HIV Burden in Blood and Tissue Are Correlated With Each Other

Abstract and Introduction

Objectives: To determine the levels of residual HIV DNA and RNA in blood and gut reservoirs in aviremic patients, assess correlations among compartmental measurements of HIV burden, and evaluate association with clinical parameters.
Design: Cross-sectional analysis of baseline data only, on 40 patients enrolled in phase II study evaluating efficacy of autologous gene-modified CD4+ and CD8+ T cells. All patients were on stable antiretroviral regimen with undetectable plasma HIV RNA (< 50 copies/ml).
Methods: Measurements repeatedly performed over 8-12 weeks pre-intervention: blood HIV DNA, analysis of rectal mucosa-associated lymphoid tissue for both HIV RNA and HIV DNA, and quantitative co-culture of HIV from CD8-depleted peripheral blood mononuclear cells (PBMC).
Results: Quantifiable levels of HIV detected in compartments despite undetectable levels of plasma HIV RNA: HIV co-culture of PBMC (88%), blood HIV DNA (95%), rectal biopsy HIV DNA (95%), rectal biopsy HIV RNA (65%). A significant correlation existed among various measures of HIV burden (HIV co-culture, blood HIV DNA, rectal biopsy HIV RNA and DNA) but not between assays and clinical parameters [duration of highly active antiretroviral therapy (HAART), type of HAART]. All assays had comparable or less variability than in plasma viral load assays; HIV co-culture had the highest coefficient of variability whereas the blood HIV DNA assay had the lowest and was considered the most reliable assay.
Conclusions: The data support safety, feasibility and high compliance of quantifying reservoirs of residual HIV in treated subjects with undetectable plasma HIV RNA. Lack of correlation between levels of HIV in residual reservoirs and duration of HAART suggests treatment-mediated viral suppression alone does not lead to reproducible decay in HIV reservoirs.

Using highly active antiretroviral therapy (HAART), it is now possible to reduce plasma HIV-1 RNA to undetectable levels.^[1] In addition to the pronounced effect on HIV-1 viremia, clinical trials have now shown that combination antiretroviral therapy (ART) delays disease progression and prolongs life.^[2,3] Although healthy, asymptomatic patients with normal levels of CD4+ T cells often have low levels of plasma viral RNA, active viral replication and T-cell turnover is still present in lymph nodes.^[4,5] Recent studies have demonstrated that viable, replication-competent virus persists for at least 2 years in the face of HAART, despite complete suppression of HIV-1 RNA in blood and in some cases, lymphoid tissue.^[6,7,8] Assays to detect HIV-1 RNA and DNA levels in lymphoid tissue have recently been described and these assays can now be used to follow the status of HIV infection in these tissues.^[9,10,11,12] What has not been clarified is the degree to which quantified levels of virus in compartments correlate with and possibly predict clinical status and whether these measures may function as surrogate markers in clinical trials and/or care.

As the gut is the largest lymphoid organ in the body and a known reservoir for HIV, it is reasonable to investigate this compartment as a readily accessible source of lymphoid tissue in subjects with undetectable plasma viral load. The interest in quantifying viral burden of gastrointestinal-associated lymphoid tissue (GALT) HIV RNA and HIV DNA is compounded by the enhanced vulnerability to HIV infection of lymphocytes at this site compared to circulating peripheral blood mononuclear cells (PBMC)^[13,14] based on activation state, memory phenotypes, expression of HIV coreceptors, and increased levels of soluble inflammatory mediators (e.g. tissue chemokines).^[15]

We have recently completed a phase II study to evaluate the efficacy of autologous CD4-zeta gene-modified CD4+ and CD8+ T cells in HIV-infected subjects with undetectable plasma HIV RNA (< 50 copies/ml) and CD4+ cell counts > 200 10⁶ cells/l on HAART for > 6 months.^[16] Such subjects have been estimated to have a total body load of latently infected CD4+ T cells with replication-competent HIV of < 10⁷ cells.^[11] The virologic endpoints of the trial focused on quantitation of reservoirs of HIV-infected cells in blood and lymphoid (mucosal) tissues before and after cell infusions and is reported elsewhere.^[16] Assays at baseline and throughout the trial included measurement of HIV DNA in blood, analysis of rectal mucosa-associated lymphoid tissue for changes in viral burden (both HIV RNA and HIV DNA), and quantitative co-culture of HIV from CD8-depleted PBMCs using an enhanced limiting dilution co-culture assay.^[6]

We now report the results from baseline, steady-state, quantitative measurements of HIV burden using five assays in blood and gut compartments. Our primary objective in this analysis was to assess the relationship between viral burden in a variety of long-lived cellular reservoirs, and to describe the relationship between virus burden and clinical status (years of HIV infection, duration of antiviral therapy and CD4+ cell count). Our secondary objective was to determine the feasibility of using novel assays for measuring outcome in patients without detectable plasma viremia.

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