Efficiency of white cell filtration and a freeze-thaw procedure for removal of HIV-infected cells from blood

Leukocyte Reduction's Role in the Attenuation of Infection Risks among Transfusion Recipients

Despite advances in the screening of donated blood for infectious agents, the risk of transmitting viral, bacterial, and protozoal infections, as well as newly emerging diseases, via transfusion persists. A complementary approach is leukocyte reduction (LR), the removal of leukocytes from donated blood by filtration. Published evidence, establishing the benefit of LR in reducing the risk of febrile nonhemolytic reactions, cytomegalovirus transmission, and human leukocyte antigen alloimmunization has led to its use for some time for the care of immunosuppressed and other individuals considered to be at high risk for such complications. Recent literature suggests that LR may be effective in reducing the risk of transmission of a number of additional transfusion-transmitted infectious agents, including herpesviruses, retroviruses, bacteria, protozoa, and prions. There is also evidence that LR may reduce the risk of transfusion-related immunomodulation, further contributing to protection against infections that would complicate treatment. With the mounting evidence of potential benefit, a number of countries, as well as many hospitals and blood centers in the United States, have adopted a policy of performing LR for all donated blood. Physicians who care for immunosuppressed patients and those who are responsible for institutional infection-control practices should remain informed of the growing body of literature on LR.

Inactivation of pathogens in platelet concentrates by using a two-step procedure

BACKGROUND AND OBJECTIVES

Platelet concentrates are contaminated with residual leucocytes and may also be infected with viruses and bacteria. We investigated whether these pathogens can be inactivated by a two-step procedure comprising photodynamic treatment in the presence of the phenothiazine dye, thionine, followed by irradiation with ultraviolet light (UV-B, wavelength range 290-330 nm).

MATERIALS AND METHODS

Platelet concentrates were prepared from buffy coats. The concentrates were spiked with different viruses, bacteria and leucocytes, then illuminated with yellow light in the presence of thionine at dye concentrations between 1 and 5 microm and with UV-B at doses up to 2.4 J/cm2. The infectivity of samples and the viability of leucocytes were assayed before and after treatment. The influence of treatment on in vitro platelet function was also examined.

RESULTS

The inactivation of free viruses in platelet concentrates by photodynamic treatment with thionine/light was significantly enhanced when it was followed by irradiation with UV-B. The inactivation of leucocytes and of bacteria by UV-B was improved when it was preceded by thionine/light. Sterile platelet concentrates were prepared from buffy coats infected with Staphylococcus epidermidis. Platelet function and the storage stability of platelet concentrates were only moderately influenced by the two decontamination steps.

CONCLUSIONS

Photodynamic treatment in the presence of the phenothiazine dye, thionine, followed by low-dose UVB, has the potential to inactivate viruses, leucocytes and bacteria, which might contaminate platelet concentrates. Both treatments complement each other.

[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.

Blood transfusion in beta thalassaemia major

Conventional treatment of beta thalassaemia major is based on regular blood transfusion from early childhood. Maximum effectiveness of transfusion therapy depends on the following. (1) Availability of safe blood. Donation programmes should aim at retaining repeat donors, who carry decreased risk of transmitting blood-borne infections. Donors should be screened with laboratory tests performed to the highest possible standard of quality. Selection of safe donors can be improved by the adoption of questionnaires containing direct questions on risk factors for transfusion transmissible infections. (2) Use of good quality red blood cells, which should be leucodepleted, preferably by filtration, that can be carried out at the bedside. (3) Regular evaluation of blood transfusion indices, including mean level of haemoglobin maintained, annual blood requirement, daily haemoglobin fall, mean transfusion interval, transfusion reaction rate. This can be assisted by the use of a computerized patient record. (4) Maintenance of a permanent record of the patient's blood group genotype (including at least Rh, Kell, Kidd and Duffy systems) and any red cell antibodies that develop. This is mandatory to ensure optimal survival of transfused red cells. (5) Continuous monitoring of transfusion transmissible infections. (6) Vaccination against hepatitis B of all suitable patients. (7) Intensive iron chelation. This should be done by regular subcutaneous administration of desferrioxamine B. Oral chelators, which are currently under laboratory and clinical evaluation, are not yet available for general use.

Reducing the infectivity of blood components--what we have learned

The safety of the nation's blood supply has improved over the last several years as a result of more intensive donor screening and viral testing. Concurrently, there has been more judicious use of blood components. Although the risk is small, transmission of blood borne viruses, bacteria and parasites can occur. Investigators have studied a myriad of processes for pathogen depletion and/or inactivation, including the use of chemicals, extended storage, filtration, heating, irradiation, photochemicals and washing. Pasteurization, methylene blue and solvent-detergent processes have been introduced in parts of Europe for improving the safety of plasma used for transfusion. The FDA is reviewing a license application for the solvent-detergent process. For red cells, use of highly efficient leukodepletion filters is believed to be equivalent to antibody testing for the prevention of CMV disease transmission. Otherwise, no successful treatments have yet been identified for red cells or platelets. Several photochemicals, which may be useful for treating these components, are being studied. However, there appear to be trade-offs between the extent of pathogen inactivation, platelet or red cell damage, and genotoxicity. These as well as other biological parameters and operational issues will need to be further evaluated before implementation can be considered.

Loss of red blood cell viability associated with limited thermal inactivation of extracellular HIV-1

The effects of incubation at mildly elevated temperatures on HIV-1 inactivation and in vitro red blood cell properties were investigated. Red cells (55% Hct) were leukodepleted (3 log10) by filtration, maintained at 45 or 47 degrees C for 4 or 8 h, and then stored at 4 degrees C. Hemolysis was twice that of controls after 42-day storage for samples treated for 4 h at 45 degrees C, and five times larger for samples heated at 47 degrees C. There was also a significant increase in the rate of potassium loss, an early decrease in ATP levels, and an initial drop in pH for samples treated at either temperature. Larger differences were observed for samples exposed to these elevated temperatures for 8 h. Osmotic deformability curves obtained by ektacytometry showed dramatic decreases in red cell deformability at both temperatures and for both time periods. HIV-1 inactivation in red cells treated at 45 degrees C (approximately 0.25 log10/h) was considerably less than that obtained in tissue culture medium (1-2 log10/h). Since the decrease in red cell deformability is likely to indicate reduced red cell function and survival, and the rate of HIV-1 inactivation is low, mild heat treatment is not an adequate process for viral inactivation of red cell products.

Reduction of HTLV-I-infected cells in blood by leukocyte filtration

Leukocyte filtration was performed with HTLV-I-infected blood and with blood supplemented with cultured HTLV-I-transformed cells. Reduction of infectivity upon leukocyte filtration was determined by the polymerase chain reaction (PCR) using primers indicative for the HTLV-I-pol and tax genes. Two different commercially available filters were used: a column-shaped cellulose acetate and a flat-bed polyester filter. Both filters yielded reduction of at least 3 10logs for cultured HTLV-I-infected cells. When blood from HTLV-I-infected individuals was used for filtration, the number of infected cells was reduced by 1-3 10logs. Although filtered blood as yet cannot be regarded as safe, it is concluded that leukocyte filtration of HTLV-I-infected blood potentially contributes to reducing the spread of HTLV-I by blood transfusion.

Frozen blood and transfusion-transmitted hepatitis C virus

The purpose of the present study was to evaluate the impact of frozen red cell transfusion on the transmission of hepatitis C virus (HCV) before the introduction of blood donor screening. Anti-HCV antibodies were detected in 59 patients with sickle-cell disease who required chronic transfusions and had exclusively received frozen red blood cells (RBC). The files were reviewed for clinical signs of chronic hepatitis C. Anti-HCV antibodies were detected in 2 adult patients; both also had clinical evidence of HCV infection. No other patient showed signs of acute or chronic HCV hepatitis. In a control group of 28 patients who had received nonfrozen RBC transfusions, the prevalence of anti-HCV antibodies was 25%. So, our study seems to indicate that the use of frozen RBC had reduced the risk of HCV contamination.

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.

Asymmetric membrane filters for the removal of leukocytes from blood

As part of a study on the mechanisms of leukocyte filtration, the influence of pore size distribution on filter efficiency was investigated. Conventional leukocyte filters are not suitable for model studies, as these filters are composed of tightly packed synthetic fibers, with a poorly defined porous structure. Therefore, open cellular polyurethane membranes with pore size distributions varying from approximately 15 to 65 microns were prepared. Filtration experiments with stacked packages of these membranes showed that leukocytes are best removed (greater than 99%) by filters with a pore size distribution of 11-19 microns. These pore sizes approach the size of leukocytes (6-12 microns). However, due to fast clogging, blood flow through these filters is rapidly reduced, which results in a low filter capacity. With an asymmetric membrane filter, in which the pore size decreases from about 65 to 15 microns in the direction of blood flow, both moderate removal of leukocytes (greater than 80%) and maintenance of flow (approximately 0.2 mL/s) are obtained. This results in efficient leukocyte removal. From cell analysis of both filtrate and filter, it is concluded that adhesion rather than sieving is the major filtration mechanism. Thus, further optimization of the filter may be achieved by surface modification.