal antibody (MAb) against West Nile virus, a related flavivirus, as a candidate therapy for humans. In this study, we generated 79 new MAbs against the DENV type 1 (DENV-1) serotype, 16 of which strongly inhibited infection in cell culture. Using structural and molecular approaches, the binding sites of these inhibitory MAbs were localized to distinct regions on domain III of the DENV-1 envelope protein. We tested the protective capacity of all of the neutralizing MAbs in mice against infection by a strain of DENV-1 from a distinct genotype. Only two of the MAbs, DENV1-E105 and DENV1-E106, showed efficacy in a post-exposure treatment model, and these antibodies efficiently neutralized all five DENV-1 genotypes. Collectively, our studies define a complex structural binding site on domain III of the envelope protein for MAbs with therapeutic potential against DENV-1.