One size doesn't fit all: Should we reconsider the introduction of cold-stored platelets in blood bank inventories?

Delayed cold-stored vs. room temperature stored platelet transfusions in bleeding adult cardiac surgery patients-a randomized multicentre pilot study (PLTS-1)

BACKGROUND

Platelets stored at 1-6 °C are hypothesized to be more hemostatically active than standard room temperature platelets (RTP) stored at 20-24 °C. Recent studies suggest converting RTP to cold-stored platelets (Delayed Cold-Stored Platelets, DCSP) may be an important way of extending platelet lifespan and increasing platelet supply while also activating and priming platelets for the treatment of acute bleeding. However, there is little clinical trial data supporting the efficacy and safety of DCSP compared to standard RTP.

METHODS

This protocol details the design of a multicentre, two-arm, parallel-group, randomized, active-control, blinded, internal pilot trial to be conducted at two cardiac surgery centers in Canada. The study will randomize 50 adult (≥ 18 years old) patients undergoing at least moderately complex cardiac surgery with cardiopulmonary bypass and requiring platelet transfusion to receive either RTP as per standard of care (control group) or DCSP (intervention group). Patients randomized to the intervention group will receive ABO-identical, buffy-coat, pathogen-reduced, platelets in platelet additive solution maintained at 22 °C for up to 4 days then placed at 4 °C for a minimum of 24 h, with expiration at 14 days after collection. The duration of the intervention is from the termination of cardiopulmonary bypass to 24 h after, with a maximum of two doses of DCSP. Thereafter, all patients will receive RTP. The aim of this pilot is to assess the feasibility of a future RCT comparing the hemostatic effectiveness of DCSP to RTP (defined as the total number of allogeneic blood products transfused within 24 h after CPB) as well as safety. Specifically, the feasibility objectives of this pilot study are to determine (1) recruitment of ≥ 15% eligible patients per center per month); (2) appropriate platelet product available for ≥ 90% of patients randomized to the cold-stored platelet group; (3) Adherence to randomization assignment (> 90% of patients administered assigned product).

DISCUSSION

DCSP represents a promising logistical solution to address platelet supply shortages and a potentially more efficacious option for the management of active bleeding. No prospective clinical studies on this topic have been conducted. This proposed internal pilot study will assess the feasibility of a larger definitive study.

TRIAL REGISTRATION

NCT06147531 (clinicaltrials.gov).

In vitro Hemostatic Functions of Cold-Stored Platelets

Background

Transfusion of platelets is a life-saving medical strategy used worldwide to treat patients with thrombocytopenia as well as platelet function disorders.

Summary

Until the end of 1960s, platelets were stored in the cold because of their superior hemostatic functionality. Cold storage of platelets was then abandoned due to better posttransfusion recovery and survival of room temperature (RT)-stored platelets, demonstrated by radioactive labeling studies. Based on these findings, RT became the standard condition to store platelets for clinical applications. Evidence shows that RT storage increases the risk of septic transfusion reactions associated with bacterial contamination. Therefore, the storage time is currently limited to 4-7 days, according to the national guidelines, causing a constant challenge to cover the clinical request. Despite the enormous efforts made to optimize storage conditions of platelets, the quality and efficacy of platelets still decrease during the short storage time at RT. In this context, during the last years, cold storage has seen a renaissance due to the better hemostatic functionality, reduced risk of bacterial contamination, and potentially longer storage time.

Key Messages

In this review, we will focus on the impact of cold storage on the in vitro platelet functions as promising alternative storage temperature for future medical applications.

Cold stored platelets in the management of bleeding: is it about bioenergetics?

When platelet concentrates (PCs) were first introduced in the 1960s as a blood component therapy, they were stored in the cold. As platelet transfusion became more important for the treatment of chemotherapy-induced thrombocytopenia, research into ways to increase supply intensified. During the late 1960s/early 1970s, it was demonstrated through radioactive labeling of platelets that room temperature platelets (RTP) had superior post-transfusion recovery and survival compared with cold-stored platelets (CSP). This led to a universal switch to room temperature storage, despite CSP demonstrating superior hemostatic effectiveness upon being transfused. There has been a global resurgence in studies into CSP over the last two decades, with an increase in the use of PC to treat acute bleeding within hospital and pre-hospital care. CSP demonstrate many benefits over RTP, including longer shelf life, decreased bacterial risk and easier logistics for transport, making PC accessible in areas where they have not previously been, such as the battlefield. In addition, CSP are reported to have greater hemostatic function than RTP and are thus potentially better for the treatment of bleeding. This review describes the history of CSP, the functional and metabolic assays used to assess the platelet storage lesion in PC and the current research, benefits and limitations of CSP. We also discuss whether the application of new technology for studying mitochondrial and glycolytic function in PC could provide enhanced understanding of platelet metabolism during storage and thus contribute to the continued improvements in the manufacturing and storage of PC.

Cold-stored platelet function is not significantly altered by agitation or manual mixing

BACKGROUND

Cold storage of platelets (CS-PLT), results in better maintained hemostatic function compared to room-temperature stored platelets (RT-PLT), leading to increased interest and use of CS-PLT for actively bleeding patients. However, questions remain on best storage practices for CS-PLT, as agitation of CS-PLT is optional per the United States Food and Drug Administration. CS-PLT storage and handling protocols needed to be determined prior to upcoming clinical trials, and blood banking standard operating procedures need to be updated accordingly for the release of units due to potentially modified aggregate morphology without agitation.

STUDY DESIGN AND METHODS

We visually assessed aggregate formation, then measured surface receptor expression (GPVI, CD42b (GPIbα), CD49 (GPIa/ITGA2), CD41/61 (ITGA2B/ITGB3; GPIIB/GPIIIA; PACI), CD62P, CD63, HLAI), thrombin generation, aggregation (collagen, adenosine diphosphate [ADP], and epinephrine activation), and viscoelastic function (ExTEM, FibTEM) in CS-PLT (Trima collection, 100% plasma) stored for 21 days either with or without agitation (Phase 1, n = 10 donor-paired units) and then without agitation with or without daily manual mixing to minimize aggregate formation and reduce potential effects of sedimentation (Phase 2, n = 10 donor-paired units).

RESULTS

Agitation resulted in macroaggregate formation, whereas no agitation caused film-like sediment. We found no substantial differences in CS-PLT function between storage conditions, as surface receptor expression, thrombin generation, aggregation, and clot formation were relatively similar between intra-Phase storage conditions.

DISCUSSION

Storage duration and not condition impacted phenotype and function. CS-PLT can be stored with or without agitation, and with or without daily mixing and standard metrics of hemostatic function will not be significantly altered.

The Missing Pieces to the Cold-Stored Platelet Puzzle

Cold-stored platelets are making a comeback. They were abandoned in the late 1960s in favor of room-temperature stored platelets due to the need for longer post-transfusion platelet recoverability and survivability in patients with chronic thrombocytopenia. However, the current needs for platelet transfusions are rapidly changing. Today, more platelets are given to patients who are actively bleeding, such as ones receiving cardiac surgeries. It has been established that cold-stored platelets are more hemostatically effective, have reduced bacterial growth, and have longer potential shelf lives. These compelling characteristics led to the recent interest in bringing back cold-stored platelets to the blood systems. However, before reinstating cold-stored platelets in the clinics again, a thorough investigation of in vitro storage characteristics and in vivo transfusion effects is required. This review aims to provide an update on the recent research efforts into the storage characteristics and functions of cold-stored platelets using modern investigative tools. We will also discuss efforts made to improve cold-stored platelets to be a better and safer product. Finally, we will finish off with discussing the relevance of in vitro data to in vivo transfusion results and provide insights and directions for future investigations of cold-stored platelets.

Time from apheresis platelet donation to cold storage: Evaluation of platelet quality and bacterial growth

BACKGROUND

Cold storage reduces posttransfusion survival of platelets; however, it can improve platelet activation, lower risk of bacterial contamination, and extend shelf-life compared to room temperature (RT) storage. To facilitate large-scale availability, manufacturing process optimization is needed, including understanding the impact of variables on platelet potency and safety. Short time requirements from collection to storage is challenging for large blood centers to complete resuspension and qualify platelets for production. This study evaluated the impact of time from platelet component collection to cold storage on in vitro properties and bacterial growth.

STUDY DESIGN AND METHODS

Double-apheresis platelet components were collected from healthy donors, suspended in 65% PAS-III/35% plasma, and split into 2 equal units. One unit was placed into cold storage within 2 h and the other unit after 8 h. Eight matched pairs were evaluated for 12 in vitro parameters. Twenty-four matched pairs were evaluated with 8 bacterial strains tested in triplicate. Samples were tested throughout 21 days of storage.

RESULTS

In vitro properties were not different between 2 and 8 h units, and trends throughout storage were similar between arms. Time to cold storage did not significantly impact bacterial growth, with <1 log₁₀ difference at all timepoints between units.

DISCUSSION

Our studies showed that extending time to cold storage from 2 to 8 h from collection did not significantly increase the bacterial growth, and the platelet component quality and function is maintained. The ability to extend the time required from collection to storage will improve blood center logistics to feasibly produce CSPs.

In Vitro Characterization and Metabolomic Analysis of Cold-Stored Platelets

Platelet concentrates are currently stored at room temperature (RP) under constant agitation for up to 5-7 days depending on national regulations. However, platelet quality deteriorates during storage and room-temperature storage also increases the risk of bacterial growth. Previous studies have shown that cold-stored platelets (CPs) have higher hemostatic functions and can be stored for up to 3 weeks. While these studies have compared the metabolic phenotypes of CPs and RPs, they have neither compared the impact of storage temperature and cold agitation (CPAs) on platelet function nor identified metabolic correlates to such parameters. In vitro analysis showed that CPAs and CPs had reduced count, faster CD62P expression, and increased lactadherin binding. Furthermore, CPAs and CPs had higher maximal aggregation and a reduced aggregation lag phase compared to RPs. Metabolomic analysis revealed that CPAs and CPs exhibited lower oxidative stress shown by preserved glutathione and pentose phosphate pools. CPAs and CPs also had reduced markers of beta-oxidation and amino acid catabolism, demonstrating reduced needs for energy. Agitation did not significantly impact in vitro function or metabolomic parameters of cold-stored platelets. Correlation of in vitro and metabolomic results highlighted important metabolites that may contribute to stored platelet functions. Raw data are publicly available through Metabolomics Workbench with the study identifier ST001644.

Validation of a SCID mouse model for transfusion by concurrent comparison of circulation kinetics of human platelets, stored under various temperature conditions, between human volunteers and mice

BACKGROUND

Initial evaluation of new platelet (PLT) products for transfusion includes a clinical study to determine in vivo recovery and survival of autologous radiolabeled PLTs in healthy volunteers. These studies are expensive and do not always produce the desired results. A validated animal model of human PLTs in vivo survival and recovery used pre-clinically could reduce the risk of failing to advance product development.

STUDY DESIGN AND METHODS

An immunodeficient (SCID) mouse model to evaluate recovery of human PLTs was compared to a radiolabeling study in human volunteers. Autologous apheresis PLTs stored for 7 days at room temperature (RT), thermo-cycled (TC), and cold temperature (CT) were radiolabeled and infused into healthy humans (n = 16). The same PLTs, non-radiolabeled, were also infused into mice (n = 160) on the same day. Blood samples from humans and mice were collected to generate clearance curves of PLTs in circulation. Flow cytometry was used to detect human PLTs in mouse blood.

RESULTS

Human and mouse PLTs were cleared with one phase exponential clearance. Relative differences for initial recovery and AUC, expressed as ratio of test and control PLTs, were similar in humans and mice. The initial recovery ratio of TC/RT was 0.73 ± 0.07 in humans and 0.67 ± 0.14 in mice. The ratio for CT/TC was 0.53 ± 0.06 in humans and 0.75 ± 0.18 in mice.

CONCLUSION

The SCID mouse model can provide information on relative differences of initial in vivo recovery and AUC between control and alternatively stored/processed human PLTs that is predictive of performance in healthy human volunteers.

TEG PlateletMapping assay results may be misleading in the presence of cold stored platelets

BACKGROUND

Viscoelastic tests (VETs) are used widely to monitor hemostasis in settings such as cardiac surgery. There has also been renewed interest in cold stored platelets (CSPs) to manage bleeding in this setting. CSPs are reported to have altered hemostatic properties compared to room temperature platelets (RTPs), including activation of GPIIb/IIIa. We investigated whether the functional differences between CSP and RTP affected the performance of the PlateletMapping VET on the TEG 5000 and 6s analyzer.

METHOD

Platelet concentrates were divided equally into CSP (stored at 4°C ± 2°C) and RTP (stored at 22°C ± 2°C) fractions. Whole blood was treated to induce platelet dysfunction (WBIPD) by incubating with anti-platelet drugs (1.0 μM ticagrelor and 10 μM aspirin) or by simulating cardiopulmonary bypass. WBIPD samples were then mixed with 20% by volume of CSPs or RTPs to model platelet transfusion before analysis using the PlateletMapping VET.

RESULTS

Addition of CSPs to WBIPD increased the PlateletMapping MA_FIBRIN and MA_ADP parameters with the TEG 5000 analyzer (both p < 0.0001 compared to addition of buffer alone). This effect was not observed with RTPs. The differential effect of CSPs on the MA_FIBRIN corrected after pre-incubation with the GPIIb/IIIa antagonist tirofiban and was quantitatively less with the PlateletMapping test for the TEG 6s analyzer which contains the GPIIb/IIa antagonist abciximab.

DISCUSSION

The PlateletMapping MA_FIBRIN and MA_ADP test results may be misleadingly high with CSPs, particularly with the TEG 5000 analyzer, most likely due to constitutive activation of GPIIb/IIIa on CSPs during storage. TEG PlateletMapping results should be interpreted with caution following CSP transfusion.

The effect of platelet storage temperature on haemostatic, immune, and endothelial function: potential for personalised medicine

Reports from both adult and paediatric populations indicate that approximately two-thirds of platelet transfusions are used prophylactically to prevent bleeding, while the remaining one-third are used therapeutically to manage active bleeding. These two indications, prophylactic and therapeutic, serve two very distinct purposes and therefore will have two different functional requirements. In addition, disease aetiology in a given patient may require platelets with different functional characteristics. These characteristics can be derived from the various manufacturing methods used in platelet product production, including collection methods, processing methods, and storage options. The iterative combinations of manufacturing methods can result in a number of unique platelet products with different efficacy and safety profiles, which could potentially be used to benefit patient populations by meeting diverse clinical needs. In particular, cold storage of platelet products causes many biochemical and functional changes, of which the most notable characterised to date include increased haemostatic activity and altered expression of molecules inherent to platelet:leucocyte interactions. The in vivo consequences, both short- and long-term, of these molecular and cellular cold-storage-induced changes have yet to be clearly defined. Elucidation of these mechanisms would potentially reveal unique biologies that could be harnessed to provide more targeted therapies. To this end, in this new era of personalised medicine, perhaps there is an opportunity to provide individual patients with platelet products that are tailored to their clinical condition and the specific indication for transfusion.

Hypothermia-induced activation of the splenic platelet pool as a risk factor for thrombotic disease in a mouse model

BACKGROUND

Hypothermia, either therapeutically induced or accidental (ie, an involuntary decrease in core body temperature to <35°C), results in hemostatic disorders. However, it remains unclear whether hypothermia enhances or inhibits coagulation, especially in severe hypothermia. The present study evaluated the thrombocytic and hemostatic changes in hypothermic mice.

METHODS

C57Bl/6 mice were placed at an ambient temperature of -20°C under general anesthesia. When the rectal temperature decreased to 15°C, 10 mice were immediately euthanized, while another 10 mice were rewarmed, kept in normal conditions for 24 hours, and then euthanized. These treatments were also performed in 20 splenectomized mice.

RESULTS

The hypothermic mice had adhesion of CD62P-positive platelets with high expression of von Willebrand factor (vWF) in their spleens, while the status of the peripheral platelets was unchanged. Furthermore, the plasma levels of platelet factor 4 (PF4) and pro-platelet basic protein (PPBP), which are biomarkers for platelet degranulation, were significantly higher in hypothermic mice than in control mice, indicating that hypothermia activated the platelets in the splenic pool. Thus, we analyzed these biomarkers in asplenic mice. There was no increase in either PF4 or PPBP in splenectomized hypothermic mice. Additionally, the plasma D-dimer elevation and microthrombosis were caused in rewarmed mice, but not in asplenic rewarmed mice.

CONCLUSIONS

Our results indicate that hypothermia leads to platelet activation in the spleen via the upregulation of vWF, and this activation causes hypercoagulability after rewarming.