Update on pathogen reduction technology for therapeutic plasma: an overview.

Human plasma for therapeutic use, besides having optimal viral safety, must contain optimal levels of all coagulation factors and protease inhibitors to be clinically effective. Several new technologies for pathogen reduction of plasma (PRT) exist and are entering the stage of clinical testing. The main objective of this overview is to provide an update on the current states of three promising photoactive technologies that target pathogen nucleic acid for pathogen inactivation, applicable to single unit fresh-frozen plasma (FFP) and to highlight the experiences gained with classical pathogen reduction of pooled plasma using solvent-detergent (SD) treatment. It should be emphasized that none of the currently applied methods inactivate all types of pathogens and all have some effect on plasma quality when compared to fresh-frozen plasma. Pooled SD-plasma is the best documented clinical product, followed by methylene blue light treated (MBLT)-plasma. Recently, Psoralen light treated (PLT)-plasma has been introduced (CE-marked product in Europe) while Riboflavin light treated (RLT)-plasma is still under development. In principal, PRT for plasma not only differs in terms of the spectrum and log of pathogen reduction potential, but also in respect to the physicochemical/biological characteristics, and profiles of the adverse reactions, particularly in vulnerable patient groups. Therefore, an additional practical step such as oil extraction followed by chromatography to remove the solvent/detergent, and filtration or the use of some special absorbing matrix is required to reduce the residual photosensitive chemicals, their metabolites and photo adducts. This is required to improve the safety margin of the final product. Moreover, while it may be convenient to think that a combined pathogen reduction technology could improve the spectrum of known pathogens to be inactivated, one needs, in practice, to balance between the degree of pathogen reduction and the loss of some plasma protein activity. From the quality point of view, SD-plasma is a pooled standardized pharmaceutical product with extensive in-process control. However, both differences in production processes and the plasma source can influence final product quality. On the other hand, single unit plasma derived from nucleic acid PRT cannot be monitored by pharmaceutical process control and demonstrates the wide range of concentrations normally observed for plasma proteins. Pooling has the disadvantage that one single plasma unit can contaminate a whole pool, but this can be offset by several advantages that pooling and the SD process offer. Among these are reduction of a possible pathogen load by dilution and by neutralizing antibodies in the plasma pool, dilution and possible neutralization of antibodies and allergens which essentially eliminates transfusion-related acute lung injury (TRALI) and reduces allergic reactions significantly, removal of residual blood cells, cell fragments and bacteria, and removal of the largest von Willebrand-factor (vWF) molecules. On the other hand, some streamlining is required for technologies using single units of plasma, such as the use of plasma from male non-transfused donors to reduce TRALI and to avoid the O blood group in order to meet current specifications for FFP [Seghatchian J. What is happening? Are the current acceptance criteria for therapeutic plasma adequate? Transfus Apheresis Sci 2004; 31:67-79], and to exploit the potential benefit to inactivate residual lymphocytes and prevent transfusion-associated graft versus host disease. The cost effectiveness of pathogen inactivation is very low (> 2 million US dollar/life year saved), if however, non-infectious complications such as TRALI are taken into account; the cost for SDP is reduced to < 50,000 British pound/life year saved for those 48 years. Finally, from the therapeutic standpoint, two important questions still remain to be answered. First, whether the various pathogen reduced plasma products are clinically interchangeable and second, whether the conventional quality requirements of FFP are still adequate for the newer plasma products. These questions can only be answered by a head to head comparison, followed by large-scale clinical trials.