Viral inactivation and reduction in cellular blood products.

Even though the risks associated with the transfusion of blood products are lower than ever before, considerable efforts are being employed to improve the safety of the blood supply. Based upon available data, a six log (99.9999%) reduction in virus level from screened and tested blood components should significantly reduce or eliminate the risk of post-transfusion infection. The objective has been to identify "generic" methods, that is, one that would be applicable to all virus. For red cells, physical and chemical approaches have been studied; for platelets, the approaches have been limited to chemical. The physical methods include depletion of leukocytes by filtration, removal of plasma by washing, and viral inactivation by heat. Among the chemicals investigated to inactivate or help displace virus are ozone, detergents, and hypochlorous acid. Several photochemicals have also received intensive investigation: merocyanine 540, a benzoporphyrin derivative, aluminum phthalocyanine, and methylene blue. For platelets, photochemical inactivation methods using merocyanine 540, and two psoralen derivatives, 8-methoxypsoralen (8-MOP) and aminomethyl trimethyl psoralen (AMT), have also been studied. Approaches which include washing are not suitable. For the most part, either viral removal or inactivation has been insufficient, or red cell or platelet damage unacceptable. However, there are a few indications that at least inactivation of a specific virus, such as HIV, may be possible without major cell damage. These studies are in their early stages and significant work remains. If feasibility is clearly shown in vitro, it is likely that in vivo primate studies to demonstrate safety and efficacy will be required.