It has been clearly demonstrated that cellular antigens (HLA, beta 2-microglobulin) are incorporated at the virion surface. The same epitope derived from beta 2-microglobulin is presented on all virus isolates. The peptide was identified by blocking the neutralizing capacity of a monoclonal antibody directed to R7V epitope: using this peptide for developing an ELISA, we have detected antibodies in nonprogressor patients with neutralizing property to laboratory strains and primary isolates. Purified anti-R7V antibodies immunoprecipitate all HIV isolates at concentration dependent. R7V is immunogenic after rabbit immunization and induces HIV immunoprecipitating and neutralizing antibodies. The patient's as well as the immunized rabbit antibodies did not bind to any cell. No autoimmune disease is found in nonprogressor patients. For all these reasons, R7V is a good candidate for an universal AIDS vaccine.