A major concern in AIDS vaccine development is the tremendous genetic heterogeneity seen between HIV isolates. In an effort to gain a better understanding of the consequences of viral heterogeneity on the efficacy of AIDS vaccines, the NIAID has established an HIV Variation Initiative consisting of a genetic cloning and sequencing laboratory funded through the Genetic Sequence Variability of HIV-l and Related Lentiviruses contract, a virology/immunology laboratory funded through the Antigenic Variation of HIV-l and Related Lentiviruses contract, and the HIV Sequence Database and Analysis Unit. Blood and tissue samples from HIV-infected individuals will be sent to the contract virology/immunology laboratory, where virus will be isolated and characterized immunologically. Genetic analysis of these same samples will be carried out by the Genetic Sequence Variability of HIV-l and Related Lentiviruses Contractor. Compilation and analysis of both the immunological and genetic data will be carried out at the Sequence Database and Analysis Unit in an effort to correlate genetic sequence to immunologic properties of the virus isolates. The Contractor will also be required to clone genes from virus isolates into various expression vectors in order to facilitate future variation studies. It is anticipated that by combining functional serology data with the genetic sequence data obtained from virus isolates, a meaningful classification system for HIV isolates will be devised that will be directly applicable to vaccine design.