Preferential S Phase Entry and Apoptosis of CD4+ T Lymphocytes of HIV-1-Infected Patients after in Vitro Cultivation

We have studied the relationship between spontaneous apoptosis and cell cycle perturbations in circulating peripheral blood lymphocytes of HIV-1-infected patients and healthy controls. PBMC obtained from HIV-1-infected patients and healthy controls were incubated in culture medium for 48 h. Cells were separated into CD4+ and CD8+ populations using immunomagnetic beads. Apoptosis and cell cycle phases were measured by propidium iodide staining and bromodeoxyuridine (BrdU) incorporation followed by flow cytometric analyses. In experiments using cells obtained from HIV-1-infected patients, spontaneous apoptosis was more frequent in CD4+ T lymphocytes than in CD8+ T lymphocytes (17.6% vs 9.5%, P < 0.005). Among healthy controls, spontaneous apoptosis in CD4+ and CD8+ T lymphocytes was comparable (4.5% vs 5.1%). Lymphocytes obtained from patients were more frequently in S phase than healthy controlsʹ cells (2.2 ± 0.9% vs 0.5 ± 0.2%, P < 0.002) and patientsʹ CD4+ cells tended to enter S phase more frequently than controlsʹ CD4+ cells (4.2% ± 3.5% vs 1.8% ± 0.5% P < 0.04), whereas the frequency of S phase CD8+ T cells was not different among patients (2.8% ± 2.9%) and controls (1.8% ± 0.5%) (P > 0.4). Kinetic analyses using BrdU and PI staining revealed that S phase cells were more likely to become apoptotic than resting (G0–G1) cells (28.4% ± 10.3% vs 11.3% ± 9.9% in patients, P < 0.04, and 15.3% ± 2.8% vs 1.8% ± 0.5% in controls, P < 0.003). Lymphocytes obtained from HIV-1-infected persons are activated in vivo to enter S phase and to undergo spontaneous apoptosis after brief in vitro cultivation. The present studies indicate that most apoptotic cells in this system are CD4+ and kinetic analyses reveal that S phase cells are more likely to undergo spontaneous apoptosis than G0–G1 cells. Accelerated cell death in HIV-1 disease may contribute to the failure of lymphocyte responsiveness to appropriate T cell receptor stimulation.