Thomas A. Rasmussen
BOSTON — For years, researchers have debated whether HIV can replicate in cells of infected patients on effective therapy, according to presenters at CROI. Previous findings suggest that ongoing cycles of viral replication may be occurring in lymph nodes. However, two studies investigating potential mechanisms of HIV persistence found no evidence that the virus replicates in the blood or lymph nodes of virally suppressed patients.
“We feel this is another piece of evidence to suggest that residual replication is unlikely occurring on very effective regimens, and if it is occurring, it occurs at very low frequencies,” Thomas A. Rasmussen, MD, PhD, an investigator on one of the studies conducted at The Peter Doherty Institute for Infection and Immunity in Melbourne, Australia, said during a press conference.
No signs of replication with ART
Although HIV latency is a well-known and significant mechanism of long-term viral persistence, it will be important to identify other potential mechanisms to develop interventions that target the viral reservoir, according to Rasmussen, who currently works in the department of infectious diseases at Aarhus University Hospital in Denmark. Two studies, he said, have previously demonstrated that residual virus replication (RVR) may be occurring in the presence of ART, which could be contributing to viral persistence. Evidence of RVR in these studies was based on an observed increase in 2-long terminal repeat (2-LTR) circles after participants’ treatment was intensified with the integrase inhibitor Isentress (raltegravir, Merck).
Rasmussen and colleagues conducted their own randomized controlled trial to further investigate RVR in virally suppressed patients on effective treatment. They randomly assigned 40 patients to intensified treatment with 50 mg of the integrase inhibitor dolutegravir given once daily (n = 21) or placebo (n = 19) in addition to background therapy for 56 days. The researchers performed frequent blood sampling to measure changes in virus activity. The primary outcome was the level of 2-LTR circles in CD4+ T cells after treatment intensification.
“During HIV replication, HIV RNA is transformed to HIV DNA, which is then integrated into the host cell genome,” Rasmussen told Infectious Disease News. “But frequently, this process is unsuccessful, and such unintegrated HIV DNA is then circularized by repair enzymes to form 1-LTR and 2-LTR. So, if you have an ongoing process of cell infection and integration of HIV DNA, and this process is inhibited by adding an integrase inhibitor, you would expect an increase in unintegrated HIV DNA. Therefore, we hypothesized that if there was residual replication, we would see a transient increase in 2-LTR shortly after intensifying ART with a drug that specifically inhibits integration of HIV DNA.”
According to Rasmussen, all analyses failed to show a substantial difference in virus activity between the dolutegravir and placebo arms, which indicates that the HIV reservoir is not sustained through ongoing cycles of replication.
“We saw no change in 2-LTR, which we interpreted as no interference with residual replication during the intervention; no change in multiple cell-associated and plasma markers of HIV persistence; and no change in the level of T cell activation or in circulating levels of inflammatory biomarkers,” he said.
Rasmussen noted that the study was powered to detect a threefold difference between patients who received dolutegravir and placebo. Therefore, minor changes below that threshold could have occurred but at insignificant frequencies.
“So, we conclude that intensifying ART with dolutegravir did not reveal or impact residual replication in blood, at least in HIV-infected individuals on ART,” he said.
No replication in lymph nodes
In a similar study, Mary Kearney, PhD, head of the translational research unit in the HIV Dynamics and Replication Program at the National Cancer Institute’s Center for Cancer Research, and colleagues explored the theory that RVR may be ongoing in lymph nodes during suppressive ART.
“There was a paper published in 2016 that suggests viral replication occurs in the lymph node,” she said during a press conference. “This was refuted by us and others, but we wanted to further investigate.”
The researchers sequenced HIV from lymph nodes and peripheral blood samples obtained from five patients who were virologically suppressed on ART for 2 to 13 years. The researchers assessed HIV RNA levels and compared the number of infected cells in each sample. They also analyzed integration sites from infected cells to determine whether there was a difference.
“You might imagine that if there is ongoing replication in the lymph node and not in the blood, we would find a different profile of HIV integration sites in these two locations,” Kearney said.
Although the researchers identified a greater fraction of infected cells in lymph nodes that expressed HIV RNA than in peripheral blood of some patients, there was no statistically significant difference in the levels of HIV in lymph node cells, suggesting that they are not on the replication pathway, according to Kearney.
“While [it] is a small sample, the results were consistent across all five [patients],” she said. “The study was well powered because we didn’t find any differences in all five patients. We conclude that ART is fully potent in the lymph node just as it is in the blood and that if we are going to cure HIV infection, we need to target cells that were already infected prior to starting treatment and that are likely persisting through clonal proliferation.” – by Stephanie Viguers
McManus WR, et al. Abstract 70. Presented at: Conference on Retroviruses and Opportunistic Infections; March 4-7, 2018; Boston.
Rasmussen TA, et al. Abstract 71. Presented at: Conference on Retroviruses and Opportunistic Infections; March 4-7, 2018; Boston.
Disclosures: Kearney and Rasmussen report no relevant financial disclosures.