Investigation of annexin V binding to lymphocytes after extracorporeal photoimmunotherapy as an early marker of apoptosis.

Background: Induction of programmed cell death is assumed to be a possible effect of extracorporeal photoimmunotherapy (ECPI).

Objective: In the present study lymphocytes of patients with cutaneous T cell lymphoma undergoing ECPI were investigated for early apoptotic events.

Methods: Annexin V, known for its selective affinity to phospholipids, was used to detect early phases of apoptosis. Simultaneous staining with propidium iodide binding to DNA allowed detection of late apoptotic/necrotic cells.

Results: At 1 h after ECPI, an increase in early apoptotic cells was found indicating a direct effect of ECPI. At 20 h after each ECPI session, a delayed increase in the number of apoptotic lymphocytes was observed in early apoptotic annexin-stained cells and in late apoptotic cells, whereas in nonirradiated cells no remarkable changes were found. Apoptosis was confirmed by altered light scattering properties and DNA fragmentation.

Conclusion: The apoptotic cell death of reinfused lymphocytes is supposed to be a therapeutic effect of ECPI.