A computerized prediction model of hazardous inflammatory platelet transfusion outcomes

The composition of single-donor apheresis platelet concentrates is influenced by the age of the donor

The aging population often faces health issues that sometimes necessitate transfusions. Transfusion services are increasingly concerned about the rising number of transfusions and the aging donor population, as both factors are crucial in maintaining the quality of blood donations. In this context, our study aims to measure the bioactive molecule cytokine levels in single donor apheresis platelet concentrates (SDA-PC) based on the donor's age and to determine whether these cytokines, in conjunction with the donor age, could contribute to transfusion adverse reactions (AR). Our findings indicate that well-known platelet molecules such as sCD62P, as well as IL-13, ADAMTS13, MIP-1α, NGAL, MCP-3, HSAA, GDF-15, CX3CL1, and MDC, were present in SDA-PC. Levels of MIP-1α, GDF-15, and sCD62P increased with donor aging, whereas levels of MDC decreased. In conclusion, most of the cytokine levels detected were elevated in cases of AR and with increasing donor age. Notably, GDF-15 was the only cytokine that showed a positive correlation with age in the context of AR.

Transfusion-Related Acute Lung Injury: from Mechanistic Insights to Therapeutic Strategies

Transfusion-related acute lung injury (TRALI) is a potentially lethal complication of blood transfusions, characterized by the rapid onset of pulmonary edema and hypoxemia within six hours post-transfusion. As one of the primary causes of transfusion-related mortality, TRALI carries a significant mortality rate of 6-12%. However, effective treatment strategies for TRALI are currently lacking, underscoring the urgent need for a comprehensive and in-depth understanding of its pathogenesis. This comprehensive review provides an updated and detailed analysis of the current landscape of TRALI, including its clinical presentation, pathogenetic hypotheses, animal models, cellular mechanisms, signaling pathways, and potential therapeutic targets. By highlighting the critical roles of these pathways and therapies, this review offers valuable insights to inform the development of preventative and therapeutic strategies and to guide future research efforts aimed at addressing this life-threatening condition.

Identification of new bioactive molecules in platelet preparation, storage, and transfusion reactions for improved transfusion management

Platelet concentrates (PCs) intended for transfusion contain bioactive molecules that can be considered Biological Response Modifiers (BRMs), mainly originating from plasma regardless of the preparation process. During storage, NGAL and GDF-15 levels increase in single donor apheresis platelet concentrates (SDA-PC), whereas in buffy coat platelet concentrates (BC-PC), the levels of MIP1α, MCP-3, and HSAA increase, and GDF-15 levels decrease. These molecules, primarily released by leukocytes, may contribute to adverse reactions (ARs) following a PC transfusion. Notably, in SDA-PC or BC-PC transfusions that result in ARs, the levels of NGAL, HSAA, and GDF-15 are significantly elevated, while the levels of MDC and CX3CL1 are significantly reduced compared to transfusions without ARs. These biomarkers could potentially serve as predictors for PCs-induced ARs.

Modulating Immune Responses: The Double-Edged Sword of Platelet CD40L

The CD40-CD40L receptor ligand pair plays a fundamental role in the modulation of the innate as well as the adaptive immune response, regulating monocyte, T and B cell activation, and antibody isotype switching. Although the expression and function of the CD40-CD40L dyad is mainly attributed to the classical immune cells, the majority of CD40L is expressed by activated platelets, either in a membrane-bound form or shed as soluble molecules in the circulation. Platelet-derived CD40L is involved in the communication with different immune cell subpopulations and regulates their functions effectively. Thus, platelet CD40L contributes to the containment and clearance of bacterial and viral infections, and additionally guides leukocytes to sites of infection. However, platelet CD40L promotes inflammatory cellular responses also in a pathophysiological context. For example, in HIV infections, platelet CD40L is supportive of neuronal inflammation, damage, and finally HIV-related dementia. In sepsis, platelet CD40L can induce extensive endothelial and epithelial damage resulting in barrier dysfunction of the gut, whereby the translocation of microbiota into the circulation further aggravates the uncontrolled systemic inflammation. Nevertheless, a distinct platelet subpopulation expressing CD40L under septic conditions can attenuate systemic inflammation and reduce mortality in mice. This review focuses on recent findings in the field of platelet CD40L biology and its physiological and pathophysiological implications, and thereby highlights platelets as vital immune cells that are essential for a proper immune surveillance. In this context, platelet CD40L proves to be an interesting target for various inflammatory diseases. However, either an agonism or a blockade of CD40L needs to be well balanced since both the approaches can cause severe adverse events, ranging from hyperinflammation to immune deficiency. Thus, an interference in CD40L activities should be likely done in a context-dependent and timely restricted manner.

Lowering platelet-count threshold for transfusion in preterm neonates decreases the number of transfusions without increasing severe hemorrhage events

Thrombocytopenia is common in preterm neonates and can be associated with hemorrhage. Most platelet transfusions are prophylactic. Previously, higher platelet-count thresholds were recommended for neonates, but this recommendation has been questioned in recent studies. In the PlaNeT2 trial, mortality and serious bleeding were more frequent in neonates with the highest platelet-count threshold than in others. Following this trial, we changed our platelet transfusion practice by lowering the platelet-count threshold for prophylactic transfusion from 50,000 to 25,000/mm3. We conducted a before-after retrospective cohort study to quantify the frequency of platelet transfusions and assess the new protocol by analyzing death and serious hemorrhage events. This retrospective monocentric study included neonates born before 37 weeks of gestation with platelet count < 150,000/mm3 during the 2 years preceding the new platelet transfusion protocol (high prophylactic transfusion threshold, 50,000/mm3) and during the 2 years after the new platelet transfusion protocol (low prophylactic transfusion threshold, 25,000/mm3). The primary outcome was the proportion of neonates receiving at least one platelet transfusion in both groups. We also compared the proportion of deaths and severe hemorrhage events. A total of 707 neonates with thrombocytopenia were identified. In the high-threshold group, 99/360 (27.5%) received at least one platelet transfusion as compared with 56/347 (16.1%) in the low-threshold group (p < 0.001). The groups did not differ in proportion of deaths or severe hemorrhage events.

CONCLUSIONS

A reduced platelet-count threshold for transfusion allowed for a significant reduction in the number of platelet transfusions without increasing severe hemorrhage events.

WHAT IS KNOWN

• A recent randomized trial suggested that restrictive platelet-count thresholds for platelet transfusion could be beneficial for preterm neonates.

WHAT IS NEW

• On lowering the platelet-count threshold for transfusion from 50,000 to 25,000/mm3, the number of transfusions significantly decreased without increasing severe hemorrhage events in a neonatal intensive care unit.

Lipidomic analysis of differently prepared platelet concentrates in additive solution during storage

BACKGROUND

Structural and biochemical changes in stored platelets are influenced by collection and processing methods. Lesions may appear during platelet concentrate storage, some of which may be involved in adverse transfusion reactions. The preparation and storage of platelet concentrates (PC) may modify and even damage the lipid mediator content. The aim of this study was to investigate the lipidomic profile identified in the supernatants of PCs according to processing and storage conditions, both after leukocyte filtration and contained in platelet additive solution (PAS), comparing single donor apheresis (SDA) products with pooled buffy coat (BC) products.

MATERIALS AND METHODS

We investigated the accumulation of various lipid mediators including lysophospholipids (LP) and eicosanoids in SDA and BC products stored for 0-5 days. All products were processed following French Blood Establishment (EFS) procedures in accordance with EDQM/GTS European Standards. Both SDA and BC were leukocyte reduced and conserved in 35% autologous donor plasma and 65% platelet additive solution. Lipidomic analysis was performed on PC supernatants using LS/MS spectrometry.

RESULTS

Our data demonstrate that lysophosphatidylcholine (LPC) levels were higher in BCs compared to SDAs, with no difference in lysophosphatidic acid (LPA) expression between the two preparation methods. Results for other eicosanoids showed greater similarity; indeed, no clear pattern emerged from analysis of eicosanoids in terms of storage time and process. In general, we observed longitudinal lipid mediator modulation for both SDAs and BCs, particularly at later time points.

DISCUSSION

The expression of LPC and some eicosanoids in BCs could be used as novel biomarkers of PC quality. Future studies are needed to explore their impact on adverse transfusion reactions.

Platelet transfusion in adults: An update

Many patients worldwide receive platelet components (PCs) through the transfusion of diverse types of blood components. PC transfusions are essential for the treatment of central thrombocytopenia of diverse causes, and such treatment is beneficial in patients at risk of severe bleeding. PC transfusions account for almost 10% of all the blood components supplied by blood services, but they are associated with about 3.25 times as many severe reactions (attributable to transfusion) than red blood cell transfusions after stringent in-process leukoreduction to less than 10⁶ residual cells per blood component. PCs are not homogeneous, due to the considerable differences between donors. Furthermore, the modes of PC collection and preparation, the safety precautions taken to limit either the most common (allergic-type reactions and febrile non-hemolytic reactions) or the most severe (bacterial contamination, pulmonary lesions) adverse reactions, and storage and conservation methods can all result in so-called PC "storage lesions". Some storage lesions affect PC quality, with implications for patient outcome. Good transfusion practices should result in higher levels of platelet recovery and efficacy, and lower complication rates. These practices include a matching of tissue ABH antigens whenever possible, and of platelet HLA (and, to a lesser extent, HPA) antigens in immunization situations. This review provides an overview of all the available information relating to platelet transfusion, from donor and donation to bedside transfusion, and considers the impact of the measures applied to increase transfusion efficacy while improving safety and preventing transfusion inefficacy and refractoriness. It also considers alternatives to platelet component (PC) transfusion.

Assessment of the soluble proteins HMGB1, CD40L and CD62P during various platelet preparation processes and the storage of platelet concentrates: The BEST collaborative study

BACKGROUND

Structural and biochemical changes in stored platelets are influenced by collection and processing methods. This international study investigates the effects of platelet (PLT) processing and storage conditions on HMGB1, sCD40L, and sCD62P protein levels in platelet concentrate supernatants (PCs).

STUDY DESIGN/METHODS

PC supernatants (n = 3748) were collected by each international centre using identical centrifugation methods (n = 9) and tested centrally using the ELISA/Luminex platform. Apheresis versus the buffy coat (BC-PC) method, plasma storage versus PAS and RT storage versus cold (4°C) were investigated. We focused on PC preparation collecting samples during early (RT: day 1-3; cold: day 1-5) and late (RT: day 4-7; cold: day 7-10) storage time points.

RESULTS

HMGB1, sCD40L, and sCD62P concentrations were similar during early storage periods, regardless of storage solution (BC-PC plasma and BC-PC PAS-E) or temperature. During storage and without PAS, sCD40L and CD62P in BC-PC supernatants increased significantly (+33% and +41%, respectively) depending on storage temperature (22 vs. 4°C). However, without PAS-E, levels decreased significantly (-31% and -20%, respectively), depending on storage temperature (22 vs. 4°C). Contrastingly, the processing method appeared to have greater impact on HMGB1 release versus storage duration. These data highlight increases in these parameters during storage and differences between preparation methods and storage temperatures.

CONCLUSIONS

The HMGB1 release mechanism/intracellular pathways appear to differ from sCD62P and sCD40L. The extent to which these differences affect patient outcomes, particularly post-transfusion platelet increment and adverse events, warrants further investigation in clinical trials with various therapeutic indications.

Bioactive lipids as biomarkers of adverse reactions associated with apheresis platelet concentrate transfusion

Platelet concentrate (PC) transfusion seeks to provide haemostasis in patients presenting severe central thrombocytopenia or severe bleeding. PCs may induce adverse reactions (AR) that can occasionally be severe (SAR). PCs contain active biomolecules such as cytokines and lipid mediators. The processing and storage of PCs creates so-called structural and biochemical storage lesions that accumulate when blood products reach their shelf life. We sought to investigate lipid mediators as bioactive molecules of interest during storage and review associations with adverse reactions post-transfusion. To facilitate understanding, we focused on single donor apheresis (SDA) PCs with approximately 31.8% of PCs being delivered in our setting. Indeed, pooled PCs are the most widely transfused products, but the study of a single donor lipid mediator is easier to interpret. We are investigating key lipid mediators involved in AR. Adverse reactions were closely monitored in accordance with current national and regional haemovigilance protocols. Residual PCs were analysed post-transfusion in a series of observations, both with and without severe reactions in recipients. A decrease in the lysophosphatidylcholine species to produce the lysophosphatidic acid species has been observed during storage and in the case of AR. Lysophosphatidic acid increased with primarily platelet-inhibitor lipids. Anti-inflammatory platelet-induced inhibition lipids were weakly expressed in cases of severe adverse reactions. We therefore propose that a decrease in lysophosphatidylcholine and an increase in lysophosphatidic acid can prospectively predict serious adverse transfusion reactions.

Differential expression of exosomal microRNAs in fresh and senescent apheresis platelet concentrates

Patients have a high risk of suffering adverse reactions after receiving platelet products stored for 5 days. Bioactive exosomes in platelet products can be accumulated during storage, which is associated with adverse reactions. MicroRNAs are one of the critical cargoes in exosomes, which participate in cell differentiation, metabolism, and immunomodulation. This study intends to elucidate and analyze the differential expression of exosomal microRNAs in apheresis platelet concentrates during storage and predict the potential functions of target genes. Apheresis platelet concentrates were used to isolate exosomes by ultracentrifugation. Exosomes were phenotyped by western blot, transmission electron microscopy, and nano flow cytometry. The differential expression of the exosomal microRNAs was obtained by a microarray test using four bags of apheresis platelets stored for 5 days compared with 1 day. The differentially expressed microRNAs between the two time points were identified, and their target genes were analyzed by miRWalk and miRDB. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to predict the target genes' functions. Fifteen bags of apheresis platelet concentrates stored for 1 day and 5 days were used to verify the microarray results by quantitative reverse transcription-polymerase chain reactions (qRT-PCR). There were 134 microRNAs in total expressed differently in the two groups (day 1 and day 5), with 57 microRNAs up-regulated and 77 down-regulated (|fold change| > 2.0 and P < .05). Thirteen up-regulated microRNAs (hsa-miR-22-3p, hsa-miR-223-3p, hsa-miR-21-5p, hsa-miR-23a-3p, hsa-miR-320b, hsa-let-7a-5p, hsa-miR-25-3p, hsa-miR-126-3p, hsa-miR-320c, hsa-miR-342-3p, hsa-miR-320d, hsa-miR-328-3p, and hsa-miR-320e) detected in all samples were selected to validate the results. The qRT-PCR results showed that five (hsa-miR-22-3p, hsa-miR-223-3p, hsa-miR-21-5p, hsa-miR-23a-3p, and hsa-miR-320b) of them were increased more than 10-fold (P < .001); four (hsa-let-7a-5p, hsa-miR-25-3p, hsa-miR-126-3p, hsa-miR-320c) more than five-fold (P < .001); two (hsa-miR-342-3p and hsa-miR-320d) more than two-fold (P < .05); and two (hsa-miR-328-3p and hsa-miR-320e) more than two-fold (P > .05). Specifically, hsa-miR-22-3p increased 14.6-fold; hsa-miR-223-3p increased 13.0-fold; and hsa-miR-21-5p increased 12.0-fold. Based on bioinformatics functional analysis, target genes of top nine microRNAs (hsa-miR-22-3p, hsa-miR-223-3p, hsa-miR-21-5p, hsa-miR-23a-3p, hsa-miR-320b, hsa-let-7a-5p, hsa-miR-25-3p, hsa-miR-126-3p, and hsa-miR-320c) were annotated with positive regulation of cell proliferation and nervous system development, and mainly enriched in regulating pluripotency of stem cells signaling pathway, prolactin signaling pathway, and FoxO signaling pathway, etc. The prolactin, FoxO, ErbB, and TNF signaling pathway were relevant to immunomodulation. In particular, hsa-miR-22-3p expression was the most different during storage, with a fold change of 14.6, which might be a key mediator.

Platelets as Key Factors in Inflammation: Focus on CD40L/CD40

Platelets are anucleate cytoplasmic fragments derived from the fragmentation of medullary megakaryocytes. Activated platelets adhere to the damaged endothelium by means of glycoproteins on their surface, forming the platelet plug. Activated platelets can also secrete the contents of their granules, notably the growth factors contained in the α-granules, which are involved in platelet aggregation and maintain endothelial activation, but also contribute to vascular repair and angiogenesis. Platelets also have a major inflammatory and immune function in antibacterial defence, essentially through their Toll-like Receptors (TLRs) and Sialic acid-binding immunoglobulin-type lectin (SIGLEC). Platelet activation also contributes to the extensive release of anti- or pro-inflammatory mediators such as IL-1β, RANTES (Regulated on Activation, Normal T Expressed and Secreted) or CD154, also known as the CD40-ligand. Platelets are involved in the direct activation of immune cells, polynuclear neutrophils (PNNs) and dendritic cells via the CD40L/CD40 complex. As a general rule, all of the studies presented in this review show that platelets are capable of covering most of the stages of inflammation, primarily through the CD40L/CD40 interaction, thus confirming their own role in this pathophysiological condition.

Protein Concentrations in Stored Pooled Platelet Concentrates Treated with Pathogen Inactivation by Amotosalen Plus Ultraviolet a Illumination

Platelet granules contain a diverse group of proteins. Upon activation and during storage, platelets release a number of proteins into the circulation or supernatant of stored platelet concentrate (PC). The aim of this work was to investigate the effect of pathogen inactivation (PI) on a selection of proteins released in stored platelets. Materials and Methods: PCs in platelet additive solution (PAS) were produced from whole blood donations using the buffy coat (BC) method. PCs in the treatment arm were pathogen inactivated with amotosalen and UVA, while PCs in the second arm were used as an untreated platelet control. Concentrations of 36 proteins were monitored in the PCs during storage. Results: The majority of proteins increased in concentration over the storage period. In addition, 10 of the 29 proteins that showed change had significantly different concentrations between the PI treatment and the control at one or more timepoints. A subset of six proteins displayed a PI-related drop in concentration. Conclusions: PI has limited effect on protein concentration stored PC supernatant. The protein’s changes related to PI treatment with elevated concentration implicate accelerated Platelet storage lesion (PSL); in contrast, there are potential novel benefits to PI related decrease in protein concentration that need further investigation.

Preventing adverse reactions in pediatric transfusions using washed platelet concentrate

Blood transfusion is an important form of supportive care in children; however, transfusion-associated adverse reactions (TARs) are a problem. As with adults, allergic transfusion reactions (ATRs) and febrile non-hemolytic transfusion reactions (FNHTRs) are major TARs, and the frequency of ATRs caused by platelet concentrate (PC) tends to be particularly high. The plasma component of the blood product is thought to be a major factor in the onset of TARs such as ATR and FNHTR. By contrast, in children, age, underlying disease, and number of blood transfusions may be relevant patient-related factors. Although acetaminophen or diphenhydramine may be used prophylactically to prevent TARs, there is no clear evidence of their effectiveness. Volume-reduced PC is used to prevent TARs; however, it may be difficult to maintain the quality of platelets. Plasma-replaced PC stored with platelet additive solution raises the concern that TARs cannot be completely prevented by residual plasma. Washed PC removes most of the plasma, so it can effectively prevent ATR and FNHTR. The recent development of platelet additive solution [M-sol, bicarbonate Ringer's solution supplemented with acid-citrate-dextrose formula A (BRS-A)] in Japan has enabled the maintenance of the quality of platelets for long periods. The clinical use of washed PC in Japan has therefore progressed. Washed PC with M-sol or BRS-A for pediatric patients can effectively prevent TARs without diminishing the transfusion effect. The supply of washed PC has begun from the Japanese Red Cross Society, and it has become possible to use washed PC at all medical institutions in Japan.

Effects and Side Effects of Platelet Transfusion

Aside from their canonical role in hemostasis, it is increasingly recognized that platelets have inflammatory functions and can regulate both adaptive and innate immune responses. The main topic this review aims to cover is the proinflammatory effects and side effects of platelet transfusion. Platelets prepared for transfusion are subject to stress injury upon collection, preparation, and storage. With these types of stress, they undergo morphologic, metabolic, and functional modulations which are likely to induce platelet activation and the release of biological response modifiers (BRMs). As a consequence, platelet concentrates (PCs) accumulate BRMs during processing and storage, and these BRMs are ultimately transfused alongside platelets. It has been shown that BRMs present in PCs can induce immune responses and posttransfusion reactions in the transfusion recipient. Several recent reports within the transfusion literature have investigated the concept of platelets as immune cells. Nevertheless, current and future investigations will face the challenge of encompassing the immunological role of platelets in the scope of transfusion.

Dysregulated pathways and differentially expressed proteins associated with adverse transfusion reactions in different types of platelet components

Platelet components (PCs) are occasionally associated with adverse transfusion reactions (ATRs). ATRs can occur regardless of the type of PC being transfused, whether it is a single-donor apheresis PC (SDA-PC) or a pooled PC (PPCs). The purpose of this study was to investigate the proteins and dysregulated pathways in both of the main types of PCs. The proteomic profiles of platelet pellets from SDA-PCs and PPCs involved in ATRs were analysed using the label-free LC-MS/MS method. Differentially expressed proteins with fold changes >|1.5| in clinical cases versus controls were characterised using bioinformatic tools (RStudio, GeneCodis3, and Ingenuity Pathways Analysis (IPA). The proteins were confirmed by western blotting. The common primary proteins found to be dysregulated in both types of PCs were the mitochondrial carnitine/acylcarnitine carrier protein (SLC25A20), multimerin-1 (MMRN1), and calumenin (CALU), which are associated with the important enrichment of platelet activation, platelet degranulation, and mitochondrial activity. Furthermore, this analysis revealed the involvement of commonly dysregulated canonical pathways, particularly mitochondrial dysfunction, platelet activation, and acute phase response. This proteomic analysis provided an interesting contribution to our understanding of the meticulous physiopathology of PCs associated with ATR. A larger investigation would assist in delineating the most relevant proteins to target within preventive transfusion safety strategies. BIOLOGICAL SIGNIFICANCE: Within platelet transfusion strategies, the two primary types of PCs predominantly processed in Europe, include (i) single donor apheresis PCs (SDA-PCs) from one donor and (ii) pooled PCs (PPCs). The current study used PCs from five buffy coats derived from five whole blood donations that were identical in ABO, RH1 and KEL1 groups. Both PC types were shown to be associated with the onset of an ATR in the transfused patient. Several common platelet proteins were found to be dysregulated in bags associated with ATR occurrences regardless of the type of PCs transfused and of their process. The dysregulated proteins included mitochondrial carnitine/acylcarnitine carrier protein (SLC25A20), which is involved in a fatty acid oxidation disorder; calumenin (CALU); and multimerin-1 (MMRN1), which is chiefly involved in platelet activation and degranulation. Dysregulated platelet protein pathways for ATRs that occurred with SDA-PCs and PPCs could support the dysregulated functions found in association with those three proteins. Those common platelet proteins may become candidates to define biomarkers associated with the onset of an ATR from PC transfusions, including monitoring during the quality steps of PC manufacturing, provided that the results are confirmed in larger cohorts. This study enriches our knowledge of platelet proteomics in PCs under pathological conditions.

Cytokines and related molecules, and adverse reactions related to platelet concentrate transfusions

Platelet transfusion is a safe process, but during or after the process the recipient may experience an adverse reaction and occasionally a serious adverse reaction (SAR). Platelet concentrate transfusion may be liable for significant absence of beneficial response. Danger may manifest clinically or biologically; in the latter case, manifestations are frequently an absence of the expected response to the blood component by the recipient. Blood platelets exert roles in inflammation, especially through the immunomodulator complex CD40/CD40L (sCD40L). In this review, we concentrate on the inflammatory potential of platelets and their participation to SARs in transfusion.

Platelet Inflammatory Response to Stress

Blood platelets play a central hemostatic role, (i) as they repair vascular epithelial damage, and (ii) they play immune defense roles, as they have the capacity to produce and secrete various cytokines, chemokines, and related products. Platelets sense and respond to local dangers (infectious or not). Platelets, therefore, mediate inflammation, express and use receptors to bind infectious pathogen moieties and endogenous ligands, among other components. Platelets contribute to effective pathogen clearance. Damage-associated molecular patterns (DAMPs) are danger signals released during inflammatory stress, such as burns, trauma and infection. Each pathogen is recognized by its specific molecular signature or pathogen-associated molecular pattern (PAMP). Recent data demonstrate that platelets have the capacity to sense external danger signals (DAMPs or PAMPs) differentially through a distinct type of pathogen recognition receptor (such as Toll-like receptors). Platelets regulate the innate immune response to pathogens and/or endogenous molecules, presenting several types of “danger” signals using a complete signalosome. Platelets, therefore, use complex tools to mediate a wide range of functions from danger sensing to tissue repair. Moreover, we noted that the secretory capacity of stored platelets over time and the development of stress lesions by platelets upon collection, processing, and storage are considered stress signals. The key message of this review is the “inflammatory response to stress” function of platelets in an infectious or non-infectious context.

Platelet concentrate supernatants alter endothelial cell mRNA and protein expression patterns as a function of storage length

BACKGROUND

Platelet transfusions are safe but can nevertheless cause serious adverse reactions (SARs). This study investigated the effects of platelet biological response modifiers (BRMs) that accumulate during storage and are commonly associated with transfusion adverse reactions.

STUDY DESIGN AND METHODS

Endothelial cells (ECs), that is, EA.hy926, were exposed in vitro to supernatants of platelet components (PCs) that had been either implicated or not in SARs. The EC Biology RT² Profiler PCR Array was used at the same time to study 84 genes related to functions of ECs. Soluble cytokines and surface expression of EC markers were determined by Luminex/enzyme-linked immunosorbent assay technology and flow cytometry, respectively. Apoptosis and scratch wound assays were performed using IncuCyte technology.

RESULTS

In vitro exposure of EA.hy926 monolayers with Day 0, 1-2, and 3-4 stored PC supernatants resulted in decreases in surface expression of markers of ECs. There was differential production of soluble BRMs in the tested cell line. Exposure to the supernatants of PCs that had been implicated in SARs showed a significant difference in the expression of the EC surface markers. EC mediators also responded differently when exposed to PC supernatants of different storage times and PCs involved in SARs.

CONCLUSION

PC supernatants collected at Day 1-2 activate fewer cell lines of ECs compared with supernatants collected at Day 3-4. Moreover, PC supernatants involved in SARs appear to alter EC activation compared with the control and storage length.

Transfusion-associated hazards: A revisit of their presentation

As a therapy or a support to other therapies, despite being largely beneficial to patients in general, transfusion it is not devoid of some risks. In a moderate number of cases, patients may manifest adverse reactions, otherwise referred to as transfusion-associated hazards (TAHs). The latest French 2016 haemovigilance report indicates that 93% of TAHs are minor (grade 1), 5.5% are moderate (grade 2) and 1.6% are severe (grade 3), with only five deaths (grade 4) being attributed to transfusion with relative certainty (imputability of level [or grade] 1 to 3). Health-care providers need to be well aware of the benefits and potential risks (to best evaluate and discuss the benefit-risk ratio), how to prevent TAHs, the overall costs and the availability of alternative therapeutic options. In high-income countries, most blood establishments (BEs) and hospital blood banks (HBBs) have developed tools for reporting and analysing at least severe transfusion reactions. With nearly two decades of haemovigilance, transfusion reaction databases should be quite informative, though there are four main caveats that prevent it from being fully efficient: (ai) reporting is mainly declarative and is thus barely exhaustive even in countries where it is mandatory by law; (aii) it is often difficult to differentiate between the different complications related to transfusion, diseases, comorbidities and other types of therapies in patients suffering from debilitating conditions; (aiii) there is a lack of consistency in the definitions used to describe and report some transfusion reactions, their severity and their likelihood of being related to transfusion; and (aiv) it is difficult to assess the imputability of a particular BC given to a patient who has previously received many BCs over a relatively short period of time. When compiling all available information published so far, it appears that TAHs can be analysed using different approaches: (bi) their pathophysiological nature; (bii) their severity; (biii) the onset scheme; (biv) a quality assessment (preventable or non-preventable); (bv) their impact on ongoing therapy. Moreover, TAHs can be reported either in a non-integrative or in an integrative way; in the latter case, presentation may also differ when issued by a blood establishment or a treating ward. At some point, a recapitulative document would be useful to gain a better understanding of TAHs in order to decrease their occurrence and severity and allow decision makers to determine action plans: this is what this review attempts to make. This review attempts to merge the different aspects, with a focus on the hospital side, i.e., how the most frequent TAHs can be avoided or mitigated.

Characterization of biologic response modifiers in the supernatant of conventional, refrigerated, and cryopreserved platelets

BACKGROUND

Alternatives to room temperature storage of platelets (PLTs) are of interest to support blood banking logistics. The aim of this study was to compare the presence of biologic response modifiers (BRMs) in PLT concentrates stored under conventional room temperature conditions with refrigerated or cryopreserved PLTs.

STUDY DESIGN AND METHODS

A three-arm pool-and-split study was carried out using buffy coat-derived PLTs stored in 30% plasma/70% SSP+. The three matched treatment arms were as follows: room temperature (20-24°C), cold (2-6°C), and cryopreserved (-80°C with DMSO). Liquid-stored PLTs were tested over a 21-day period, while cryopreserved PLTs were tested immediately after thawing and reconstitution in 30% plasma/70% SSP+ and after storage at room temperature.

RESULTS

Coagulation factor activity was comparable between room temperature and cold PLTs, with the exception of protein S, while cryopreserved PLTs had reduced Factor (F)V and FVIII activity. Cold-stored PLTs retained α-granule proteins better than room temperature or cryopreserved PLTs. Cryopreservation resulted in 10-fold higher microparticle generation than cold-stored PLTs, but both groups contained significantly more microparticles than those stored at room temperature. The supernatant from both cold and cryopreserved PLTs initiated faster clot formation and thrombin generation than room temperature PLTs.

CONCLUSION

Cold storage and cryopreservation alter the composition of the soluble fraction of stored PLTs. These differences in coagulation proteins, cytokines, and microparticles likely influence both the hemostatic capacity of the components and the auxiliary functions.

Modeling the effect of platelet concentrate supernatants on endothelial cells: focus on endocan/ESM-1

BACKGROUND

Platelets (PLTs) are prone to activation and the release of biologic response modifiers (BRMs) under storage conditions. The transfusion inflammatory reaction in the vascular compartment involves endothelial cell activation due to cell-cell interactions and BRMs infused with the blood products. Endocan/ESM-1 is a proteoglycan secreted by endothelial cells under the control of proinflammatory cytokines. We aimed to measure endocan activity in supernatants of PLT components (PCs), implicated in serious adverse reactions (SARs) or not (no.AR), sampled at different stages during storage.

STUDY DESIGN AND METHODS

PLT function, by quantification of soluble CD62P, and their ability to produce endocan were assessed. Functional testing of PC supernatants was performed on EA.hy926 endothelial cells in vitro by exposing them to PC supernatants from each group (no.AR or SARs); EA.hy926 activation was evaluated by their production of interleukin (IL)-6 and endocan.

RESULTS

PLT endocan secretion was not induced in response to PLT surface molecule agonists, and no significant correlation was observed between sCD62P and endocan concentration after PLT activation. However, we observed a significant increase in the secretion of IL-6 and endocan after EA.hy926 activation by all PC supernatants. IL-6 and endocan secretion were significantly higher for cells stimulated with SAR than those stimulated with no.AR PC supernatants, as well as cell apoptosis.

CONCLUSION

The correlation between the secretion of endocan and that of IL-6 by endothelial cells suggests that endocan can be used as a predictive marker of inflammation for the quality assessment of transfusion grade PLTs.

Consequences of Transfusing Blood Components in Patients With Trauma: A Conceptual Model

Transfusion of blood components is often required in resuscitation of patients with major trauma. Packed red blood cells and platelets break down and undergo chemical changes during storage (known as the storage lesion) that lead to an inflammatory response once the blood components are transfused to patients. Although some evidence supports a detrimental association between transfusion and a patient's outcome, the mechanisms connecting transfusion of stored components to outcomes remain unclear. The purpose of this review is to provide critical care nurses with a conceptual model to facilitate understanding of the relationship between the storage lesion and patients' outcomes after trauma; outcomes related to trauma, hemorrhage, and blood component transfusion are grouped according to those occurring in the short-term (≤30 days) and the long-term (>30 days). Complete understanding of these clinical implications is critical for practitioners in evaluating and treating patients given transfusions after traumatic injury.

Determination of predictors of severity for recipient adverse reactions during platelet product transfusions

The introduction of allogeneic cells is not a natural process, even if the transfusion is therapeutic and - when no alternative exists, as is often the case - essential. Transfusion of cellular products creates some level of danger sensed by recipients. Danger may manifest itself clinically or biologically, in which case we are dealing with recipient adverse reactions. Platelet concentrate transfusion in particular may be responsible for notable adverse reactions. Some appear to be inevitable, while others are tied to recipient factors: either health or genetic characteristics. The authors' research is specifically focused on platelet storage lesion and stress factors, and the means of controlling them to ensure greater recipient tolerance.

Transfusion as an Inflammation Hit: Knowns and Unknowns

Transfusion of blood cell components is frequent in the therapeutic arsenal; it is globally safe or even very safe. At present, residual clinical manifestations are principally inflammatory in nature. If some rare clinical hazards manifest as acute inflammation symptoms of various origin, most of them linked with conflicting and undesirable biological material accompanying the therapeutic component (infectious pathogen, pathogenic antibody, unwanted antigen, or allergen), the general feature is subtler and less visible, and essentially consists of alloimmunization or febrile non-hemolytic transfusion reaction. The present essay aims to present updates in hematology and immunology that help understand how, when, and why subclinical inflammation underlies alloimmunization and circumstances characteristic of red blood cells and – even more frequently – platelets that contribute inflammatory mediators. Modern transfusion medicine makes sustained efforts to limit such inflammatory hazards; efforts can be successful only if one has a clear view of each element’s role.

Leucocyte cytokines dominate platelet cytokines overtime in non-leucoreduced platelet components

BACKGROUND

Leucoreduction of blood components, including platelet components, is strongly encouraged but not yet universal, especially outside high income countries. As both leucocytes and platelets secrete copious amounts of pro-inflammatory cytokines/chemokines under various conditions and during storage, we investigated the potential of the respective secretory programmes of these cells in order to evaluate their subsequent pathophysiological effects.

MATERIAL AND METHODS

A total of 158 individual non-leucoreduced platelet components were obtained from Tunisian donors and tested for characteristic biological response modifiers (BRM) of leukocytes (IL-1β, IL-8), platelets (sCD62P, sCD40L) and both cell types (TNF-α, RANTES) in the presence or absence of thrombin stimulation and after different periods of storage (up to 5 days). BRM levels were determined using enzyme-linked immunosorbent assays and Luminex technology. Platelet-leucocyte aggregate formation during storage was analysed using flow cytometry.

RESULTS

Leucocyte- and platelet-associated BRM had clearly distinct profiles both at the onset (day 0) and termination (day 5) of the observation period but altered during the intermediate period so that their respective importance was inverted; in fact, the profiles were merged and indistinguishable on days 2-3. The leucocyte-derived BRM largely dominated over platelet-derived ones and further altered the BRM platelet secretion programme.

DISCUSSION

This study contributes substantial, new information on leucocyte/platelet interactions and their likely role in transfusion when leucodepletion cannot be performed or is only partially achieved.

Transfusion-related acute lung injury: transfusion, platelets and biological response modifiers

Transfusion-related acute lung injury (TRALI) may be induced by plasma, platelet concentrates and red blood cell concentrates. The mechanism leading to TRALI is thought to involve two steps. The priming step consists of previous inflammatory pathological conditions or external factors attracting leukocytes to lung vessels and creating conditions favorable for the second step, in which anti-HLA or anti-HNA antibodies or biologically active lipids, usually in transfused blood products, stress leukocytes and inflame lung epithelia. Platelets may be involved in the pathogenesis of TRALI because of their secretory potential and capacity to interact with other immune cells. There is no drug based-prophylaxis, but transfusion strategies are used to mitigate the risk of TRALI.

Levels of human platelet-derived soluble CD40 ligand depend on haplotypes of CD40LG-CD40-ITGA2

Increased circulating soluble CD40 ligand (sCD40L) is commonly associated with inflammatory disorders. We aimed to investigate whether gene polymorphisms in CD40LG, CD40 and ITGA2 are associated with a propensity to secrete sCD40L; thus, we examined this issue at the level of human platelets, the principal source of sCD40L. We performed single polymorphism and haplotype analyses to test for the effect of twelve polymorphisms across the CD40LG, CD40 and ITGA2 genes in blood donors. ITGA2 presented a positive association with rs1126643, with a significant modification in sCD40L secretion (carriers of C allele, P = 0.02), unlike the investigated CD40LG and CD40 polymorphisms. One CD40LG haplotype (TGGC) showing rs975379 (C/T), rs3092952 (A/G), rs3092933 (A/G) and rs3092929 (A/C) was associated with increased sCD40L levels (1.906 μg/L (95% CI: 1.060 to 2.751); P = 0.000009). The sCD40L level was associated with the inter-chromosomal CD40LG/CD40/ITGA2 haplotype (ATC), displaying rs3092952 (A/G), rs1883832 (C/T) and rs1126643 (C/T), with increased sCD40L levels (P = 0.0135). Our results help to decipher the genetic role of CD40LG, CD40 and ITGA2 with regard to sCD40L levels found in platelet components. Given the crucial role of sCD40L, this haplotype study in a transfusion model may be helpful to further determine the role of haplotypes in inflammatory clinical settings.

Improving platelet transfusion safety: biomedical and technical considerations

Platelet concentrates account for near 10% of all labile blood components but are responsible for more than 25% of the reported adverse events. Besides factors related to patients themselves, who may be particularly at risk of side effects because of their underlying illness, there are aspects of platelet collection and storage that predispose to adverse events. Platelets for transfusion are strongly activated by collection through disposal equipment, which can stress the cells, and by preservation at 22 °C with rotation or rocking, which likewise leads to platelet activation, perhaps more so than storage at 4 °C. Lastly, platelets constitutively possess a very large number of bioactive components that may elicit pro-inflammatory reactions when infused into a patient. This review aims to describe approaches that may be crucial to minimising side effects while optimising safety and quality. We suggest that platelet transfusion is complex, in part because of the complexity of the "material" itself: platelets are highly versatile cells and the transfusion process adds a myriad of variables that present many challenges for preserving basal platelet function and preventing dysfunctional activation of the platelets. The review also presents information showing--after years of exhaustive haemovigilance--that whole blood buffy coat pooled platelet components are extremely safe compared to the gold standard (i.e. apheresis platelet components), both in terms of acquired infections and of immunological/inflammatory hazards.

Mitochondrial damage-associated molecular patterns as potential proinflammatory mediators in post-platelet transfusion adverse effects

BACKGROUND

Platelet concentrates (PCs) are the most common blood components eliciting nonhemolytic transfusion reactions (NHTRs), such as allergic transfusion reactions and febrile reactions. However, the precise mechanisms of NHTRs in PC transfusion remain largely unknown. Previous studies reported that mitochondria-derived damage-associated molecular patterns (DAMPs) could be important mediators of innate cell inflammation. Platelets (PLTs) represent a major reservoir of mitochondria in the blood circulation. The aim of this study was to determine the possible involvement of mitochondrial DAMPs in NHTRs.

STUDY DESIGN AND METHODS

The amount of mitochondrial DAMPs was determined as an index of total copy numbers of mitochondrial DNA (mtDNA), including mtDNA itself and free mitochondria, using quantitative real-time polymerase chain reaction. To examine whether neutrophils, monocytes, and basophils were activated by mitochondrial DAMPs in vitro, an in vitro whole blood cell culture assay was performed.

RESULTS

In blood components associated with NHTRs, the mean total mtDNA concentration was highest in PCs followed in order by fresh-frozen plasma and red blood cells. The amount of mtDNA in NHTR PCs was higher than that in control PCs without NHTRs. The mitochondrial DAMPs present in NHTR PCs was high enough to activate neutrophils, monocytes, and basophils, when costimulated with N-formyl-l-methionyl-l-leucyl-l-phenylalanine or HLA antibodies.

CONCLUSION

PLT-derived mitochondrial DAMPs are candidate risk factors for the onset of NHTRs.

Thrombocytopenia and platelet transfusion in the neonate

Neonatal thrombocytopenia is widespread in preterm and term neonates admitted to neonatal intensive care units, with up to one-third of infants demonstrating platelet counts <150 × 10(9)/L. Thrombocytopenia may arise from maternal, placental or fetal/neonatal origins featuring decreased platelet production, increased consumption, or both mechanisms. Over the past years, innovations in managing neonatal thrombocytopenia were achieved from prospectively obtained clinical data on thrombocytopenia and bleeding events, animal studies on platelet life span and production rate and clinical use of fully automated measurement of reticulated platelets (immature platelet fraction). This review summarizes the pathophysiology of neonatal thrombocytopenia, current management including platelet transfusion thresholds and recent developments in megakaryopoietic agents. Furthermore, we propose a novel index score for bleeding risk in thrombocytopenic neonates to facilitate clinician's decision-making when to transfuse platelets.

Platelet components associated with adverse reactions: predictive value of mitochondrial DNA relative to biological response modifiers

BACKGROUND

Biological response modifiers (BRMs), secreted by platelets (PLTs) during storage, play a role in adverse events (AEs) associated with transfusion. Moreover, mitochondrial DNA (mtDNA) levels in PLT components (PCs) are associated with AEs. In this study we explore whether there is a correlation between pathogenic BRMs and mtDNA levels and whether these markers can be considered predictors of transfusion pathology.

STUDY DESIGN AND METHODS

We investigated a series of reported AEs after PC transfusion, combining clinical observations and mathematical modeling systems.

RESULTS

mtDNA was consistently released during the first days of PC storage; however, mtDNA release was earlier in "pathogenic" than in nonpathogenic PCs. PC supernatants with high levels of mtDNA along with soluble CD40 ligand (sCD40L) were significantly associated with occurrences of AEs. The fact that mtDNA did not associate with the 14 BRMs tested suggests the role of mtDNA in PC transfusion-linked inflammation is independent of that of BRMs, known to be associated with AEs. We present evidence that PLTs generate distinct pathogenic secretion profiles of BRMs and mtDNA. The calculated area under the curve for mtDNA was significantly associated with AEs, although less stringently predictive than those of sCD40L or interleukin-13, standard predictors of AE. The established model predicts that distinct subtypes of AEs can be distinguished, dependent on mtDNA levels and PC storage length.

CONCLUSIONS

Further work should be considered to test the propensity of mtDNA in PLT concentrates to generate inflammation and cause an AE.

Development of a highly resolutive method, using a double quadruplex tetra-primer-ARMS-PCR coupled with capillary electrophoresis to study CD40LG polymorphisms

Polymorphisms in the CD40 ligand gene (CD40LG) are associated with various immunological disorders such as tumors, autoimmune and infectious diseases. The aim of this study was to develop a highly optimized double quadruplex tetra-primer amplification refractory mutation system PCR (double quadruplex T-ARMS-PCR) coupled with capillary electrophoresis to allow genotyping of eight relevant candidate CD40LG SNPs and to establish haplotypes. After conducting the double quadruplex T-ARMS-PCR, the genotypes obtained through agarose electrophoresis were compared with those obtained through capillary electrophoresis. This strategy was applied to analyze the genetic patterns of CD40LG in two distinct cohorts of blood donors (211 French and 274 Tunisian). The T-ARMS-PCR method was rapid, inexpensive, reproducible and reliable for SNP determination. Regarding the separation technique, capillary electrophoresis allows traceable and semi-automated analysis while agarose electrophoresis remains a cost-effective technique that does not require specialized or costly equipment. Using these methods, we identified significantly different genetic heterogeneity between the two investigated populations (p ≤ 0.0001) and we also extensively characterized their haplotypes. The obtained genotype distribution and the optimized quadruplex T-ARMS-PCR technique coupled with capillary electrophoresis provides valuable information for studying pathologic inflammation leading to various diseases in which CD40LG might be a candidate gene.

[Blood transfusion and inflammation as of yesterday, today and tomorrow]

Blood transfusion is made possible principally by use of donated homologous components that - in turn - can be perceived as sources of danger by recipients. This may create an innate immune response dominated by inflammation, especially when transfusion is repeated. Residual leukocytes in blood components can source inflammatory lesions but considerably less than used to be prior to systematic, early and stringent - in process - leukoreduction. Every blood component can cause inflammation, though barely in the case of therapeutic plasma (in such a case, this is mainly restricted to allergy). Iron that may be freed by red blood cells but also processing and storage lesions such as the emission of microparticles can reveal themselves as pro-inflammatory. Platelets in platelet components represent the main source of inflammatory and/or allergic hazards in transfusion; this is linked with processing and storage lesions but also with the platelet physiology itself. It is of utmost importance to avoid inflammatory adverse events in patients that are fragile because of their primary condition and/or treatment; this stands for their safety, as inflammation can be extremely severe and even lethal, and also for their comfort; this increases efficacy of transfusion programs while reducing the overall costs.

Platelets and infections - complex interactions with bacteria

Platelets can be considered sentinels of vascular system due to their high number in the circulation and to the range of functional immunoreceptors they express. Platelets express a wide range of potential bacterial receptors, including complement receptors, FcγRII, Toll-like receptors but also integrins conventionally described in the hemostatic response, such as GPIIb-IIIa or GPIb. Bacteria bind these receptors either directly, or indirectly via fibrinogen, fibronectin, the first complement C1q, the von Willebrand Factor, etc. The fate of platelet-bound bacteria is questioned. Several studies reported the ability of activated platelets to internalize bacteria such as Staphylococcus aureus or Porphyromonas gingivalis, though there is no clue on what happens thereafter. Are they sheltered from the immune system in the cytoplasm of platelets or are they lysed? Indeed, while the presence of phagolysosome has not been demonstrated in platelets, they contain antimicrobial peptides that were shown to be efficient on S. aureus. Besides, the fact that bacteria can bind to platelets via receptors involved in hemostasis suggests that they may induce aggregation; this has indeed been described for Streptococcus sanguinis, S. epidermidis, or C. pneumoniae. On the other hand, platelets are able to display an inflammatory response to an infectious triggering. We, and others, have shown that platelet release soluble immunomodulatory factors upon stimulation by bacterial components. Moreover, interactions between bacteria and platelets are not limited to only these two partners. Indeed, platelets are also essential for the formation of neutrophil extracellular traps by neutrophils, resulting in bacterial clearance by trapping bacteria and concentrating antibacterial factors but in enhancing thrombosis. In conclusion, the platelet-bacteria interplay is a complex game; its fine analysis is complicated by the fact that the inflammatory component adds to the aggregation response.

The signaling role of CD40 ligand in platelet biology and in platelet component transfusion

The CD40 ligand (CD40L) is a transmembrane molecule of crucial interest in cell signaling in innate and adaptive immunity. It is expressed by a variety of cells, but mainly by activated T-lymphocytes and platelets. CD40L may be cleaved into a soluble form (sCD40L) that has a cytokine-like activity. Both forms bind to several receptors, including CD40. This interaction is necessary for the antigen specific immune response. Furthermore, CD40L and sCD40L are involved in inflammation and a panoply of immune related and vascular pathologies. Soluble CD40L is primarily produced by platelets after activation, degranulation and cleavage, which may present a problem for transfusion. Soluble CD40L is involved in adverse transfusion events including transfusion related acute lung injury (TRALI). Although platelet storage designed for transfusion occurs in sterile conditions, platelets are activated and release sCD40L without known agonists. Recently, proteomic studies identified signaling pathways activated in platelet concentrates. Soluble CD40L is a good candidate for platelet activation in an auto-amplification loop. In this review, we describe the immunomodulatory role of CD40L in physiological and pathological conditions. We will focus on the main signaling pathways activated by CD40L after binding to its different receptors.

Are polymorphisms of the immunoregulatory factor CD40LG implicated in acute transfusion reactions?

The CD40 ligand (CD40L/CD154), a member of TNF superfamily, is notably expressed on activated CD4+ T-cells and stimulated platelets. CD40L is linked to a variety of pathologies and to acute transfusion reactions (ATR). Mutations in this gene (CD40LG) lead to X-linked hyper-IgM syndrome. Some CD40LG polymorphisms are associated with variable protein expression. The rationale behind this study is that CD40L protein has been observed to be involved in ATR. We wondered whether genetic polymorphisms are implicated. We investigated genetic diversity in the CD40LG using DHPLC and capillary electrophoresis for screening and genotyping (n = 485 French and Tunisian blood donors). We identified significant difference in the CD40LG linkage pattern between the two populations. Variant minor alleles were significantly over-represented in Tunisian donors (P<0.0001 to 0.0270). We found higher heterogeneity in the Tunisian, including three novel low frequency variants. As there was not a particular pattern of CD40LG in single apheresis donors whose platelet components induced an ATR, we discuss how this information may be useful for future disease association studies on CD40LG.