HIV reservoirs are dominated by genetically younger and clonally enriched proviruses

Abstract

In order to cure HIV, we need to better understand the within-host evolutionary origins of the small reservoir of genome-intact proviruses that persists within infected cells during antiretroviral therapy (ART). Most prior studies on reservoir evolutionary dynamics however did not discriminate genome-intact proviruses from the vast background of defective ones. We reconstructed within-host pre-ART HIV evolutionary histories in six individuals and leveraged this information to infer the ages of intact and defective proviruses sampled after an average >9 years on ART, along with the ages of rebound and low-level/isolated viremia occurring during this time. We observed that the longest-lived proviruses persisting on ART were exclusively defective, usually due to large deletions. In contrast, intact proviruses and rebound HIV exclusively dated to the years immediately preceding ART. These observations are consistent with genome-intact proviruses having shorter lifespans, likely due to the cumulative risk of elimination following viral reactivation and protein production. Consistent with this, intact proviruses (and those with packaging signal defects) were three times more likely to be genetically identical compared to other proviral types, highlighting clonal expansion as particularly important in ensuring their survival. By contrast, low-level/isolated viremia sequences were genetically heterogeneous and sometimes ancestral, where viremia may have originated from defective proviruses. Results reveal that the HIV reservoir is dominated by clonally-enriched and genetically younger sequences that date to the untreated infection period when viral populations had been under within-host selection pressures for the longest duration. Knowledge of these qualities may help focus strategies for reservoir elimination.

The replication-competent HIV reservoir is a genetically restricted, younger subset of the overall pool of HIV proviruses persisting during therapy, which is highly genetically stable over time

“…We cannot therefore discriminate intact from defective proviruses. In fact, using data from another study [ 30 ], we estimate a 22% overall average likelihood (range 2–35% depending on the participant) that an intact env-gp120 sequence comes from a genomically intact provirus. Because we only sequenced part of the HIV genome, we also cannot definitively characterize proviruses as clonal, which would require full-genome sequencing and integration site characterization.…”

“…Doing so can shed light on the lineage origins and ages of persisting proviruses, but the results of these two studies were not entirely concordant: while one suggested that “younger” HIV lineages may be preferentially eliminated during the initial years of ART (though this did not reach statistical significance [ 6 ]), the other supported relative proviral genetic stability even in the longer-term (though the primary goal of the latter analysis was to investigate whether residual HIV replication occurs during ART, not to evaluate proviral genetic stability over time [ 5 ]). Even fewer studies have compared the within-host evolutionary origins and ages of proviruses persisting on ART with those of HIV sequences emerging from the reservoir (i.e., as rebound viremia) [ 30 ], which have been shown to include within-host recombinants of unknown origin [ 31 ]. Such analyses can help illuminate how the rebound-competent reservoir in blood may be distinctive from the overall, largely defective, proviral pool.…”