Subpopulations of long-lived and short-lived T cells in advanced HIV-1 infection

Abstract

Antigenic stimulation of T cells gives rise to short-lived effector cells and long-lived memory cells. We used two stable isotope-labeling techniques to identify kinetically distinct subpopulations of T cells and to determine the effect of advanced infection with HIV-1. Long-term deuterated water (2H2O) incorporation into DNA demonstrated biphasic accrual of total and of memory/effector (m/e)-phenotype but not naive-phenotype T cells, consistent with the presence of short-lived and longer-lived subpopulations within the m/e-phenotype T cell pool. These results were mirrored by biphasic die-away kinetics in m/e- but not naive-phenotype T cells after short-term 2H-glucose labeling. Persistent label retention was observed in a subset of m/e-phenotype T cells (presumably memory T cells), confirming the presence of T cells with very different life spans in humans. In advanced HIV-1 infection, much higher proportions of T cells were short-lived, compared to healthy controls. Effective long-term anti-retroviral therapy restored values to normal. These results provide the first quantitative evidence that long-lived and quiescent T cells do indeed predominate in the T cell pool in humans and determine T cell pool size, as in rodents. The greatest impact of advanced HIV-1 infection is to reduce the generation of long-lived, potential progenitor T cells.

Figure 1

In vivo stable isotope labeling protocols. (a) Long-term ²H₂O administration. ²H₂O was given daily for 9 weeks after a priming regimen. T cells and monocytes/granulocytes were sampled at times shown. Urine and saliva were sampled as shown, to measure body ²H₂O enrichment. (b) ²H₂-glucose incorporation/die-away curves. ²H₂-glucose was given over 48 hours with follow-up blood draws for T cells as shown. Blood glucose enrichments were measured during the i.v. ²H₂-glucose infusion. Mono/granulo, monocytes/granulocytes; Glc, glucose. Arrows indicate times of stable isotope label administration or sample collection.

Figure 2

Time course of long-term oral ²H₂O label incorporation into CD4⁺ and CD8⁺ T cell DNA in different groups. (a) Time course of fractional synthesis of T cell DNA in different clinical groups. f, fractional synthesis or percent newly divided cells present, as described in Results. (b) ²H₂O enrichment in body water. ²H₂O was given as an initial loading dose on day 0 then given daily for 9 weeks by mouth. Urine and saliva were collected weekly and ²H₂O enrichment was measured by GC/MS (10, 22). (c) ²H-enrichment in blood monocytes/granulocytes (average for group as a whole). (d) Summary of phase I and phase II T cell proliferation during long-term ²H₂O incorporation in the three groups: healthy controls, untreated HIV-1/AIDS, and LT ARV therapy. *P < 0.05 vs. normal controls; **P < 0.05 vs. HIV-1/AIDS. Number of subjects shown above bars. Data shown are mean ± SD.

Figure 3

Time course of label die-away after intravenous ²H-glucose incorporation into CD4⁺ and CD8⁺ T cell DNA in different groups. (a) Representative ²H-glucose incorporation/decay curves in CD4⁺ T cell DNA. A healthy HIV-1 seronegative control subject (top panels) and an HIV-1/AIDS subject (bottom panels) are shown. Persistently labeled m/e-phenotype cells presumably represent true memory T cells; cells that die-away in phase I presumably represent short-lived, effector-type T cells. (b) Mean values of fractional die-away of labeled CD4⁺ and CD8⁺ T cells after pulse i.v. ²H-glucose administration in HIV-1–seronegative controls (n = 12), untreated HIV-1/AIDS (n = 13), and long-term effective ARV therapy (LT ARV) (n = 10). The fractions of labeled cells remaining after phase I die-away (through week 3 after label administration) and phase II die-away (through weeks 5–7), both compared with peak labeling, are shown. *P < 0.05 vs. controls. **P < 0.05 vs. phase I die-away (by paired t test).

Figure 4

Calculations regarding production rates and pool sizes of kinetically distinct subpopulations of CD4⁺ T cells, with comparison between healthy control subjects and advanced HIV-1/AIDS patients. Basis of quantitative estimations is described in Results. An average CD4⁺ T cell count of 1000 cells/μl (healthy controls) and 300 cells/μl (HIV-1/AIDS) was used in the calculations. (a) Daily production rates of kinetically distinct subpopulations (cells/μl/day). (b) Pool sizes of kinetically distinct subpopulations (cells/μl).