The global spread of the arthropod borne flaviviruses dengue (DENV1-4) and Zika (ZIKV) viruses are major global public health challenges. World health organizations are calling for scientific communities to respond to this emerging threat with vaccines, therapeutics and diagnostics. However, existing gaps in fundamental knowledge about DENV and ZIKV immunity, specifically how type-specific immunity to each serotype develops and is sustained, makes rational vaccine development particularly difficult. The dominant immunity model comes from human challenge studies on DENV (1910?s-1940?s) and posits that first infection induces neutralizing antibodies that provide life-long sterilizing immunity to repeat infections by the same (homotypic) serotype virus, and this model has been extended to ZIKV without rigorous evaluation. However, recent studies from DENV endemic regions provide evidence of homotypic re-infection and natural immune boosting over time and our preliminary data from a non-endemic, Portland, Oregon resident DENV and ZIKV immune cohort show type- specific Abs decay ? lose both potency and breadth - over time, calling into question sterilizing immunity and leading us to hypothesize that natural flavivirus (ZIKV and DENV) protective immunity is context dependent: in endemic transmission settings intermittent asymptomatic boosting maintains potency and breadth of virus specific immunity and in non-endemic or very low transmission settings potency and breadth of flavivirus immunity significantly wanes. To test this hypothesis, we propose to prospectively characterize and compare DENV and ZIKV immunity in a regularly re-exposed endemic cohort in Ponce, Puerto Rico with immunity in an un-boosted, non-endemic cohort of DENV immunes in Portland. This is a controversial and novel hypothesis that will call for substantial supporting evidence, hence we will compare and contrast three highly relevant and related markers of boosting between the two cohorts: The potency and breadth of neutralizing serum DENV and ZIKV specific Abs (Aim 1), the frequency of and potency of DENV and ZIKV non-structural protein 1 (NS1) specific antibodies (Aim 2), and the frequency and specificity of DENV and ZIKV specific memory B-cells (MBCs) (Aim 3). We expect to find that Abs and MBCs decline at a significantly greater rate in individuals from the non- endemic setting compared to the endemic setting supporting the hypothesis that boosting plays a critical role in natural immunity for these viruses, with implications for future vaccine development. Because MBCs are functionally linked to Abs, quantifying virus specific MBCs tests a mechanistic connection between repeat infection and Ab titer boosting. Our proposed work will comprehensively assess the role transmission context plays in flavivirus immunity using two highly relevant and mechanistically linked determinants (Ab and MBC). Irrespective of specific results, the knowledge obtained from the proposed work will be essential to DENV vaccine development and mechanistic understanding of flavivirus Ab mediated immunity.
The proposed research evaluates DENV and ZIKV immunity in humans living in endemic and non-endemic settings. This knowledge is critical to understanding the potency, breadth, determinants and correlates of ZIKV and DENV immunity as well as effective evaluation and improvement of this vaccine that is critical to control this globally important disease. The results of this project are highly and directly relevant to the NIH?s mission fostering innovative research strategies to reduce the burden of illness and disease.
