- No Sign of Ongoing HIV Replication in Lymph Nodes During ART
Exhaustive analysis of paired lymph node and blood cell samples in 5 people on suppressive antiretroviral therapy (ART) turned up no evidence of ongoing HIV replication in lymph nodes when viral load remains undetectable in plasma . National Institutes of Health researchers and collaborators believe their findings suggest that "HIV infection is likely maintained by the proliferation of cells infected prior to ART, not by ongoing cycles of viral replication in either the peripheral blood or the lymph nodes."
Work over the past few years yielded conflicting findings on whether HIV continues to replicate in sanctuary sites when viral load remains below 50 copies in blood during ART [2,3]. Sometimes analysis of the same data produced divergent conclusions [3,4]. Addressing this controversy, Mary Kearney and collaborators conducted a new study to determine whether HIV continues to replicate in lymph nodes during suppressive ART.
The investigation had three parts: (1) analysis of HIV proviral genetics before ART and after 2 to 13 years of suppressive ART in paired lymph node mononuclear cell (LNMC) and peripheral blood mononuclear cells (PBMC) samples, (2) analysis of HIV integration sites in paired lymph node and blood samples, and (3) analysis of HIV RNA expression levels in single cells in paired samples. The investigators characterized proviral populations and expression by cell-associated RNA- and DNA- single-genome sequencing of p6-PR-RT. They compared proviral sequences phylogenetically and by testing for panmixia. They identified infected cell clones by integration site assay in PBMCs and LNMCs from one donor.
The analysis involved LNMC and PBMC samples from 5 people with continuous viral suppression during ART ranging from 1.8 to 12.9 years. All 5 participants come from the SCOPE cohort, "a prospective study of HIV-1 infected volunteers designed to provide a specimen bank of samples with carefully characterized clinical data" . HIV DNA could be detected in all PBMC samples at levels ranging from 14 to 3226 copies per million cells. One person had fewer than 8 HIV DNA copies per million cells in LNMC, while LNMC levels ranged from 423 to 3637 copies per million cells in the other 4.
Phylogenetic analysis of pre-ART proviral DNA in PBMCs and on-treatment proviral DNA in PBMCs and LNMCs showed no detectable HIV replication when viral load is undetectable at those sites. Comparison of on-therapy proviral DNA in PBMCs and LNMC disclosed (1) no compartmentalization between peripheral blood and lymph nodes and (2) no detectable viral replication during HIV suppression in peripheral blood.
Comparing on-therapy proviral DNA in LNMCs after 4.3 and 5.5 years of ART in one person, the researchers detected no change in the HIV population over time. Comparing on-therapy proviral DNA in LNMCs from the left and right inguinal lymph nodes of a single person revealed no difference in HIV populations at these different sites.
Kearney explained that "if clonal expansion generates cells with identical proviruses, they should have the same integration site in the human genome." Thus integration site analysis offers a surrogate for HIV proviral diversity. This experiment confirmed identical expanded viral clones in peripheral blood and lymph nodes. Further analysis determined that the same fraction of infected cells had unspliced HIV RNA in lymph nodes and peripheral blood.
The investigators concluded that no evidence indicates ongoing HIV replication in lymph nodes when ART controls HIV replication in peripheral blood. They determined that infected cells are well mixed between blood and lymph nodes, a finding that argues against compartmentalization. The collaborators proposed that eradicating HIV will depend on eliminating cells infected before ART begins, not on developing antiretrovirals with better lymph node penetration.
1. McManus WR, Bale MJ, Spindler J, et al. No evidence for ongoing HIV replication in lymph nodes during suppressive ART. 25th Conference on Retroviruses and Opportunistic Infections (CROI). March 4-7, 2018. Boston. Abstract 70.
2. Kearney MF, Spindler J, Shao W, et al. Lack of detectable HIV-1 molecular evolution during suppressive antiretroviral therapy. PLoS Pathog. 2014;10:e1004010.
3. Lorenzo-Redondo R, Fryer HR, Bedford T, et al. Persistent HIV-1 replication maintains the tissue reservoir during therapy. Nature. 2016;530:51-56.
4. Rosenbloom DIS, Hill AL, Laskey SB, Siliciano RF. Re-evaluating evolution in the HIV reservoir. Nature. 2017;551:E6-E9.
5. ClinicalTrials.gov. SCOPE: Observational Study of the Consequences of the Protease Inhibitor Era. ClinicalTrials.gov identifier NCT00187512.