Temporal relationship between elongation of the HIV type 1 glycoprotein 120 V2 domain and the conversion toward a syncytium-inducing phenotype.

The second and third variable domains (V2 and V3) of the human immunodeficiency virus type 1 (HIV-1) gp120 envelope molecule have been shown to be determinants of syncytium-inducing (SI) capacity. Previously we have reported evidence that increased length of the V2 domain and duplication or relocation of potential N-linked glycosylation sites in V2 might be used as prognostic markers for evolution toward an SI phenotype. Here, we used a PCR assay that discriminates a 6-nucleotide difference in the length of the V2 domain, with a sensitivity of 1 elongated V2 domain when present in a background of 125 to 625 short V2 domains. Analysis of DNA isolated directly from PBMCs from 11 HIV-1-infected individuals prior to SI phenotype conversion revealed, however, that the usefulness of this PCR for V2 length polymorphism as predictive marker for SI phenotype evolution is limited. The strong association as observed in our previous study between elongation of the V2 domain and an SI phenotype prompted us to expand our first analysis. An extremely significant correlation was observed between V2 length and virus phenotype for samples obtained at about the moment of SI conversion, but not for samples obtained 3 to 35 months after SI phenotype conversion, suggesting that changes in V2 may be only transiently required to allow SI phenotype evolution. This possibly only transient nature of V2 elongation may explain the discrepancy between results by our group and others.