Photodynamic sterilization of red cells and its effect on contaminating white cells: viability and mechanism of cell death

BACKGROUND: Phthalocyanines are useful sensitizers for photodynamic sterili zation of red cell concentrates. Various lipid-enveloped viruses can be ina ctivated with only limited red cell damage. Because white cells are in invo lved in the immunomodulatory effects of blood transfusions, the study of th e effect of photodynamic treatment on these cells is imperative. STUDY DESIGN AND METHODS: White cell-enriched red cell suspensions were pho todynamically treated with either the hydrophobic Pc4 (HOSiPcOSi-(CH3)(2)(C H2)(3)N(GH(3))(2)) or water-soluble aluminum phthalocyanine tetrasulfonate (AIPCS(4)) under virucidal conditions. Viability of white cell subpopulatio ns on Days 0, 1, and 4 after treatment was determined by fluorescence-activ ated cell sorting by flow cytometric analysis of propidium iodide uptake. A poptosis induction was studied by DNA ladder formation and staining for an early marker of apoptosis (annexin V). RESULTS: Treatment with Pc4 causes a significant decrease in cell viability of all white cells, as shown by prodidium iodide uptake. Monocytes and gra nulocytes are the most sensitive, and lymphocytes are relatively more resis tant. Some of the cells die by apoptosis, which is induced within 30 minute s after treatment. Treatment with AIPCS(4) damages only monocytes; other ce ll populations are not affected. CONCLUSIONS: Physicochemical properties of the photosensitizers partly dete rmine their effect on white cells. Differences in intracellular localizatio n are likely to be responsible for the effects observed.