Figure 2.

Envelopes of viruses circulating in newly infected subjects confer lower replication capacity than those of viruses circulating in the transmitting partner. Shown are replication kinetics observed among recombinant viruses incorporating envelopes from a newly infected individual sampled prior to seroconversion (circles) and the linked transmitting partner (squares). Replication was examined in CD4⁺ T cells from 4 different human immunodeficiency virus type 1–negative volunteer blood donors (A–D). Generation of the replication-competent recombinant virus incorporating the envelopes from each partner and the infection assay was described previously [47]. The CD4⁺ T cells were exposed to equivalent amounts of infectious virus, estimated using titers from a luciferase reporter cell line, TZM-bl. The amount of infectious virus present in the culture supernatant was assessed as relative light units (RLUs) generated from TZM-bl cells. In CD4⁺ T cells from all 4 donors, virus incorporating the transmitting partner's envelopes replicates at higher levels than virus from the newly infected individual.