Photodynamic sterilization of cellular blood products

The inactivation of viruses in cellular blood products is a relatively new application of photodynamic treatment. This reviews will give an overview of results obtained on this subject at the departments of Molecular Cell Biology and Immunohematology & Bloodbank, Leiden University Medical Center, Leiden, The Netherlands. The crucial factor in the sterilization of blood products is the quality of the different cellular components. Therefore an extensive study into the shelf-life of photodynamically-treated red blood cell suspensions was performed. Also variations in the treatment and storage protocol were evaluated for their contribution to the preservation of the red blood cells. Besides excisting protocols, also a new series of photosensitizers was assayed. Two sensitizers from this series, nicknamed Sylsens A and B, showed efficient virucidal activity with only very limited damage to red blood cells. Since RBCC contain a certain number of leukocytes, which are involved in the immunomodulative effects of blood transfusions, it is important to assess the effect of photodynamic treatment on these cells. Therefore, the viability and the mechanism of cell death of the various leukocyte subpopulations after virucidal treatment with different photosensitizers were determined. It has been shown that both the efficacy and the specificity of a photodynamic treatment can be influenced by the fluence rate used during illumination. A photochemical study into this phenomenon and its potential use in sterilization of RBCC was performed. For different reasons, identification of the viral targets for photodynamic treatment is important: it will contribute to the search for optimal inactivation conditions with respect to sensitizer properties and illumination protocols, and furthermore it is necessary for validation of the inactivation protocol. The primary targets for the inactivation of the lipid-enveloped Vesicular Stomatitis Virus by a hydrophilic and a hydrophobic photosensitizer were determined.