Precise Quantitation of the Latent HIV-1 Reservoir: Implications for Eradication Strategies

Abstract

The quantitative viral outgrowth assay (QVOA) provides a precise minimal estimate of the reservoir of resting CD4(+) T-cell infection (resting cell infection [RCI]). However, the variability of RCI over time during antiretroviral therapy (ART), relevant to assess potential effects of latency-reversing agents or other interventions, has not been fully described. We performed QVOA on resting CD4(+) T cells obtained via leukapheresis from 37 human immunodeficiency virus (HIV)-infected patients receiving stable suppressive ART for a period of 6 years. Patients who started ART during acute (n = 17) or chronic (n = 20) HIV infection were studied once HIV RNA levels were <50 copies/mL for ≥ 6 months. Using random effects analysis of 160 RCI measurements, we found that RCI declined significantly over time (P < .001), with an estimated mean half-life of 3.6 years (95% confidence interval, 2.3-8.1 years), remarkably consistent with findings of prior studies. There was no evidence of more rapid decay in acute versus chronic HIV infection (P = .99) for patients suppressed ≥ 6 months. RCI was reliably estimated with longitudinal measurements generally showing < 2-fold variation from the previous measure. When QVOA is performed in this format, RCI decreases of >6-fold were rare. We suggest that a 6-fold decline is a relevant threshold to reliably identify effects of antilatency interventions on RCI.

Keywords: HIV; IUPM; QVOA; RCI; SCA; latency.

Figure 1.

Decay of resting CD4⁺ T-cell infection in virally suppressed patients. Each data point represents an independent measurement. Each symbol/shape represents one patient. Blue symbols represent patients treated during acute human immunodeficiency virus (HIV) infection and red symbols those treated during chronic infection. Zidovudine (AZT) and didanosine (DDI) were the first line of therapy for 3 patients treated during chronic HIV infection. Abbreviation: IUPM, infectious units per million resting CD4⁺ T cells.

Figure 2.

Reproducibility of the quantitative viral outgrowth assay. Multiple independent measurements of resting cell infection (RCI) in 37 suppressed patients over time show the limited variability of the assay. RCI was reliably estimated with longitudinal measurements generally showing <2-fold variation from the previous measurement. Abbreviation: IUPM, infectious units per million resting CD4⁺ T cells.

Figure 3.

Correlation between low-level viremia (LLV) and the size of the resting CD4⁺ T-cell reservoir. In 26 patients for whom LLV measurements were available, Pearson's correlation was used in a univariate analysis to examine the relationship between mean single-copy assay (SCA) and infectious units per million resting CD4⁺ T cell (IUPM) values.