The long-term objective of this proposal is to establish the immunological mechanisms that permit up to a third of HIV vertically-infected children to live well beyond 5 years of life, in contrast, to those rapid progressors who expire from opportunistic infections and severe immunsuppression within the first few years of life. This project is in full implementation and has been very successful in generating data important to all pediatric HIV researchers. Because of its success, additional support for immunology core laboratories has been obtained from an outside organization.