Biotinylation of platelets for transfusion purposes a novel method to label platelets in a closed system

Biotin labeling allows for post-transfusion functional assessment of stored human platelets in mice

BACKGROUND

Platelet radiolabeling with radioisotopes is currently used for human platelet recovery and survival studies. Biotinylation enables ex vivo post-transfusion platelet function testing. Whether platelet biotinylation itself affects platelet function is controversial.

STUDY DESIGN AND METHODS

Platelet concentrates from healthy humans were stored for 6 days. Samples were obtained at 1 or 2 and 6 days, and platelets were labeled following a radiolabeling protocol using saline instead of radioactive indium-111 (sham radiolabeling [sham-RL]). Alternatively, a newly developed biotinylation protocol, a washing protocol, or an unmanipulated control sample were used. Platelet function was assessed by flow cytometry after stimulation with platelet agonists and labeling of platelets with platelet activation markers. To test whether platelets can be activated after transfusion, labeled platelets were transfused into nonobese diabetic/severe combined immunodeficiency mice, and samples were obtained 1 h after transfusion.

RESULTS

The activation profile of biotinylated platelets was comparable to sham-RL platelets before transfusion except for significantly less α-degranulation and more phosphatidyl serine exposure on storage day 1/2. There was no significant difference between sham-RL and biotinylated platelets on storage day 6. Sham-RL and biotinylated platelets were significantly less activatable than washed and unmanipulated control platelets. After transfusion, the activation profile of biotinylated platelets was largely indistinguishable from unmanipulated ones.

DISCUSSION

The decrease in activation level in biotinylated platelets we and others observed appears mainly due to the physical manipulation during the labeling process. In conclusion, biotinylated platelets allow for post-transfusion function assessment, a major advantage over radiolabeling.

Evaluation of a method to fluorescently label platelets for in-human recovery and survival studies

BACKGROUND AND OBJECTIVES

Platelets for transfusion are evaluated for in vivo quality using recovery and survival measurements in healthy human subjects. Radiolabelling is the standard for tracing platelets post-transfusion but imposes logistical and technical limitations. This study investigates the in vitro feasibility of labelling platelets with the calcein family of fluorescent dyes as an alternative to radioisotopes or biotin.

MATERIALS AND METHODS

Protocols for radiolabelling were adapted for use with calcein acetoxymethyl ester (CAM) and biotin. Labelled platelets were analysed by flow cytometry and evaluated for activation and function. We tested feasibility for labelling without manipulation of platelets and for multiplexing of samples.

RESULTS

Labelling at 2 μg CAM/1010 platelets resulted in >99% of CAM+ platelets. There was no significant difference in activation or aggregation between CAM-labelled or biotinylated platelets and vehicle controls although %CD62P+ was significantly lower in platelets that were not processed for labelling. Addition of CAM to the platelet storage bag labelled >95% of platelets. Platelet populations labelled with different dyes could be distinguished by flow cytometry.

CONCLUSION

These data provide a rationale for further development of CAM and other fluorescent dyes as tools for measuring post-transfusion kinetics of platelets.

Indocyanine Green-Labeled Platelets for Survival and Recovery Studies

Introduction

Before being implemented in daily clinical routine, new production strategies for platelet concentrates (PCs) must be validated for their efficacy. Besides in vitro testing, the establishment of new methods requires the labeling of platelets for in vivo studies of platelets' survival and recovery. Indocyanine green (ICG) is a Food and Drug Administration-approved near-infrared (NIR) fluorescent dye for diagnostic use in vivo, suitable for non-radioactive direct cell labeling of platelets.

Methods

Platelets from PCs in storage solutions with different plasma concentrations were labeled with ICG up to concentrations of 200 μm. Whole blood (WB) was used as an ex vivo matrix to monitor the labeling stability of ICG-labeled platelets. The impact of labeling processes was assessed by the quantification of CD62P expression and PAC-1 binding as platelet function markers. Platelet aggregation was analyzed by light transmission aggregometry. ICG-labeling efficiency and stability of platelets were determined by flow cytometry.

Results

Platelets from PCs could be successfully labeled with 10 μm ICG after 1 and 4 days of storage. The best labeling efficiency of 99.8% ± 0.1% (immediately after labeling) and 81% ± 6.2% (after 24 h incubation with WB) was achieved by plasma replacement by 100% platelet additive solution for the labeling process. Since the washing process slightly impaired platelet function, ICG labeling itself did not affect platelets. Immediately after the ICG-labeling process, plasma was re-added, resulting in a recovered platelet function.

Conclusion

We developed a Good Manufacturing Practice compatible protocol for ICG fluorescent platelet labeling suitable for survival and recovery studies in vivo as a non-radioactive labeling alternative.

Biotinylated Platelets: A Promising Labeling Technique?

Labeling of platelets (PLTs) is essential for research purposes, in order to measure the recovery and survival of transfused PLTs in vivo. Biotinylation is a promising new alternative to the gold standard of radioactive labeling. This review highlights 4 key publications that provide significant insights into biotin-labeled PLTs (bioPLTs). Stohlawetz et al. established that transfusion of bioPLTs in human recipients is possible. De Bruin et al. developed a standardized, reproducible protocol for biotinylation of PLTs as a promising method to trace and isolate transfused PLTs in vivo, with reduced levels of PLT activation markers. Muret et al. developed a nonwashing biotin labeling method to implement in a blood bank environment. Finally, in a preclinical study, Ravanat et al. showed that different densities of biotin can be used to concurrently monitor multiple populations of human PLTs in the circulation of the same subject. These studies have made major contributions to the development of bioPLTs as a viable option for use in human research, and indicate that bioPLTs can be safely administered, preferably at a low density of biotin.

Aged versus fresh autologous platelet transfusion in a two-hit healthy volunteer model of transfusion-related acute lung injury

BACKGROUND

Transfusion-related acute lung injury (TRALI) is a severe complication of blood transfusion that is thought of as a two-hit event: first the underlying patient condition (e.g., sepsis), and then the transfusion. Transfusion factors include human leukocyte antigen antibodies or biologic response modifiers (BRMs) accumulating during storage. Preclinical studies show an increased TRALI risk with longer stored platelets, clinical studies are conflicting. We aim to discover whether longer platelet concentrate (PC) storage time increases TRALI risk in a controlled human experiment.

STUDY DESIGN AND METHODS

In a randomized controlled trial, 18 healthy male volunteers received a first hit of experimental endotoxemia (2 ng/kg lipopolysaccharide), and a second hit of fresh (2-day old) or aged (7-day old) autologous PC, or physiological saline. After 6 h, changes in TRALI pathways were determined using spirometry, chest X-ray, and bronchoalveolar lavage (BAL).

RESULTS

All subjects reacted adequately to lipopolysaccharide infusion and satisfied SIRS criteria (increased pulse [>90/min] and temperature [>38°C]). There were no differences between the saline, fresh, and aged PC groups in BAL-fluid protein (95 ± 33 μg/ml; 83 ± 21 μg/ml and 104 ± 29 μg/ml, respectively) and relative neutrophil count (1.5 ± 0.5%; 1.9 ± 0.8% and 1.3 ± 0.8%, respectively), nor in inflammatory BAL-fluid BRMs (Interleukin-6, CXCL8, TNFα , and myeloperoxidase), clinical respiratory parameters, and spirometry results. All chest X-rays were normal.

CONCLUSIONS

In a human endotoxemia model of autologous platelet transfusion, with an adequate first hit and platelet storage lesion, transfusion of 7-day-old PC does not increase pulmonary inflammation compared with 2-day-old PC.

Two novel platelet biotinylation methods and their impact on stored platelet concentrates in a blood bank environment

BACKGROUND

Storage of platelet concentrates (PCs) has an impact on platelet quality and possibly affects their functions after transfusion. The influence of processing and storage conditions of PCs on their in vivo function upon transfusion is unknown. One option for investigating this question is to implement an ex vivo labeling of human platelets, to analyze them after transfusion into heathy volunteers and/or patients. In this study, we developed two labeling methods employing biotin.

METHODS

Two methods of biotinylation were compared to a control (standard PC). The "Bio-Wash" process used washing steps to label all platelets within the PC; for the other method, "Bio-Direct," one fifth of the PC were directly labeled without washing steps. The control and the two biotinylated PCs were analyzed over 7 days of storage. Labeling efficiency, platelet counts, phenotypes, and functions, along with time and costs, were evaluated to select the best process.

RESULTS

Both methods achieved a stable labeling through the storage, with similar platelet counts and metabolism in comparison to control PCs. Bio-Wash showed higher activation phenotype and lower aggregation response in comparison to the Bio-Direct method. The Bio-Direct was performed within 1.5 h versus 3 h for the Bio-Wash. However, the Bio-Direct required 12 mg of biotin instead of 8 mg for the other process.

CONCLUSION

We set up two methods of biotinylation that can be easily implemented in a blood bank environment. The Bio-Direct process was preferred to the Bio-Wash because of its similarity, from a functional and phenotypic point of view, with standard PCs.

Current challenges in platelet transfusion

The supply of platelets for transfusion is a logistical challenge due to the physiology of platelets and current measures of transfusion performance dictating storage at 22°C and a short product shelf-life (<7 days). Demand for platelets has increased in recent years and changes in the demographics of the population may enhance this further. Many studies have been conducted to understand what the optimal dose and trigger for transfusion should be, mainly in hematology patients who are the largest cohort that receive platelets, mostly to prevent bleeding. Emerging data suggests that for bleeding patients, where immediate hemostasis is a key consideration, the current standard product may not be optimal. Alternative platelet preparation methods/storage options that may improve the hemostatic properties of platelets are under active development. In parallel with research into alternative platelet products that might enhance hemostasis, better measures for assessing bleeding risk and platelet efficacy are needed.

Human platelets labeled at two discrete biotin densities are functional in vitro and are detected in vivo in the murine circulation: A promising approach to monitor platelet survival in vivo in clinical research

BACKGROUND

The production of platelet concentrates (PCs) is evolving, and their survival capacity needs in vivo evaluation. This requires that the transfused platelets (PLTs) be distinguished from those of the recipient. Labeling at various biotin (Bio) densities allows one to concurrently trace multiple PLT populations, as reported for red blood cells.

STUDY DESIGN AND METHODS

A method is described to label human PLTs at two densities of Bio for future clinical trials. Injectable-grade PLTs were prepared in a sterile environment, using injectable-grade buffers and good manufacturing practices (GMP)-grade Sulfo-NHS-Biotin. Sulfo-NHS-Biotin concentrations were chosen to maintain PLT integrity and avoid potential alloimmunization while enabling the detection of circulating BioPLTs. The impact of biotinylation on human PLT recirculation was evaluated in vivo in a severe immunodeficient mouse model using ex vivo flow cytometry.

RESULTS

BioPLTs labeled with 1.2 or 10 μg/ml Sulfo-NHS-Biotin displayed normal ultrastructure and retained aggregation and secretion capacity and normal expression of the main surface glycoproteins. The procedure avoided detrimental PLT activation or apoptosis signals. Transfused human BioPLT populations could be distinguished from one another and from unlabeled circulating mouse PLTs, and their survival was comparable to that of unlabeled human PLTs in the mouse model.

CONCLUSIONS

Provided low Sulfo-NHS-Biotin concentrations (<10 μg/ml) are used, injectable-grade BioPLTs comply with safety regulations, conserve PLT integrity, and permit accurate in vivo detection. This alternative to radioisotopes, which allows one to follow different PLT populations in the same recipient, should be valuable when assessing new PC preparations and monitoring PLT survival in clinical research.

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.