Sexually-transmitted/founder HIV-1 cannot be directly predicted from plasma or PBMC-derived viral quasispecies in the transmitting partner

Abstract

Objective: Characterization of HIV-1 sequences in newly infected individuals is important for elucidating the mechanisms of viral sexual transmission. We report the identification of transmitted/founder viruses in eight pairs of HIV-1 sexually-infected patients enrolled at the time of primary infection ("recipients") and their transmitting partners ("donors").

Methods: Using a single genome-amplification approach, we compared quasispecies in donors and recipients on the basis of 316 and 376 C2V5 env sequences amplified from plasma viral RNA and PBMC-associated DNA, respectively.

Results: Both DNA and RNA sequences indicated very homogeneous viral populations in all recipients, suggesting transmission of a single variant, even in cases of recent sexually transmitted infections (STIs) in donors (n = 2) or recipients (n = 3). In all pairs, the transmitted/founder virus was derived from an infrequent variant population within the blood of the donor. The donor variant sequences most closely related to the recipient sequences were found in plasma samples in 3/8 cases and/or in PBMC samples in 6/8 cases. Although donors were exclusively (n = 4) or predominantly (n = 4) infected by CCR5-tropic (R5) strains, two recipients were infected with highly homogeneous CXCR4/dual-mixed-tropic (X4/DM) viral populations, identified in both DNA and RNA. The proportion of X4/DM quasispecies in donors was higher in cases of X4/DM than R5 HIV transmission (16.7-22.0% versus 0-2.6%), suggesting that X4/DM transmission may be associated with a threshold population of X4/DM circulating quasispecies in donors.

Conclusions: These suggest that a severe genetic bottleneck occurs during subtype B HIV-1 heterosexual and homosexual transmission. Sexually-transmitted/founder virus cannot be directly predicted by analysis of the donor's quasispecies in plasma and/or PBMC. Additional studies are required to fully understand the traits that confer the capacity to transmit and establish infection, and determine the role of concomitant STIs in mitigating the genetic bottleneck in mucosal HIV transmission.

Figure 1. Evolutionary relationships between the HIV-1 env genes in the eight donor/recipient pairs.

The evolutionary history was inferred using the Neighbor-Joining method . The optimal tree with the sum of branch length = 2.01912678 is shown. The tree is drawn to scale, with branch length in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Maximum Composite Likelihood method and the unit is the number of base substitutions per site. Codon positions included were 1^st+2^nd+3^rd+noncoding. All positions containing gaps and missing data were eliminated from the dataset. There were a total of 230 positions in the final dataset. Phylogenetic analyses were conducted in MEGA4 . For each recipient, viruses isolated from PBMC-derived DNA (•) and plasma RNA (○) are represented, with a different color for each donor/recipient pair. Asterisks indicate branches with bootstrap values greater than 98%.

Figure 2. Evolutionary relationships between the HIV-1 env genes in donor/recipient pair #1.

The evolutionary history was inferred using the Neighbor-Joining method . The optimal tree with the sum of branch length = 0.28572580 is shown. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Maximum Composite Likelihood method and the unit is the number of base substitutions per site. Codon positions included were 1st+2nd+3rd+Noncoding. All positions containing gaps and missing data were eliminated from the dataset (Complete deletion option). There were a total of 500 positions in the final dataset. Phylogenetic analyses were conducted in MEGA4 . For the recipient, viruses from PBMC-derived DNA (•) and plasma RNA (○) are represented. For the donor, strains from PBMC-derived DNA (▾) and plasma RNA (∇) are represented.

Figure 3. Comparative Highlighter analyses of env diversity in a donor-recipient HIV-1 transmission pair.

(A) Recipient#1 shows evidence of infection with a single virus. (B) Donor#1 was the chronically infected partner of recipient#1. The same reference amplicon, a V3 RNA sequence from recipient plasma, was used to depict the viral diversity in both individuals.