This proposal to fund the Western New England Maternal Pediatric Adolescent AIDS Clinical Trials Unit (WNE-MPAACTU) is submitted in response to RFA-AI-05-002. The WNE-MPAACTU is a consortium of clinical sites consisting of a main unit at the University of Massachusetts Medical School in Worcester, MA, and Clinical Trials Sites at Baystate Medical Center in Springfield, MA and Connecticut Children's Medical Center in Hartford, CT. Consortium investigators have worked together since 1990 to define the pathogenesis of mother-to-child HIV-1 transmission (MTCT) and pediatric HIV-1 infection and are highly experienced in the design and implementation of pathogenesis-based clinical trials. WNE-MPAACTU goals are: 1) To improve our understanding of the pathogenesis of MTCT and pediatric HIV-1 infection; 2) To improve prevention strategies for pediatric and adolescent HIV-1 infection, including the development of an effective preventive vaccine; and 3) To improve treatment strategies for pediatric and adolescent HIV-1 infection, including the management of co-morbidities and ART toxicities. These goals are most aligned with the goals of the International Maternal Pediatric Adolescent Clinical Trials (IMPAACT) network, which will conduct Vaccine, Translational Research/Drug Development, Optimization of Clinical Care, and Prevention of MFCT studies. Based on past performance and projected accruals, WNE-PACTU has been selected as an IMPAACT highly-preferred core site. WNE-MPAACTU investigators have played leadership roles in IMPAACT's development and will continue to contribute to the IMPAACT scientific agenda through leadership, training and mentorship, and protocol design, implementation, and accrual. ADMINISTRATIVE COMPONENT: