Platelet quality measured with dynamic light scattering correlates with transfusion outcome in hematologic malignancies

What about Platelet Function in Platelet Concentrates?

The characterization of platelet concentrates (PCs) in transfusion medicine has been performed with different analytical methods and platelet lesions (from biochemistry to cell biology) have been documented. In routine quality assessment and validation of manufacturing processes of PCs for transfusion purposes, only basic parameters are monitored and the platelet functions are not included. However, PCs undergo several manipulations during the processing and the basic parameters do not provide sensitive analyses to properly picture out the impact of the blood component preparation and storage on platelets. To improve the transfusion supply chain and the platelet functionalities, additional parameters should be used. The present short review will focus on the different techniques to monitor ex vivo platelet lesions from phenotype characterization to advanced omic analyses. Then, the opportunities to use these methods in quality control, process validation, development, and research will be discussed. Functional markers should be considered because they would be an advantage for the future developments in transfusion medicine.

Comparison of the platelet activation status of single-donor platelets obtained with two different cell separator technologies

BACKGROUND

The microparticle content (MP%) of apheresis platelets-a marker of platelet activation-is influenced by donor factors and by external stressors during collection and storage. This study assessed the impact of apheresis technology and other factors on the activation status (MP%) of single-donor apheresis platelets.

STUDY DESIGN AND METHODS

Data from six US hospitals that screened platelets by measuring MP% through dynamic light scattering (ThromboLUX) were retrospectively analyzed. Relative risks (RRs) were derived from univariate and multivariable regression models, with activation rate (MP% ≥15% for plasma-stored platelets; ≥10% for platelet additive solution [PAS]-stored platelets) and MP% as outcomes. Apheresis platform (Trima Accel vs Amicus), storage medium (plasma vs PAS), pathogen reduction, storage time, and testing location were used as predictors.

RESULTS

Data were obtained from 7511 platelet units collected using Trima (from 16 suppliers, all stored in plasma, 20.0% were pathogen-reduced) and 2456 collected using Amicus (from four different collection facilities of one supplier, 65.0% plasma-stored, 35.0% PAS-stored, none pathogen-reduced). Overall, 30.0% of Trima platelets were activated compared to 45.6% of Amicus platelets (P < .0001). Multivariable analysis identified apheresis platform as significantly associated with platelet activation, with a lower activation rate for Trima than Amicus (RR: 0.641, 95% confidence interval [CI]: 0.578; 0.711, P < .0001) and a 6.901% (95% CI: 5.926; 7.876, P < .0001) absolute reduction in MP%, when adjusting for the other variables.

CONCLUSION

Trima-collected platelets were significantly less likely to be activated than Amicus-collected platelets, irrespective of the storage medium, the use of pathogen reduction, storage time, and testing site.

The quality of platelet concentrates related to corrected count increment: linking in vitro to in vivo

BACKGROUND

Storage of platelet concentrates (PCs) results in reduced recovery and survival of transfused platelets (PLTs). Upon storage PLTs develop storage lesion that can be monitored by several laboratory tests. However, correlation of these descriptive tests with corrected count increments (CCIs), a marker frequently used to establish the effectiveness of PLT transfusions, is limited or unknown. This study investigated to what extent a functional test or a combined in vitro rating score improves the correlation of laboratory tests with 1-hour CCI.

STUDY DESIGN AND METHODS

PCs were analyzed using six different laboratory tests (n = 123) before transfusion in a prophylactic setting to 74 hematooncologic patients. Linear regression and Spearman correlation were used to determine associations between descriptive (either separately or combined in an in vitro rating score) or functional test results and 1-hour CCIs obtained after transfusion.

RESULTS

CD62P expression (r = -0.45), annexin V binding (r = -0.36), the updated in vitro rating score (r = 0.50), and PLT responsiveness after thrombin receptor activator for peptide-6 (TRAP) (r = 0.43-0.57) or adenosine diphosphate stimulation (r = 0.11-0.51) significantly correlated to 1-hour CCIs obtained after transfusion, whereas lactate concentration, ThromboLUX score, and thromboelastography measurements did not. The strongest correlations were observed for in vitro rating score and PLT responsiveness after TRAP stimulation and these tests could explain 24 and 33% of the observed variation in 1-hour CCI, respectively.

CONCLUSION

Combining descriptive markers in one in vitro rating score improved correlation to 1-hour CCI compared to the tests separately. Of all tests investigated, mean PLT responsiveness after TRAP stimulation showed the strongest clinical correlation and was best able to predict the 1-hour CCI.

Routine Screening Method for Microparticles in Platelet Transfusions

Platelet inventory management based on screening microparticle content in platelet concentrates is a new quality improvement initiative for hospital blood banks. Cells fragment off microparticles (MP) when they are stressed. Blood and blood components may contain cellular fragments from a variety of cells, most notably from activated platelets. When performing their roles as innate immune cells and major players in coagulation and hemostasis, platelets change shape and generate microparticles. With dynamic light scattering (DLS)-based microparticle detection, it is possible to differentiate activated (high microparticle) from non-activated (low microparticle) platelets in transfusions, and optimize the use of this scarce blood product. Previous research suggests that providing non-activated platelets for prophylactic use in hematology-oncology patients could reduce their risk of becoming refractory and improve patient care. The goal of this screening method is to routinely differentiate activated from non-activated platelets. The method described here outlines the steps to be performed for routine platelet inventory management in a hospital blood bank: obtaining a sample from a platelet transfusion, loading the sample into the capillary for DLS measurement, performing the DLS test to identify microparticles, and using the reported microparticle content to identify activated platelets.

Could Microparticles Be the Universal Quality Indicator for Platelet Viability and Function?

High quality means good fitness for the intended use. Research activity regarding quality measures for platelet transfusions has focused on platelet storage and platelet storage lesion. Thus, platelet quality is judged from the manufacturer's point of view and regulated to ensure consistency and stability of the manufacturing process. Assuming that fresh product is always superior to aged product, maintaining in vitro characteristics should preserve high quality. However, despite the highest in vitro quality standards, platelets often fail in vivo. This suggests we may need different quality measures to predict platelet performance after transfusion. Adding to this complexity, platelets are used clinically for very different purposes: platelets need to circulate when given as prophylaxis to cancer patients and to stop bleeding when given to surgery or trauma patients. In addition, the emerging application of platelet-rich plasma injections exploits the immunological functions of platelets. Requirements for quality of platelets intended to prevent bleeding, stop bleeding, or promote wound healing are potentially very different. Can a single measurable characteristic describe platelet quality for all uses? Here we present microparticle measurement in platelet samples, and its potential to become the universal quality characteristic for platelet production, storage, viability, function, and compatibility.

A study protocol for a randomised controlled trial evaluating clinical effects of platelet transfusion products: the Pathogen Reduction Evaluation and Predictive Analytical Rating Score (PREPAReS) trial

INTRODUCTION

Patients with chemotherapy-induced thrombocytopaenia frequently experience minor and sometimes severe bleeding complications. Unrestrictive availability of safe and effective blood products is presumed by treating physicians as well as patients. Pathogen reduction technology potentially offers the opportunity to enhance safety by reducing bacterial and viral contamination of platelet products along with a potential reduction of alloimmunisation in patients receiving multiple platelet transfusions.

METHODS AND ANALYSIS

To test efficacy, a randomised, single-blinded, multicentre controlled trial was designed to evaluate clinical non-inferiority of pathogen-reduced platelet concentrates treated by the Mirasol system, compared with standard plasma-stored platelet concentrates using the percentage of patients with WHO grade ≥ 2 bleeding complications as the primary endpoint. The upper limit of the 95% CI of the non-inferiority margin was chosen to be a ≤ 12.5% increase in this percentage. Bleeding symptoms are actively monitored on a daily basis. The adjudication of the bleeding grade is performed by 3 adjudicators, blinded to the platelet product randomisation as well as by an automated computer algorithm. Interim analyses evaluating bleeding complications as well as serious adverse events are performed after each batch of 60 patients. The study started in 2010 and patients will be enrolled up to a maximum of 618 patients, depending on the results of consecutive interim analyses. A flexible stopping rule was designed allowing stopping for non-inferiority or futility. Besides analysing effects of pathogen reduction on clinical efficacy, the Pathogen Reduction Evaluation and Predictive Analytical Rating Score (PREPAReS) is designed to answer several other pending questions and translational issues related to bleeding and alloimmunisation, formulated as secondary and tertiary endpoints.

ETHICS AND DISSEMINATION

Ethics approval was obtained in all 3 participating countries. Results of the main trial and each of the secondary endpoints will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NTR2106; Pre-results.

Cryopreservation alters the membrane and cytoskeletal protein profile of platelet microparticles

BACKGROUND

Cryopreservation of platelets (PLTs) in dimethyl sulfoxide (DMSO) and storage at -80 °C extends the PLT shelf life to at least 2 years, allowing greater accessibility in military and rural environments. While cryopreserved PLTs have been extensively characterized, the microparticles formed as a result of cryopreservation are yet to be fully described.

STUDY DESIGN AND METHODS

Apheresis PLTs were cryopreserved at -80 °C with 5% DMSO and sampled before freezing and after thawing. Microparticle number, size, surface receptor phenotype, and function were assessed by microscopy, flow cytometry, dynamic light scattering, and thrombin-generating capacity. Proteomic changes were examined using two-dimensional gel electrophoresis and Western blotting.

RESULTS

PLT cryopreservation resulted in a 15-fold increase in the number of microparticles compared to fresh PLTs. The surface receptor phenotype of these microparticles differed to microparticles from fresh PLTs, with more microparticles expressing glycoprotein (GP)IV, GPIIb, and the GPIb-V-IX complex. Cryopreservation drastically altered the abundance of many cytoskeletal proteins in the PLT microparticles, including actin, filamin, gelsolin, and tropomyosin. Despite these changes, PLT microparticles were functional and contributed to phosphatidylserine- and tissue factor- induced thrombin generation.

CONCLUSION

This study demonstrates that PLT microparticles formed by cryopreservation are phenotypically distinct from those present before freezing. These differences may be associated with the procoagulant properties of cryopreserved PLTs.

Correlation of the hypotonic shock response and extent of shape change with the new ThromboLUX ™

ThromboLUX (TLX)-Score was compared with hypotonic shock response (HSR) and extent of shape change (ESC) in 99 samples from 42 platelet concentrates. Tests were performed in parallel and duplicate. Mean values for TLX Score, HSR and ESC were 30.3 ± 3.8%, 69.0 ± 12.2% and 23.2 ± 4.9%, respectively. We found no significant correlation between TLX Score and HSR or ESC (r = -0.158, P = 0.118 and r = -115, P = 0.255, respectively), whereas HSR and ESC correlated significantly (r = 0.351, P < 0.001). As TLX Score did not show significant correlation with HSR and ESC, the value of TLX for platelet quality testing remains unclear. Studies comparing these parameters with transfusion outcome are needed.

The influence of four different anticoagulants on dynamic light scattering of platelets

For testing of dynamic light scattering of platelets with ThromboLUX (TLX) in platelet-rich plasma (PRP) derived from venous whole blood (vWB), anticoagulation is needed. We compared TLX score in PRPs containing citrate, ethylene-diamine-tetraacetic-acid (EDTA), citrate-phosphate-dextrose-adenine (CPDA) or citrate-theophylline-adenosine-dipyridamole. Initial and late TLX scores were measured after 30-120 min or four to six hours, respectively. Compared with citrate, mean differences in initial TLX score were only significant for CPDA. Also, mean differences between initial and late TLX scores were only significant for CPDA. TLX failed to detect EDTA-induced platelet alterations. The clinical relevance of TLX needs further studies.

Characterization of platelet concentrates using dynamic light scattering

BACKGROUND

Each year, millions of platelet transfusions save the lives of cancer patients and patients with bleeding complications. However, between 10 and 30% of all platelet transfusions are clinically ineffective as measured by corrected count increments, but no test is currently used to identify and avoid these transfusions. ThromboLUX(®) is the first platelet test intended to routinely characterize platelet concentrates prior to transfusion.

METHODS

ThromboLUX is a non-invasive, optical test utilizing dynamic light scattering to characterize a platelet sample by the relative quantity of platelets, microparticles, and other particles present in the sample. ThromboLUX also determines the response of platelets to temperature changes. From this information the ThromboLUX score is calculated. Increasing scores indicate increasing numbers of discoid platelets and fewer microparticles. ThromboLUX uses calibrated polystyrene beads as a quality control standard, and accurately measures the size of the beads at multiple temperatures.

RESULTS

Results from apheresis concentrates showed that ThromboLUX can determine the microparticle content in unmodified samples of platelet concentrates which correlates well with the enumeration by flow cytometry. ThromboLUX detection of microparticles and microaggregates was confirmed by microscopy.

CONCLUSION

ThromboLUX provides a comprehensive and novel analysis of platelet samples and has potential as a noninvasive routine test to characterize platelet products to identify and prevent ineffective transfusions.

Flow cytometric assessment of agonist-induced P-selectin expression as a measure of platelet quality in stored platelet concentrates

BACKGROUND

Platelet (PLT) function in PLT concentrates declines during storage and is further affected by pathogen reduction treatment. Flow cytometric assessment of agonist-induced P-selectin expression can be used to assess PLT function in patients with thrombocytopenia. The aim of this study was to evaluate how this functional test relates to established in vitro measures of PLT function.

STUDY DESIGN AND METHODS

Six units of PLTs in plasma and 6 units of riboflavin and ultraviolet (Mirasol, TerumoBCT)-treated PLTs in plasma were sampled on Days 2, 6, 8, and 10 after donation. PLT concentration, Annexin 5A staining, ThromboLUX (LightIntegra) thrombelastography, and P-selectin expression, both in unstimulated PLTs and in response to concentration series of adenosine diphosphate, collagen-related peptide, and thrombin receptor-activating peptide (TRAP), were measured.

RESULTS

For PLTs in plasma Annexin 5A expression increased by 0.60% (95% confidence interval [CI], 0.40%-0.80%) and P-selectin expression increased by 1.2% (95% CI, 0.80%-1.6%) per day. Responsiveness to TRAP simultaneously decreased by 1.3% (95% CI, 0.80%-1.8%) per day. After Mirasol treatment ThromboLUX scores decreased 3.3 points (95% CI, 0.2-6.4 points) from 22 to 19 points, Annexin 5A expression increased by 4.8% (95% CI, 3.3%-6.2%), and P-selectin expression increased by 13% (95% CI, 10%-16%), all averaged over the entire storage period. Responsiveness to TRAP simultaneously decreased by 19% (95% CI, 17%-21%).

CONCLUSIONS

Our results suggest flow cytometric measurement of agonist-induced P-selectin expression can measure PLT quality decline over the entire range encountered during 10-day storage of both standard PLTs and Mirasol-treated PLTs in plasma.

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.

A comparison of washed and volume-reduced platelets with respect to platelet activation, aggregation, and plasma protein removal

BACKGROUND

Washed or volume-reduced platelets (PLTs) are occasionally requested for patients with a history of allergic or anaphylactic transfusion reactions. However, conclusive data are not available as to which method is more suitable.

STUDY DESIGN AND METHODS

A direct comparison of saline-washed and volume-reduced PLTs was performed by splitting 11 units of 6-day-old apheresis PLT units. PLT activation, aggregation, plasma protein, and PLT count were determined before and after each procedure. To assess whether washing using neutral, calcium-free Ringer's acetate (NRA) would better preserve PLT function, 8 additional units of apheresis PLTs were split and were washed in saline or NRA.

RESULTS

Saline washing resulted in significantly increased number of activated, P-selectin-expressing PLTs compared to volume reduction (24.2% vs. 10.3%, p = 0.001). Aggregation was also significantly reduced (-40.6% vs. -0.8%, p = 0.004). Plasma protein removal was significantly better for saline-washed than volume-reduced PLTs (96% vs. 51.1%, p < 0.001). PLT recovery was not significantly different for saline-washed versus volume-reduced PLTs (70.5% vs. 80.7%, p = 0.079). There was no difference between washing in saline or NRA with regard to PLT activation and loss of aggregation.

CONCLUSIONS

PLT washing with saline or NRA significantly increases PLT activation and decreases PLT aggregability. On the other hand, volume reduction does not adequately remove plasma proteins. Therefore, PLT washing should be reserved for patients with a history of severe allergic or anaphylactic transfusion reactions. We suggest that fresher PLTs be selected to improve the functionality of washed PLTs.

The platelet storage lesion

The gradual loss of quality in stored platelets as measured collectively with various metabolic, functional, and morphologic in vitro assays is known as the platelet storage lesion. With the advent of pathogen reduction technologies and improved testing that can greatly reduce the risk for bacterial contamination, the platelet storage lesion is emerging as the main challenge to increasing the shelf life of platelet concentrates. This article discusses the contribution of platelet production methods to the storage lesion, long-established and newly developed methods used to determine platelet quality, and the significance for clinical transfusion outcome. Highlighted are the novel technologies applied to platelet storage including platelet additive solutions and pathogen inactivation.

Novel test for microparticles in platelet-rich plasma and platelet concentrates using dynamic light scattering

BACKGROUND

The level and clinical importance of platelet (PLT)-derived microparticles (PMPs) in PLT-rich plasma (PRP) and PLT transfusions is largely unknown due to the lack of technology to routinely determine the number and size of PMP in PLT samples. Dynamic light scattering (DLS) is ideally suited to measure particles of submicron size but has previously been limited to the analysis of PLT-free samples.

STUDY DESIGN AND METHODS

PMPs were enumerated in 81 PRP and 79 apheresis PLT concentrate (APC) samples from the same donors using ThromboLUX (LightIntegra Technology, Inc.), a new DLS PLT quality test. The ThromboLUX results were compared with flow cytometry. Phase contrast and differential interference contrast (DIC) microscopy were used to qualitatively determine PMP levels.

RESULTS

The relative counts of PMPs measured by flow cytometry strongly correlated with the relative light scattering intensities of the PMP determined by ThromboLUX in both PRP (R = 0.7596, p < 0.0001) and APC (R = 0.6572, p < 0.0001) samples. High or low PMP levels in PLT samples were confirmed by phase contrast and DIC microscopy. The mean PMP radius measured with ThromboLUX, an absolute sizing technology, was 117.1 ± 77.6 nm as determined from the distribution of PMP content in all PLT samples investigated in this study.

CONCLUSIONS

Correlation with flow cytometry and microscopy showed that ThromboLUX is well suited to measure PMP concentration and size distribution in PLT concentrate samples. In combination with noninvasive sampling, ThromboLUX could provide routine microparticle enumeration of PLT-containing samples.