Project Summary The four serotypes of dengue virus pose a significant and increasing disease risk to endemic areas (40% of the world) and (via mosquito vector spread or travel) to areas not yet endemic. Tetravalent dengue vaccines are critical to prevent dengue illness. They must generate concurrent and durable protection against all serotypes without increasing risk of severe disease via imbalanced immunity leading to antibody-dependent enhancement of infection. Given concerns with imbalanced dengue vaccine candidates, it is critical to define components and mechanisms of durable four-serotype protection following vaccination, particularly in people (especially children) who have not established protective immunity via sequential natural exposures. This proposal builds on the work of long-standing collaborative investigators involved in developing the NIH live-attenuated tetravalent dengue vaccine TetraVax (TV) in studies in the U.S. and in dengue-endemic Bangladesh. TV protected dengue-naïve individuals from experimental infection six months later with dengue virus serotype 2 challenge and induced robust dengue serotype-specific B cell and CD4+ and CD8+ T cell responses. Key questions include: the durability of protective responses, whether similar protective mechanisms are at play in individuals in dengue- endemic areas and in individuals previously exposed to dengue prior to vaccination. In Aim 1 we will evaluate the development of serotype-specific B cells producing antibodies with neutralizing and Fc effector functions as well as virus-specific CD4+ and CD8+ T cell responses throughout a 6–12-year period after TV vaccination and assess whether these responses correlate with protection from subsequent DENV2 challenge. In Aim 2 we will demonstrate the importance, persistence, and function of serotype-specific neutralizing vs. enhancing antibodies following TV of dengue-naïve adults. In Aim 3 we will investigate whether TV vaccination contributes to protection in dengue-exposed individuals via potent cross-reactive neutralizing antibodies. Overall, these insights into immune mechanisms of durable protection will help answer persistent questions about dengue vaccine risk and efficacy. Leveraged with highly controlled clinical studies these data should be broadly generalizable to the understanding of safe and durable immunity following any tetravalent dengue vaccine.

PROJECT NARRATIVE The four serotypes of dengue virus cause 100 million cases of disease annually in humans. Durable tetravalent dengue vaccines are necessary to control disease but must safely protect against all four serotypes. We propose to use human specimens available from innovative dengue vaccine/viral challenge models and apply novel cellular and molecular approaches to define how vaccine-induced development of dengue-specific immunity safely and durably protects against infection and disease.