[Seminar] Design and Biophysical characterization of structure-based vacine antigens against HIV-1 and Zika viruses

Seminar

Title: Design and Biophysical characterization of structure-based vacine antigens against HIV-1 and Zika viruses

Speaker: Isabelle Viana

Affiliation: Instituto Aggeu Magalhães, Oswaldo Cruz Foundation, Brazil

Host: Prof. Cláudio M. Soares, Protein Modeling

Abstract:

Current HIV-1 vaccine development approaches focus on stimulation of pan- neutralizing antibodies (pnAbs) that recognize functional sites on the HIV-1 Envelope spike.

Although conserved, these neutralizing epitopes are masked or structurally dynamic, resulting in weak antibody response in natural infections. Only rare individuals develop an antibody response directed to them. Our goal is to engineer antigenic structures capable of exposing a stable conformation of these epitopes and thus inducing B-cell secretion of HIV-1 pnAbs. The HIV-1 Envelope membrane-proximal external region (MPER) is one of those target sites for the pnAbs 2F5, Z13 and 4E10. We postulated that conformationally stable structures are better immunogens and can elicit the production of better antibodies. To test this hypothesis we have engineered a protein with increased exposure of a stable conformation of the 2F5 epitope. We grafted the 2F5 epitope into a scaffold protein Top7 (Top7-2F5 chimera). Molecular dynamics (MD) simulations were used to engineer the grafting site and to assess protein stability. Circular dichroism analysis confirmed the remarkable structural stability of Top7-2F5. ELISA and surfasse plasmon resonance assays demonstrated that 2F5 pnAb showed a superior affinity to the Top7- 2F5 (1.4e-9M) as compared to 9-mer (7.06e-8M) and 23-mer MPER (1.27e- 8M) peptides. MD analysis indicated that the structure of the 9-mer residues grafted into the Top7 is 3-fold more likely to correspond to the native conformation as compared to 23-mer MPER peptide. Following, 2F5-specific memory B-cells from patient-derived PBMCs were identified by flow cytometry and activated to induce pnAbs secretion in vitro. These results show that MD simulations can help engineer vaccine antigens capable of enhancing protective antibody responses. Using similar combination of computational and experimental methods, we have also developed a DNA vaccine against against Zika virus (ZIKV). This strategy also combines two strong molecular adjuvants that enhance the processing and exposure of the ZIKV vaccine antigens through the MHC class II molecules. The potential of this strategy to elicit protection against ZIKV infection has been assessed in vitro and in vivo using mouse models.