Biocompatibility of a new cell separator studied by flow cytometry: analyses of platelet antigens during apheresis and storage

Methods for testing platelet function for transfusion medicine

BACKGROUND

Currently only indirect measures are required for monitoring the function of platelets in platelet concentrates (PC).

METHODS

This is an overview on currently available commercialized methods that have been used to determine platelet function in donors, concentrates and after transfusion. We show examples for the application of the no/low shear methods light-transmission aggregometry, flow cytometry, multiple electrode aggregometry, thrombelastography and dynamic light scattering, and those applying high shear, the platelet function analyzer-100, and the cone and plate analyzer. Advantages and disadvantages of the various methods to screen donors, evaluate the haemostatic properties maintained in the PC and after transfusion are discussed, based on considerations of platelet physiology, and the feasibility of the various procedures. This survey focuses on reports from the last 10 years, as the technology for the production of PCs has advanced significantly during the last few years.

CONCLUSION

Specific aspects of platelet function can be assessed by the no/low shear methods, while the high shear methods provide more general analysis of platelet haemostatic competence. Yet, there is no strong evidence that the in vitro data correspond with the clinical outcome.

Phosphatidylserine exposure in platelet concentrates during the storage period: differences between the platelets collected with different cell separators

BACKGROUND AND OBJECTIVES

Platelet alterations occur during the production and storage of platelet concentrates, the so called "storage lesion". We studied the platelet alterations during the storage period in apheresis concentrates, employing flow cytometry for phosphatidylserine (PS) detection on platelets during the five days of storage.

MATERIAL AND METHODS

Twenty-seven single donor platelet concentrates harvested with the Cobe Trima, Baxter Amicus, or Haemonetics MCS+ were analyzed for PS exposure by flow cytometry on the day of production (day 1) and on days 3 and 5 of storage. Furthermore PS expression was analyzed in platelet donors' blood samples withdrawn before plateletpheresis.

RESULTS

PS expression on platelets gave the following median values: in blood donors before apheresis it was 1.12% (0.13-1.78) in platelets concentrates on the first day (2 h after apheresis) 2.06% (0.66-15.2), the third day 6.57% (1.98-51.13) and the fifth day 23.04% (3.86-80.23). All differences between median values of PS expression in blood samples before apheresis, and platelets concentrates on days 1, 3 and 5 of storage, are statistically significant. The expression of PS in platelet concentrates was analyzed in relation to the blood cell separator used for the collection procedure and showed the following results: on day 1 the median values of PS in platelet concentrates collected with the three different blood cell separators, Trima, Cobe and MCS, did not show statistically significant differences. On day 3, the platelets concentrates collected with the Trima and with the MCS showed differences that were statistically significant. Those were respectively 10.59% (4.56-51.13) and 3.53% (1.98-12.61), p = 0.005. The PS expression in platelet concentrates collected with the Trima and MCS showed differences that are also statistically significant on day 5 at respectively 32.4% (9.61-80.23) and 8.57% (3.86-48.42), p = 0.005.

CONCLUSIONS

PS exposure in platelet concentrates on days 3 and 5 rise to levels that could compromise the quality of the platelet units. Improvements in standardized platelet quality controls, and in platelet collection systems are required to reduce the storage lesions in platelets concentrates.

Binding of activated platelets to WBCs in vivo after transfusion

BACKGROUND

During preparation and storage of apheresis concentrates, platelets are being activated. One of the alterations that occur during this process is an increased expression of P-selectin (CD62p) on the cytoplasmic surface of platelets. This neoepitope represents a ligand for the binding of platelets to WBCs. It has been suggested that the activation of platelets is associated with the sequestration of platelets after transfusion. In this in vivo study, the binding of platelets to WBCs was analyzed following transfusion of platelet concentrates (PCs).

STUDY DESIGN AND METHODS

Double apheresis concentrates were prepared with two different cell separators. One of the split products was stored for 1 to 2 days and the other one for 3 to 5 days. Flow cytometry was applied to analyze the degree of platelet activation in vitro, and also to measure the extent of platelet binding to WBC subclasses in vivo after transfusion into patients.

RESULTS

The results of this study show that platelet activation occurs during apheresis and storage of PCs. After transfusion of the PCs, no significant binding of platelets to T or B-cells could be detected. However, a significant binding of platelets to monocytes and neutrophil granulocytes occurs. While in Baxter PCs stored for 1-2 days the amount of platelet-leukocyte aggregates in vivo was higher compared to COBE PCs, no such difference could be detected anymore for the PCs stored for 3-5 days.

CONCLUSION

This study demonstrates that binding of activated platelets occurs to monocytes and neutrophil granulocytes but not to T- and B-cells in the circulation after transfusion. In addition, the interaction of platelets and WBCs is dependent on the degree of P-selectin expression. Platelets showing a higher degree of activation adhere to WBCs to a higher degree than nonactivated platelets.

Platelet function testing in apheresis products: flow cytometric, resonance thrombographic (RTG) and rotational thrombelastographic (roTEG) analyses

During storage of platelet concentrates, quality control of the units is mandatory. This includes the important testing of the hemostatic function of platelets. So far, mostly platelet aggregation analyses have been performed. In this study, new approaches were tested to evaluate the applicability of modern techniques for quality monitoring. Plateletpheresis was performed with two different cell separators (AMICUS cell separator, Fenwal, Baxter Healthcare, Deerfield, USA; COBE Spectra, COBE BCT, Lakewood, USA). In each procedure split products (n = 22) were prepared and stored for 1-2 days (n = 22) or 3 5 days (n = 22). Platelet hemostatic capacity was tested by applying flow cytometry. platelet aggregation (platelet-rich-plasma [PRP]+agonist), resonance thrombography (RTG; PRP, no agonist) and rotational thrombelastography (roTEG; PRP+agonist). Flow cytometric analyses did not reveal significant changes in structural (CD41a. CD42b) or activation-dependent antigens (CD62p, CD63, LIBS, RIBS). Also, differences in the data from the flow cytometric reactivity tests were not significant between the two groups. In platelet aggregation assays, shape change (p = 0.8), maximum aggregation (p = 0.4), and maximum gradient (p = 0.8) did not show significant differences between the two groups. In the RTG test, differences between r-time (reaction time; p = 0.4), and f-time (clot formation time [fibrin influence]; p = 0.3), and in roTEG r-time (coagulation time; p = 0.1) and k-time (clot formation time; p = 1.0) were not significant. P-time (clot formation time [platelet influence]) and M (maximum amplitude) in RTG, and k-time and MA (maximum amplitude) in roTEG showed a slight decrease in platelet function (p < or = 0.05). We conclude that platelet function is well maintained during storage. This is reflected by the results of immunological and platelet function assays. Rotational thrombelastography (in the case of PRP) and especially resonance thrombography represent promising methods for quality control of platelet concentrates and rapidly provide information about the status of platelet function and the whole clotting process.