Ultraviolet C light pathogen inactivation treatment of platelet concentrates preserves integrin activation but affects thrombus formation kinetics on collagen in vitro

Universal irradiation of platelets: Does irradiation affect the quality, effectiveness, and safety of platelets for transfusion?

We aimed to identify any detrimental effects on platelet quality and clinical effectiveness, of irradiated platelets compared to non-irradiated platelets for transfusion. The review was conducted in accordance with PRISMA guidelines. The protocol was prospectively registered on PROSPERO [CRD42023441930]. Our search identified 3002 references, of which we included 44 studies. Forty-one were in vitro only studies, two studies were in healthy volunteers, and one study reported clinical outcomes in thrombocytopenic patients. X-ray was used exclusively in three studies, and alongside gamma irradiation in one study. Two studies did not report the source of irradiation. The remaining 38 studies used gamma irradiation only. We assessed risk of bias (ROB) for studies reporting clinical and in vivo outcomes using ROB 2.0 (3 studies). We adapted a ROB tool designed for animal studies to assess ROB for the studies reporting in vitro outcomes (43 studies). We assessed the certainty of the evidence for the eight outcomes deemed most important to assess platelet quality and clinical effectiveness (where day 0 is the day of the blood draw). Overall, gamma irradiation has little to no effect on most markers of platelet quality and effectiveness. Where there is evidence of detriment from irradiation, differences are small in vitro, and are unlikely to affect clinical outcomes following transfusion. However, the evidence base is limited. Only half the studies could be included in any analysis. There is very limited evidence for x-ray as a source of irradiation and, given the potential benefits of using x-ray over gamma irradiation (ease of use and safety requirements), we would welcome further research comparing x-ray to gamma, and x-ray to a non-irradiated control.

Irradiation of platelets in Transfusion Medicine: risk and benefit judgments

Irradiation of platelet products is generally used to prevent transfusion-associated graft-versus-host disease (TA-GvHD) as well as transfusion-transmitted infections. As an essential prerequisite, gamma-irradiation of blood products prior to transfusion is required in patients who may develop TA-GVHD. Most studies suggest that gamma irradiation has no significant effect on the quality of platelet products; however, more recent studies have shown that the oxidative effects of gamma irradiation can lead to the induction of platelet storage lesion (PSL) and to some extent reduce the efficiency of transfused platelets. As the second widely used irradiation technique, UV-illumination was primarily introduced to reduce the growth of infectious agents during platelet storage, with the advantage that this method can also prevent TA-GvHD. However, the induction of oxidative conditions and platelet pre-activation that lead to PSL is more pronounced after UV-based methods of pathogen reduction. Since these lesions are large enough to clearly affect the post-transfusion platelet recovery and survival, more studies are needed to improve the safety and effectiveness of pathogen reduction technologies (PRTs). Therefore, pointing to other benefits of PRTs, such as preventing TA-GvHD or prolonging the shelf life of products by eliminating the possibility of pathogen growth during storage, does not yet seem to justify their widespread use due to above-mentioned effects. Even for gamma-irradiated platelets, some researchers have suggested that due to decreased 1-hour post-transfusion increments and increased risk of platelet refractoriness, their use should be limited to the patients who may develop TA-GVHD. It is noteworthy that due to the effect of X-rays in preventing TA-GvHD, some recent studies are underway to examine its effects on the quality and effectiveness of platelet products and determine whether X-rays can be used as a more appropriate and cost-effective alternative to gamma radiation. The review presented here provides a detailed description about irradiation-based technologies for platelet products, including their applications, mechanistic features, advantages, and disadvantages.

UV light-emitting diode (UV-LED) at 265 nm as a potential light source for disinfecting human platelet concentrates

The risk of sepsis through bacterial transmission is one of the most serious problems in platelet transfusion. In processing platelet concentrates (PCs), several methods have been put into practice to minimize the risk of bacterial transmission, such as stringent monitoring by cultivation assays and inactivation treatment by photoirradiation with or without chemical agents. As another potential option, we applied a light-emitting diode (LED) with a peak emission wavelength of 265 nm, which has been shown to be effective for water, to disinfect PCs. In a bench-scale UV-LED exposure setup, a 10-min irradiation, corresponding to an average fluence of 9.2 mJ/cm2, resulted in >2.0 log, 1.0 log, and 0.6 log inactivation (mean, n = 6) of Escherichia coli, Staphylococcus aureus, and Bacillus cereus, respectively, in non-diluted plasma PCs. After a 30-min exposure, platelet counts decreased slightly (18 ± 7%: mean ± SD, n = 7); however, platelet surface expressions of CD42b, CD61, CD62P, and PAC-1 binding did not change significantly (P>0.005), and agonist-induced aggregation and adhesion/aggregation under flow conditions were well maintained. Our findings indicated that the 265 nm UV-LED has high potential as a novel disinfection method to ensure the microbial safety of platelet transfusion.

The Role of Glutamine in the Prevention of Ultraviolet-C-Induced Platelet Activation

Background and Objectives. The primary function of platelets is to prevent bleeding. The use of UV-C light in the treatment of platelets has become a valuable method for preserving the efficacy of platelet concentrates in blood banks. However, its deleterious effect remains, such as the activation of platelets, thus causing the platelets to lose their physiological function. In this study, we intended to demonstrate the impact of UV-C on platelets and how the use of glutamine could mitigate the loss of physiological function of the platelets caused by UV-C. Materials and Methods. This study was conducted using mouse platelets. We assessed calcium signaling using Fura-2 AM incubation and dense granule secretion of the platelets using luminescence assay by measuring ATP. At the molecular level, the activation of integrin using PAC-1 antibody was analyzed. Phosphorylation of immune-precipitated cPLA2 was assessed using a specific antibody. All the experiments were carried out with or without glutamine in the presence of UV-C. Positive and negative controls were used in all experiments to validate the findings. Results. We have demonstrated that physiological and biochemical damage arises as a result of the exposure of platelet concentrate to UV-C and that the use of glutamine could alleviate this damage. Various experiments, thrombus formation, integrin activation, and phosphorylation of cPLA2 were preserved using 50 mM of glutamine in the presence of UV-C, which reduces 50% of platelet viability. Conclusions. Our study demonstrates that the storage of platelet concentrates under the UV-C activates their physiological process and renders them to the thrombus formation, hence decreasing their viability. The presence of a moderate amount of glutamine can alleviate the toxic effect of UV-C, and platelet concentrates could be kept viable for a long time.

In vitro thrombus formation and in vivo hemostasis mediated by platelets irradiated with bactericidal ultraviolet C from xenon flash under flow conditions

BACKGROUND

We previously reported a flow path-ultraviolet C (UVC) irradiation system for platelet concentrates (PCs) with platelet additive solution (PAS) to minimize contamination by bacteria. Here, we investigated functionalities of irradiated platelets (PLTs) in in vitro thrombus formation and in vivo hemostasis.

STUDY DESIGN AND METHODS

PAS-PCs were irradiated with flash UVC using the flow path system. Their variables (PLT count, mean platelet volume, pH, glucose, lactate, glycoprotein [GP] Ib, and activated integrin αIIbβ3) were evaluated. Static adhesion to collagen or fibrinogen was analyzed using fluorescent microscopy. Thrombus formation under flow conditions was assessed using a collagen-coated bead column. Adenosine diphosphate (ADP)-induced Akt phosphorylation was determined by western blot. In vivo hemostasis and circulatory survival of PLTs were assessed with a rabbit bleeding model.

RESULTS

All variables, except for GPIb expression, were slightly, but significantly, impaired after flash UVC irradiation throughout the 6-day storage period. No difference was observed in static adhesion to either collagen or fibrinogen between irradiated and nonirradiated PAS-PCs. In vitro thrombus formation of flash UVC-irradiated PAS-PCs was significantly greater than that of nonirradiated PAS-PCs. ADP-induced Akt phosphorylation was enhanced in irradiated PAS-PCs. In vivo hemostatic efficacy was comparable between the groups on Day 1. The efficacy declined in nonirradiated PAS-PCs on Day 5, while it was retained in flash UVC-irradiated PAS-PCs. Circulatory survival of PLTs was lower in irradiated PAS-PCs.

CONCLUSIONS

PAS-PCs irradiated with UVC from xenon flash have favorable properties to achieve hemostasis compared with nonirradiated PAS-PCs.

What about Platelet Function in Platelet Concentrates?

The characterization of platelet concentrates (PCs) in transfusion medicine has been performed with different analytical methods and platelet lesions (from biochemistry to cell biology) have been documented. In routine quality assessment and validation of manufacturing processes of PCs for transfusion purposes, only basic parameters are monitored and the platelet functions are not included. However, PCs undergo several manipulations during the processing and the basic parameters do not provide sensitive analyses to properly picture out the impact of the blood component preparation and storage on platelets. To improve the transfusion supply chain and the platelet functionalities, additional parameters should be used. The present short review will focus on the different techniques to monitor ex vivo platelet lesions from phenotype characterization to advanced omic analyses. Then, the opportunities to use these methods in quality control, process validation, development, and research will be discussed. Functional markers should be considered because they would be an advantage for the future developments in transfusion medicine.

New strategies for the control of infectious and parasitic diseases in blood donors: the impact of pathogen inactivation methods

Around 70 infectious agents are possible threats for blood safety.

The risk for blood recipients is increasing because of new emergent agents like West Nile, Zika and Chikungunya viruses, or parasites such as Plasmodium and Trypanosoma cruzi in non-endemic regions, for instance.

Screening programmes of the donors are more and more implemented in several Countries, but these cannot prevent completely infections, especially when they are caused by new agents.

Pathogen inactivation (PI) methods might overcome the limits of the screening and different technologies have been set up in the last years.

This review aims to describe the most widely used methods focusing on their efficacy as well as on the preservation integrity of blood components.

Antimicrobial blue light for decontamination of platelets during storage

Platelet (PLT) storage is currently limited to 5 days in clinics in the United States, in part, due to an increasing risk for microbial contamination over time. In light of well-documented antimicrobial activity of blue light (405-470 nm), we investigated potentials to decontaminate microbes during PLT storage by antimicrobial blue light (aBL). We found that PLTs produced no detectable levels of porphyrins or their derivatives, the chromophores that specifically absorb blue light, in marked contrast to microbes that generated porphyrins abundantly. The difference formed a basis with which aBL selectively inactivated contaminated microbes prior to and during the storage, without incurring any harm to PLTs. In accordance with this, when contamination with representative microbes was simulated in PLT concentrates supplemented with 65% of PLT additive solution in a standard storage bag, all "contaminated" microbes tested were completely inactivated after exposure of the bag to 405 nm aBL at 75 J/cm2 only once. While killing microbes efficiently, this dose of aBL irradiation exerted no adverse effects on the viability, activation or aggregation of PLTs ex vivo and could be used repeatedly during PLT storage. PLT survival in vivo was also unaltered by aBL irradiation after infusion of aBL-irradiated mouse PLTs into mice. The study provides proof-of-concept evidence for a potential of aBL to decontaminate PLTs during storage.

Pathogen reduction of blood components during outbreaks of infectious diseases in the European Union: an expert opinion from the European Centre for Disease Prevention and Control consultation meeting

Pathogen reduction (PR) of selected blood components is a technology that has been adopted in practice in various ways. Although they offer great advantages in improving the safety of the blood supply, these technologies have limitations which hinder their broader use, e.g. increased costs. In this context, the European Centre for Disease Prevention and Control (ECDC), in co-operation with the Italian National Blood Centre, organised an expert consultation meeting to discuss the potential role of pathogen reduction technologies (PRT) as a blood safety intervention during outbreaks of infectious diseases for which (in most cases) laboratory screening of blood donations is not available. The meeting brought together 26 experts and representatives of national competent authorities for blood from thirteen European Union and European Economic Area (EU/EEA) Member States (MS), Switzerland, the World Health Organization, the European Directorate for the Quality of Medicines and Health Care of the Council of Europe, the US Food and Drug Administration, and the ECDC. During the meeting, the current use of PRTs in the EU/EEA MS and Switzerland was verified, with particular reference to emerging infectious diseases (see Appendix). In this article, we also present expert discussions and a common view on the potential use of PRT as a part of both preparedness and response to threats posed to blood safety by outbreaks of infectious disease.

The senotherapeutic nicotinamide riboside raises platelet nicotinamide adenine dinucleotide levels but cannot prevent storage lesion

BACKGROUND

Supplementation of the nicotinamide adenine dinucleotide (NAD) precursor nicotinamide riboside (NR) has recently been shown to increase life‐span of cells, tissues, and entire organisms. [Correction added on 13 December 2019, after first online publication: In the preceding sentence, “adenine nicotinamide” was revised to “nicotinamide adenine.”] The impact of NR on platelet longevity has not been tested.

STUDY DESIGN AND METHODS

A pool‐and‐split design of buffy coat derived platelet concentrates (PCs) was used. One arm was treated with cumulative doses of NR‐triflate, the control arm with sodium triflate. Storage lesion was monitored for 23 days. Platelet metabolic and functional parameters were tested. Clearance of human platelets was measured in a mouse model of transfusion.

RESULTS

Total intracellular NAD levels in platelets decreased two‐fold from 4.8 ± 0.5 fmol (mean ± SD, n = 6) to 2.1 ± 1.8 fmol per 10³ control cells, but increased almost 10‐fold to 41.5 ± 4.1 fmol per 10³ NR treated platelets. This high intracellular NAD level had no significant impact on platelet count, mean platelet volume, swirling, nor on lactate and glucose levels. Platelet aggregation and integrin α_IIbβ₃ activation declined steadily and comparably in both conditions. GPIbα levels were slightly lower in NR‐treated platelets compared to control, but this was not caused by reduced receptor shedding because glycocalicin increased similarly. Apoptotic markers cytochrome c, Bcl‐xL, cleaved caspase‐3, and Bak were not different throughout storage for both conditions. Platelet survival in a mouse model of transfusion was not different between NR‐treated and control platelets.

CONCLUSION

Platelets carry the cellular machinery to metabolize NR into NAD at rates comparable to other eukaryotic cells. Unlike those cells, platelet life‐span cannot be prolonged using this strategy.

The long and winding road to pathogen reduction of platelets, red blood cells and whole blood

Pathogen reduction technologies (PRTs) have been developed to further reduce the current very low risks of acquiring transfusion-transmitted infections and promptly respond to emerging infectious threats. An entire portfolio of PRTs suitable for all blood components is not available, but the field is steadily progressing. While PRTs for plasma have been used for many years, PRTs for platelets, red blood cells (RBC) and whole blood (WB) were developed more slowly, due to difficulties in preserving cell functions during storage. Two commercial platelet PRTs use ultra violet (UV) A and UVB light in the presence of amotosalen or riboflavin to inactivate pathogens' nucleic acids, while a third experimental PRT uses UVC light only. Two PRTs for WB and RBC have been tested in experimental clinical trials with storage limited to 21 or 35 days, due to unacceptably high RBC storage lesion beyond these time limits. This review summarizes pre-clinical investigations and selected outcomes from clinical trials using the above PRTs. Further studies are warranted to decrease cell storage lesions after PRT treatment and to test PRTs in different medical and surgical conditions. Affordability remains a major administrative obstacle to PRT use, particularly so in geographical regions with higher risks of transfusion-transmissible infections.

Impact of cold storage on platelets treated with Intercept pathogen inactivation

BACKGROUND

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

STUDY DESIGN AND METHODS

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

RESULTS

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

CONCLUSION

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

Correlation between platelet thrombus formation on collagen-coated beads and platelet aggregation induced by ADP

BACKGROUND

The thrombus-forming ability is a critical in vitro parameter to assess platelets (PLTs), but flow-based methods using collagen-coated materials generally require multistep, proficiency, and advanced analysis.

STUDY DESIGN AND METHODS

Commercially available collagen-coated bead columns were examined to assess thrombus-forming ability of PLTs. The retention rate as an index of thrombus formation was calculated using the PLT count before and after column passage. Thrombi were imaged by anti-CD41 using a fluorescent microscope. PLT aggregation was measured by light-transmitting aggregometry.

RESULTS

The retention rate was low when apheresis-collected PLT concentrates (PCs) were suspended in plasma either with or without Ca²⁺. Reconstitution of PCs with red blood cells (RBCs) increased the retention rate with good reproducibility on repeated-measurements, and therefore, PLT samples were reconstructed with RBCs in subsequent experiments. The retention rate of PCs varied widely in a product-dependent manner, and was correlated with the aggregation rate induced by ADP, but not that by collagen. Using platelet-rich-plasma, antagonists of P2Y₁ or P2Y₁₂ receptors for ADP reduced both the retention and aggregation of PLTs. Acetylsalicylic acid reduced retention, although it had no effect on ADP-induced aggregation. Prostaglandin E₁ significantly inhibited both retention and aggregation. These anti-PLT reagents resulted in reduced or no thrombus formation on the beads.

CONCLUSION

The collagen-coated bead column was useful to readily examine the thrombus-forming ability of PLTs. Variance of the PLT retention rate was correlated with responsiveness to ADP. Results from anti-PLT reagents revealed that thrombus formation on collagen-coated beads was similar to in vivo thrombus development.

Cryopreservation of UVC pathogen-inactivated platelets

BACKGROUND

Extending the platelet (PLT) shelf life and enhancing product safety may be achieved by combining cryopreservation and pathogen inactivation (PI). Although studied individually, limited investigations into combining these treatments has been performed. The aim of this study was to investigate the effect of PI treating PLTs before cryopreservation on in vitro PLT quality and function.

STUDY DESIGN AND METHODS

ABO-matched buffy coat-derived PLTs in PLT additive solution (SSP+; Macopharma) were pooled and split to form matched pairs (n = 8). One unit remained untreated and the other was treated with the THERAFLEX UV-Platelets System (UVC; Macopharma). For cryopreservation, 5% to 6% dimethyl sulfoxide was added to the PLTs, and they were frozen at -80°C. After being thawed, untreated cryopreserved PLTs (CPPs) and UVC-treated CPPs (UVC-CPPs) were resuspended in plasma. In vitro quality was assessed immediately after thawing and after 24 hours of room temperature storage.

RESULTS

UVC-CPPs had lower in vitro recovery compared to CPPs. By flow cytometry, PLTs demonstrated a similar abundance of GPIX (CD42a), GPIIb (CD41a), and GPIbα (CD42b-HIP1), while the activation of GPIIb/IIIa (PAC-1) was increased in UVC-CPPs compared to CPPs. UVC-CPPs demonstrated greater phosphatidylserine exposure (annexin V) and microparticle shedding but similar P-selectin (CD62P) abundance compared to CPPs. UVC-CPPs displayed similar functionality to CPPs when assessed using aggregometry, thromboelastography, and thrombin generation.

CONCLUSIONS

This study demonstrates the feasibility of cryopreserving UVC-PI-treated PLT products. UVC-PI treatment may increase the susceptibility of PLTs to damage caused during cryopreservation, but this is more pronounced during postthaw storage at room temperature.

The role of pathogen-reduced platelet transfusions on HLA alloimmunization in hemato-oncological patients

BACKGROUND

Platelet transfusions can induce alloimmunization against HLA antigens. The use of pathogen-reduced platelet concentrates (PCs) was suggested to reduce HLA alloimmunization and concomitant transfusion refractoriness.

METHODS

This study investigated HLA alloimmunization in available samples from 448 hemato-oncological patients who were randomized for the Pathogen Reduction Evaluation and Predictive Analytical Rating Score (PREPAReS) trial to receive either untreated or pathogen-reduced PCs (Mirasol, Terumo BCT Inc.). Anti-HLA Class I and II antibodies were determined before the first platelet transfusion and weekly thereafter using multiplex assay with standard cutoffs to detect low- as well as high-level antibodies.

RESULTS

When using the lower cutoff, in patients who were antibody negative at enrollment, 5.4% (n = 12) developed anti-HLA Class I antibodies after receiving untreated PCs, while this was significantly higher in patients receiving pathogen-reduced PCs, 12.8% (n = 29; p = 0.009, intention-to-treat [ITT] analysis). A similar but nonsignificant trend was observed in the per-protocol (PP) analysis (5.4% vs. 10.1%; p = 0.15). HLA class II antibody formation was similar between both types of PCs in the ITT analysis, while the PP analysis showed a trend toward lower immunization after receiving pathogen-reduced PCs. Multivariate analysis identified receiving pathogen-reduced platelets as an independent risk factor for HLA Class I alloimmunization (ITT: odds ratio [95% confidence interval] = 3.02 [1.42-6.51], PP: odds ratio [95% confidence interval] = 2.77 [1.00-5.40]), without affecting HLA Class II alloimmunization. When using the high cutoff value, the difference in HLA Class I alloimmunization between study arms remained significant in the ITT analysis and again was not significant in the PP analysis.

CONCLUSION

Our data clearly indicate that Mirasol pathogen inactivation does not prevent HLA Class I or II alloimmunization after platelet transfusions.

General overview of blood products in vitro quality: Processing and storage lesions

Blood products are issued from blood collection. Collected blood is immediately mixed with anticoagulant solutions that immediately induce chemical and/or biochemical modifications. Collected blood is then transformed into different blood products according to various steps of fabrication. All these steps induce either reversible or irreversible "preparation-related" lesions that combine with "storage-related" lesions. This short paper aims to provide an overview of the alterations that are induced by the "non-physiological" processes used to prepare blood products that are used in clinical practice.

Biomolecular Consequences of Platelet Pathogen Inactivation Methods

Pathogen inactivation (PI) for platelet concentrates (PC) is a fairly recent development in transfusion medicine that is intended to decrease infectious disease transmission from the donor to the receiving patient. Effective inactivation of viruses, bacteria and eukaryotic parasites adds a layer of safety, protecting the blood supply against customary and emerging pathogens. Three PI methods have been described for platelets. These are based on photochemical damage of nucleic acids which prevents replication of most infectious pathogens and contaminating donor leukocytes. Because platelets do not replicate, the collateral damage to platelet function is considered low to non-existing. This is disputable however because photochemistry is not specific for nucleic acids and significantly affects platelet biomolecules as well. The impact of these biomolecular changes on platelet function and hemostasis is not well understood, but is increasingly being studied. The results of these studies can help explain current and future clinical observations with PI platelets, including the impact on transfusion yield and bleeding. This review summarizes the biomolecular effects of PI treatment on platelets. We conclude that despite a comparable principle of photochemical inactivation, all three methods affect platelets in different ways. This knowledge can help blood banks and transfusion specialists to guide their choice when considering the implementation or clinical use of PI treated platelets.

Storage-Induced Platelet Apoptosis Is a Potential Risk Factor for Alloimmunization Upon Platelet Transfusion

Platelet transfusion can elicit alloimmune responses leading to alloantibody formation against donor-specific polymorphic residues, ultimately resulting in platelet transfusion refractoriness. Universal leukoreduction significantly reduced the frequency of alloimmunization after platelet transfusion, thereby showing the importance of white blood cells (WBCs) in inducing this alloresponse. It is, however, unknown if the residual risk for alloimmunization is caused by WBCs remaining after leukoreduction or if alloimmunization can be induced by platelets themselves. This study investigated the capacity of platelets to induce alloimmunization and identified potential product-related risk factors for alloimmunization. First, internalization of allogeneic platelets by dendritic cells (DCs) was demonstrated by confocal microscopy. Second, after internalization, presentation of platelet-derived peptides was shown by mass spectrometry analysis of human leukocytes antigen (HLA)-DR eluted peptides. Third, platelet-loaded DCs induced platelet-specific CD4 T cell responses. Altogether, this indicates a platelet-specific ability to induce alloimmunization. Therefore, factors enhancing platelet internalization may be identified as risk factor for alloimmunization by platelet concentrates. To investigate if storage of platelets is such a risk factor, internalization of stored platelets was compared with fresh platelets and showed enhanced internalization of stored platelets. Storage-induced apoptosis and accompanied phosphatidylserine exposure seemed to be instrumental for this. Indeed, DCs pre-incubated with apoptotic platelets induced the strongest IFN-γ production by CD4 T cells compared with pre-incubation with untreated or activated platelets. In conclusion, this study shows the capacity of platelets to induce platelet-specific alloimmune responses. Furthermore, storage-induced apoptosis of platelets is identified as potential risk factor for alloimmunization after platelet transfusions.

Ultraviolet-Based Pathogen Inactivation Systems: Untangling the Molecular Targets Activated in Platelets

Transfusions of platelets are an important cornerstone of medicine; however, recipients may be subject to risk of adverse events associated with the potential transmission of pathogens, especially bacteria. Pathogen inactivation (PI) technologies based on ultraviolet illumination have been developed in the last decades to mitigate this risk. This review discusses studies of platelet concentrates treated with the current generation of PI technologies to assess their impact on quality, PI capacity, safety, and clinical efficacy. Improved safety seems to come with the cost of reduced platelet functionality, and hence transfusion efficacy. In order to understand these negative impacts in more detail, several molecular analyses have identified signaling pathways linked to platelet function that are altered by PI. Because some of these biochemical alterations are similar to those seen arising in the context of routine platelet storage lesion development occurring during blood bank storage, we lack a complete picture of the contribution of PI treatment to impaired platelet functionality. A model generated using data from currently available publications places the signaling protein kinase p38 as a central player regulating a variety of mechanisms triggered in platelets by PI systems.

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

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

Pathogen reduction technologies: The pros and cons for platelet transfusion

The transfusion of platelets is essential for diverse pathological conditions associated with thrombocytopenia or platelet disorders. To maintain optimal platelet quality and functions, platelets are stored as platelet concentrates (PCs) at room temperature under continuous agitation-conditions that are permissive for microbial proliferation. In order to reduce these contaminants, pathogen reduction technologies (PRTs) were developed by the pharmaceutical industry and subsequently implemented by blood banks. PRTs rely on chemically induced cross-linking and inactivation of nucleic acids. These technologies were initially introduced for the treatment of plasma and, more recently, for PCs given the absence of a nucleus in platelets. Several studies verified the effectiveness of PRTs to inactivate a broad array of bacteria, viruses, and parasites. However, the safety of PRT-treated platelets has been questioned in other studies, which focused on the impact of PRTs on platelet quality and functions. In this article, we review the literature regarding PRTs, and present the advantages and disadvantages related to their application in platelet transfusion medicine.

Reduction of bacteria and human immunodeficiency virus Type 1 infectivity of platelet suspension in plasma using xenon flash-pulse light in a bench-scale trial

BACKGROUND

Current pathogen reduction systems for platelet concentrates (PCs) require addition of chemical compounds and/or reduction of plasma content in PCs. We have investigated a new method using xenon (Xe) flash-pulse light without additional compounds or plasma replacement.

STUDY DESIGN AND METHODS

An aliquot of apheresis platelets (PLTs) in plasma inoculated with bacteria or human immunodeficiency virus Type 1 (HIV-1) was irradiated with Xe flash-pulse light (Xe flash phototreatment). Bacterial growth was monitored up to 6 days of storage, whereas HIV-1 infectivity was assayed just after treatment. Pairs of Xe flash-phototreated and untreated PCs were examined for PLT lesion during the storage period.

RESULTS

Under the current conditions, a low titer (1.8 colony-forming units [CFUs]/mL) of Staphylococcus aureus did not proliferate during the 6-day storage period, but grew in some cases at high-titer (24.0 CFUs/mL) inoculation. HIV-1 infectivity was reduced by 1.8 log. PLT recovery of the treated PCs was lower than untreated ones. An increase of mean PLT volume and glucose consumption, together with a decrease of hypotonic shock response and pH, were enhanced by the treatment. CD62P- and PAC-1-positive PLTs increased after the treatment, indicating the induction of PLT activation. Among biologic response modifiers, soluble CD40 ligand was significantly increased in the treated PCs on Day 6.

CONCLUSIONS

Xe flash phototreatment could prevent bacterial proliferation and reduce HIV-1 infectivity in 100% plasma PCs without any additional compounds, but enhanced PLT storage lesions. Further improvement is required to increase the potency of pathogen inactivation with reducing PLT damage.

Microfluidic Flow Chambers Using Reconstituted Blood to Model Hemostasis and Platelet Transfusion In Vitro

Blood platelets prepared for transfusion gradually lose hemostatic function during storage. Platelet function can be investigated using a variety of (indirect) in vitro experiments, but none of these is as comprehensive as microfluidic flow chambers. In this protocol, the reconstitution of thrombocytopenic fresh blood with stored blood bank platelets is used to simulate platelet transfusion. Next, the reconstituted sample is perfused in microfluidic flow chambers which mimic hemostasis on exposed subendothelial matrix proteins. Effects of blood donation, transport, component separation, storage and pathogen inactivation can be measured in paired experimental designs. This allows reliable comparison of the impact every manipulation in blood component preparation has on hemostasis. Our results demonstrate the impact of temperature cycling, shear rates, platelet concentration and storage duration on platelet function. In conclusion, this protocol analyzes the function of blood bank platelets and this ultimately aids in optimization of the processing chain including phlebotomy, transport, component preparation, storage and transfusion.

Blood-Borne Pathogens: A Canadian Blood Services Centre for Innovation Symposium

Testing donations for pathogens and deferring selected blood donors have reduced the risk of transmission of known pathogens by transfusion to extremely low levels in most developed countries. Protecting the blood supply from emerging infectious threats remains a serious concern in the transfusion medicine community. Transfusion services can employ indirect measures such as surveillance, hemovigilance, and donor questioning (defense), protein-, or nucleic acid based direct testing (detection), or pathogen inactivation of blood products (destruction) as strategies to mitigate the risk of transmission-transmitted infection. In the North American context, emerging threats currently include dengue, chikungunya, and hepatitis E viruses, and Babesia protozoan parasites. The 2003 SARS and 2014 Ebola outbreaks illustrate the potential of epidemics unlikely to be transmitted by blood transfusion but disruptive to blood systems. Donor-free blood products such as ex vivo generated red blood cells offer a theoretical way to avoid transmission-transmitted infection risk, although biological, engineering, and manufacturing challenges must be overcome before this approach becomes practical. Similarly, next generation sequencing of all nucleic acid in a blood sample is currently possible but impractical for generalized screening. Pathogen inactivation systems are in use in different jurisdictions around the world, and are starting to gain regulatory approval in North America. Cost concerns make it likely that pathogen inactivation will be contemplated by blood operators through the lens of health economics and risk-based decision making, rather than in zero-risk paradigms previously embraced for transfusable products. Defense of the blood supply from infectious disease risk will continue to require innovative combinations of surveillance, detection, and pathogen avoidance or inactivation.

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A symposium on blood-borne pathogens was held September 26, 2015, in Toronto, Canada.

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Transmission-transmitted infections remain a threat to the blood supply.

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The residual risk from established pathogens is small; emerging agents are a concern.

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Next generation sequencing and donor-free blood are not yet practical approaches.

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Pathogen inactivation technology is being increasingly used around the world.

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Health economic concerns will likely guide future advances in this area.

In vitro Quality of Platelets with Low Plasma Carryover Treated with Ultraviolet C Light for Pathogen Inactivation

BACKGROUND

The THERAFLEX UV-Platelets system uses shortwave ultraviolet C light (UVC, 254 nm) to inactivate pathogens in platelet components. Plasma carryover influences pathogen inactivation and platelet quality following treatment. The plasma carryover in the standard platelets produced by our institution are below the intended specification (<30%).

METHODS

A pool and split study was carried out comparing untreated and UVC-treated platelets with <30% plasma carryover (n = 10 pairs). This data was compared to components that met specifications (>30% plasma). The platelets were tested over storage for in vitro quality.

RESULTS

Platelet metabolism was accelerated following UVC treatment, as demonstrated by increased glucose consumption and lactate production. UVC treatment caused increased externalization of phosphatidylserine on platelets and microparticles, activation of the GPIIb/IIIa receptor (PAC-1 binding), and reduced hypotonic shock response. Platelet function, as measured with thrombelastogram, was not affected by UVC treatment. Components with <30% plasma were similar to those meeting specification with the exception of enhanced glycolytic metabolism.

CONCLUSION

This in vitro analysis demonstrates that treatment of platelets with <30% plasma carryover with the THERAFLEX UV-Platelets system affects some aspects of platelet metabolism and activation, although in vitro platelet function was not negatively impacted. This study also provides evidence that the treatment specifications of plasma carryover could be extended to below 30%.