Spontaneous ex vivo apoptosis of peripheral blood mononuclear cells in patients with head and neck cancer

Abstract

Proportions of apoptotic (TUNEL+) peripheral blood mononuclear cells (PBMCs) were measured by flow cytometry in patients with head and neck cancer and normal controls at the time of blood draws (0 time) and after 24-h incubation. PBMCs were incubated at 37 degrees C in medium (spontaneous apoptosis) and in the presence of CH-11 antibody (anti-Fas) or tumor necrosis factor (TNF)-alpha, both capable of inducing DNA fragmentation in activated T cells expressing the TNF family of receptors. PBMCs obtained from the patients had significantly higher (P < 0.0001) proportion of apoptotic cells than PBMCs of controls at 0 time as well as after 24-h incubation. Ex vivo apoptosis included all subsets of PBMCs: CD3+ T cells, CD16+ CD56+ natural killer cells, CD19+ B cells, and CD14+ monocytes, as determined by two-color flow cytometry. However, T cells represented the largest PBMC subset undergoing apoptosis, and lymphocytes rather than monocytes were the major TUNEL+ PBMC population. Among T cells, the level of spontaneous ex vivo apoptosis was nearly as high as that of CH-11 antibody-induced or TNF-alpha-induced apoptosis, indicating that activated Fas+ and TNFR1+ T cells were preprogrammed in vivo to die. Also, elevated levels of spontaneous apoptosis at time 0 in patients with head and neck cancer (P < 0.0001) indicated that a higher fraction of PBMCs was undergoing apoptosis in vivo in patients than controls. Together, the data suggest that an increased rate of turnover of lymphocytes is associated with cancer and may be responsible for functional lymphocyte imbalance, even in treated patients who have no evident disease.