Project 3: Determinants of Vaccine Efficacy (Project Leader: Behar) Abstract The bacterium Mycobacterium tuberculosis (Mtb) causes tuberculosis (TB), which is a leading cause of global morbidity and mortality. Given the rapid spread of drug resistant Mtb strains, the long-term solution must be a safe and effective vaccine. Much well-deserved attention has been devoted to developing new vaccines against TB during the past twenty years, but without notable success yet. Key knowledge gaps include the role of human genetics in vaccine-induced protection, the nature of protective immunity itself, and the identification of clinically useful correlate measures. Moreover, given the challenges in testing vaccines in NHPs, improved small animal models are of strong interest. To study how variation in genetics and immunity affect TB vaccine efficacy, we have comprehensively analyzed BCG-elicited protection in genetically diverse Collaborative Cross (CC) and Diversity Outbred (DO) mice. CC / DO mice have vaccine responses that differ quantitatively and qualitatively from B6 mice, and more closely resemble the variable outcomes observed in natural human populations. Our data provide a rigorous basis for correlative and mechanistic studies to identify pathways associated with vaccine-induced immunity. In Aim 1, we will analyze BCG-induced immunity in CC strains that vary in their ability to be protected by BCG. We expect to distinguish a subset of transcriptional signatures and immunological features that correlate with BCG- induced protection from the pool of immune perturbations triggered by BCG but not associated with protection. In Aim 2, we will identify alternative vaccine strategies that protect diverse CC/DO mice from TB. Three novel vaccine strategies will be compared with the goal to identify CoP and to evaluate the use of CC/DO mice as preclinical models for vaccine testing. In Aim 3, the features identified in vaccinated CC/DO mice will be used to discover human immunological and transcriptional pathways that are associated with different TB outcomes, using prospectively collected clinical samples from RePORT South Africa, and BCG and M72 vaccination trials. Finally, Aim 4 will evaluate novel mechanisms of vaccine-induced immunity. For example, BCG-protected CC strains have distinct immune responses after vaccination and Mtb challenge. One of these, Th17-skewed responses, are associated with protection in mice, NHP, and humans, but the mechanisms are largely unknown. In several CC strains, but not B6 mice, BCG elicits Th1/17 responses that are associated with protection. Moreover, we identified a genetic locus that controls vaccine-induced protection in DO mice and Th1/17 cytokine production in CC strains. We will evaluate engineered mouse strains to define mechanisms of Th1/17-mediated protection and search for the causative variants underlying these quantitative trait loci (QTL). Thus, in close collaboration with all projects and cores in this pr...