Unique V3 Loop Sequence Derived from the R2 Strain of HIV-Type 1 Elicits Broad Neutralizing Antibodies

Abstract

DNA vaccines expressing the envelope (Env) of the human immunodeficiency virus type 1 (HIV-1) have been relatively ineffective at generating high-titer long-lasting neutralizing antibodies. In this tudy DNA vaccines were constructed to express the gp120 subunit of Env from the isolate HIV-1R2 using both wild-type and codon- ptimized gene sequences. Three copies of the murine C3d were added to the carboxyl terminus to enhance the immunogenicity of the expressed fusion protein. Mice (BALB/c) vaccinated with DNA plasmid expressing the gp120R2 using codon-optimized Env sequences elicited high-titer anti-Env antibodies regardless of conjugation to C3d. In contrast only ice vaccinated with DNA using wild-type gp120R2 sequences fused to mC3d3 had detectable anti- Env antibodies. Interestingly mice vaccinated with DNA expressing gp120R2 from codon-optimized equences elicited antibodies that neutralized both homologous and heterologous HIV-1 isolates. To determine if the unique sequence found in the crown of the V3 loop of the EnvR2 was responsible or the elicitation of the cross-clade neutralizing antibodies the codons encoding for the Pro-Met (amino acids 313–314) were introduced into the sequences encoding the gp120ADA (R5) or gp12089.6 (R5X4). Mice vaccinated with gp120ADA–mC3d3–DNA with the Pro–Met mutation had antibodies that neutralized HIV-1 infection but not the gp12089.6–mC3d3–DNA. Therefore the use of the unique sequences in the EnvR2 introduced into an R5 tropic envelope in conjunction with C3d fusion was effective at broadening the number of viruses that could be neutralized. However the introduction of this same sequence into an R5X4-tropic envelope was ineffective in eliciting improved cross-clade neutralizing antibodies. Originally published AIDS Research and Human Retroviruses Vol. 20 No. 11 Nov 200