Dengue virus neutralizing antibody: a review of targets, cross-reactivity, and antibody-dependent enhancement

Abstract

Dengue is the most common viral infection spread by mosquitoes, prevalent in tropical countries. The acute dengue virus (DENV) infection is a benign and primarily febrile illness. However, secondary infection with alternative serotypes can worsen the condition, leading to severe and potentially fatal dengue. The antibody raised by the vaccine or the primary infections are frequently cross-reactive; however, weakly neutralizing, and during subsequent infection, they may increase the odds of antibody-dependent enhancement (ADE). Despite that, many neutralizing antibodies have been identified against the DENV, which are thought to be useful in reducing dengue severity. Indeed, an antibody must be free from ADE for therapeutic application, as it is pretty common in dengue infection and escalates disease severity. Therefore, this review has described the critical characteristics of DENV and the potential immune targets in general. The primary emphasis is given to the envelope protein of DENV, where potential epitopes targeted for generating serotype-specific and cross-reactive antibodies have critically been described. In addition, a novel class of highly neutralizing antibodies targeted to the quaternary structure, similar to viral particles, has also been described. Lastly, we have discussed different aspects of the pathogenesis and ADE, which would provide significant insights into developing safe and effective antibody therapeutics and equivalent protein subunit vaccines.

Keywords: antibody engineering; antibody-dependent enhancement; cross-reactivity; dengue virus; neutralizing antibodies; subunit vaccine.

Figure 1

Structural organization of dengue virus envelope protein. The RNA genome of dengue virus is composed of a single ORF, flanking by 5’ and 3’ untranslated region. The ORF includes coding sequence of three structural proteins, and seven non-structural proteins. The envelope (E) is the most significant structural protein of dengue virus surface. The monomer of each of the envelope protein is arranged into head-to-tail homo-dimer and 90 of such dimers are arrange in icosahedral symmetry to constitute the complete surface of dengue virus. Each of the monomeric envelope protein consists of three ecto-domains: EDI, EDII and EDIII. The domain I, II and III are denoting by red, golden and violet color respectively.

Figure 2

Multiple sequence alignment of non-structural (NS) proteins of DENV serotypes 1 to 4. The amino acid sequences of (A) NS1 (B) NS2A and NS2B (C) NS3 (D) NS4A, 2K and NS4B (E) NS5 are taken from polyprotein having accession no. QTH36735.1, NP_056776.2, YP_001621843.1, NP_073286.1 for DENV serotypes 1 to 4 respectively. Fully conserved amino acids are indicated with black dots while variable amino acids are displayed in the Clustal Omega format using Jal view. As per the Global Similarity (BLOSUM62) analysis, the sequence similarity index for NS1, NS2, NS3, NS4 and NS5 proteins are 0.77 ± 0.03, 0.51 ± 0.04, 0.82 ± 0.03, 0.75 ± 0.02, and 0.79 ± 0.02, respectively.

Figure 3

Sequence alignment of Envelope proteins ecto-domains (60 to 400 residues) of four dengue serotypes. Fully conserved amino acids are indicated with black stars (*) at the bottom of each row. Domains I, II, and III are schematically indicated with red, yellow, and blue color bars. Secondary structures are shown above the amino acid cluster (arrows indicate β strands, and the lines indicate helices). Each of the β strands of domains I, II, and III have been denoted with (A₀ to H₀), (a to l), and (A to G), respectively. The interacting residues of serotype-specific and cross-neutralizing antibodies are marked with blue and yellow shaded boxes, respectively, and their corresponding antibodies are mentioned above the bars with the same color-shed. The antibodies which were identified without any ADE effects are shown with blue letter code name and mentioned above the sequence alignment.

Figure 4

Monoclonal antibodies targeting DENV E protein. Domains I, II, and III are schematically indicated with red, yellow, and blue colors, respectively. Antibodies in the light blue shed are serotype-specific that target mainly domain I, hinge between domain I and II, and lateral ridge of domain III. In contrast, the antibodies in the light-yellow color are cross-reactive and target mainly FL and bc loop of domain II and A strand of domain III. The antibodies which were identified without any ADE effects are shown with blue letter code name.

Figure 5

Neutralizing antibodies targeting quaternary epitope of dengue E protein. Domains I, II, and III are schematically indicated with red, yellow, and blue colors, respectively. Both the top and the side view are displayed one ‘head to tail’ dimer of dengue E protein. Seven of the neutralizing antibodies are shown here schematically that target quaternary epitope in both top and side view of an E dimer. The antibodies which were identified without any ADE effects are shown with red letter code name.

Figure 6

Pathogenesis and antibody-dependent dengue virus enhancing model. While antibodies of primary dengue virus infection bind to an infectious DENV particle during a subsequent infection with the homologous serotype, protective immunity is conferred. However, secondary dengue virus infection with alternative serotypes unable to completely neutralize the virus particle. Instead, the Ab–virus complex interacts to the Fc receptors (FcγR) on circulating monocytes, making it simpler for the virus to infect them, leads to increased viral replication and a higher risk of dengue with warning signs (DWS+)/severe dengue (SD).