Impact of epitope permutations in the antibody response of mice to a multi-epitope polypeptide of the V3 loop of human immunodeficiency virus type 1

Our group have produced in Escherichia coli and evaluated the immunogenicit y of different multi-epitope polypeptides (MEPs) bearing one copy of V3 loo p sequential B cell epitopes from several isolates of human immunodeficienc y virus type 1 (HIV-1) gp120. One of these MEPs called TAB9 comprises the 1 5 central amino acids of the V3 loop from isolates LR150, JY1, RF, MN, BRVA and IIIB in this order. Antibodies against all V3 regions were elicited af ter immunization of rabbits, macaques and humans with TAB9. In contrast, mi ce immunized with this protein only developed antibodies against epitopes J Y1, LR150 and MN in that order (JY1 > LR150 > MN > > > RF, BRVA, IIIB) rese mbling an immunodominant gradient from the N-terminus to the C-terminal por tion of this construction. To assess what role the location of the V3 epito pes in TAB9 could play, we constructed the protein TAB16, by altering the p osition of V3 epitopes in TAB9 primary structure and compared the pattern o f antibodies elicited by both MEN in H-2(d) Balb/c mice. The MEP TAB16 elic ited antibody titers comparable to that of the sera from mice immunized wit h TAB9. There were no statistical differences in antibody titers between bo th groups (P > 0.05). JY1, LR150 and MN V3 epitopes were again immunodomina nt in mice immunized with TAB16 fusion protein. The highest antibody titers detected in both groups among V3 epitopes corresponded to JY1, now located at the C-terminus of the permuted chimera. Antibodies against V3 epitopes RF, BRVA and IIIB were again not detected. Additionally, the MN V3 epitope showed to be significantly more immunogenic in its new orientation in TAB16 , possibly as a result of a higher degree of accessibility in the surface o f the protein. The results of the present investigation strongly suggest th at the sequential order or the intramolecular position of V3 epitopes insid e the primary structure of TAB9 and TAB16 MEPs does not interfere with the global immunogenicity or with the hierarchy of immunodominance of these reg ions. (C) 2001 Elsevier Science B.V. All rights reserved.