Utilizing the DENV Human Challenge Model to define the molecular determinants of the memory B cell response following heterologous DENV infections
Ciara Gimblet-Ochieng1, Huy Tu2, Ellen Young3, Ethan Fritch3, Sean Diehl2, Stephen Whitehead4, Anna Durbin5, Ralph Baric3 and Aravinda M. de Silva1
1Department of Microbiology and Immunology, University of North Carolina School of Medicine, Chapel Hill, NC, USA; 2Department of Microbiology and Molecular Genetics, Vaccine Testing Center, Larner College of Medicine, Burlington, VT, USA; 3Department of Epidemiology, University of North Carolina School of Public Health, Chapel Hill, NC, USA; 4Laboratory of Infectious Diseases, NIAID, National Institutes of Health, Bethesda, MD, USA; 5Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
Dengue virus (DENV) is a mosquito-borne flavivivirus responsible for the syndromes dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS). Vaccine efforts have been complicated by varying protection against all 4 serotypes of the virus and poor performance in DENV naïve individuals. Individuals who have experienced naturally occurring secondary DENV infections develop serotype cross-reactive strongly neutralizing antibodies (Abs), but it remains unclear how these responses are formed, what targets they recognize, and how they are maintained over time. In this study we utilize a human challenge model, in which subjects were infected with an attenuated DENV1 strain (n=6) or placebo (n = 2), followed by an attenuated DENV2 strain 9 months later. Plasma and PBMC samples were collected at various time-points before and after the second infection. To examine how the DENV serotype cross-reactive (CR) and type-specific (TS) neutralizing Ab responses evolve following sequential DENV infections, we used antibody depletion assays, and neutralization assays with recombinant chimeric DENVs. Following the primary DENV1 infection, the majority of the neutralizing Ab response (68.7%) was directed against TS epitopes on DENV1. Following the secondary DENV2 infection, individuals developed high levels of neutralizing Abs to all 4 serotypes. The majority of the DENV1 (95.1%), DENV2 (85.3%), DENV3 (100%) and DENV4 (98.6%) neutralizing antibodies recognized epitopes that were conserved (cross-reactive) between serotypes. Studies to map the conserved epitopes recognized by serum neutralizing Abs are on-going. Additionally, we are sequencing the memory B cells following primary and secondary DENV infections to analyze somatic hypermutations in the Ab repertoire. Our results and on-going experiments will provide valuable information about how the memory B cell response develops following heterologous DENV infections to provide cross-reactive and protective immunity.