Depletion of white cells from platelet concentrates with a new adsorption filter

Activation of Piezo1 channels in compressed red blood cells augments platelet-driven contraction of blood clots

BACKGROUND

Piezo1 is a mechanosensitive cationic channel that boosts intracellular [Ca2+]i. Compression of red blood cells (RBCs) during platelet-driven contraction of blood clots may cause the activation of Piezo1.

OBJECTIVES

To establish relationships between Piezo1 activity and blood clot contraction.

METHODS

Effects of a Piezo1 agonist, Yoda1, and antagonist, GsMTx-4, on clot contraction in vitro were studied in human blood containing physiological [Ca2+]. Clot contraction was induced by exogenous thrombin. Activation of Piezo1 was assessed by Ca2+ influx in RBCs and with other functional and morphologic features.

RESULTS

Piezo1 channels in compressed RBCs are activated naturally during blood clot contraction and induce an upsurge in the intracellular [Ca2+]i, followed by phosphatidylserine exposure. Adding the Piezo1 agonist Yoda1 to whole blood increased the extent of clot contraction due to Ca2+-dependent volumetric shrinkage of RBCs and increased platelet contractility due to their hyperactivation by the enhanced generation of endogenous thrombin on activated RBCs. Addition of rivaroxaban, the inhibitor of thrombin formation, or elimination of Ca2+ from the extracellular space abrogated the stimulating effect of Yoda1 on clot contraction. The Piezo1 antagonist, GsMTx-4, caused a decrease in the extent of clot contraction relative to the control both in whole blood and in platelet-rich plasma. Activated Piezo1 in compressed and deformed RBCs amplified the platelet contractility as a positive feedback mechanism during clot contraction.

CONCLUSION

The results obtained demonstrate that the Piezo1 channel expressed on RBCs comprises a mechanochemical modulator of blood clotting that may be considered a potential therapeutic target to correct hemostatic disorders.

Human leukocyte antigen alloimmunization prevention mechanisms in blood transfusion

In many fields of clinical medicine and blood transfusion, the human leukocyte antigen (HLA) system is crucial. Alloimmunization happens as a result of an immune response to foreign antigens encountered during blood transfusion. This gives rise to alloantibodies against red blood cells (RBCs), HLA, or human platelet antigen (HPA). HLA alloimmunization following allogeneic transfusion was shown to be a result of contaminating white blood cells (WBCs) present in the product. It is a common complication of transfusion therapy that leads to difficulties in clinical intolerance and refractoriness to platelet transfusion during patient management. Single-donor platelets, prophylactic HLA matching, leukoreduction, and irradiation of cellular blood products are some of the mechanisms to prevent HLA alloimmunization during a blood transfusion. Now, the best approach to reduce the occurrence of primary HLA alloimmunization is the removal of WBCs from the blood by filtration.

Paper-Based Cytometer for the Detection and Enumeration of White Blood Cells According to Their Immunophenotype

Total and differential white blood cell (WBC) counts are vital metrics used routinely by clinicians to aid in the identification of diseases. However, the equipment necessary to perform WBC counts restricts their operation to centralized laboratories, greatly limiting their accessibility. Established solutions for the development of point-of-care assays, namely lateral flow tests and paper-based microfluidic devices, are inherently limited in their ability to support the detection of WBCs─the pore sizes of materials used to fabricate these devices (e.g., membranes or chromatography papers) do not permit passive WBC transport via wicking. Herein, we identify a material capable of the unimpeded transport of WBCs in both lateral and vertical directions: a coffee filter. Through in situ labeling with an enzyme-labeled affinity reagent, our paper-based cytometer detects WBCs according to their immunophenotype. Using two cultured leukocyte lines (Jurkat D1.1 T cells and MAVER-1 B cells), we demonstrate the specific, colorimetric enumeration of each target cell population across the expected physiological range for total lymphocytes, 1000-4000 cells μL^-1. Additionally, we highlight a potential application of this type of device as a screening tool for detecting abnormal cell counts outside the normal physiological range and in subclasses of cell types, which could aid in the identification of certain diseases (e.g., CD4+ T lymphocytes, an important biomarker for HIV disease/AIDS). These results pave the way for a new class of paper-based devices─those capable of controlled white blood cell transport, labeling, capture, and detection─thus expanding the opportunities for low-cost, point-of-care cytometers.

Total leukocyte control for elective coronary bypass surgery does not improve short-term outcome

BACKGROUND

Despite early promise as a means of reducing the inflammatory response to surgery and subsequent organ damage, the evidence of the clinical value of leukocyte filtration remains equivocal.

METHODS

Three hundred patients presenting for routine coronary artery bypass surgery were randomized to a total leukocyte filtration group (filters in five different locations) and a control group with a standard 40-mum filter in the bypass return line only. Data on efficacy and safety of leukocyte filtration were collected by research and postoperative care staff who were blinded to the mode of filtration.

RESULTS

Leukofiltration achieved a transient fall in white cells immediately after surgery (p = 0.07) and a sustained fall in platelets, which was still significant on the second postoperative day (p = 0.0001). However, there were no significant differences in postoperative hospital stay, the primary outcome variable (p = 0.35), in ICU stay (p = 0.92), or mortality (p = 1.0). There were no differences in postoperative cardiac status including cardiac output (p = 0.16), inotrope (p = 0.93) or balloon pump (p = 0.48) requirement, or 24-hour troponin (p = 0.60). Similarly there were no differences in pulmonary or renal function (intubation time (p = 0.83), respiratory index (p = 0.19) rise in creatinine (p = 0.13) or hemofiltration (1.0)). Leukofitration was not associated with a statistically significant increase in bleeding or requirement for blood or blood products. It was associated with a decrease approaching significance (p = 0.1) in number and severity of postoperative wound infections. Three filters were blocked during use but were changed without incident or compromise to patient safety.

CONCLUSIONS

Leukocyte filtration is safe but not efficacious in improving short-term outcome.

A brief history of blood filtration: clot screens, microaggregate removal, and leukocyte reduction

A historical perspective of the evolution of blood filtration is presented. Topics addressed include recognition of aggregates in blood as mediators of morbidity, targeted for removal with gross clot screens, and evolution through the implementation of universal leukocyte reduction. Future directions for the development of blood filters are also described.

Intravascular and total body platelet equilibrium in healthy volunteers and in thrombocytopenic patients transfused with single donor platelets

Instrument platelet counts used in corrected count increment (CCI) and percent platelet recovery (PPR) formulas presume the transfused platelets are in equilibrium during the first hour after platelet transfusion. The timing of the pre-transfusion count affects CCI results, and we postulate that timing of CCI post transfusion affects CCI results. Platelet equilibrium using indium-111 platelet transfusions has not been reported. Platelet redistribution was studied in 16 healthy volunteers and 12 thrombocytopenic patients by generally infusing less than 72-hr stored single-donor platelets along with an aliquot of indium-111-labeled platelets by intravenous push. Counts were measured at 10, 15, 20, 60, and 120 min, and 24, 48, 72 hr along with continuous body scanning for 2 hr in healthy volunteers, and static organ scanning in patients and volunteers. Results indicated transfused platelets do not reach intravascular equilibrium for 60 min post-infusion and that the 10-min count cannot detect platelet refractoriness. However, total body equilibrium varies considerably between normal volunteers and thrombocytopenic patients. It is recommended to continue with the 1-hr post transfusion count.

Clinical evaluation of a leucocyte-depleting blood cardioplegia filter (BC1B) for elective open-heart surgery

Activation of leucocytes during extracorporeal circulation has attracted attention in recent years as a cause of reperfusion injury in open-heart surgery patients. In the present study, 40 adult patients undergoing elective open-heart surgery were randomized into two groups: 20 using the Pall BC1B leucocyte-depleting filter for blood cardioplegia (group 1) and the other 20 without the filter (group 2). In order to determine if the filter was effective in protecting the myocardium, CPK-MB and troponin-T (TnT) were measured. In addition, efforts were also made to determine appropriate sites at which the BC1B blood cardioplegia filter should be positioned. There were no significant differences between the two groups in terms of conditions of perfusion. No adverse effects were seen in either group. The total leucocyte reduction rate through the filter was 98.1% with the passage of 2 liters of blood through the filter. A pressure drop of 4.4 +/- 3.2 mmHg was observed through the filter during use. Statistically significant differences were noted between the two groups in CPK-MB (p = 0.031) and TnT (p = 0.004). Findings obtained in previous studies demonstrate that the various advantages of leucocyte reduction, shown in experimental studies, can be translated into clinical advantages. In conclusion, based on the results in this clinical study showing significant difference in CPK-MB and TnT which are known effective indicators for myocardial injury, between leucoreduced and non-leucoreduced group, the Pall BC1B leucocyte-depleting filter for blood cardioplegia has been shown to be effective in alleviating reperfusion injury in open-heart surgery patients.

Role of platelets in myocardial ischemia-reperfusion injury in dogs

We investigated the involvement of circulating platelets in myocardial ischemia-reperfusion injury in canine autoperfused heart-lung preparations using filters to deplete platelets and/or leukocytes. The left anterior descending (LAD) coronary artery was occluded for 40 min, followed by 40 min reperfusion, in 3 groups: a leukocyte-platelet-depleted (LPD) group, in which both leukocytes and platelets were depleted; a leukocyte-depleted (LD) group, in which leukocytes alone were depleted; and a control group. There were no differences in hemodynamics or arrhythmias among groups before or during coronary occlusion. After reperfusion, the maximum rate of change in left ventricular pressure during systole and diastole was significantly higher in the LPD group than in the control and LD groups. The LPD group also showed gradual recovery of regional myocardial function and a decrease in the frequency of premature ventricular contractions. The LD group showed a slight improvement in cardiac function and arrhythmias compared with the control group. Although there was no significant difference in the pulmonary arterial plasma level of thromboxane B2 at any stage among groups, the control group showed an increase after reperfusion. These results suggest that platelets are important in reperfusion injury and that the depletion of both leukocytes and platelets effectively protects against reperfusion injury.

Strategy of leukocyte filtration for immunomodulation: development of stainless steel leukocyte filter

Commercially available leukocyte filters are frequently used to prepare leukocyte depleted blood products for prevention of transfusion reactions. Recently, immunomodulation by using leukocyte filtration was evaluated. At this time, a new leukocyte filter was fabricated with a 4 microm diameter stainless steel fiber. The goal of this study was to assess the efficiency of the stainless steel filter for leukocyte and platelet removal by comparison with the polyester filter that is commercially available. The production of humoral factors, including interleukin-1 beta, tumor necrosis factor-alpha, and interleukin-1 receptor antagonist (IL-1 Ra), was also evaluated. The results show that the stainless steel filter has more than 2 times greater efficiency in leukocyte removal than the polyester filter. Furthermore, the cytokine studies indicate good biocompatibility of the filter, and the stainless steel filter has a possibility of inhibiting inflammatory cytokines by inducing interleukin-1 receptor.

Transfusion of platelet concentrates--clinical evaluation of two preparations

The aim of this study was to compare the clinical effect of transfusion of platelet concentrates (PC) prepared from pooled buffy coats (BC) and PCs collected from a single donor (SD) by an apheresis technique. The influence of storage time and various clinical conditions was also studied. Thirty-two patients suffering from haematological malignancies were given a total of 326 platelet concentrates; 180 BC-PCs and 146 SD-PCs, median 7 transfusions per patient. BC-PCs contained 312 +/- 52 x 10(9) and SD-PCs 383 +/- 133 x 10(9) platelets/unit (mean +/- SD). The mean storage time of BC-PC was 3 d and that of SD-PC 1 d. The mean platelet count of the patients before transfusion was 11 +/- 8 x 10(9)/L. Regression analysis showed a significant decrease of the post-transfusion platelet corrected count increment (CCI) during storage of PCs for 1-5 d (BC-PC: p < 0.01; SD-PC: p < 0.05). There was no difference in platelet increment between BC-PC and SD-PC. Human leukocyte antigen (HLA) alloimmunization was the major cause of clinical refractoriness to random donor platelet transfusions but splenomegaly also caused low CCI values.

Leucodepletion of blood products by filtration

The leucocytes present in red cell and platelet components have been implicated in several important immunological and infective complications of blood transfusion. Recent developments in blood filtration technology allow the production of leucodepleted blood products (residual leucocytes < 5 x 10(6) per transfused unit) in the laboratory or at the bedside with the potential to prevent these adverse effects. Quality assurance remains an important problem, particularly for bedside filtration. Prestorage filtration may have significant advantages for red cell and platelet production. There is strong clinical evidence that 3 log10 leucodepletion prevents or delays febrile reactions in patients receiving multiple red cell transfusions and can reduce cytomegalovirus transmission. Leucodepletion to prevent HLA alloimmunisation, platelet refractoriness and febrile reactions in patients receiving red cell and platelet support remains controversial. Transfused leucocytes induce 'immunosuppressive' changes in the recipient, but recent studies cast doubt on the association with cancer recurrence after surgery. However, leucodepleted blood may reduce the incidence of postoperative infection. Leucodepletion by filtration is expensive and there is a requirement for well-designed prospective clinical studies focusing on appropriate filtration technology (and alternatives), clinical outcome and cost-effectiveness.

[Ineffectiveness of platelet transfusions in the course of thrombocytopenia of central origin. Work Group coordinated by ANDEM]

This study, conducted under the auspices of ANDEM, was aimed at determining the reasons for the inefficacy of platelet transfusions for thrombocytopenia of central origin, and to establish recommendations for therapy and prevention. It was based on a critical review of the literature. Three main causes of inefficacy were identified: an immunological conflict (mainly anti-HLA alloimmunization), clinical status, and the quality of platelet preparations (especially storage time). Our recommendations depend on several factors, such as the degree of urgency, the cause of platelet refractoriness, clinical status and the availability of platelet preparations. The mainstay of the recommendations is prevention, based on the quality of platelet preparations (as fresh as possible, in adequate number preferably obtained by apheresis and ABO compatible) and on the prevention of anti-HLA alloimmunization.

Effect of filtration on subsequently stored platelet concentrates

The effect of filtration on the quality of platelet concentrates (PC) during storage was investigated. Two leukocyte depletion filters (Pall PL50HF and Sepacell PL-10A) were applied to filter PC made from a pool of 4 buffy coats. For each experiment 3 PC were pooled and divided into 3 identical PC to eliminate differences between the PC. Two PC were filtered, and the third PC served as an unfiltered control. A total of 12 experiments was performed. Before filtration, volumes of the PC were 263 +/- 11.7 ml (mean +/- SD). Platelet and leukocyte counts per PC were 241 +/- 25.9 x 10(9) and 7.2 +/- 1.8 x 10(6), respectively. After filtration leukocyte counts did not exceed 5 x 10(4) in any of the PC. In the PC filtered with the Pall PL50HF the mean platelet loss was approximately 14% and with the Sepacell PL-10A, 17%. During a 9-day storage period the pH, PO2, PCO2, bicarbonate, lactate and glucose concentration and LDH release as well as the morphology, examined by the swirling effect and microscopically, were not significantly different in filtered and unfiltered units. Filtration through the 2 investigated leukocyte depletion filters for PC did not adversely affect in vitro viability of the platelets during storage.

Effect of prestorage leukocyte removal on the cytokine levels in stored platelet concentrates

The effect of the prestorage removal of leukocytes from platelet concentrates (PC) on the cytokine levels during its storage was studied. Two methods for leukocyte removal were examined: filtration and preparation of the PC by the buffy coat method. Cytokine levels were measured at various storage times. Highly increased levels of tumor necrosis factor-alpha (TNF-alpha; 120 +/- 131 ng/l) and interleukin 6 (IL-6; 988 +/- 494 ng/l) were found after a 5-day storage in the control group, whereas no increased levels were found in filtered PC (TNF-alpha 14 +/- 4 ng/l, IL-6 < 4 ng/l) or in buffy coat PC (TNF-alpha 8 +/- 2 ng/l, IL-6 < 4 ng/l). Furthermore an effect of the pooling of buffy coats or PC on the cytokine levels was not found. Transfusion of PC containing high levels of IL-6 and TNF-alpha has been associated with febrile transfusion reactions in the recipient and therefore the prestorage leukocyte removal might prevent these febrile transfusion reactions. The preparation of buffy coat PC, through its simplicity, seems to be the method of choice.

Effect of prestorage leukocyte reduction on proteins of platelets obtained by apheresis

The effect of prestorage leukocyte reduction was evaluated on platelet concentrates (PCs) obtained by apheresis using the 'surge' technique. Two hours after collection, the PCs were divided into 2 equal units. One unit was filtered through a Sepacell PL-10a, producing a filtered PC (FPC). The second unit constituted a non-filtered PC (NFPC). FPCs and NFPCs were stored at room temperature in 1,400-ml CLX bags on a horizontal agitator up to 7 days. We analyzed platelet samples obtained during storage from NFPCs and FPCs at days 1, 3 and 7. The expression of membrane glycoproteins (GP)Ib and GPIIb/IIIa (assessed by flow cytometry), platelet response to thrombin and ristocetin (aggregometry) and global platelet protein pattern (studied by high-resolution two-dimensional gel electrophoresis) remained stable over the 7 days of storage in NFPCs as well as in FPCs. However, in both preparations, the expression of GMP-140 (flow cytometry) progressively increased during storage. Our in vitro study indicates that early leukocyte reduction by filtration of apheresis PCs does not induce modifications in platelet GPs and protein patterns.

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

Polyurethane membrane filters and filters coated with poly(ethyleneimine) were used to investigate the influence of leukocyte adhesion during filtration. Treatment of the filters with an aqueous solution of 1% (w/v) poly(ethyleneimine) (PEI) led to the introduction of amine groups at the filter surfaces, as was confirmed by X-ray photoelectron spectroscopy. The modification procedure did not significantly change the porous structure in the filters, as was demonstrated by SEM and porometry. Using 14C-labeled poly(ethyleneimine) it was shown that nearly a complete coverage (approximately 0.1 mg/m2) was achieved that did not desorb from the filter surface during contact with blood plasma. When the filtration was carried out with purified leukocytes in the absence of red cells, platelets, and blood plasma, the number of cells removed by modified filters (> 95%) was significantly higher as compared to the removal with unmodified filters (approximately 80%). However, no significant differences between the filters were found when the filtration was performed with whole blood. This finding was unexpected, because it was shown before that immobilization of poly(ethyleneimine) on solid polyurethane film, surfaces promoted the adhesion of leukocytes from whole blood. Apparently, the adhesive properties of the PEI diminish during filtration. Filter coating of commercial leukocyte filters composed of polyester fibers also had no effect on the removal of leukocytes from whole blood. It was postulated that morphological factors, such as filter shape, roughness, tortuosity, and porosity rather than the physicochemical properties of the filter surface influence cell adhesion to the filter surface, and through that the filtration process.

Filtration through a polyester white cell-reduction filter of plasma-poor platelet concentrates prepared with an acetate-containing additive solution

It is of practical importance to known whether the adsorption of platelets and contaminating white cells (WBCs) by the WBC-reduction filter is altered when platelet concentrates (PCs) are prepared in a plasma-poor condition with an acetate-containing additive solution (Seto sol). Plasma-poor PCs with 11-percent residual plasma were prepared from apheresis platelet-rich plasma by using a sterile docking device with steam-sterilized Seto sol. Seto sol contains 115 mM (115 mmol/L) NaCl, 4 mM (4 mmol/L) KCl, 3 mM (3 mmol/L) MgCl2, 10 mM (10 mmol/L) Na3PO4, 15 mM (15 mmol/L) acetate, 3 mM (3 mmol/L) Na3 citrate, and 10 mM (10 mmol/L) glucose (pH 7.1). The solution was steam-sterilized under nitrogen gas. On Days 1 and 5, pooled Seto sol PCs (2.4 x 10(11) platelets) were filtered with a polyester filter at a flow rate of 10 mL per minute. The WBC-removal rate was over 99.9 percent with a platelet recovery of 88 percent following Day 1 filtration. These values were very similar to those of plasma PCs, and 84-percent recovery was achieved following Day 5 filtration. However, when 1 unit of Seto sol PCs with half the number of platelets was filtered with the polyester filter, platelet recovery was about 16 to 17 percent less than that of plasma PCs. Platelet quality was maintained if pooled Seto sol PCs were filtered on Day 1 and stored for over 4 days. Filtration did not alter platelet function in 1-day-old or 5-day-old Seto sol PCs.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of platelet transfusion reactions before and after implementation of leukocyte-depleted platelet concentrates by filtration

To determine the impact of platelet leukodepletion by filtration on the overall prevalence of reported transfusion reactions associated with platelet concentrates, we audited platelet transfusion reactions after infusion of platelet concentrates reported at University Hospitals of Cleveland over 6 months before (interval 1, July 1, 1989 to December 31, 1989) and after (interval 2, July 1, 1990 to December 31, 1990) implementation of the Pall PL 50 filter on our adult Hematology-Oncology inpatient unit (Division 60). Thirty-two (1.7%) of 1,901 random, pooled platelet transfusion events resulted in blood bank transfusion reaction workups in interval 1, compared to 90 (5.3%) of 1,704 in interval 2 (p < 0.001). The Division 60 service accounted for more of our hospital-wide platelet reactions after implementation of the filter in interval 2 (84%) than before filtration in interval 1 (42%), p = 0.002. The prevalence of reaction workups for Division 60 was 0.6% for interval 1, compared to 4.3% for interval 2 (p < 0.001). No differences were found between interval 1 and interval 2 for the rate of discontinuation of platelet transfusion (36 vs. 32%, p = 0.14), rate of premedication for platelet transfusion (72 vs. 65%, p = 0.6), percentage of direct antiglobulin test-positive reactions (17 vs. 5.4%, p = 0.09), percentage showing icteric/hemolyzed serum (15 vs. 4.4%, p = 0.09), or reactions believed to be due to red blood cell incompatibility (8.8 vs. 1.1%, p = 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)

[Filtration of platelet concentrates. Technical aspects, quantitative results. Group PSL]

This work summarizes a multicentric study (20 Blood Transfusion Centers) concerning the use of different filters applied to platelet collection. The results are good with the different filters and platelets concentrates evaluation. Nevertheless, we have seen a great heterogeneity of platelet concentrates. This characteristic could explain the variability in filter performances. Maybe we have to adapt some type of filter with specific platelet concentrates. In conclusion, it is important to continue the evaluation of new platelet concentrate filters, in order to increase the performances and the filtration quality. Clinical trials seem to be useful in the future to appreciate the effects of filtered platelets on alloimmunization and CMV transmission.

A randomized trial comparing the use of fresh and stored platelets in the treatment of bone marrow transplant recipients

Patients undergoing allogeneic bone marrow transplantation (BMT) were randomized into two groups. One group (n = 21) received single donor platelet concentrates (PC) that were as fresh as possible, the other group (n = 18) received single donor PC stored for 2 to 5 days. Actual mean storage times for PC were 1.12 +/- 1.25 (mean +/- SD) and 2.67 +/- 1.30 d, respectively (p < 0.001). The total need for platelets during 60 d after BMT in patients receiving fresh PC was 22.1 +/- 17.8 x 10(9) platelet/liter blood volume/d, and for stored PC 29.2 +/- 19.2 x 10(9) platelets/liter blood volume/d (n.s.). A multiple regression analysis of the data showed no correlation between PC storage time and the PC requirement (p = 0.85). Posttransfusion corrected count increment (CCI) at 1 hour was 10.4 +/- 5.1 for PC stored 0-1 d, 10.3 +/- 7.0 for PC stored 2-3 d, and 11.4 +/- 9.2 for PC stored 4-5 d. The corresponding CCI, at 18 h were 6.5 +/- 4.4, 5.4 +/- 3.3 and 6.8 +/- 4.6. We conclude that there is no major difference between fresh and stored single donor PC.

Amino acid metabolism during platelet storage for transfusion

Previous studies indicated that the concentration of ammonia rises during storage of platelet concentrates (PC) at 22 degrees C for transfusion and that fuels other than glucose are important for metabolism. Therefore, in the current study, we measured the concentrations of 17 plasma amino acids during PC storage; 16 of these either rose or were unchanged while the concentration of glutamine fell to zero by day 4. As the concentration of glutamine fell, the concentration of glutamate rose with a relationship suggesting that 65-75% of the glutamine was metabolized no further than glutamate. Phosphate-dependent glutaminase activity was present in platelets at 22.3 +/- 6.3 nmol/min/mg protein, a level similar to that seen in lymphocytes and macrophages. Leucodepletion studies excluded a significant contribution of contaminating leucocytes to these measurements. Thrombin stimulation did not increase the rate of glutamine metabolism. Analysis of the rates of glutamine metabolism suggests that it accounts for most of the ammonia produced during PC storage. However, it appears to be relatively insignificant as a metabolic fuel. The role of glutamine metabolism for platelets is uncertain. It may be a vestige of a pathway in the megakaryocyte. The ammonia which it produces may be deleterious for platelets and for patients with liver disease who receive PC infusions.

Transfusion results of filtered and subsequently stored random platelet suspensions prepared from buffy coats

There is almost general agreement that removal of leukocytes from blood components reduces the incidence of HLA-antibody formation and refractoriness to random platelet transfusions. Recently filters have become available, which are able to reduce leukocyte contamination in platelet suspensions with acceptable platelet loss. We evaluated a cellulose acetate (CA) and a polyester (PE) filter, and stored buffy coat-derived platelet suspensions after filtration. Both filters are effective for the removal of leukocytes to levels below 5 x 10(6) per transfusate. For the CA filter, platelet recovery was 73 +/- 13% yielding 256 +/- 53 x 10(9) platelets per transfusate from 6 donors. For the PE filter, platelet recovery was 90 +/- 9% and 327 +/- 51 x 10(9) platelets per transfusate. When a loading dose of less than 5 x 10(8) leukocytes was applied, 98% of the CA-filtered suspensions and 100% of the PE-filtered suspensions contained less than 5 x 10(6) residual leucocytes. In 123 patients transfusion results of CA-filtered platelet suspensions stored for 72 h, were compared with those obtained by non-stored, non filtered, random platelet suspensions which had been leukocyte depleted by differential centrifugation. Platelet increments 1 and 20 h after transfusion showed no statistical difference between CA-filtered platelet transfusions stored for 72 h and non-stored, non-filtered platelet transfusions. In a new cohort of 117 patients, two filters and various postfiltration storage times were compared. Using both filters, the 1-hour posttransfusion increments decreased to approximately 60% after 96 h of storage compared to results of storage periods of 72 h or less.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation of how different filters affect some biochemical properties of stored platelet concentrates

The aim of the present study was to investigate how four different filters, i.e. Imugard IG500 (Terumo, Japan), Miropore (Miramed, Italy), Pall P1-100 (Pall, USA) and Sepacell P1-10A (Asahi, Japan) affect some biochemical properties of platelet concentrates. The work was conducted using 42 pairs of platelet concentrates. After 2 days of storage, one of the preparations was filtered and the other served as an unfiltered control. Immediately after filtration, determination of the platelet count, desarginated activated complement factor 3 (C3a des arg) and the extracellular and total concentrations of platelet factor 4 (PF4) and lactate dehydrogenase (LDH) were carried out on both these platelet concentrates. After an additional storage period of 3 d, extracellular concentrations of PF4 and LDH were determined on both concentrates. A significant decrease of extracellular PF4 concentration was found immediately after filtration when Pall P1-100 and Imugard IG500 were used. During the 3-d storage after filtration, the concentrates filtered with Imugard IG500 and Pall P1-100 demonstrated significantly higher platelet lysis as compared to the unfiltered controls. It is concluded that the present work demonstrates storage instability after filtration with Imugard IG500 and Pall P1-100. Therefore, platelet concentrates filtered with these filters would not appear to be suitable for storage.

In vitro leucocyte adhesion to modified polyurethane surfaces. I. Effect of ionizable functional groups

To study the effect of ionizable functional groups on the adhesion of leucocytes to surfaces, both poly(ethyleneimine) and poly(acrylic acid) were immobilized on polyurethane films, resulting in the introduction of amine and carboxylic acid groups, respectively. This was confirmed by contact angle measurements and XPS analysis. In vitro adhesion of granulocytes and lymphocytes on untreated and modified surfaces was compared. The number of adherent cells on modified surfaces as a function of time was significantly higher than on untreated surfaces. This effect was most pronounced for the adhesion of lymphocytes to surfaces modified with amine groups. In this case, the number of adherent cells after 1 h of exposure was three times higher than on untreated surfaces. A moderate enhancement of leucocyte adhesion was observed in the case of surfaces modified with carboxylic acid groups. There is evidence that these groups were not ionized under the experimental conditions used. The modification procedures described may be used to improve polyurethane filters for the removal of leucocytes from blood.

In vitro evaluation of a high-efficiency leukocyte adherence filter

In view of the currently available data, prevention of alloimmunization requires filters with higher efficiency to achieve a reduction in the number of leukocytes below 10 million per transfusion. Two versions (Pall PL-100 and PL-50) of the new generation leukocyte-depletion filters were studied. Single donor (SDPC)- and pooled multiple donor (MDPC) platelets were run in parallel. At a flow rate of 10 ml/min, the PL-100 filter was shown to effectively reduce the number of residual leukocytes to far below the critical immunogenic threshold of 10 million in all SDPC units and in 77% of MDPC units. Apheresis platelets appear not only to be better depleted than pooled multiple donor platelets, but also to have a better post-filtration platelet recovery (96% versus 84%). The efficiency of the smaller version of the filter (Pall-50) was higher than that of the Pall-100 filter for both single and pooled multiple donor platelet concentrates (PC). Leukocytes were absent in more than 92% of units in both types of concentrates. The maximal number of detected leukocytes was 2.2 million in a pool of 6 units. The outcome of filtration of 5-day-old pooled platelets was less favorable than filtration of 1- or 2-day-old pooled platelets, indicating that filtration soon after preparation is preferred to filtration after storage. Post-filtration platelet integrity, activation state, function, and morphology were all well preserved in both single and multiple PCs.

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.

Leukocyte removal filtration of platelet concentrates. A study of platelet loss using 111In-labelled platelets and dynamic gamma camera scintigraphy

111In labelled platelets and gamma camera scintigraphy were used for the study of the platelet loss during leukocyte removal filtration of stored platelets. Two different filters were examined, Imugard IG500 and Pall PL100, and platelet pools containing varying number of platelet concentrates were filtered. It was found that a sizeable amount of the platelets was trapped within the filter. Some of the trapped platelets could be recovered by rinsing the filters with normal saline. The most appropriate rinsing volume to recover lost platelets seemed to match with the "dead space" volume within the filter. It is concluded that radiolabelled platelets and gamma camera scintigraphy appears to be an excellent method to investigate the dynamic events of platelet loss during leukocyte removal filtration. This technique should be well applicable for the study of technological advances in filter construction.

Postoperative erythroderma with change of HLA phenotypes from heterozygotes to homozygotes: a report of two cases

Fatal "postoperative erythroderma" (POE) developed in 2 patients treated with liver lobectomy and the transfusion of fresh blood. Their clinical features and skin-histological findings were indicative of acute graft-versus-host disease (GVHD). The HLA phenotypes of circulating lymphocytes of the 2 patients were heterozygous but became homozygous late in the clinical course and were identical with those of the blood donors. One of the patient's haplotypes was identical with the donor's homozygous haplotype. These findings suggest the mechanism of development of POE in apparently immunocompetent patients. The donor's T lymphocytes are histocompatible with the patient's tissues, are not rejected, and become engrafted. The patient's tissues are not histocompatible with the donor's, so that GVHD develops.

Leukocyte-poor blood components: issues and indications

Leukocyte-poor blood components (LPBC) have now become part of the armamentarium of available transfusable blood components. Indications for the use of LPBC vary in accordance with the underlying clinical condition, as well as the intended objectives of the transfusion therapy. Technological advances have made it possible to prepare LPBC using rather simple procedures. However, any manipulation of blood components and the additional use of filters, washing, rinsing solutions, etc. inevitably result in additional costs to the patient, the health-care institution, or third-party payers. Requests for LPBC involve the preparation of RBC or platelets, leuko-depleted by at least one log. Transfusion of LPBC must be done in a logical fashion that meets the needs of the patient. Currently, LPBC is indicated for patients with a history of nonhemolytic febrile transfusion reactions to delay alloimmunization to HLA antigens and avoidance of cytomegalovirus (CMV) infection.

Concepts about current conditions for the preparation and storage of platelets

Substantial experimentation over the last 20 years has led to the conditions that are currently used to prepare and store platelets. Although platelet rich plasma is used in most instances to prepare platelet concentrates, there may be some benefit associated with the use of buffy coats as the source component. Extension of the maximum allowable storage time for platelets to 5 days has been possible as a result of defining the conditions which allow for the better retention of platelet properties. Storage temperature, permeability of the storage container, volume of platelet suspension, and the need to agitate platelets have been identified as key parameters that maintain platelet viability and functional properties. Storage in the 20 to 24 degrees C range prevents a reduction in posttransfusion viability that occurs when platelets are maintained at lower temperatures. Adequate influx of oxygen through container walls to support platelet metabolism and, to a lesser degree, adequate efflux of produced carbon dioxide are essential for maintaining pH levels, a key parameter that also influences posttransfusion viability. Permeability is influenced by container size and material, by use of a satisfactory volume of plasma and by agitating the container. Although platelet concentrates prepared from whole blood have been primarily used to delineate appropriate storage conditions, they also apply to platelets harvested by aphersis technology. Storage under currently used conditions, although providing products with acceptable clinical efficacy, is associated with a reduction in viability and functional characteristics. The development of storage media, specific for platelets, may minimize the occurrence of deleterious changes.

[Preparation of leukocyte-depleted human platelet concentrates by centrifugation and filtration of a pool of sterilely connected buffy-coats]

We describe a new method for the preparation of standardised therapeutic doses of leukocyte depleted platelets. The first step is to remove the buffy-coat from whole blood units drawn on triple Siamese ACD/SAGM bags (Maco-Pharma) by means of a Compomat (NPBI). The second step is to connect (SCD Haemonetics) six buffy-coats and one plasma to a special kit (Maco-Pharma) including a PALL PL 100 filter; after centrifugation, the supernatant platelet concentrate is extracted, filtered and recovered in a 2 litre TOTM PVC bag. The volume, the number of platelets and leukocytes of these pools are measured. A comparison of these parameters is made with therapeutic doses prepared in the same way without filtration. Besides, pH measurements up to the 6th day of storage and bacteriological checks are carried out. The results show: no platelet loss related to filtration; a synergy between the preparation process out of buffy-coats and the filtration: so each dose contains less than 10(6) leukocytes; a good pH level allowing the storage for five days as it is associated to the bacteriological safety of the functionally closed system. This technique makes it possible to transfuse only leukocyte depleted platelet concentrates. In addition, it offers new prospects for standardisation and quality improvement.

In vitro evaluation of a new dual screen microaggregate filter

We compared a new second generation 40/150 mum dual screen microaggregate filter with a currently available 40 mum screen microaggregate filter. The evaluation included comparison of filter flow rate, capacity, degree of microaggregate removal, degree of leukocyte removal, and extent of filtration-induced hemolysis. We also studied the effect of both devices on filtration of stored platelet concentrates. The 40/150 mum dual screen microaggregate filter showed results comparable to that of the control screen filter following filtration of various types of units of red blood cells as well as units of stored platelet concentrates. Importantly, mean flow rates with the new 40/150 mum filter of 45 g/min after gravity filtration of 1600 mL of blood, make the filter suitable for use in trauma or other massive transfusion settings. We conclude that this new second generation microaggregate filter is suitable for use in clinical transfusion practice.

Comparison of platelet activation and membrane glycoprotein Ib and IIb-IIIa expression after filtration through three different leukocyte removal filters

We evaluated three filters used for leukocyte removal from platelet concentrates: Imugard IG 500, Pall PL100 and Sepacell PL-10A. Filter performance, platelet activation and expression of membrane glycoproteins Ib and IIb-IIIa were evaluated. Imugard, Pall and Sepacell showed median postfiltration in vitro platelet recoveries of 88, 84 and 80%, and total residual leukocyte counts of 16.1, 7.5 and 0.6 x 10(6)/pool of 8 platelet concentrates, respectively. Mean platelet volume was reduced after filtration with all filters. Postfiltration values of glycoproteins Ib and IIb-IIIa, and of activation markers GMP 140 and gp 53 were not significantly different from prefiltration values. Filtration through Imugard, Pall and Sepacell did not induce significant platelet activation or modifications of platelet membrane glycoproteins Ib and IIb-IIIa.

Leukocyte depletion filters: a comparison of efficiency

Four commercially available leukocyte depletion filters were evaluated using a flow cytometric technique to determine the efficiency of each type of filter. The Sepacell R-500A and the PALL RC50 were the most efficient in leukocyte depletion having a mean depletion percentage of 99.3% and 99.5%, respectively. The PALL RC100 which is used for two units also had a 99.3% depletion with the first unit but with the second unit the depletion dropped to 94.2%. The imugard IG-500 had a 97.3% depletion. Red cell recovery ranged from 87.4% for the PALL RC50 to 92.2% for the Sepacell R-500A.