Hydroxyurea exerts an anti-proliferative effect on T cells but has no direct impact on cellular activation

Abstract

Hydroxyurea (HU) is a cytostatic drug which has been used as an anti-HIV agent due mainly to its synergistic activity when combined with certain anti-retrovirals. In addition, HU might have a beneficial effect on parameters involved in the pathogenesis of HIV infection, such as immune activation. To test this hypothesis, the effect of HU on T cell proliferation and T cell activation, as well as the potential association between these two phenomena, were examined in an in vitro model. HU exerted a dose-dependent anti-proliferative effect on T cells, and modulated the expression of different activation markers. In cells exposed to HU, expression of CD25 and CD38 diminished in a dose-dependent manner, whereas expression of CD69 increased. However, when the expression of these markers was examined separately on proliferating and non-proliferating lymphocytes, HU did not exert any significant effect. Thus, the effect of HU on T cell activation is not direct and seems to be mediated through its effect on T cell proliferation.

Fig. 1

Effect of hydroxyurea (HU) upon the proliferative ability of lymphocytes in response to phytohaemagglutinin stimulation, as evaluated by carboxyfluorescein succinimidyl ester staining (left graph) and by [³H]-thymidine uptake (right graph). Each point on the graphs represents the mean value of at least three different experiments. ¶P < 0·05 for the difference with respect to HU 0.

Fig. 2

Effect of hydroxyurea (HU) on the expression of activation markers CD25 and CD69 by T cells at different time-points after phytohaemagglutinin stimulation: day 1 (•), day 2 (▪) and day 3 (○). Each point on the graphs represents the mean value of at least three different experiments. *P < 0·05 for the difference with respect to HU 0 at day 2. ¶P < 0·05 for the difference with respect to HU 0 at day 3.

Fig. 3

Effect of hydroxyurea (HU) on the expression of activation markers CD25, CD69 and CD38 by T cells at different time-points after phytohaemagglutinin stimulation: day 3 (•), day 5 (▪), day 7 (○) and day 10 (□). Each point on the graphs represents the mean value of at least three different experiments. ¶P < 0·05 for the difference with respect to HU 0.

Fig. 4

Effect of hydroxyurea (HU) on the expression of activation markers CD25, CD69 and CD38 by T cells at different time-points after phytohaemagglutinin stimulation. HU was added to the culture at day 0 (•), day 1 (▪) or day 2 (○) and the expression of activation markers measured at day 3. Additionally HU was added at day 3 (□) and the analysis was carried out at day 7. ¶P < 0·05 for the difference with respect to HU 0.

Fig. 5

Relationship between T cell proliferation and activation. Left column: effect of cell division of small (•) and large (○) T cells on the expression of activation markers CD25, CD69 and CD38 after 3 days of phytohaemaglutinin (PHA) stimulation. Middle and right columns: effect of hydroxyurea (HU) on the expression of activation markers CD25, CD69 and CD38 by T cells after PHA stimulation in small (middle) and large (right) cells, non-dividing (•) or dividing (○) once. ¶P < 0·05 for the difference with respect to 0 divisions in the left column or with respect to HU 0 in the middle and right columns.