ABSTRACT One million children develop TB annually; but current TB diagnostics exhibit poor performance in children, and the vast majority (96%) of the 205,000 children who die of TB-related causes each year do not receive treatment. Such children often present with non-specific symptoms and paucibacillary TB – particularly those co-infected with HIV – and are not diagnosed, and may then progress to disseminated or extrapulmonary TB cases that can rapidly progress in the absence of appropriate treatment. In young children, difficulty obtaining sputum samples used by most front-line TB diagnostics reduces the ability to accurately diagnose TB and monitor its response to treatment. Thus, non-sputum-based diagnostics are urgently needed to address this problem, but current versions of such assays either demonstrate poor sensitivity for active TB or cannot differentiate active disease from latent TB infection or accurately monitor treatment responses. We have reported that detection of virulence factors secreted by Mycobacterial tuberculosis (Mtb) in serum can diagnose all forms of TB in children (pulmonary and extrapulmonary TB), including paucibacillary and HIV- associated TB cases. We have recently shown that multiplex detection of HIV- and Mtb-derived protiens in serum can sensitively diagnose HIV and TB in young children, and simultaneously monitor their response to HIV and TB treatment. This is a critical issue for those at highest risk for mortality; very young children who may be exposed and/or infected with both pathogens while breastfeeding, during the first two years of life. Based on our success in identifying pathogen-specific peptide biomarkers and developing corresponding diagnostic assays, we propose to develop a multiplex HIV and TB assay for improved detection and monitoring of HIV viral load and all stages of TB, from early infection to active TB disease, in young children suspected HIV and TB infections or HIV/TB co-infections. We propose to achieve this goal through the pursuit of three interlinked specific aims where we will: 1) establish an assay for multiplex quantification of serum levels of TB-derived factors associated with each stage of TB development, from early infection to active TB disease in an infant non-human primate TB model that closely recapitulates the pathology of HIV and TB infection and co-infection; 2) develop a predictive model based on correlations between TB stage markers, immune responses and TB pathology in this disease model; and 3) conduct a multi-center validation of this multiplex assay to diagnose HIV infection and latent TB infections and early and active TB disease in HIV-exposed pediatric cohorts with carefully annotated clinical, radiological and bacteriological data. Employing a non-human primate model of HIV/TB co-infection and quantitative proteomics will allow us to identify TB-associated changes corresponding to symptom development and immune changes associated with disease progression th...