Project Summary The goal of generating a licensed vaccine that can provide long-lived immunity against infection with Plasmodium falciparum, the protozoan parasite that causes the most lethal form of malaria, is yet unrealized. Currently, the malaria vaccine candidate that has undergone the most extensive clinical testing is RTS,S, a subunit vaccine based on the circumsporozoite protein (CSP), expressed on the surface of the infectious sporozoite stage of the parasite. Yet, as seen with many other vaccine strategies, protection induced by vaccination with RTS,S is not only suboptimal, it also wanes rapidly and there is negligible prevention of clinical disease measured four years after immunization. A critical bottleneck for the generation of a protective malaria vaccine is therefore understanding how to generate long-lived, Plasmodium-specific immune memory, especially in people in malaria endemic countries. One promising approach is to gain greater insight into the immune response to whole attenuated sporozoite vaccines, which can lead to the development of high levels (>60%) of sterile immunity in malaria naïve subjects when tested by challenge using controlled human malaria infection (CHMI) and has shown for the first time protection against infection in malaria-exposed subjects in Africa. In this application, we will focus on three major questions that are critical to enhancing our understanding of how immunity can be maintained after whole sporozoite vaccination: 1) how does the innate immune response after sporozoite vaccination influence the development of long-lived adaptive memory, 2) how does previous malaria infection alter the generation of sporozoite vaccine-induced memory and 3) how can we harness recently characterized memory cell signatures in the blood to understand the maintenance of long-lived immune cells in the tissues after sporozoite vaccination. Our team consists of experts in immunology, vaccinology, parasitology and collaborators that conduct sporozoite vaccine trials, and will pursue a fully integrated approach to address these questions. To answer these questions, we will use both relevant human samples obtained from malaria-naïve and malaria pre-exposed subjects who received different modes of whole sporozoite vaccination, as well as murine malaria models, which allow immune system perturbations and access to target organs. We will combine our unique expertise with novel tools and techniques to provide key insights into how immunological memory can be maintained after immunization, which will broadly inform vaccination strategies for malaria, as well as other infectious diseases for which vaccines are not currently available.