In vitro evaluation of the hemostatic effectiveness of cryopreserved platelets

Cryopreservation affects platelet macromolecular composition over time after thawing and differently impacts on cancer cells behavior in vitro

Cryopreservation affects platelets' function, questioning their use for cancer patients. We aimed to investigate the biochemical events that occur over time after thawing to optimize transfusion timing and evaluate the effect of platelet supernatants on tumor cell behavior in vitro. We compared fresh (Fresh-PLT) with Cryopreserved platelets (Cryo-PLT) at 1 h, 3 h and 6 h after thawing. MCF-7 and HL-60 cells were cultured with Fresh- or 1 h Cryo-PLT supernatants to investigate cell proliferation, migration, and PLT-cell adhesion. We noticed a significant impairment of hemostatic activity accompanied by a post-thaw decrease of CD42b+ , which identifies the CD62P--population. FTIR spectroscopy revealed a decrease in the total protein content together with changes in their conformational structure, which identified two sub-groups: 1) Fresh and 1 h Cryo-PLT; 2) 3 h and 6 h cryo-PLT. Extracellular vesicle shedding and phosphatidylserine externalization (PS) increased after thawing. Cryo-PLT supernatants inhibited cell proliferation, impaired MCF-7 cell migration, and reduced ability to adhere to tumor cells. Within the first 3 hours after thawing, irreversible alterations of biomolecular structure occur in Cryo-PLT. Nevertheless, Cryo-PLT should be considered safe for the transfusion of cancer patients because of their insufficient capability to promote cancer cell proliferation, adhesion, or migration.

Identification of platelet subpopulations in cryopreserved platelet components using multi-colour imaging flow cytometry

Cryopreservation of platelets, at  - 80 °C with 5-6% DMSO, results in externalisation of phosphatidylserine and the formation of extracellular vesicles (EVs), which may mediate their procoagulant function. The phenotypic features of procoagulant platelets overlap with other platelet subpopulations. The aim of this study was to define the phenotype of in vitro generated platelet subpopulations, and subsequently identify the subpopulations present in cryopreserved components. Fresh platelet components (n = 6 in each group) were either unstimulated as a source of resting platelets; or stimulated with thrombin and collagen to generate a mixture of aggregatory and procoagulant platelets; calcium ionophore (A23187) to generate procoagulant platelets; or ABT-737 to generate apoptotic platelets. Platelet components (n = 6) were cryopreserved with DMSO, thawed and resuspended in a unit of thawed plasma. Multi-colour panels of fluorescent antibodies and dyes were used to identify the features of subpopulations by imaging flow cytometry. A combination of annexin-V (AnnV), CD42b, and either PAC1 or CD62P was able to distinguish the four subpopulations. Cryopreserved platelets contained procoagulant platelets (AnnV+/PAC1-/CD42b+/CD62P+) and a novel population (AnnV+/PAC1-/CD42b+/CD62P-) that did not align with the phenotype of aggregatory (AnnV-/PAC1+/CD42b+/CD62P+) or apoptotic (AnnV+/PAC1-/CD42b-/CD62P-) subpopulations. These data suggests that the enhanced haemostatic potential of cryopreserved platelets may be due to the cryo-induced development of procoagulant platelets, and that additional subpopulations may exist.

Cryopreserved platelets in bleeding management in remote hospitals: A clinical feasibility study in Sweden

Background

Balanced transfusions, including platelets, are critical for bleeding patients to maintain hemostasis. Many rural hospitals have no or limited platelet inventory, with several hours of transport time from larger hospitals. This study aimed to evaluate the feasibility of using cryopreserved platelets that can be stored for years, in remote hospitals with no or limited platelet inventory.

Material and methods

Three remote hospitals participated in a prospective study including adult bleeding patients where platelet transfusions were indicated. Cryopreserved platelets were prepared in a university hospital, concentrated in 10 ml, transported on dry ice, and stored at -80°C at the receiving hospital. At request, the concentrated platelet units were thawed and diluted in fresh frozen plasma. The indications, blood transfusion needs, and laboratory parameters pre- and post-transfusion, as well as logistics, such as time from request to transfusion and work efforts in preparing cryopreserved platelets, were evaluated.

Results

Twenty-three bleeding patients were included. Nine patients (39%) were treated for gastrointestinal bleeding, five (22%) for perioperative bleeding, and four (17%) for trauma bleeding. The transfusion needs were 4.9 ± 3.3 red blood cell units, 3.2 ± 2.3 plasma units, and 1.9 ± 2.2 platelet units, whereof cryopreserved were 1.5 ± 1.1 (mean ± SD). One patient had a mild allergic reaction. We could not show the difference in laboratory results between pre- and post-transfusion of the cryopreserved units in the bleeding patients. The mean time from the order of cryopreserved platelets to transfusion was 64 min, with a range from 25 to 180 min.

Conclusion

Cryopreserved platelets in remote hospitals are logistically feasible in the treatment of bleeding. The ability to have platelets in stock reduces the time to platelet transfusion in bleeding patients where the alternative often is many hours delay. Clinical effectiveness and safety previously shown in other studies are supported in this small feasibility study.

Frozen for combat: Quality of deep-frozen thrombocytes, produced and used by The Netherlands Armed Forces 2001-2021

BACKGROUND

The Netherlands Armed Forces (NLAF) are using -80°C deep-frozen thrombocyte concentrate (DTC) since 2001. The aim of this study is to investigate the effect of storage duration and alterations in production/measurement techniques on DTC quality. It is expected that DTC quality is unaffected by storage duration and in compliance with the European guidelines for fresh and cryopreserved platelets.

STUDY DESIGN AND METHODS

Pre-freeze and post-thaw product platelet content and recovery were collected to analyze the effects of dimethyl sulfoxide (DMSO) type, duration of frozen storage (DMSO-1 max 12 years and DMSO-2 frozen DTC max 4 years at -80°C) and type of plasma used to suspend DTC. Coagulation characteristics of thawed DTC, plasma and supernatant of DTC (2× 2500 G) were measured with Kaolin thromboelastography (TEG) and phospholipid (PPL) activity assay.

RESULTS

Platelet content and recovery of DTC is ±10%-15% lower in short-stored products and remained stable when stored beyond 0.5 years. Thawed DTC (n = 1724) were compliant to the European guidelines (98.1% post-thaw product recovery ≥50% from original product, 98.3% ≥200 × 10⁹ platelets/unit). Compared to DMSO-1, products frozen with DMSO-2 showed ±8% reduced thaw-freeze recovery, a higher TEG clot strength (MA 58 [6] vs. 64 [8] mm) and same ±11 s PPL clotting time. The use of cold-stored thawed plasma instead of fresh thawed plasma did not influence product recovery or TEG-MA.

DISCUSSION

Regardless of alterations, product quality was in compliance with European guidelines and unaffected by storage duration up to 12 years of -80°C frozen storage.

Implementation of a low-titer stored whole blood transfusion program for civilian trauma patients: Early experience and logistical challenges

INTRODUCTION

Cold-stored low titer group O whole blood (LTOWB) is increasingly utilized in the initial resuscitation of exsanguinating trauma patients. We report on our early experience with LTOWB, focusing on logistics, implementation challenges, and outcomes.

METHODS

In February, 2019, LTOWB was incorporated into the massive transfusion protocol (MTP) activated for trauma patients in the emergency department (ED.) Up to 4 units of LTOWB were included in the MTP cooler, depending on availability, and were transfused prior to transfusion of any other blood products from the MTP cooler. Demographics, injury characteristics, and outcomes were obtained, and the logistics of LTOWB availability were reviewed.

RESULTS

Over a 12-month period, MTP was activated for 74 trauma patients. Of those, 38 (51%) MTP included at least one unit of LTOWB, with 19/38 (50%) including 4 LTOWB units. A total of 177 units of LTOWB were purchased during the study period, and of those, 74 (42%) expired before use. Patients who received LTOWB had a similar mortality compared to those who received component therapy (39% vs. 47%; Odds Ratio [95% CI]: 0.7 [0.3, 2.0]; p = 0.72,) however, they were able to achieve a significantly higher plasma:pRBC ratio during the duration of MTP activation (mean [SD] 0.8 [0.2] vs. 0.4 [0.4]; mean difference [95% CI]: 0.4 [0.2, 0.5]; p < 0.01.) CONCLUSIONS: Our early experience with LTOWB transfusion demonstrates feasibility, but also highlights challenges with inventory management. These findings triggered changes to our protocol aiming at minimizing wastage. The use of LTOWB may yield a higher plasma:pRBC ratio early during the resuscitation period. Further investigation is required to explore whether this may yield a survival advantage.

LEVEL OF EVIDENCE

III (Therapeutic/Care Management).

In-vitro thromboelastographic characterization of reconstituted whole blood utilizing cryopreserved platelets

Conducting in-vitro thrombosis research presents numerous challenges, the primary of which is working with blood products, whether whole blood or fractionated whole blood, that have limited functional shelf-lives. As a result, being able to significantly prolong the clotting functionality of whole blood via fractionation and recombination promises greater accessibility via resource minimization in the realm of thrombosis research. Whole blood with CPDA1 from healthy volunteers was fractionated and stored as frozen platelet-free plasma (PFP, -20°C), refrigerated packed red blood cells (pRBCs, 4°C) and cryopreserved platelets (-80°C). Subsequent recombination of the above components into their native ratios were tested via thromboelastography (TEG) to capture clotting dynamics over a storage period of 13 weeks in comparison to refrigerated unfractionated WB+CPDA1. Reconstituted whole blood utilizing PFP, pRCBs and cryopreserved platelets were able to maintain clot strength (maximum amplitude) akin to day-0 whole blood even after 13 weeks of storage. Clots formed by reconstituted whole blood exhibited quicker clotting dynamics with nearly two-fold shorter R-times and nearly 1.3-fold increase in fibrin deposition rate as measured by TEG. Storage of fractionated whole blood components, in their respective ideal conditions, provides a means of prolonging the usable life of whole blood for in-vitro thrombosis research. Cryopreserved platelets, when recombined with frozen PFP and refrigerated pRBCs, are able to form clots that nearly mirror the overall clotting profile expected of freshly drawn WB.

Frozen and cold-stored platelets: reconsidered platelet products

Platelet transfusion, both prophylactic and therapeutic, is a key element in modern medicine. Currently, the standard platelet product for clinical use is platelet concentrates at room temperature (20-24°C) under gentle agitation. As this temperature favors bacterial growth, storage is limited to 5-7 days, which result in high wastage rate, and complicates inventory and product availability at remote areas. Frozen and/or cold storage would ameliorate those disadvantages by reducing the risk of bacterial contamination and by extending the product shelf-life to weeks or even years. Consequently, the usefulness in transfusion medicine of platelet cryopreservation and refrigeration, two old and scarcely used platelet storage approaches, is reemerging. Indeed, there have been substantial recent research efforts to characterize both cold and cryopreserved platelets. Most recent studies indicate that cryopreserved and cold platelets display a pro-coagulant profile that may produce the rapid hemostatic response which is needed in bleeding patients. Thus, it seems appropriate that blood banks and blood transfusion centers explore the possibility of split platelet inventories consisting of platelets stored at room temperature and cryopreserved and cold-stored platelets.

Reconstituted cryopreserved platelets synthesize proteins during short-term storage and packaging a defined subset into microvesicles

BACKGROUND

Cryopreservation of platelets (PLTs) could allow extension of their shelf-life to years, compared to days for liquid stored platelets. Due to their greater hemostatic effect, reconstituted cryopreserved platelets (cryo-PLTs) would be able to support bleeding emergencies. Since protein synthesis has been linked to PLT functions, such as clot formation and immune responses, the translational capacity of reconstituted cryo-PLTs was assessed upon thawing and short-term storage.

METHODS/MATERIALS

Platelets were frozen at -80°C with 5-6% DMSO. Upon thawing, they were reconstituted in plasma and then aliquoted (12 ml) into mini-bags and assessed over 24 h of storage at RT. One series served as control; the second and third series were spiked with either 300 μM puromycin (Pm) or 227 nM biotin-labeled Pm. Samples were tested for in vitro quality and PLT microvesicle enumeration by flow cytometry. Protein synthesis in cryo-PLTs was assessed using a modified method based on puromycin-associated nascent chain proteomics.

RESULTS

In vitro parameters of reconstituted and subsequently stored platelets were consistent with previously published results. Mass-spectrometry analyses identified that 22 proteins were synthesized in PLTs and 13 of those were observed in platelet microvesicles (PMVs).

CONCLUSION

Cryo-PLTs can synthesize proteins upon reconstitution and storage. Discovery of a subset of these proteins in the PMV suggests a role in vesicle encapsulation, possibly in a selective manner. This observation provides novel insights into the capacity for protein synthesis in cryo-PLTs and the potential regulation of protein packaging into PMV.

Cryopreserved buffy-coat-derived platelets reconstituted in platelet additive solution: A safe and available product with sufficient haemostatic effectiveness

BACKGROUND

Platelets (PLTs) stored at 20-24 °C have a short shelf life of only 5 days, which can result in their restricted availability. PLT cryopreservation extends the shelf life to 2 years.

METHODS

We implemented a method of PLT freezing at -80 °C in 5-6% dimethyl sulfoxide. Buffy-coat-derived leucodepleted fresh PLTs blood group O (FP) were used for cryopreservation. Cryopreserved pooled leucodepleted PLTs (CPP) were thawed at 37 °C, reconstituted in PLT additive solution SSP + and compared to FP regarding PLT content, PLT concentration, pH, volume, PLT loss, anti-A/B antibody titre, total protein, plasma content, and PLT swirling. Clot properties were evaluated via rotational thromboelastometry. PLT microparticle number and surface receptor phenotype were assessed via flow cytometry.

RESULTS

CPP met the required quality parameters. The mean freeze-thaw PLT loss was 22.24 %. Anti-A/B antibody titre and plasma content were significantly lower in CPP. CPP were characterised by faster clot initiation and form stable PLT clots. The number of PLT microparticles increased 25 times in CPP and there were more particles positive for the activation marker CD62 P compared to FP.

CONCLUSION

Thawing and reconstitution are easy and fast processes if platelet additive solution is used. Low anti-A/B antibody titre and plasma content make possible the use of CPP of blood group O reconstituted in SSP + as universal ABO products, including clinical situations where washed PLTs are required. Clot properties evaluated via rotational thromboelastometry demonstrated that CPP retain a significant part of their activity compare to FP and are haemostatically effective.

Cryopreservation of platelets treated with riboflavin and UV light and stored at -80°C for 1 year

BACKGROUND

The combination of pathogen reduction technologies (PRTs) and cryopreservation can contribute to building a safe and durable platelet (PLT) inventory. Information about cryopreserved riboflavin and UV light-treated PLTs is scarce.

STUDY DESIGN AND METHODS

Twenty-four buffy coat (BC) PLT concentrates were grouped into 12 type-matched pairs, pooled, and divided into 12 non-PRT-treated control units and 12 riboflavin and UV light PRT-treated test units. Both were cryopreserved with 5% DMSO and stored at -80°C for 1 year. The cryopreservation method used was designed to avoid the formation of aggregates. PLT variables (PLT recovery, swirling, pH, MPV, and LDH) and hemostatic function measured by thromboelastography (TEG) were analyzed before cryopreservation (day 1) and post-cryopreservation at day 14 and months 3, 6, and 12 of storage at -80°C. The analyses were carried out within 1-h post-thaw.

RESULTS

No aggregates were found in either PLT group at any time. Swirling was observed in both groups. MPV increased and mean pH values decreased over time (p < .001), but the mean pH value was never below 6.4 in either group after 12 months of storage at -80°C. PLT recovery was good and clotting time became significantly shorter over the storage period in both groups (p < .001).

CONCLUSION

Our cryopreservation and thawing method prevented aggregate formation in cryopreserved riboflavin-UV-light-treated PLTs, which exhibited good recovery, swirling, pH > 6.4, and procoagulant potential, as evidenced by a reduced clotting time after 12 months of storage at -80°C. The clinical relevance of these findings should be further investigated in clinical trials.

Insights into the Procoagulant Profile of Patients with Systemic Lupus Erythematosus without Antiphospholipid Antibodies

We aimed to identify the key players in the prothrombotic profile of patients with systemic lupus erythematosus (SLE) not mediated by antiphospholipid antibodies, as well as the potential utility of global coagulation tests to characterize hemostasis in these patients. Patients with SLE without antiphospholipid antibodies and without signs of thrombosis were included. The kinetics of clot formation were determined by ROTEM^®. Platelet activation markers were determined by flow cytometry. Thrombin generation associated with Neutrophil Extracellular Traps (NETs) and microparticles (MPs) was measured by calibrated automated thrombogram (CAT). The plasma levels of PAI-1 were also determined. ROTEM^® showed a procoagulant profile in SLE patients. SLE patients had activated platelets and more leukocyte/platelet aggregates at basal conditions. The plasma PAI-1 and platelet aggregates correlated with several ROTEM^® parameters. The thrombin generation associated withthe tissue factor (TF) content of MPs and with NETs was increased. Our results suggest the utility of global tests for studying hemostasis in SLE patients because they detect their procoagulant profile, despite having had neither antiphospholipid antibodies nor any previous thrombotic event. A global appraisal of hemostasis should, if possible, be incorporated into clinical practice to detect the risk of a thrombotic event in patients with SLE and to consequently act to prevent its occurrence.

Frozen Platelets-Development and Future Directions

Storage requirements and outdating of platelets represent a continued challenge for blood banks. These hurdles are confounded for rural area hospitals or in military deployments. Over 60 years of research and development into frozen platelets have generated a stable and reproducible product. Valeri's method to freeze platelets in 6% dimethyl sulfoxide (DMSO) and storage at -80°C allows for long-term storage alleviating burdens placed on blood banks. Clinical studies show that frozen platelet transfusions are safe with no related thrombotic or other serious adverse events. There are ongoing efforts to demonstrate cryopreserved platelet (CPP) superiority in efficacy studies designed in trauma or cardiac surgery patients. Technical advances in CPP manufacturing including closed system manufacturing, applications of pathogen reduction technology and potency standard characterization add to the appeal of CPP as an alternative to traditional liquid-stored platelets (LP) in settings of supply shortages, mass casualty, active bleeding, rapid provision of HLA-compatible platelets, and remote care.

The use of cryopreserved platelets in a trauma-induced hemorrhage model

BACKGROUND

Cryopreserved platelet products can be stored for years and are mainly used in military settings. Following thawing, cryopreserved platelets are activated, resulting in faster clot formation but reduced aggregation in vitro, rendering their efficacy in bleeding unknown. Also, concerns remain on the safety of these products. The aim was to investigate the efficacy and safety of cryopreserved platelets in a rat model of traumatic hemorrhage.

STUDY DESIGN AND METHODS

After 1 hour of shock, rats (n = 13/group) were randomized to receive a balanced transfusion pack (1:1:1 red blood cell:plasma:platelet) made from syngeneic rat blood, containing either liquid stored platelets or cryopreserved platelets. Primary outcome was the transfusion volume required to obtain a mean arterial pressure (MAP) of 60 mmHg. Secondary outcomes were coagulation as assessed by thromboelastometry (ROTEM®) and organ failure as assessed by biochemistry and histopathology.

RESULTS

The transfusion volume to obtain a MAP of 60 mmHg was lower in animals receiving cryopreserved platelets (5.4 [4.1-7.1] mL/kg) compared to those receiving liquid stored platelets (7.5 [6.4-8.5] mL/kg, p < 0.05). ROTEM® clotting times were shorter (45 [41-48] vs. 49 [45-53]sec, p < 0.05), while maximum clot firmness was slightly lower (68 [67-68] vs. 69 [69-71]mm, p < 0.01). Organ failure was similar in both groups.

CONCLUSIONS

Use of cryopreserved platelets required less transfusion volume to reach a targeted MAP compared to liquid stored platelets, while organ injury was similar. These results provide a rationale for clinical trials with cryopreserved platelets in (traumatic) bleeding.

Calcium chelation: a novel approach to reduce cryopreservation-induced damage to frozen platelets

BACKGROUND

Cryopreserved platelets are phenotypically and functionally different to conventionally stored platelets. Calcium may be released from internal stores during the freeze-thaw process, initiating signaling events which lead to these alterations. It was hypothesized that the addition of a calcium chelator prior to cryopreservation may mitigate some of these changes.

METHODS

Buffy coat-derived platelets that had been pooled and split were tested fresh and following cryopreservation (n = 8 per group). Platelets were cryopreserved using 5%-6% dimethylsulfoxide (DMSO) or were supplemented with increasing concentrations of the internal calcium chelator, BAPTA-AM (100 μM, 200 μM, or 400 μM), prior to storage at -80°C.

RESULTS

Supplementation of platelets with BAPTA-AM prior to freezing improved platelet recovery in a dose response manner (400 μM: 84 ± 2%) compared to standard DMSO cryopreserved platelets (70 ± 4%). There was a loss of GPIbα, GPVI, and GPIIb/IIIa receptors on platelets following cryopreservation, which was rescued when platelets were supplemented with BAPTA-AM (400 μM: p < 0.0001 for all). Platelet activation markers, such as phosphatidylserine and P-selectin, were externalized on platelets following cryopreservation. However, the addition of BAPTA-AM significantly reduced the increase of these activation markers on cryopreserved platelets (400 μM: p < 0.0001 for both). Both cryopreserved platelet groups exhibited similar functionality as assessed by thromboelastography, forming clots at a faster rate than fresh platelets.

CONCLUSIONS

This study demonstrates that calcium plays a crucial role in mediating cryopreservation-induced damage to frozen platelets. The addition of the calcium chelator, BAPTA-AM, prior to cryopreservation reduces this damage.

Platelet Biochemistry and Morphology after Cryopreservation

Platelet cryopreservation has been investigated for several decades as an alternative to room temperature storage of platelet concentrates. The use of dimethylsulfoxide as a cryoprotectant has improved platelet storage and cryopreserved concentrates can be kept at −80 °C for two years. Cryopreserved platelets can serve as emergency backup to support stock crises or to disburden difficult logistic areas like rural or military regions. Cryopreservation significantly influences platelet morphology, decreases platelet activation and severely abrogates platelet aggregation. Recent data indicate that cryopreserved platelets have a procoagulant phenotype because thrombin and fibrin formation kicks in earlier compared to room temperature stored platelets. This happens both in static and hydrodynamic conditions. In a clinical setting, low 1-h post transfusion recoveries of cryopreserved platelets represent fast clearance from circulation which may be explained by changes to the platelet GPIbα receptor. Cryopreservation splits the concentrate in two platelet subpopulations depending on GPIbα expression levels. Further research is needed to unravel its physiological importance. Proving clinical efficacy of cryopreserved platelets is difficult because of the heterogeneity of indications and the ambiguity of outcome measures. The procoagulant character of cryopreserved platelets has increased interest for use in trauma stressing the need for double-blinded randomized clinical trials in actively bleeding patients.

Platelet in vitro assays: their correspondence with their in vivo hemostatic potential

Developments during the past few years have resulted in multiple kinds of platelet products for transfusion. This involves different collection methods, containers, preservative solutions, modifications of storage temperatures and durations, and additional treatments such as pathogen reduction. Much experience has been obtained testing these processes in vitro to seek indications of in vivo effectiveness. Availability of an in vitro method that correlated with in vivo effectiveness would be extremely valuable for these different kinds of platelet products and as more innovation in platelet preparation occurs in the future. This report reviews the methods for in vitro platelet testing with a view to their in vivo implications and whether such testing could be helpful in projecting the clinical effectiveness of different platelet products.

A randomized, controlled pilot clinical trial of cryopreserved platelets for perioperative surgical bleeding: the CLIP-I trial (Editorial, p. 2759)

BACKGROUND

Cryopreservation extends platelet (PLT) shelf life from 5 to 7 days to 2 to 4 years. However, only 73 patients have been transfused cryopreserved PLTs in published randomized controlled trials (RCTs), making safety data insufficient for regulatory approval.

STUDY DESIGN AND METHODS

The Cryopreserved vs. Liquid Platelet (CLIP) study was a double-blind, pilot, multicenter RCT involving high-risk cardiothoracic surgical patients in four Australian hospitals. The objective was to test, as the primary outcome, the feasibility and safety of the protocol. Patients were allocated to study group by permuted block randomization, with patients and clinicians blinded by use of an opaque shroud placed over each study PLT unit. Up to 3 units of cryopreserved or liquid-stored PLTs were administered per patient. No other aspect of patient care was affected. Adverse events were actively sought.

RESULTS

A total of 121 patients were randomized, of whom 23 received cryopreserved PLTs and 18 received liquid-stored PLTs. There were no differences in blood loss (median, 715 mL vs. 805 mL at 24 hr; difference between groups 90 mL [95% CI, -343.8 to 163.8 mL], p = 0.41), but the Bleeding Academic Research Consortium criterion for significant postoperative hemorrhage in cardiac surgery composite bleeding endpoint occurred in nearly twice as many patients in the liquid-stored group (55.6% vs. 30.4%, p = 0.10). Red blood cell transfusion requirements were a median of 3 units in the cryopreserved group versus 4 units with liquid-stored PLTs (difference between groups, 1 unit [95% CI, -3.1 to 1.1 units]; p = 0.23). Patients in the cryopreserved group were more likely to be transfused fresh-frozen plasma (78.3% vs. 27.8%, p = 0.002) and received more study PLT units (median, 2 units vs. 1 unit; difference between groups, 1 unit [95% CI, -0.03 to 2.0 units]; p = 0.012). There were no between-group differences in potential harms including deep venous thrombosis, myocardial infarction, respiratory function, infection, and renal function. No patient had died at 28 days, and postoperative length of stay was similar in each group.

CONCLUSION

In this pilot RCT, compared to liquid-stored PLTs, cryopreserved PLTs were associated with no evidence of harm. A definitive study testing safety and hemostatic effectiveness is warranted.

Impact of cold storage on platelets treated with Intercept pathogen inactivation

BACKGROUND

Pathogen inactivation and cold or cryopreservation of platelets (PLTs) both significantly affect PLT function. It is not known how PLTs function when both are combined.

STUDY DESIGN AND METHODS

Standard PLT concentrates (PCs) were compared to pathogen‐inactivated PCs treated with amotosalen photochemical treatment (AS‐PCT) when stored at room (RT, 22°C), cold (4°C, n = 6), or cryopreservation (−80°C, n = 8) temperatures. The impact of alternative storage methods on both arms was studied in flow cytometry, light transmittance aggregometry, and hemostasis in collagen‐coated microfluidic flow chambers.

RESULTS

Platelet aggregation of cold‐stored AS‐PCT PLTs was 44% ± 11% compared to 57% ± 14% for cold‐stored standard PLTs and 58% ± 21% for RT‐stored AS‐PCT PLTs. Integrin activation of cold‐stored AS‐PCT PLTs was 53% ± 9% compared to 77% ± 6% for cold‐stored standard PLTs and 69% ± 13% for RT‐stored AS‐PCT PLTs. Coagulation of cold‐stored AS‐PCT PLTs started faster under flow (836 ± 140 sec) compared to cold‐stored standard PLTs (960 ± 192 sec) and RT‐stored AS‐PCT PLTs (1134 ± 220 sec). Fibrin formation rate under flow was also highest for cold‐stored AS‐PCT PLTs. This was in line with thrombin generation in static conditions because cold‐stored AS‐PCT PLTs generated 297 ± 47 nmol/L thrombin compared to 159 ± 33 nmol/L for cold‐stored standard PLTs and 83 ± 25 nmol/L for RT‐stored AS‐PCT PLTs. So despite decreased PLT activation and aggregation, cold storage of AS‐PCT PLTs promoted coagulation. PLT aggregation of cryopreserved AS‐PCT PLTs (23% ± 10%) was not significantly different from cryopreserved standard PLTs (25% ± 8%).

CONCLUSION

This study shows that cold storage of AS‐PCT PLTs further affects PLT activation and aggregation but promotes (pro)coagulation. Increased procoagulation was not observed after cryopreservation.

Comparison between manufacturing sites shows differential adhesion, activation, and GPIbα expression of cryopreserved platelets

BACKGROUND

Transfusion of cryopreserved platelets (cryoplatelets) is not common but may replace standard liquid-preserved platelets (PLTs) in specific circumstances. To better understand cryoplatelet function, frozen concentrates from different manufacturing sites were compared.

STUDY DESIGN AND METHODS

Cryoplatelets from Denver, Colorado (DEN); Sydney, Australia (SYD); and Ghent, Belgium (GHE) were compared (n = 6). A paired noncryopreserved control was included in Ghent. Microfluidic-flow chambers were used to study PLT adhesion and fibrin deposition in reconstituted blood. Receptor expression was measured by flow cytometry. Coagulation in static conditions was evaluated by rotational thromboelastometry (ROTEM).

RESULTS

Regardless of the manufacturing site, adhesion of cryoplatelets under shear flow (1000/sec) was significantly (p < 0.05) reduced compared to control. Expression of GPIbα was decreased in a subpopulation of cryoplatelets comprising 45% ± 11% (DEN), 63% ± 9% (GHE), and 94% ± 6% (SYD). That subpopulation displayed increased annexin V binding and decreased integrin activation. PLT adhesion, agglutination, and aggregation were moreover decreased in proportion to that subpopulation. Fibrin deposition under shear flow was normal but initiated faster (546 ± 163 sec GHE) than control PLTs (631 ± 120 sec, p < 0.01), only in the absence of tissue factor. In static conditions, clotting time was faster, but clot firmness decreased compared to control. Coagulation was not different between manufacturing sites.

CONCLUSION

Cryopreservation results in a subset of PLTs with enhanced GPIbα shedding, increased phosphatidylserine expression, reduced integrin response, and reduced adhesion to collagen in microfluidic models of hemostasis. The proportion of this phenotype is different between manufacturing sites. The clinical effects, if any, will need to be verified.

Buffy coat-derived platelets cryopreserved using a new method: Results from in vitro studies

Cryopreservation for the long-term storage of platelets (PLTs) is a useful method to overcome the limits of platelet shortage. This is an in vitro prospective study to evaluate the count, viability, and function of buffy coat-derived pooled platelet concentrates (BC-PLTs), treated with dimethyl sulphoxide (DMSO) and cryopreserved (CRY BC-PLTs) at -80 °C with a modified Valeri method. PLTs were stored in 6% DMSO with a patented kit. Overall, 49 BC-PLTs from 245 healthy volunteer donors were prepared, cryopreserved, and analysed before and after 3, 6, and 9 months of storage. In flow cytometry, a statistically significant reduction in CD 42b (92.7 ± 4.29% at T0 vs. 23.6 ± 27.5% at T3, 16.38 ± 12.54% at T6, and 17.3 ± 9.6% at T9) and PAC-1 (1.9 ± 1.34% at T0 vs. 0.62 ± 0.4% at T3, 0.63 ± 0.83% at T6, and 0.49 ± 0.48% at T9) was observed after storage. CRY BC-PLTs showed a good and stable endogenous thrombin generation potential (nM min): 529.25 ± 98.64 at T0 vs. 533.04 ± 103.15 at T9 months. CRY BC-PLTs showed a good viability in vitro, according to currently accepted criteria for cryopreserved PLTs.

Blood products and procoagulants in traumatic bleeding: use and evidence

PURPOSE OF REVIEW

Death from uncontrolled haemorrhage is one of the leading causes of trauma-related mortality and is potentially preventable. Advances in understanding the mechanisms of trauma-induced coagulopathy (TIC) have focused attention on the role of blood products and procoagulants in mitigating the sequelae of TIC and how these therapies can be improved.

RECENT FINDINGS

A host of preclinical and clinical studies have evaluated blood product availability and efficacy in trauma. Recently published randomized controlled trials have investigated the ratio of platelet:plasma:red cell transfusion and the role of early cryoprecipitate in trauma. Demand for readily available plasma has led to changes particularly in the use of thawed group A plasma. Furthermore, ex-vivo and early clinical work has demonstrated variations in the haemostatic activity of different plasma, platelet and whole blood products. A number of multicentre trials are in progress aiming to answer key questions regarding tranexamic acid, procoagulant factor and fibrinogen concentrates and their effect on trauma outcomes.

SUMMARY

There are promising results from ex-vivo studies in manufacturing and storage of blood products to optimize haemostatic activity and availability, particularly with alternative plasma and platelet products and whole blood. There is an urgent need for these products needs to be tested prospectively.

Refrigeration, cryopreservation and pathogen inactivation: an updated perspective on platelet storage conditions

Conventional storage of platelet concentrates limits their shelf life to between 5 and 7 days due to the risk of bacterial proliferation and the development of the platelet storage lesion. Cold storage and cryopreservation of platelets may facilitate extension of the shelf life to weeks and years, and may also provide the benefit of being more haemostatically effective than conventionally stored platelets. Further, treatment of platelet concentrates with pathogen inactivation systems reduces bacterial contamination and provides a safeguard against the risk of emerging and re-emerging pathogens. While each of these alternative storage techniques is gaining traction individually, little work has been done to examine the effect of combining treatments in an effort to further improve product safety and minimize wastage. This review aims to discuss the benefits of alternative storage techniques and how they may be combined to alleviate the problems associated with conventional platelet storage.

Immunomodulatory effect of cryopreserved platelets: altered BDCA3+ dendritic cell maturation and activation in vitro

BACKGROUND

Cryopreservation of platelets (PLTs) is useful in remote areas to overcome logistic problems associated with supply and can extend the shelf life to 2 years. During cryopreservation, properties of PLTs are modified. Whether changes in the cryopreserved PLT (CPP) product are associated with modulation of recipients' immune function is unknown. We aimed to characterize the immune profile of myeloid dendritic cells (mDCs) and the specialized blood DC antigen (BDCA)3⁺ subset after exposure to CPPs.

STUDY DESIGN AND METHODS

Using an in vitro whole blood model of transfusion, the effect of CPPs on mDC and BDCA3⁺ DC surface antigen expression and inflammatory mediator production was examined using flow cytometry. In parallel, polyinosinic:polycytidylic acid (poly(I:C)) or lipopolysaccharide (LPS) was utilized to model processes activated in viral or bacterial infection, respectively.

RESULTS

Cryopreserved PLTs had minimal impact on mDC responses but significantly modulated BDCA3⁺ DC responses in vitro. Exposure to CPPs alone up regulated BDCA3⁺ DC CD86 expression and suppressed interleukin (IL)-8, tumor necrosis factor (TNF)-α, and interferon-γ inducible protein (IP)-10 production. In both models of infection-related processes, exposure to CPPs down regulated BDCA3⁺ DC expression of CD40, CD80, and CD83 and suppressed BDCA3⁺ DC production of IL-8, IL-12, and TNF-α. CPPs suppressed CD86 expression in the presence of LPS and IP-10 and IL-6 production with poly(I:C).

CONCLUSION

Cryopreserved PLTs may be immunosuppressive, and this effect is more evident when processes associated with infection are concurrently activated, especially for BDCA3⁺ DCs. This suggests that transfusion of CPPs in patients with infection may result in impaired BDCA3⁺ DC responses.

Quality Assessment of Established and Emerging Blood Components for Transfusion

Blood is donated either as whole blood, with subsequent component processing, or through the use of apheresis devices that extract one or more components and return the rest of the donation to the donor. Blood component therapy supplanted whole blood transfusion in industrialized countries in the middle of the twentieth century and remains the standard of care for the majority of patients receiving a transfusion. Traditionally, blood has been processed into three main blood products: red blood cell concentrates; platelet concentrates; and transfusable plasma. Ensuring that these products are of high quality and that they deliver their intended benefits to patients throughout their shelf-life is a complex task. Further complexity has been added with the development of products stored under nonstandard conditions or subjected to additional manufacturing steps (e.g., cryopreserved platelets, irradiated red cells, and lyophilized plasma). Here we review established and emerging methodologies for assessing blood product quality and address controversies and uncertainties in this thriving and active field of investigation.

Safety and efficacy of cryopreserved autologous platelet concentrates in HLA-alloimmunized patients with hematologic malignancies

BACKGROUND

Curative chemotherapy approaches in patients with malignancies and platelet (PLT) transfusion refractoriness due to alloimmunization may be hampered by the lack of suitable PLT donors. For these patients, transfusion of cryopreserved autologous PLTs is an option, but is time- and resource-consuming. We aimed at further simplifying this process.

STUDY DESIGN AND METHODS

A retrospective single-center analysis was conducted on the transfusion of cryopreserved autologous PLTs in nine female alloimmunized, PLT transfusion-refractory patients treated for acute leukemia (n = 8) and non-Hodgkin's lymphoma (n = 1). No additional processing was used before transfusion, and most notably, washing and centrifugation steps were omitted. Clinical efficacy and safety, as well as a flow cytometric assessment of structural and functional PLT changes, were analyzed.

RESULTS

A total of 40 autologous PLT concentrates were thawed at bedside and transfused a median of 32 (range, 9 to 994) days after cryopreservation. No major bleeds and no severe dimethyl sulfoxide toxicity were observed. The median PLT count increments did not differ 1 and 18 to 24 hours after transfusion and reached 6 × 10⁹ /L (interquartile range [IQR], 3 × 10⁹ -7.5 × 10⁹ /L) and 6 × 10⁹ /L (IQR, 2.5 × 10⁹ -9.5 × 10⁹ /L), respectively. Cryopreservation resulted in partial activation of one-third of the PLTs. In vitro stimulation with strong agonists induced additional full activation of cryopreserved PLTs: median, 55% (IQR, 42%-60%) after thrombin and 39% (IQR, 36%-39%) after convulxin.

CONCLUSION

The transfusion of cryopreserved autologous PLTs is feasible and safe. Despite the cryopreservation process, PLT functionality is partially maintained.

Generation of Platelet Microparticles after Cryopreservation of Apheresis Platelet Concentrates Contributes to Hemostatic Activity

OBJECTIVE

In the last decade, substantial evidence has accumulated about the use of cryopreserved platelet concentrates, especially in trauma. However, little reference has been made in these studies to the morphological and functional changes of platelets. Recently platelets have been shown to be activated by cryopreservation processes and to undergo procoagulant membrane changes resulting in the generation of platelet-derived microparticles (PMPs), platelet degranulation, and release of platelet-derived growth factors (PDGFs). We assessed the viabilities and the PMP and PDGF levels of cryopreserved platelets, and their relation with thrombin generation.

MATERIALS AND METHODS

Apheresis platelet concentrates (APCs) from 20 donors were stored for 1 day and cryopreserved with 6% dimethyl sulfoxide. Cryopreserved APCs were kept at -80 °C for 1 day. Thawed APCs (100 mL) were diluted with 20 mL of autologous plasma and specimens were analyzed for viabilities and PMPs by flow cytometry, for thrombin generation by calibrated automated thrombogram, and for PDGFs by enzyme-linked immunosorbent assay testing.

RESULTS

The mean PMP and PDGF levels in freeze-thawed APCs were significantly higher (2763±399.4/µL vs. 319.9±80.5/µL, p<0.001 and 550.9±73.6 pg/mL vs. 96.5±49 pg/mL, p<0.001, respectively), but the viability rates were significantly lower (68.2±13.7% vs. 94±7.5%, p<.001) than those of fresh APCs. The mean endogenous thrombin potential (ETP) of freeze-thawed APCs was significantly higher than that of the fresh APCs (3406.1±430.4 nM.min vs. 2757.6±485.7 nM.min, p<0.001). Moreover, there was a significant positive poor correlation between ETP levels and PMP levels (r=0.192, p=0.014).

CONCLUSION

Our results showed that, after cryopreservation, while levels of PMPs were increasing, significantly higher and earlier thrombin formation was occurring in the samples analyzed despite the significant decrease in viability. Considering the damage caused by the freezing process and the scarcity of evidence for their in vivo superiority, frozen platelets should be considered for use in austere environments, reserving fresh platelets for prophylactic use in blood banks.