Antibody response in rabbits against two HIV-1 multi-epitope polypeptides bearing different copies of V3 epitopes fused to the N terminal fragment of N. meningitidis P64K protein

We have previously reported the synthesis and evaluation of the Multi-Epitope Polypeptide (MEP) TAB4. This protein contains the V3 region of gp120 from the HIV-1 isolates LR150, JY1, RF, MN, BRVA and, IIIB fused to the 26 amino acid terminal fragment of human interleukin 2 (hIL2). The main objective of the present study was the replacement of the hIL2 sequence for another of bacterial origin, and therefore suitable for humans trials. We also explored the effect of the inclusion of a different number of V3 epitopes on the immunogenicity of MEPs. For these purposes we constructed two novel MEPs derived from TAB4: (a) TAB9, which contains the same six V3 regions but the stabilizing sequence from hIL2 was replaced by a 47 amino acid fragment from the protein P64K of Neisseria meningitidis. (b) TAB13, which contains two more V3 regions with the central sequence GPGQ and GQGQ and the same P64 fragment. The new stabilizing region was as efficient as the IL2 in allowing the expression of TAB9 in E. coli and did not affect the immunogenicity of the V3 epitopes in rabbits. Additionally, TAB9 was significantly more immunogenic than TAB13 eliciting higher antibody titers against the protein and V3 peptides.