Measuring Recent Thymic Emigrants in Blood of Normal and HIV-1–Infected Individuals before and after Effective Therapy

Abstract

The role of the thymus in HIV-1 pathogenesis remains unclear. We developed an assay to quantify the number of recent thymic emigrants in blood based on the detection of a major excisional DNA byproduct (termed α1 circle) of T cell receptor rearrangement. By studying 532 normal individuals, we found that α1 circle numbers in blood remain high for the first 10–15 yr of life, a sharp drop is seen in the late teen years, and a gradual decline occurs thereafter. Compared with age-matched uninfected control individuals, α1 circle numbers in HIV-1–infected adults were significantly reduced; however, there were many individuals with normal α1 circle numbers. In 74 individuals receiving highly active antiretroviral therapy, we found no appreciable effect on α1 circle numbers in those whose baseline values were already within the normal range, but significant increases were observed in those with a preexisting impairment. The increases in α1 circle numbers were, however, numerically insufficient to account for the rise in levels of naive T lymphocytes. Overall, it is difficult to invoke thymic regenerative failure as a generalized mechanism for CD4 lymphocyte depletion in HIV-1 infection, as α1 circle numbers are normal in a substantial subset of HIV-1–infected individuals.

T cell responses to highly active antiretroviral therapy defined by chemokine receptors expression, cytokine production, T cell receptor repertoire and anti-HIV T-lymphocyte activity

“…The faster increase in CD4 1 naive cells observed herein could be explained by a lesser HIV-induced blockade of T cell renewal occurring in patients with moderate immunodeficiency as well as to a more preserved thymic tissue [24]. In addition, other mechanisms such as the peripheral expansion of naive lymphocytes or the reversion of phenotype from memory cells have been invoked to explain the increase of naive cells during HAART, as recently proposed by Zhang et al [25] showing that the thymic output, evaluated by measuring the TCR excisional circles (TRECs), does not enterely account for the HAART-induced rise in naive cells.…”

Changes in thymus volume in adult HIV-infected patients under HAART: correlation with the T-cell repopulation

“…New tools have been recently developed to better assess thymus function. Using a molecular marker of recent thymic emigrants, a DNA circle from the T-cell rearrangement process named TREC [8], an increase in naïve T-cells carrying this circle after HAART has been described [9]. Another approximation to assess the thymus role in HIV-1 infected patients would be the evaluation of thymic volume by computed tomography (CT).…”

The CD16+ Monocyte Subset Is More Permissive to Infection and Preferentially Harbors HIV-1 In Vivo

“…Real-time PCR quantification of HIV-1 DNA was used for two of six in vitro infection experiments with HIV-1 Ba-L and for the comparison of HIV-1 copy numbers in cell populations by amplification of a conserved region of HIV-1 gag-5ЈLTR using the primers SL19 and SL20 and the beacon SL30 as described previously (53,54). Standard curves were generated using known numbers of ACH2 cells, which contain one integrated HIV-1 copy per cell in a HIV-1-negative PBMC background.…”

“…For each experiment, cell numbers were standardized by real-time PCR for the CCR5 gene using the primers LK46 and LK47 and the beacon LK155 as previously described (53) or iQ SYBR Green Supermix (Bio-Rad) in selected experiments. Real-time PCR quantification of HIV-1 DNA was used for two of six in vitro infection experiments with HIV-1 Ba-L and for the comparison of HIV-1 copy numbers in cell populations by amplification of a conserved region of HIV-1 gag-5ЈLTR using the primers SL19 and SL20 and the beacon SL30 as described previously (53,54).…”