Our goal is to study viral and immunological factors involved in the pathogenesis of HIV/AIDS as to identify those factors that can induce a special state of the infection process. At this scope we focus our attention mainly on models as mother-to-child transmission of HIV-1 and disease progression in children and adults, in which we dissect the fundamental mechanisms involved in prevention of transmission or promotion of delayed progression of the disease. The acquired knowledge on the phenotypic and antigenic variation of HIV-1 is translated into developing potential vaccine candidates.