[Post-transfusional cytomegalovirus infections: incidence and methods of prevention. CMV group of SNTS]

[Evolution of techniques for preparation of labile blood products (LBP): pathogen inactivation in LBP]

The techniques for inactivation of pathogens in labile blood products (LBP) would appear to be the new strategy which will permit us to increase transfusion safety in the face of the risks of transmission of pathogenic agents by LBP. Various methods are in the course of development or already validated and used in France. The latter only apply however to plasma or platelet concentrates. The mechanisms of action and the efficacy of inactivation and attenuation of pathogenic agents vary with the different techniques. Each of these constitutes a preparative procedure composed of unit steps which have to be fully mastered in order to ensure the quality and transfusion efficacy of the treated product.

[Viral attenuation of labile blood products]

Viral inactivation is one of the possibilities to reduce the residual risk of blood products. It is now applied to all plasma derived products (PDP). Application of such techniques to labile blood products (LBP) is difficult for two main reasons: any method should inactivate cell-associated viruses and should avoid any injury of the cells constituting the active ingredient. Physical techniques may reduce the viral content of cellular BPL (leucodepletion, washing, gamma irradiation), but none of them is active enough to comply with the present requirements for efficacy. An important work has been dedicated to the development of virus photoinactivation techniques. They consist of the addition of a photoreagent followed by illumination at an appropriate wavelength which results in a photochemical reaction responsible for the viral inactivation. Treatment of platelet concentrates by psoralen derivatives and UV-A illumination significantly inactivate in vitro enveloped and naked viruses, free and cell-associated viruses and also sequences integrated in the viral genome. Recent progresses have led to these results without detectable functional alteration of platelets and mutagenicity. Viral inactivation of red blood cells yet did not reach the same level because hemoglobin does not allow the use of the photoreagent compounds applicable to platelet concentrates. Viral decontamination of fresh frozen plasma by solvent and detergent, active on enveloped viruses, has been used in France since 1992. Other techniques of comparable efficacy, have received an agreement in other countries. The research on viral inactivation of LBP could prove to be of great importance in the near future in bringing additional safety to patients not only for the residual viral risk but maybe also for the residual bacterial risk of LBP.

[Leukocyte depletion of blood products and post-transfusion infections]

The transmission of unwanted infection agents to patients, through white blood cells, in blood products is now well established. Therefore the leukodepletion procedure undertaken in blood banks is justified. Leukodepletion prior to transfusion prevents the transmission of leukocyte-associated viruses such as CMV, EBV and HTLV 1 and 2 of viruses present both in plasma and inside leukocytes such as HTLV 1 and 2 viruses and B 19 parvovirus. The mechanism of the immunosuppressive effect of transfusion is still uncertain. The risks of transmitting bacterial diseases through blood transfusions is also a well-known source of concern, particularly the transmission of Yersinia Enterocolitica. However such an event seems to be prevented through leukocyte depletion by filtration when these procedures are performed after a hold of whole blood at 22 degrees C for 6 to no longer than 24 hours. Leukocyte-free blood components prepared by filtration may have a sufficiently reduced rate of infection to provide adequate prophylaxis. In any case the final number of leukocytes should be < or = 10(6) per unit of blood product. Leukocyte filtration must be performed before the onset of a disintegration process of granulocytes.