Poly(ethyleneimine) modified filters for the removal of leukocytes from blood

An in vitro system for testing leucocyte and leukaemic cell line adhesion to synthetic fibres

Leucocyte adhesion is an important phenomenon in antimicrobial defence, inflammation and immunological mechanisms and has been shown to be dependent upon specialized adhesion molecules. To prevent side-effects related to blood transfusion (e.g. anti-human leucocyte antigen immunization and transmission of infectious agents) leucocyte reduction of blood products is now systematically performed in various countries. The most common system used for leucoreduction is blood filtration. For further understanding of the mechanisms responsible for the interaction between leucocytes and the fibres present in filters we used a flow chamber to study the adhesion of leucocytes and leukaemic cell lines to different types of fibre. Adhesion was quantified using video-microscopy and computer image analysis. Our results demonstrate that adhesion to filter fibres was dependent on the expression of beta2-integrins CD11--CD18 and was inhibited by anti-CD18. The amount of fibres present, their spatial arrangement and the physicochemical characteristics of the fibres were important factors in leucocyte adhesion. Leucocyte adhesion was the highest to polyethylene terephthalate (PET) and polyimide fibres. Lymphocytes or lymphocytic cell lines were poorly adherent to PET fibres. The retaining capacity of leucocyte filters can be improved by taking into account the different parameters for the design of new filters

Six filters for the removal of white cells from red cell concentrates, evaluated at 4 degrees C and/or at room temperature

BACKGROUND

Six filters were tested for their ability to remove white cells from buffy coat-depleted red cell concentrates at various temperatures.

STUDY DESIGN AND METHODS

Cellselect FR, BPF4, and Sepacell filters were tested at both room temperature (RT) and 4 degrees C. The Leucoflex filter was tested only at 4 degrees C, while the Cellselect Optima Plus and Imugard filters were tested only at RT. Donor-dependent differences were excluded by pooling and subsequently dividing 9 red cell concentrates; 12 sets of experiments were performed.

RESULTS

With all filters, red cell concentrates containing <5 x 10(6) white cells per unit were obtained. The lowest numbers of residual white cells were achieved with the Leucoflex (at 4 degrees C, 0.15 +/- 0.11 x 10(6), the Sepacell (at 4 degrees C, 0.23 +/- 0.14 x 10(6), the Imugard (at RT, 0.24 +/- 0.14 x 10(6), and the BPF4 (at 4 degrees C, 0.25 +/- 0.24 x 10(6); differences not significant). With the Cellselect FR, filtration at 4 degrees C resulted in 0.86 +/- 0.37 x 10(6) white cells per unit, a level not significantly different from that obtained with the BPF4 and Sepacell filters at RT (1.16 +/- 0.43 x 10(6) and 0.80 +/- 0.36 x 10(6) white cells, respectively). Filtration at RT with the Cellselect FR and Cellselect Optima Plus resulted in red cell concentrates with 1.79 +/- 0.69 x 10(6) and 2.29 +/- 0.69 x 10(6) white cells, respectively (p<0.01).

CONCLUSION

All filters conformed to the current standards for white cell reduction; the process was less efficient at RT than at 4 degrees C. For routine application, the composition of the red cell concentrate, the temperature, and logistic preferences should be taken into account in the final choice of filter; before implementation, the chosen filter must be validated under routine conditions.

Improved removal of white cells with minimal platelet loss by filtration of apheresis platelets during collection

BACKGROUND

Filtration of apheresis platelets to remove white cells (WBCs) requires operator intervention after the collection procedure (postcollection filtration), which may cause variable and unsatisfactory filter performance (WBC removal and platelet loss). The MCS+ LN9000 apheresis system filters platelets through a WBC-reduction filter during each collection cycle (continuous filtration) at a flow rate of 15 to 25 mL per minute. Apheresis platelets obtained by continuous filtration were evaluated in terms of platelet loss, WBC removal, and platelet storage properties and then were compared to unfiltered apheresis platelets and to apheresis platelets that underwent postcollection filtration. Two WBC-reduction filters were tested (LRF6 and LRFXL).

STUDY DESIGN AND METHODS

In 70 apheresis platelets, postcollection filtration was performed by using the LRF6 at flow rates of 80 mL per minute (n = 30) and 50 mL per minute (n = 30) and the LRFXL at 50 mL per minute (n = 10). One hundred fifty-eight apheresis platelets underwent continuous filtration through the LRF6 (n = 58) or the LRFXL (n = 100). Unfiltered apheresis platelets (controls) (n = 30) were obtained by the same collection protocol.

RESULTS

Estimated platelet loss with continuous filtration was 7 percent for the LRFXL and 3 percent for the LRF6. A reduction in the filtration flow rate from 80 to 50 mL per minute with postcollection filtration through the LRF6 resulted in markedly lower WBC levels, with 10 percent versus 57 percent of the apheresis platelets having WBC counts <1 x 10(5), respectively. Additional improvements in WBC removal were found with continuous filtration; 85 percent of the apheresis platelets filtered with the LRF6 and 100 percent of the apheresis platelets filtered with the LRFXL had WBC counts <1 x 10(5).

CONCLUSIONS

Continuous or postcollection filtration of freshly collected apheresis platelets resulted in minimal platelet loss. Better WBC removal from apheresis platelets was obtained with continuous filtration than with postcollection filtration, likely because of the slower flow rate. Platelet storage quality was not affected by filtration.

Update on leucocyte depletion of blood components by filtration

It has long been recognized that allogenic leucocytes from donor blood are responsible for serious untoward effects in some transfused patients such as alloimmunization, febrile reactions, platelet refractoriness, transfusion associated acute lung injury, immunosuppression as well as transmission or reactivation of viruses such as CMV, HTLV or EBV. Leucocytes are also known to accelerate the rate of storage lesion. The optimal method to remove leucocytes from blood components has been shown to be filtration. However, many variables exist in the properties of leuco-depletion filters (material, composition, surface charge, mechanisms of leucocyte entrapment), the blood components to be filtered (composition, age), and the filtration method (pre- or post-storage, priming and rinsing, temperature, flow rate). In this paper principles of filtration and subsequent logistic consequences will be discussed. It is recommended to carefully select a filter for a specific blood component and to perform leuco-depletion procedures under controlled conditions according to validated methods meeting Good Manufacturing Practice (GMP) and Good Laboratory Practice (GLP).

A mathematical model for the leukocyte filtration process

Leukocyte filters are applied clinically to remove leukocytes from blood. In order to optimize leukocyte filters, a mathematical model to describe the leukocyte filtration process was developed by modification of a general theoretical model for depth filtration. The model presented here can be used to predict the time-dependent leukocyte filtration as a function of cell-cell interaction in the filter, filter efficiency, filter capacity, filter dimensions, and leukocyte concentration in the suspension applied to the filter. The results of different leukocyte filtration experiments previously reported in the literature could be well described by the present model. (c) 1995 John Wiley & Sons, Inc.

Surface field of forces and protein adsorption behavior of poly(hydroxyethylmethacrylate) films deposited from plasma

Polymeric films were deposited from hydroxyethylmethacrylate (HEMA) plasma on non-woven poly(butyleneterephtalate) (PBT) filter materials. To test the effect of deposition conditions on surface properties, film were deposited using a constant monomer flow rate and a discharge power ranging from 40-100 W. Surface composition and surface energetics were evaluated by Electron Spectroscopy for Chemical Analysis (ESCA) and contact angle measurement, respectively. Albumin (Alb) and fibrinogen (Fg) adsorption from single protein solutions to the plasma-coated filters was measured. Results illustrate the marked effects of the deposition condition on the surface composition, the surface field of forces, and the protein adsorption behavior. The latter is modeled by the application of the Good-van Oss-Chaudhury theory of Lewis acid-base contribution to interfacial energetics. Materials endowed with widely different properties are obtained from the same monomer and different deposition conditions, a result that must be taken into account both in the production step, to assure constant quality, and in the development of specifically tailored materials.