Is Eradication Possible for the Reservoir of HIV in Resting Memory CD4 cells??

1999 Retrovirus Conference--Abstract 155: The use of real-time PCR to quantify HIV unspliced (US) mRNA in patients on effective antiretroviral therapy.

Aaron Diamond AIDS Research Center, New York, NY.

If replication of HIV is effectively inhibited, the reservoir of HIV in resting memory CD4+ lymphocytes should decay with time. However, if there is persistent replication below the limits of detection of currently available assays, the reservoir will persist due to replenishment.

AIM: To determine if the detection of US mRNA in PBMC of patients on effective antiviral therapy for at least 2 years may serve as an indicator for persistent viral replication.

METHOD: We developed a novel assay using real-time PCR and molecular beacons to detect US mRNA in PBMC of patients treated within 90 days of primary infection. The assay is sensitive (50 copies/µg RNA) and dynamic (range of 8 logs). No post-PCR manipulation is required, and amplification and analysis of 96 samples can be performed in 3 hours.

RESULTS: Patients were classified as either well suppressed (WS; defined as plasma viremia persistently undetectable, n=20) or partially suppressed (PS; defined as >2 episodes of plasma RNA >50 copies/ml after plasma viremia became undetectable; n=7; mean number of episodes 3; range 2-5). US mRNA in PBMC declined on treatment (median copy number at 0, 12 and 24 months: WS = 3446, 60, <50 copies; PS = 3487, 193, 200 copies), with a decay half-life of ~7 days for WS patients. The proportion of patients with undetectable US mRNA over time (at 0, 6, 12, 18, 24 months) was significantly higher in WS patients (WS =0, 0.2, 0.3, 0.6, 0.7; PS = 0, 0, 0, 0, 0.2). However, 5/20 WS patients had persistently detectable US after 24 months.

CONCLUSION: These results demonstrate that intermittent low-level detection of plasma RNA as infrequently as 2 times over 24 months of therapy may reflect persistent viral replication. Measurement of US mRNA may provide a more sensitive and persistent marker of residual viral replication in patients with undetectable plasma viremia by standard assays.

Commentary: I'm reprinting this abstract because it raises a couple of questions to me. The reservoir identified by Siliciano and so widely heralded by everyone as not capable of being reduced by therapy may be due to be replenished by ongoing replication not because a reservoir of virus sits in cells unaffected by therapy. It is this reservoir (latent HIV in memory CD4 cells) that many feel presents a major obstacle to eradication. Of course other reservoirs may also present obstacles to eradication. The notion that the Siliciano reservoir remains due to replenishment from ongoing viral replication is not a new notion. But has been mentioned repeatedly by all the researchers working on this subject including Ho, Siliciano and others. The suggestion has been made that if this reservoir is controlled by ongoing replication its possible that more potent therapy might succeed in stopping this ongoing replication. Just a thought. But a thought that I think David Ho has suggested.