Project 1: Vaccines are the most accessible and probably most effective means of protecting humans from infectious agents. While a wealth of vaccines has been developed, natural evolution and engineering for bioterrorism purposes create novel biothreats for which novel vaccines may represent the most potent countermeasures. Vaccines need to be tested in vivo but studies in mice often cannot be directly extrapolated to humans because of differences in their immune systems. Hence, the need for pre-clinical models of the human immune system for testing vaccine potency. With this in mind, we have constructed mice with a human immune system (Humouse). There, NOD/SCID mice transplanted with human CD34+ HPCs develop naive B cells and all subsets of human dendritic cells (DCs) including myeloid DCs and plasmacytoid DCs in the bone marrow/blood, Langerhans cells in the skin and interstitial DCs in other tissues including lung. In our current, first generation model, naive/memory T cells are adoptively transferred. The Technical Development Component is expected to construct a second generation model with a complete human immune system. This project is designed to demonstrate the validity of the Humouse (first and second generations) for testing vaccine potency. We will evaluate the induction of specific cellular and humoral immune responses using Influenza virus as a model pathogen and Influenza vaccine as a model vaccine. The ultimate parameter will be the protection of mice from virus rechallenge. AIM 1 will establish how subsets of human DC in Humouse interact with Influenza virus in vivo. AIM 2 will establish the capacity of Humouse to mount protective Influenza-specific recall T cell immunity. AIM 3 will establish the capacity of Humouse to mount protective Influenza-specific primary T cell immunity. AIM 4 will establish the capacity of Humouse to mount protective humoral immune responses. This project will validate the use of mice with a full human immune system (Humouse) for in vivo testing of human vaccine potency.