The dynamic basis for T-cell depletion in late-stage HIV-1 disease remains controversial. Using a new, non-radioactive, endogenous labeling technique, we report direct measurements of circulating T-cell kinetics in normal and in HIV-1-infected humans. In healthy, HIV-1-seronegative subjects, CD4+ and CD8+ T cells had half-lives of 87 days and 77 days, respectively, with absolute production rates of 10 CD4+ T cells/microl per day and 6 CD8+ T cells/microl per day. In untreated HIV-1-infected subjects (with a mean CD4 level of 342 cells/microl), the half-life of each subpopulation was less than 1/3 as long as those of healthy, HIV-1-seronegative subjects but was not compensated by an increased absolute production rate of CD4+ T cells. After viral replication was suppressed by highly active antiretroviral therapy for 12 weeks, the production rates of circulating CD4+ and CD8+ T cells were considerably elevated; the kinetic basis of increased CD4 levels was greater production, not a longer half-life, of circulating cells. These direct measurements indicate that CD4+ T-cell lymphopenia is due to both a shortened survival time and a failure to increase the production of circulating CD4+ T cells. Our results focus attention on T-cell production systems in the pathogenesis of HIV-1 disease and the response to antiretroviral therapy.

The mechanism of CD4+ T cell depletion in human immunodeficiency virus (HIV)-1 infection remains controversial. Using deuterated glucose to label the DNA of proliferating cells in vivo, we studied T cell dynamics in four normal subjects and seven HIV-1–infected patients naive to antiretroviral drugs. The results were analyzed using a newly developed mathematical model to determine fractional rates of lymphocyte proliferation and death. In CD4+ T cells, mean proliferation and death rates were elevated by 6.3- and 2.9-fold, respectively, in infected patients compared with normal controls. In CD8+ T cells, the mean proliferation rate was 7.7-fold higher in HIV-1 infection, but the mean death rate was not significantly increased. Five of the infected patients underwent subsequent deuterated glucose labeling studies after initiating antiretroviral therapy. The lymphocyte proliferation and death rates in both CD4+ and CD8+ cell populations were substantially reduced by 5–11 weeks and nearly normal by one year. Taken together, these new findings strongly indicate that CD4+ lymphocyte depletion seen in AIDS is primarily a consequence of increased cellular destruction, not decreased cellular production.

We describe here a method for measuring DNA replication and, thus, cell proliferation in slow turnover cells that is suitable for use in humans. The technique is based on the incorporation of 2 H2O into the deoxyribose (dR) moiety of purine deoxyribonucleotides in dividing cells. For initial validation, rodents were administered 4% 2 H2O in drinking water. The proliferation rate of mammary epithelial cells in mice was 2.9% per day and increased 5-fold during pregnancy. Administration of estradiol pellets (0 -200 g) to ovariectomized rats increased mammary epithelial cell proliferation, according to a doseresponse relationship up to the 100 g dose. Similarly, proliferation of colon epithelial cells was stimulated in a dose-response manner by dietary cholic acid in rats. Bromodeoxyuridine labeling correlated with the 2 H2O results. Proliferation of slow turnover cells was then measured. Vascular smooth muscle cells isolated from mouse aorta divided with a half-life in the range of 270 -400 days and die-away values after 2 H2O wash-out confirmed these slow turnover rates. The proliferation rate of an adipocyte-enriched fraction from mouse adipose tissue depots was 1-1.5% new cells per day, whereas obese ad libitum-fed ob͞ob mice exhibited markedly higher fractional and absolute proliferation rates. In humans, stable long-term 2 H2O enrichments in body water were achieved by daily 2 H2O intake, without toxicities. Labeled dR from fully turned-over blood cells (monocytes or granulocytes) exhibited a consistent amplification factor relative to body 2 H2O enrichment (Ϸ3.5-fold). The fraction of newly divided naive-phenotype T cells after 9 weeks of labeling with 2 H2O was 0.056 (CD4 ؉ ) and 0.043 (CD8 ؉ ) (replacement rate <0.1% per day). In summary, 2 H2O labeling of dR in DNA allows safe, convenient, reproducible, and inexpensive measurement of cell proliferation in humans and experimental animals and is well suited for slow turnover cells. deuterated water ͉ cell proliferation ͉ DNA synthesis ͉ adipogenesis ͉ vascular smooth muscle cell proliferation