Review of in vivo studies of dimethyl sulfoxide cryopreserved platelets

Bacterial Contamination of Platelet Products

Transfusion of bacterially contaminated platelets, although rare, is still a major cause of mortality and morbidity despite the introduction of many methods to limit this over the past 20 years. The methods used include improved donor skin disinfection, diversion of the first part of donations, use of apheresis platelet units rather than whole-blood derived pools, primary and secondary testing by culture or rapid test, and use of pathogen reduction. Primary culture has been in use the US since 2004, using culture 24 h after collection of volumes of 4-8 mL from apheresis collections and whole-blood derived pools inoculated into aerobic culture bottles, with limited use of secondary testing by culture or rapid test to extend shelf-life from 5 to 7 days. Primary culture was introduced in the UK in 2011 using a "large-volume, delayed sampling" (LVDS) protocol requiring culture 36-48 h after collection of volumes of 16 mL from split apheresis units and whole-blood derived pools, inoculated into aerobic and anaerobic culture bottles (8 mL each), with a shelf-life of 7 days. Pathogen reduction using amotosalen has been in use in Europe since 2002, and was approved for use in the US in 2014. In the US, recent FDA guidance, effective October 2021, recommended several strategies to limit bacterial contamination of platelet products, including pathogen reduction, variants of the UK LVDS method and several two-step strategies, with shelf-life ranging from 3 to 7 days. The issues associated with bacterial contamination and these strategies are discussed in this review.

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.

A randomized cross-over study of cryopreserved platelets in prophylactic transfusions of thrombocytopenic patients

BACKGROUND

The short shelf-life of liquid-stored platelets (LP) at 20-24°C poses shortage and wastage challenges. Cryopreserved platelets have significantly extended shelf-life, and were safe and efficacious for therapeutic transfusions of bleeding patients in the Afghanistan conflict and phase 2 randomized studies. Although hematology patients account for half of platelets demand, there is no randomized study on prophylactic cryopreserved platelet transfusions in them.

METHODS

We performed a phase 1b/2a randomized cross-over study comparing the safety and efficacy of cryopreserved buffy coat-derived pooled platelets (CP) to LP in the prophylactic transfusions of thrombocytopenic hematology patients.

RESULTS

A total of 18 adults were randomly assigned 1:1 to CP and LP for their first thrombocytopenic period (TP) of up to 28-days. A total of 14 crossed over to the other platelet-arm for the second TP. Overall, 17 subjects received 51 CP and 15 received 52 LP. CP-arm had more treatment emergent adverse event (29.4% vs. 13.3% of subjects, 9.8% vs. 3.8% of transfusions) than LP-arm but all were mild. No thromboembolism was observed. Both arms had similar bleeding rates (23.5% vs. 26.7% of subjects) which were all mild. Subjects in CP-arm had lower average corrected count increments than LP-arm (mean [SD] 5.6 [4.20] vs. 22.6 [9.68] ×109 /L at 1-4 h, p < .001; 5.3 [4.84] vs. 18.2 [9.52] ×109 /L at 18-30 h, p < .001). All TEG parameters at 1-4 h and maximum amplitude (MA) at 18-30 h improved from baseline post-CP transfusion (p < .05) though improvements in K-time and MA were lower than LP (p < .05).

DISCUSSION

During shortages, CP may supplement LP in prophylactic transfusions of thrombocytopenic patients.

Cryopreserved Platelets in a Non-Toxic DMSO-Free Solution Maintain Hemostatic Function In Vitro

Dimethyl sulfoxide (DMSO) is regularly used as a cryoprotectant agent for the cryopreservation of platelets. However, DMSO is considered toxic. We therefore hypothesized that saline could be used as a non-toxic medium for the cryopreservation of platelets. Double-dose buffy coat platelets (n = 10) were divided and cryopreserved at -80 °C using 5-6% dimethyl sulfoxide (DMSO) or in NaCl (9 mg/mL). Paired testing was conducted pre-freeze, post-thaw (PT 1 h). Upon analysis, each bag was thawed and reconstituted in fresh plasma. Analyses included cell counts and the metabolic, phenotypic, and functional properties of the platelets together with thromboelastometry. The cryopreserved platelets showed several biochemical and ultrastructural changes compared to pre-freezing. Platelet recovery was approximately 17% higher in DMSO-free units (p < 0.001), but the platelet viability was reduced (p < 0.001). However, using controlled freezing (n = 6), the platelet viability was improved. The clot formation time (CFT) was comparable, but DMSO-free platelets showed slightly decreased maximum clot firmness (MCF) (p = 0.034). By reducing the reconstituted plasma volume, a reduced CFT and increased MCF were obtained (p < 0.001). This study demonstrates that platelets can be cryopreserved in saline without the addition of DMSO, with high recovery and maintained hemostatic function. However, controlled freezing is required to optimize platelet quality.

Cryopreserved platelets washed with a dialysis machine for dimethyl sulphoxide removal

BACKGROUND AND OBJECTIVES

Cryopreserved platelets (cPLTs) can be stored for years and are mainly used in military settings. However, the commonly used cryoprotectant dimethyl sulphoxide (DMSO) has toxic side effects when utilized in high quantities. We developed a novel method to aseptically remove DMSO from thawed cPLTs by dialysis.

MATERIALS AND METHODS

One unit of platelets (N = 6) was mixed with 75 mL of 27% DMSO within 4 days after collection and stored at -80°C for 1 week. The platelet counts, platelet distribution width, mean platelet volume (MPV), platelet activity, platelet release, platelet aggregation, platelet metabolism indicators and platelet ultrastructural features (determined by electron microscopy) of the samples at the pre-freeze, post-thaw wash (post-TW) and 24 h post-thaw wash (24-PTW) stages were determined and compared.

RESULTS

The DMSO clearance rate from the post-TW platelets was 95.56 ± 1.3%, and the platelet recovery rate after washing was 74.66 ± 6.34%. The total count, activity, release factors, aggregation and thrombolytic ability of the post-TW platelets were lower, whereas the MPV and apoptosis rates were higher compared with those of the pre-freeze platelets. The lactic acid, glucose and potassium ions released from the platelets during washing were filtered away by the dialyser, which significantly reduced their concentration. However, 24-PTW platelets were metabolically active, resulting in a decrease in pH and glucose content and an increase in lactic acid content. The level of potassium ions remained low after 24 h of storage and washing. The pre-freeze platelets maintained their normal disc shape and exhibited an open canalicular system (OCS) and a dense tubular system. The cPLTs appeared irregular after washing, with protruding pseudopodia and an extensive OCS, which increased the release of their contents.

CONCLUSION

We developed a novel dialysis method to effectively remove DMSO from cPLTs under aseptic conditions and maintain platelet quality. The clinical efficacy of our method remains to be determined. However, the function of the platelets declined 24 h after washing, making them unsuitable for transfusion.

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.

Targeting biophysical cues to address platelet storage lesions

Platelets play vital roles in vascular repair, especially in primary hemostasis, and have been widely used in transfusion to prevent bleeding or manage active bleeding. Recently, platelets have been used in tissue repair (e.g., bone, skin, and dental alveolar tissue) and cell engineering as drug delivery carriers. However, the biomedical applications of platelets have been associated with platelet storage lesions (PSLs), resulting in poor clinical outcomes with reduced recovery, survival, and hemostatic function after transfusion. Accumulating evidence has shown that biophysical cues play important roles in platelet lesions, such as granule secretion caused by shear stress, adhesion affected by substrate stiffness, and apoptosis caused by low temperature. This review summarizes four major biophysical cues (i.e., shear stress, substrate stiffness, hydrostatic pressure, and thermal microenvironment) involved in the platelet preparation and storage processes, and discusses how they may synergistically induce PSLs such as platelet shape change, activation, apoptosis and clearance. We also review emerging methods for studying these biophysical cues in vitro and existing strategies targeting biophysical cues for mitigating PSLs. We conclude with a perspective on the future direction of biophysics-based strategies for inhibiting PSLs. STATEMENT OF SIGNIFICANCE: Platelet storage lesions (PSLs) involve a series of structural and functional changes. It has long been accepted that PSLs are initiated by biochemical cues. Our manuscript is the first to propose four major biophysical cues (shear stress, substrate stiffness, hydrostatic pressure, and thermal microenvironment) that platelets experience in each operation step during platelet preparation and storage processes in vitro, which may synergistically contribute to PSLs. We first clarify these biophysical cues and how they induce PSLs. Strategies targeting each biophysical cue to improve PSLs are also summarized. Our review is designed to draw the attention from a broad range of audience, including clinical doctors, biologists, physical scientists, engineers and materials scientists, and immunologist, who study on platelets physiology and pathology.

Platelet Transfusion for Trauma Resuscitation

Purpose of Review

To review the role of platelet transfusion in resuscitation for trauma, including normal platelet function and alterations in behavior following trauma, blood product transfusion ratios and the impact of platelet transfusion on platelet function, platelet function assays, risks of platelet transfusion and considerations for platelet storage, and potential adjunct therapies and synthetic platelets.

Recent Findings

Platelets are a critical component of clot formation and breakdown following injury, and in addition to these hemostatic properties, have a complex role in vascular homeostasis, inflammation, and immune function. Evidence supports that platelets are activated following trauma with several upregulated functions, but under conditions of severe injury and shock are found to be impaired in their hemostatic behaviors. Platelets should be transfused in balanced ratios with red blood cells and plasma during initial trauma resuscitation as this portends improved outcomes including survival. Multiple coagulation assays can be used for goal-directed resuscitation for traumatic hemorrhage; however, these assays each have drawbacks in terms of their ability to measure platelet function. While resuscitation with balanced transfusion ratios is supported by the literature, platelet transfusion carries its own risks such as bacterial infection and lung injury. Platelet supply is also limited, with resource-intensive storage requirements, making exploration of longer-term storage options and novel platelet-based therapeutics attractive. Future focus on a deeper understanding of the biology of platelets following trauma, and on optimization of novel platelet-based therapeutics to maintain hemostatic effects while improving availability should be pursued.

Summary

While platelet function is altered following trauma, platelets should be transfused in balanced ratios during initial resuscitation. Severe injury and shock can impair platelet function, which can persist for several days following the initial trauma. Assays to guide resuscitation following the initial period as well as storage techniques to extend platelet shelf life are important areas of investigation.

There and Back Again: The Once and Current Developments in Donor-Derived Platelet Products for Products for Hemostatic Therapy

Over 100 years ago, Duke transfused whole blood to a thrombocytopenic patient to raise the platelet count and prevent bleeding. Since then, platelet transfusions have undergone numerous modifications from whole blood-derived platelet-rich plasma to apheresis-derived platelet concentrates. Similarly, the storage time and temperature have changed. The mandate to store platelets for a maximum of 5-7 days at room temperature has been challenged by recent clinical trial data, ongoing difficulties with transfusion-transmitted infections, and recurring periods of shortages, further exacerbated by the COVID-19 pandemic. Alternative platelet storage approaches are as old as the first platelet transfusions. Cold-stored platelets may offer increased storage times (days) and improved hemostatic potential at the expense of reduced circulation time. Frozen (cryopreserved) platelets extend the storage time to years but require storage at -80 °C and thawing before transfusion. Lyophilized platelets can be powder-stored for years at room temperature and reconstituted within minutes in sterile water but are probably the least explored alternative platelet product to date. Finally, whole blood offers the hemostatic spectrum of all blood components but has challenges, such as ABO incompatibility. While we know more than ever before about the in vitro properties of these products, clinical trial data on these products are accumulating. The purpose of this review is to summarize the findings of recent preclinical and clinical studies on alternative, donor-derived platelet products.

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.

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.

Platelet Transfusion-Insights from Current Practice to Future Development

Since the late sixties, therapeutic or prophylactic platelet transfusion has been used to relieve hemorrhagic complications of patients with, e.g., thrombocytopenia, platelet dysfunction, and injuries, and is an essential part of the supportive care in high dose chemotherapy. Current and upcoming advances will significantly affect present standards. We focus on specific issues, including the comparison of buffy-coat (BPC) and apheresis platelet concentrates (APC); plasma additive solutions (PAS); further measures for improvement of platelet storage quality; pathogen inactivation; and cold storage of platelets. The objective of this article is to give insights from current practice to future development on platelet transfusion, focusing on these selected issues, which have a potentially major impact on forthcoming guidelines.

Ex Vivo Manufacture of Megakaryocytes and Platelets from Stem Cells: Recent Advances Toward Transfusion in Humans

The generation of ex vivo functional megakaryocytes (MK) and platelets is an important issue in transfusion medicine as donor dependence implies in limitations, such as shortage of eligible volunteers. Indeed, platelet transfusion is still a procedure that saves the lives of patients with defective platelet production. Recent technological development has enabled the isolation and expansion of stem cells that can be used as a source for the production of functional platelets for transfusion. In this review, we discuss recent approaches of in vitro or ex vivo production of MK and platelets, suggesting that, in the near future, donor-independent sources may become a possibility. The feasibility of using these cells in the clinic may be safer, and in vitro manipulation could generate universally compatible products, solving problems related to platelet refractoriness. However, functionality and survival testing of these products in human beings are scarce; therefore, additional studies are needed to consolidate this purpose.

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.

The immune potential of ex vivo stored platelets: a review

Platelets are now acknowledged as key regulators of the immune system, as they are capable of mediating inflammation, leucocyte recruitment and activation. This activity is facilitated through platelet activation, which induces significant changes in the surface receptor profile and triggers the release of a range of soluble biological response modifiers (BRMs). In the field of transfusion medicine, the immune function of platelets has gained considerable attention as this may be linked to the development of adverse transfusion reactions. Further, component manufacturing and storage methodologies may impact the immunoregulatory role of platelets, and an understanding of this impact is crucial and should be considered alongside their haemostatic characteristics. This review highlights the key interactions between platelets and traditional immune modulators. Further, the potential impact of current and novel component storage methodologies, such as refrigeration and cryopreservation, on this functional capacity is examined, highlighting why further knowledge in this area would be of benefit.

Human Adipose Tissue Cryopreservation: Impact of Different Calf Serum Concentrations on Tissue Viability

Adipose tissue, which is harvested in large quantities during liposuction, has no blood supply and becomes necrotic within a few hours, if not immediately transplanted. Cryopreservation of adipose tissue allows these samples to be stored and used in diverse fundamental experiments, especially in fat-grafting animal tests that could provide a theoretical basis for clinical applications. Traditionally, fetal bovine serum (FBS) has been added as a cryoprotectant (CPA) to maintain the maximum viability of different tissues after freezing and thawing. Calf serum (CS) comes from the same species as FBS but is more economical compared with FBS-containing medium. The optimal concentration of CS in CPA for banking adipose tissue has not been studied. Here, we studied the cell survival rate, cell viability, tissue structural integrity, number of adipose-derived stem cells and blood vessels, and survival after transplantation into nude mice via ultrastructural evaluation of adipose tissue cryopreserved for 6 months in condition A (60% CS, 15% dimethyl sulfoxide [DMSO], 25% Dulbecco's modified Eagle's medium [DMEM]) and condition B (30% CS, 15% DMSO, 55% DMEM). Our results indicate that CS in addition to CPA results in adequate preservation of adipose tissue, especially when a higher concentration of CS (60%) is used in the CPA.

Effects of the COVID-19 pandemic on supply and use of blood for transfusion

The COVID-19 pandemic has major implications for blood transfusion. There are uncertain patterns of demand, and transfusion institutions need to plan for reductions in donations and loss of crucial staff because of sickness and public health restrictions. We systematically searched for relevant studies addressing the transfusion chain-from donor, through collection and processing, to patients-to provide a synthesis of the published literature and guidance during times of potential or actual shortage. A reduction in donor numbers has largely been matched by reductions in demand for transfusion. Contingency planning includes prioritisation policies for patients in the event of predicted shortage. A range of strategies maintain ongoing equitable access to blood for transfusion during the pandemic, in addition to providing new therapies such as convalescent plasma. Sharing experience and developing expert consensus on the basis of evolving publications will help transfusion services and hospitals in countries at different stages in the pandemic.

Clinical-grade cryopreserved doxorubicin-loaded platelets: role of cancer cells and platelet extracellular vesicles activation loop

Background

Human platelets (PLT) and PLT-extracellular vesicles (PEV) released upon thrombin activation express receptors that interact with tumour cells and, thus, can serve as a delivery platform of anti-cancer agents. Drug-loaded nanoparticles coated with PLT membranes were demonstrated to have improved targeting efficiency to tumours, but remain impractical for clinical translation. PLT and PEV targeted drug delivery vehicles should facilitate clinical developments if clinical-grade procedures can be developed.

Methods

PLT from therapeutic-grade PLT concentrate (PC; N > 50) were loaded with doxorubicin (DOX) and stored at − 80 °C (DOX-loaded PLT) with 6% dimethyl sulfoxide (cryopreserved DOX-loaded PLT). Surface markers and function of cryopreserved DOX-loaded PLT was confirmed by Western blot and thromboelastography, respectively. The morphology of fresh and cryopreserved naïve and DOX-loaded PLT was observed by scanning electron microscopy. The content of tissue factor-expressing cancer-derived extracellular vesicles (TF-EV) present in conditioned medium (CM) of breast cancer cells cultures was measured. The drug release by fresh and cryopreserved DOX-loaded PLT triggered by various pH and CM was determined by high performance liquid chromatography. The thrombin activated PEV was analyzed by nanoparticle tracking analysis. The cellular uptake of DOX from PLT was observed by deconvolution microscopy. The cytotoxicities of DOX-loaded PLT, cryopreserved DOX-loaded PLT, DOX and liposomal DOX on breast, lung and colon cancer cells were analyzed by CCK-8 assay.

Results

15~36 × 10⁶ molecules of DOX could be loaded in each PLT within 3 to 9 days after collection. The characterization and bioreactivity of cryopreserved DOX-loaded PLT were preserved, as evidenced by (a) microscopic observations, (b) preservation of important PLT membrane markers CD41, CD61, protease activated receptor-1, (c) functional activity, (d) reactivity to TF-EV, and (e) efficient generation of PEV upon thrombin activation. The transfer of DOX from cryopreserved PLT to cancer cells was achieved within 90 min, and stimulated by TF-EV and low pH. The cryopreserved DOX-loaded PLT formulation was 7~23-times more toxic to three cancer cells than liposomal DOX.

Conclusions

Cryopreserved DOX-loaded PLT can be prepared under clinically compliant conditions preserving the membrane functionality for anti-cancer therapy. These findings open perspectives for translational applications of PLT-based drug delivery systems.

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.

Buffy coat-derived platelets cryopreserved using a new method: Results from a pivotal clinical trial on thrombocytopenic patients with acute leukaemia

The administration of cryopreserved platelets (PLTs) may overcome the limits of platelet shortage and availability, especially during some seasons or in specific contexts like rural areas. After in vitro validation studies, ad hoc prepared 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, were transfused in patients with severe thrombocytopenia secondary to chemotherapy for acute leukaemia (AL). Five inpatients were enrolled in the pivotal clinical trial NCT02032134: 4 males and 1 female with a mean age of 71 years (range: 65-80). Four patients were diagnosed with acute myeloid leukaemia and 1 had acute lymphoblastic leukaemia.Transfusion of one Unit of CRY BC-PLTs resulted effective in active bleeding control in two patients without any adverse reaction or concomitant antihaemorrhagic therapies. CRY BC-PLTs met the currently accepted criteria for cryopreserved PLTs, their transfusion in patients with AL was safe. (Clinical trial: NCT02032134).

Towards increasing shelf life and haemostatic potency of stored platelet concentrates

PURPOSE OF REVIEW

Platelet transfusion is a widely used therapy in treating or preventing bleeding and haemorrhage in patients with thrombocytopenia or trauma. Compared with the relative ease of platelet transfusion, current practice for the storage of platelets is inefficient, costly and relatively unsafe, with platelets stored at room temperature (RT) for upto 5-7 days.

RECENT FINDINGS

During storage, especially at cold temperatures, platelets undergo progressive and deleterious changes, collectively termed the 'platelet storage lesion', which decrease their haemostatic function and posttransfusion survival. Recent progress in understanding platelet activation and host clearance mechanisms is leading to the consideration of both old and novel storage conditions that use refrigeration and/or cryopreservation to overcome various storage lesions and significantly extend platelet shelf-life with a reduced risk of pathogen contamination.

SUMMARY

A review of the advantages and disadvantages of alternative methods for platelet storage is presented from both a clinical and biological perspective. It is anticipated that future platelet preservation involving cold, frozen and/or pathogen reduction strategies in a proper platelet additive solution will enable longer term and safer platelet storage.

Haemostatic responsiveness and release of biological response modifiers following cryopreservation of platelets treated with amotosalen and ultraviolet A light

BACKGROUND

Due to the risk of replication of contaminating pathogens, platelets have a limited storage time of 5 days, which can be prolonged to 7 days by the use of pathogen inactivation technologies. Cryopreservation (CP) may be an alternative to permit longer storage periods and increased availability. However, the preparation of platelets can result in secretion of biological response modifiers (BRM), which can cause adverse transfusion reactions in the recipient. We investigated the impact of CP on platelet function and release of BRM in untreated (conventional) and pathogen-inactivated (PI) platelet concentrates.

MATERIALS AND METHODS

Twelve buffy coat-derived platelet units were treated with amotosalen and ultraviolet A light to inactivate pathogens. Twelve untreated units were used as controls. The 24 units were cryopreserved and in vitro variables were analysed before and after CP. The in vitro variables investigated included platelet surface receptors and activation markers by flow cytometry, and coagulation time by viscoelastography. A panel of BRM, including cytokines, was investigated.

RESULTS

CP of both conventional and PI platelets resulted in a significant increase of BRM with similar increases of most of the BRM after CP of conventional and PI platelet concentrates. The increase in some of the BRM correlated significantly with shortened coagulation time, increased P-selectin expression, reduced mitochondrial transmembrane potential, and reduced capacity to respond to stimulation with ADP and collagen.

DISCUSSION

Cryopreservation of both conventional and PI platelets results in secretion of BRM. The increase in some of the BRM correlated with changes in platelet function variables and suggests that BRM release is affected, in part, in a similar way by CP as are changes in platelet function variables. PI with amotosalen and ultraviolet A light in combination with CP did not affect the release of immunomodulatory factors more than CP alone did.

Transfusion of cryopreserved platelets exacerbates inflammatory liver and lung injury in a mice model of hemorrhage

BACKGROUND

Platelets are essential for primary hemostasis and also play an important role in inflammatory reactions. The hemostatic property of cryopreserved platelets (CPPs) has been confirmed in the treatment of bleeding casualties, but inflammatory injury induced by CPP transfusion is relatively unclear. We aim to investigate the effects of CPP transfusion on inflammatory organ injury in mice after hemorrhage.

METHODS

Mice were subjected to a volume-controlled hemorrhage over 1 hour, and then were transfused with fresh platelets (FPs), Liquid-stored platelets (LPPs), CPPs, or fresh frozen plasma (FFP, control). At 6 hours posttransfusion, mice were sacrificed, and blood and tissues were sampled. Tissue sections were examined histologically and by immunohistochemical staining of neutrophils and macrophages. Plasma alanine aminotransferase, hepatic myeloperoxidase activity and inflammatory cytokine levels were measured.

RESULTS

Transfusion of stored platelets (LPPs and CPPs) caused more serious histological injury in liver and lung compared with FPs and FFP (p < 0.05). However, kidney histological injury was similar among groups. Significantly higher numbers of Ly-6G-positive neutrophils were detected in liver and of F4/80-positive macrophages in liver and lung of mice transfused with LPPs or CPPs compared with FPs or FFP (p < 0.05). Transfusion of CPPs caused the most severe inflammatory liver injury, as reflected by alanine aminotransferase levels, hepatic macrophage infiltration, and hepatic myeloperoxidase activity and inflammatory cytokine levels (macrophage inflammatory protein-2, tumor necrosis factor-α, and interleukin-1β).

CONCLUSION

Cryopreserved platelet transfusion is more likely to aggravate hemorrhage-induced liver and lung injury by activating macrophage and facilitating neutrophil infiltration into hepatic tissues.

Cooling and Cryopreservation of Equine Platelet-Rich Plasma With Dimethyl Sulfoxide and Trehalose

Equine platelet-rich plasma (PRP) has been used in horses to repair bone, articular and tendinous lesions, laminitis, and even endometritis. However, platelets have a very limited lifespan, which makes it difficult to prepare and use PRP, except in loco. With the aim to produce PRP with higher platelet viability for clinical purposes, the effects of the cryoprotectants dimethyl sulfoxide (DMSO) and trehalose were evaluated on cooled (4°C) and cryopreserved (-196°C) equine PRP. The protocols of cooling and cryopreservation were performed independently, comparing the following treatments: fresh PRP, PRP + 6% DMSO, PRP + 300 mM of trehalose, and PRP only. The PRP samples were prepared by double centrifugation of the blood of six ponies, further divided into four aliquots. The cooled or cryopreserved aliquots were stored for 14 days. All samples were evaluated for the platelet count, the mean platelet volume, and the release of transforming growth factor beta 1 (TGF-β1). The number of platelets in the fresh PRP and cooled samples was similar; however, platelet count was higher in the fresh PRP than in cryopreserved samples. The release of TGF-β1 was higher in the fresh PRP (105891 ± 52398 pg/mL), but the stored samples still released significant amounts of this growth factor (27291 ± 9625 pg/mL).

Cryopreservation of buffy coat-derived platelet concentrates photochemically treated with amotosalen and UVA light

BACKGROUND

Cryopreserved platelets (CPPs) are considered a promising approach for extended platelet storage, bridging inventory shortages of conventionally stored platelets. It is unknown if platelet concentrates exposed to photochemical treatment (PCT) with amotosalen and ultraviolet A (UVA) light, to inactivate pathogens, are suitable for freezing. The objective of this study was to analyze potential effects of PCT on CPPs as compared with untreated CPPs.

STUDY DESIGN AND METHODS

A total of 12 PCT-treated and 12 untreated platelet units from buffy coats were cryopreserved at -80°C in 5% dimethyl sulfoxide. CPPs of both types were rapidly thawed at 37°C and resuspended in 200 mL fresh plasma. In vitro properties were analyzed prefreezing, postfreezing and thawing, and on Day 1 after thawing.

RESULTS

Directly after thawing, no major differences in platelet content, lactase hydrogenase, adenosine triphosphate, mitochondrial membrane potential, CD62P, CD42b, and platelet endothelial cell adhesion molecule were seen between PCT-CPPs and conventional CPPs. Agonist-induced PAC-1 expression and contribution of CPPs to blood coagulation in an experimental rotational thromboelastometry setup were also similar between the groups. On Day 1 after thawing, the CPPs of both types performed less well. The PCT-CPPs tended to be more affected by the freezing process than the conventional CPPs.

CONCLUSIONS

PCT-CPPs appeared slightly more susceptible to lesion effects by freezing than conventional CPPs, in particular in assays on Day 1 after thawing, but these differences were small relative to the dramatic effects of the freezing process itself.

Platelet transfusion: Current challenges

Since the late sixties, platelet concentrates are transfused to patients presenting with severe thrombocytopenia, platelet function defects, injuries, or undergoing surgery, to prevent the risk of bleeding or to treat actual hemorrhage. Current practices differ according to the country or even in different hospitals and teams. Although crucial advances have been made during the last decades, questions and debates still arise about the right doses to transfuse, the use of prophylactic or therapeutic strategies, the nature and quality of PC, the storage conditions, the monitoring of transfusion efficacy and the microbiological and immunological safety of platelet transfusion. Finally, new challenges are emerging with potential new platelet products, including cold stored or in vitro produced platelets. The most debated of these points are reviewed.

Comprehensive review of platelet storage methods for use in the treatment of active hemorrhage

This review considers the various methods currently in use, or under investigation, for the storage of platelets intended for use in the treatment of active hemorrhage. The current standard practice of storing platelets at room temperature (RT) (20°C-24°C) optimizes circulating time, but at the expense of hemostatic function and logistical considerations. A number of alternatives are under investigation. Novel storage media additives appear to attenuate the deleterious changes that affect RT stored platelets. Cold storage was originally abandoned due to the poor circulating time of platelets stored at 4°C, but such platelets may actually be more hemostatically effective, with a number of other advantages, compared to RT stored platelets. Periodically re-warming cold stored platelets (temperature cycling, TC) may combine the hemostatic efficacy of cold stored platelets with the longer circulating times of RT storage. Alternatives to liquid storage include cryopreservation (freezing) or lyophilization (freeze-drying). The former has had some limited clinical use and larger clinical trials are underway, while the latter is still in the preclinical stage with promising in vitro and in vivo results. The importance of platelet transfusion in the management of active hemorrhage is now well accepted, so it is timely that platelet storage methods are reviewed with consideration of not only their circulating time, but also their hemostatic efficacy.

Cryopreservation and its clinical applications

Cryopreservation is a process that preserves organelles, cells, tissues, or any other biological constructs by cooling the samples to very low temperatures. The responses of living cells to ice formation are of theoretical interest and practical relevance. Stem cells and other viable tissues, which have great potential for use in basic research as well as for many medical applications, cannot be stored with simple cooling or freezing for a long time because ice crystal formation, osmotic shock, and membrane damage during freezing and thawing will cause cell death. The successful cryopreservation of cells and tissues has been gradually increasing in recent years, with the use of cryoprotective agents and temperature control equipment. Continuous understanding of the physical and chemical properties that occur in the freezing and thawing cycle will be necessary for the successful cryopreservation of cells or tissues and their clinical applications. In this review, we briefly address representative cryopreservation processes, such as slow freezing and vitrification, and the available cryoprotective agents. In addition, some adverse effects of cryopreservation are mentioned.

Preparation of Platelet Concentrates for Research and Transfusion Purposes

Platelets are specialized cellular elements of the blood that play central roles in physiologic and pathologic processes of hemostasis, wound healing, host defense, thrombosis, inflammation, and tumor metastasis. Activation of platelets is crucial for platelet function that includes a complex interplay of adhesion, signaling molecules, and release of bioactive factors. Transfusion of platelet concentrates is an important treatment component for thrombocytopenia and bleeding. Recent progress in high-throughput mRNA and protein profiling techniques has advanced the understanding of platelet biological functions toward identifying novel platelet-expressed and secreted proteins, analyzing functional changes between normal and pathologic states, and determining the effects of processing and storage on platelet concentrates for transfusion. It is important to understand the different standard methods of platelet preparation and how they differ from the perspective for use as research samples in clinical chemistry. Two simple methods are described here for the preparation of research-scale platelet samples from whole blood, and detailed notes are provided about the methods used for the preparation of platelet concentrates for transfusion.

Transfusion: -80°C Frozen Blood Products Are Safe and Effective in Military Casualty Care

INTRODUCTION

The Netherlands Armed Forces use -80°C frozen red blood cells (RBCs), plasma and platelets combined with regular liquid stored RBCs, for the treatment of (military) casualties in Medical Treatment Facilities abroad. Our objective was to assess and compare the use of -80°C frozen blood products in combination with the different transfusion protocols and their effect on the outcome of trauma casualties.

MATERIALS AND METHODS

Hemovigilance and combat casualties data from Afghanistan 2006-2010 for 272 (military) trauma casualties with or without massive transfusions (MT: ≥6 RBC/24hr, N = 82 and non-MT: 1-5 RBC/24hr, N = 190) were analyzed retrospectively. In November 2007, a massive transfusion protocol (MTP; 4:3:1 RBC:Plasma:Platelets) for ATLS® class III/IV hemorrhage was introduced in military theatre. Blood product use, injury severity and mortality were assessed pre- and post-introduction of the MTP. Data were compared to civilian and military trauma studies to assess effectiveness of the frozen blood products and MTP.

RESULTS

No ABO incompatible blood products were transfused and only 1 mild transfusion reaction was observed with 3,060 transfused products. In hospital mortality decreased post-MTP for MT patients from 44% to 14% (P = 0.005) and for non-MT patients from 12.7% to 5.9% (P = 0.139). Average 24-hour RBC, plasma and platelet ratios were comparable and accompanying 24-hour mortality rates were low compared to studies that used similar numbers of liquid stored (and on site donated) blood products.

CONCLUSION

This report describes for the first time that the combination of -80°C frozen platelets, plasma and red cells is safe and at least as effective as standard blood products in the treatment of (military) trauma casualties. Frozen blood can save the lives of casualties of armed conflict without the need for in-theatre blood collection. These results may also contribute to solutions for logistic problems in civilian blood supply in remote areas.

Alternatives to allogeneic platelet transfusion

Allogeneic platelet transfusions are widely used for the prevention and treatment of bleeding in thrombocytopenia. Recent evidence suggests platelet transfusions have limited efficacy and are associated with uncertain immunomodulatory risks and concerns about viral or bacterial transmission. Alternatives to transfusion are a well-recognised tenet of Patient Blood Management, but there has been less focus on different strategies to reduce bleeding risk by comparison to platelet transfusion. Direct alternatives to platelet transfusion include agents to stimulate endogenous platelet production (thrombopoietin mimetics), optimising platelet adhesion to endothelium by treating anaemia or increasing von Willebrand factor levels (desmopressin), increasing formation of cross-linked fibrinogen (activated recombinant factor VII, fibrinogen concentrate or recombinant factor XIII), decreasing fibrinolysis (tranexamic acid or epsilon aminocaproic acid) or using artificial or modified platelets (cryopreserved platelets, lyophilised platelets, haemostatic particles, liposomes, engineered nanoparticles or infusible platelet membranes). The evidence base to support the use of these alternatives is variable, but an area of active research. Much of the current randomised controlled trial focus is on evaluation of the use of thrombopoietin mimetics and anti-fibrinolytics. It is also recognised that one alternative strategy to platelet transfusion is choosing not to transfuse at all.

A review of the application of autologous blood transfusion

Autologous blood transfusion (ABT) has been gradually attracting more attention due to the increasingly prominent problem of blood transfusion safety and blood shortage in recent years. With the rapid development of blood conservation techniques, blood component separation technology, blood transfusion medicine and a constant increase in clinical needs, ABT technology has been expanded and innovated to a large degree. In this study, the development of preoperative autologous blood donation (PABD), acute normovolemic hemodilution (ANH), intraoperative and postoperative autotransfusion, and other new technologies and theories are reviewed and existing questions are analyzed. Challenges and applications are also discussed in order to provide reference for peers.

Characterization of procoagulant extracellular vesicles and platelet membrane disintegration in DMSO-cryopreserved platelets

BACKGROUND

Freezing is promising for extended platelet (PLT) storage for transfusion. 6% DMSO cryopreserved PLTs (CPPs) are currently in clinical development. CPPs contain significant amount of platelet membrane vesicles (PMVs). PLT-membrane changes and PMV release in CPP are poorly understood, and haemostatic effects of CPP PMVs are not fully elucidated. This study aims to investigate PLT-membrane alterations in CPPs and provide comprehensive characterization of CPP PMVs, and their contribution to procoagulant activity (PCA) of CPPs.

METHODS

CPPs and corresponding liquid-stored PLTs (LSPs) were characterized by flow cytometry (FC), fluorescence polarization (FP), nanoparticle tracking analysis (NTA), electron microscopy (SEM, TEM), atomic force microscopy (AFM) and thrombin-generation (TG) test.

RESULTS

SEM and TEM revealed disintegration and vesiculation of the PLT-plasma membrane and loss of intracellular organization in 60% PLTs in CPPs. FP demonstrated that 6% DMSO alone and with freezing-thawing caused marked increase in PLT-membrane fluidity. The FC counts of annexin V-binding PMVs and CD41a(+) PMVs were 68- and 56-folds higher, respectively, in CPPs than in LSPs. The AFM and NTA size distribution of PMVs in CPPs indicated a peak diameter of 100 nm, corresponding to exosome-size vesicles. TG-based PCA of CPPs was 2- and 9-folds higher per PLT and per volume, respectively, compared to LSPs. Differential centrifugation showed that CPP supernatant contributed 26% to CPP TG-PCA, mostly by the exosome-size PMVs and their TG-PCA was phosphatidylserine dependent.

CONCLUSIONS

Major portion of CPPs does not show activation phenotype but exhibits grape-like membrane disintegration with significant increase of membrane fluidity induced by 6% DMSO alone and further aggravated by freezing-thawing process. DMSO cryopreservation of PLTs is associated with the release of PMVs and marked increase of TG-PCA, as compared to LSPs. Exosome-size PMVs have significant contribution to PCA of CPPs.