Increased apoptosis of circulating T cells in myelodysplastic syndromes.

The mechanism of T cell lymphopenia in myelodysplastic syndromes (MDS) is unknown. We investigated apoptosis in freshly isolated and cultured lymphocytes; the latter were used to detect cells not yet apoptotic but destined for apoptosis. Apoptosis increased in both fresh and cultured T cells in MDS compared with those from healthy controls. Furthermore, in lymphopenic MDS patients the lymphocyte count correlated negatively with the degree of T cell apoptosis. MDS T cells showed increased Fas expression. However, in MDS but not in controls, the degree of T cell apoptosis was independent of the Fas expression level, and exogenous anti-Fas antibodies did not modulate T cell apoptosis. Mechanisms other than the Fas-Fas ligand pathway may induce T cell apoptosis in MDS.