The human immunodeficiency virus type 2 (HIV-2)-related isolate, referred to as HIV-2 EHO, has been isolated from an Ivory Coast patient with acquired immunodeficiency syndrome (AIDS). Infection of CD4 expressing cells with this highly infectious virus mediates a cytopathic effect characterized by single-cell killing as a consequence of apoptosis. Nucleotide sequence analysis of the HIV-2 EHO genome revealed a significant degree of divergence of its envelope gene from that of other known HIV-2 strains. This divergence for the deduced amino acid sequence corresponding to the extracellular envelope glycoprotein was 26 to 30%. These unique genetic and biological properties suggest that the HIV-2 EHO isolate is a distinct prototype in the HIV-2 family. (C) 1994 Academic Press, Inc.