Background:  Heterosexually transmitted subtype A HIV found early in infection have shorter less glycosylated envelope variable loops compared to the variants found during the chronic phase of infection. We hypothesize that these envelope differences likely confer phenotypic properties, which may be important for the selection of viruses during transmission. 

Methods:  Multiple subtype A envelope variants were isolated from 1 to 6 months post-infection and 24 to 47 months after estimated infection from 9 heterosexually infected ART-naïve subjects. Chimeric envelopes with a subject’s V1-V5 segment in a common subtype A envelope backbone were used to generate replication-competent recombinant viruses. Replication kinetics were examined by measuring serial p24 levels in cells with varying densities of CD4 and CCR5 receptors. Infections with serial dilutions of the CCR5 inhibitor, TAK779, and soluble CD4, PRO1008-1 were used to assess sensitivity to receptor inhibitors. All comparisons between early and chronic infection sequences were done using a matched-pairs signed-rank test. 

Results:  To date, we have evaluated a total of 22 sequences, 1 early infection sequence and a median of 4 (range 2 to 6) chronic infection sequences each from 5 different subjects. Early-infection sequences had significantly lower number of V1-V2 potential N-linked glycosylation sites (PNGS) than chronic infection sequences (p = 0.05). There was no significant difference in V1-V2 or V1-V4 length and in the number of V1-V4 PNGS. Viruses with early and chronic infection envelope sequences showed no significant replication differences in cells with high levels of both CD4 and CCR5 receptors. Viruses with early infection V1-V5 had about 10-fold lower p24 levels at day 7 in cells with low CCR5 and high CD4 densities (p = 0.04) and showed >5-fold greater sensitivity to TAK779 (p = 0.08) compared to the viruses with chronic infection sequences. Viruses with early and chronic infection envelopes had no significant p24 differences in infections of cells with low CD4 and medium CCR5 densities or in their sensitivity to PRO1008-1. 

Conclusions:  These preliminary results suggest that heterosexually transmitted subtype A variants with less glycosylated envelopes are not better at utilizing low levels of CD4 receptor. Furthermore, envelope modifications in the V1-V5 regions over the course of infection increase the ability to use the CCR5 receptor.