Induction of antibodies binding to the membrane proximal external region of gp36 of HIV-2.

OBJECTIVE: The ability to induce neutralizing antibodies may be the most important feature of an antiretroviral vaccine, preventing infection of target cells and subsequent integration of the virus into the cellular genome where the virus may persist. Broadly neutralizing antibodies directed against conserved epitopes in the membrane proximal external region (MPER) of the transmembrane envelope (TM) protein gp41 of HIV-1 such as the monoclonal antibodies (mAb) 2F5 and mAb 4E10 have been found in infected individuals; however, all attempts to induce such antibodies failed. In individuals infected with HIV-2 such antibodies were not yet reported. METHODS: Two recombinant proteins corresponding to the ectodomain of the TM protein gp36 of HIV-2 were produced, rats were immunized and sera were analyzed for binding and neutralizing antibodies. RESULTS: Although binding antibodies were induced, none of the sera neutralized HIV-2. Most interestingly, epitope mapping showed specific binding of the antibodies to the MPER of gp36, to a region homologous to the binding site of the mAb 4E10 in gp41 of HIV-1. CONCLUSIONS: Although MPER-specific antibodies were induced by vaccination with gp36, these antibodies did not neutralize HIV-2. This is similar to the situation with HIV-1, but in contrast to that with gammaretroviruses.