The present invention deals with a modified polypeptide comprising three contiguous segments N, L and C represented by the formula N-L-C and comprising : a N-helix region of gp41 (N), a C-helix region of gp41 (C), and a connecting loop comprising a synthetic linker (L) between the N and C-helices, the linker replacing amino acids 593- 617 of gp41, the numbering scheme being based upon the prototypic isolate HIV-1 HxB2 Clade B strain, said polypeptide comprising the calveolin-1 neutralizing and 98.6 D epitopes, but not 2F5 and 4E10 epitopes, not the fusion peptide, the polypeptide having a minimal immunogenic cross-reactivity with human interleukin 2 (IL2).