Abstract: The present invention relates to modified HIV-1 envelope proteins which express epitopes that produce a broadly cross reactive neutralizing response, their methods of use and antibodies which bind to these epitopes.

Abstract: The present invention relates to a retrovirus isolated from a chimpanzee and designated as SIV.sub.cpz-ant and to variants of this virus, having the following essential morphological and immunological properties: the virus exhibits a tropism for T4 lymphocytes, the virus does not exhibit cytopathic effect with the formation of giant cells in the lymphocytes that it infects, the virus has a diameter of approximately 130 nm, the virus possesses a magnesium dependent reverse transcriptase activity, it can be cultivated in T4 receptor-bearing immortalized cell-lines, lysates of the virus containing a p27 protein that is immunologically distinct from the p25 of HIV-1 and p19 protein of HTLV-1 on Western Blot, lysates of the virus containing a gp140 protein which is immunologically distinct from the gp120 of HIV-1 and gp140 of HTLV-1 by Western Blot analysis, the lysate of the virus contains an additional transmembrane glycoprotein with a molecular weight of 44,000 to 50,000 kD.