Construction, biological activity, and immunogenicity of synthetic envelope DNA vaccines based on a primary, CCR5-tropic, early HIV type 1 isolate (BX08) with human codons

So far codon-optimized HIV-1 envelope genes have been investigated for the T cell line-adapted strain MN, which differs in several aspects from primar y isolates. Envelopes of primary isolates may be more relevant for vaccine purposes. This article describes for the first time the engineering and cha racterization of four "humanized" genes encoding the secreted gp120/gp140, or the membrane-bound gp150/gp160, of a primary CCR-5 tropic, clade B, clin ical isolate HIV-1(BX08). The genes were built in fragments for easy casset te exchange of regions important for immunogenicity, function, and expressi on. The transcription and expression of the synthetic genes in mammalian ce ll lines were Rev independent and highly increased. Increased expression of membrane-bound gp160 induced a high cytopathic effect in U87.CD4.CCR5 cell s. Gene gun and intramuscular DNA vaccination in mice induced a strong spec ific cytotoxic T lymphocyte response independent of the gene construct, exp ression level, or DNA immunization route. In contrast, the highest anti-gp1 20 antibody levels were induced by synthetic genes encoding the secreted gl ycoproteins followed by gp160/gp150. Unlike HIV-1(MN), HIV-1(BX08) V3 was n ot immune dominant. Despite the high antibody response only low and inconsi stent neutralizing titers to the homologous HIV-1 isolate were measured. Ho wever, neutralization of SHIV89.6P could be obtained. Thus, the neutralizin g epitopes on the cell line-adapted SHIV89.6P and HIV-1(MN) may be more ant igenically available for the cross-neutralizing antibodies induced. In conc lusion, complete "humanization" of the DNA vaccine genes failed to induce a consistent neutralizing antibody response, albeit expression and immunogen icity of the primary HIV-1 glycoproteins were greatly improved. Optimizatio n in terms of improving neutralization may require further modifications of the DNA vaccine gene. The synthetic cassette construct described is a conv enient tool developed to investigate this further.