Pre-transfusion storage of red blood cells (RBCs) induces aging in vitro driven by metabolic and oxidative stress, limiting transfusion efficacy. Unlike nucleated cells where multiple hallmarks characterize aging, proteostasis is expected to play a main role in anucleate RBCs, including proteasomal protein degradation. Although proteasomal activity declines during aging in vitro, its role in generating downstream alterations and post-transfusion clearance remains unclear. We hypothesized that proteasome inhibition accelerates RBC aging in vitro, particularly following re-exposure to physiological conditions. We evaluated the impact of proteasome inhibition (i.e., epoxomicin) on RBC quality during storage and physiological restoration in vitro. Additionally, young and old RBC subpopulations were compared. Proteasome inhibition during storage depleted ATP and altered RBC morphology without immediate oxidative damage. Physiological restoration of proteasome-inhibited RBCs caused accelerated ATP depletion, massive protein aggregation, reduced deformability, hemolysis, and phosphatidylserine exposure, particularly in long-stored RBCs. Strikingly, RBCs aged in vivo also exhibited low proteasomal activity and behaved similarly to stored RBCs following physiological restoration. In conclusion, proteasomal dysfunction is a key hallmark of RBC aging and senescence, driving molecular and cellular modifications that mark RBCs for clearance in vivo. Therefore, enhancing proteasomal function could improve RBC storage quality and transfusion efficacy.

IntroductionThe treatment of chronic viral infections can often bring viral replication under control. However, chronic immune activation persists and can lead to the development of comorbid conditions, such as cardiovascular disease and cancer. This is particularly true for people living with HIV (PLWH), who have significantly more extracellular vesicles from membrane budding, also called plasma microparticles (MPs), than healthy individuals (HDs), and a much more immunomodulatory phenotype. We hypothesized that the number and phenotypic heterogeneity of MPs can trigger a functional remodeling of immune responses in PLWH, preventing full immune restoration.MethodsWe investigated the rapid impact of three types of MPs — derived from membrane budding in platelets (CD41a+ PMPs), monocytes (CD14+ MMPs) and lymphocytes (CD3+ LMPs) in the plasma of PLWH or HDs—on four cell types (CD4+ and CD8+T lymphocytes, monocytes and DCs).ResultsThese investigations of the short multiple interactions and functions of MPs with these cells revealed an increase in the secretion of cytokines such as IFNg, IL2, IL6, IL12, IL17 and TNFa by the immune cells studied following interactions with MPs. We show that this functional remodeling of immune cells depends not only on the number, but also on the phenotype of MPs.ConclusionThese data suggest that the large numbers of MPs and their impact on functional remodeling in PLWH may be incompatible with the effective control of chronic infections, potentially leading to chronic immune activation and the onset of comorbid diseases.

Background Despite recent progress, the prognosis of patients with transthyretin (TTR) cardiac amyloidosis remains poor; this is primarily due to late diagnosis, when irreversible damage has already occurred. Today’s diagnostic work-up still relies on peripheral tissue or a cardiac biopsy, while circulating levels of TTR or other plasma markers have little diagnostic value. Although extracellular vesicles (EVs, as key mediators of intercellular communication) may reflect disease-specific molecular changes, their protein cargo has not yet been explored in the context of TTR amyloidosis (ATTR) cardiomyopathy. Objectives To characterize the plasma EV proteome in ATTR cardiomyopathy and identify potential biomarkers for pathophysiological pathways, diagnosis, or prognosis. Methods We performed mass-spectrometry-based, label-free, proteomic profiling of plasma EVs from 65 patients with hypertrophic cardiomyopathy due to TTR amyloidosis (the ATTR+ group, n=41) or non-amyloid cardiac disease (the ATTR- group, n=24). The groups were matched by age and sex. Results A distinct protein signature comprising 117 deregulated proteins was identified in EVs from ATTR+ patients. The ATTR+ EVs were enriched in proteins associated with vascular homeostasis, coagulation, and inflammation. At least 18 of these proteins formed an interconnected network centered on plasmin/plasminogen. Notably, EV levels of TTR and plasminogen levels were elevated, while the level of alpha2-antiplasmin (plasmin’s primary inhibitor) was low. This imbalance is particularly relevant because plasmin is known to promote amyloidogenesis via TTR cleavage. Conclusions Our findings provide new insights into the molecular mechanisms underlying ATTR cardiomyopathy and suggest that plasma EV proteins are potential diagnostic or prognostic biomarkers and/or therapeutic targets. CONDENSED ABSTRACT TTR amyloidosis (ATTR) causes severe cardiac damage, which is often diagnosed late. Through a comparative proteomic analysis of plasma extracellular vesicles (EVs) in patients with ATTR cardiomyopathy vs. patients with other cardiomyopathies, we identified several proteins of relevance to the pathophysiology of ATTR. Our analysis is the first to have highlighted an enrichment of plasmin/plasminogen (known to initiate the amyloidogenic process) and TTR in circulating EVs. Our results might foster the development of (i) diagnostic and prognostic markers for ATTR cardiomyopathy that do not require invasive procedures, and (ii) new therapeutic strategies. ![Figure][1] ETHICAL APPROVAL The present analysis was based on blood samples collected as part of a research project entitled "Study of the myocardial microenvironment and toxicity of amyloid proteins in patients with cardiac amyloidosis", which was approved by an institutional review board (CPP Sud- Méditerranée II, Marseille, France; approval references: 2021T2-12/2021-A00950-41 and 2022-A02416-37). ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes

IntroductionThe immunological profiles of CD4+ T lymphocytes (TLs) from patients with hematological malignancies differ between patients who have and have not received transfusions. There may be several reasons for these differences, including the presence of extracellular vesicles (EVs) derived from plasma membrane budding and present in the platelet concentrates. Indeed, EVs can modulate the immune system through interactions with many immune cells, but the underlying mechanisms remain incompletely understood.MethodsWe therefore investigated how interactions with CD41a+ EVs cause immune cells to change phenotype and function. CD41a+ EVs were cultured with TLs, B lymphocytes, and monocytes. Given the potential involvement of monocytes in leukemia progression, we performed a new original multi-omics study to confirm the protein changes and gene activation observed following interaction with CD41a+ EVsResultsThe CD41a+ EVs had immunomodulatory effects on all these cell types but this effect depended on the numbers of EVs. CD4+ TLs required large numbers of CD41a+ EVs for activation, whereas monocytes were the most sensitive. With the new multi-omics technique, we confirmed the direct effects of CD41a+ EVs on protein phenotype and gene activation.ConclusionTransfusion EVs should be considered during the immunological follow-up of patients after transfusion to detect immunological effects on malignant hemopathies, and during the development of new immunotherapies.

IntroductionCD39 plays an important role in the immunoregulation and inhibition of effector cells. It is expressed on immune cells, including Tregs, and on extracellular vesicles (EVs) budding from the plasma membrane. Platelet transfusion may induce alloimmunization against HLA-I antigens, leading to refractoriness to platelet transfusion with severe consequences for patients. Tregs may play a key role in determining whether alloimmunization occurs in patients with hematologic disorders. We hypothesized that CD39+ EVs might play an immunoregulatory role, particularly in the context of platelet transfusions in patients with hematologic disorders. Such alloimmunization leads to the production of alloantibodies and is sensitive to the regulatory action of CD39.MethodsWe characterized CD39+ EVs in platelet concentrates by flow cytometry. The absolute numbers and cellular origins of CD39+ EVs were evaluated. We also performed functional tests to evaluate interactions with immune cells and their functions.ResultsWe found that CD39+ EVs from platelet concentrates had an inhibitory phenotype that could be transferred to the immune cells with which they interacted: CD4+ and CD8+ T lymphocytes (TLs), dendritic cells, monocytes, and B lymphocytes (BLs). Moreover, the concentration of CD39+ EVs in platelet concentrates varied and was very high in 10% of concentrates. The number of these EVs present was determinant for EV-cell interactions. Finally, functional interactions were observed with BLs, CD4+ TLs and CD39+ EVs for immunoglobulin production and lymphoproliferation, with potential implications for the immunological management of patients.

IntroductionPeople living with HIV (PLWH) now benefit from combined antiviral treatments that durably control viral replication. These antiretroviral treatments decrease mortality and improve quality of life in PLWH, but do not completely control the excessive non-specific activation of the immune system in PLWH. This chronic immune activation is a key element of HIV immunopathology that contributes to the pathophysiology of inflammatory comorbid conditions, such as cardiovascular disorders, cancer and autoimmune diseases. Circulating non-exosomal extracellular vesicles, also known as microparticles (MPs) are detected in these diseases and have been linked to immune activation. The objective of this study was to characterize the MPs present in PLWH and to assess their association with chronic immune activation.MethodsWe performed flow cytometry for the complete phenotypic characterization of MPs from fresh plasma from PLWH and from people without HIV as the control group. The absolute number, size and cellular origin of MPs were evaluated. The immunoregulatory profile was determined by cell origin, for MPs derived from platelets (PMPs), monocytes (MMPs) and T lymphocytes (LMPs).ResultsPLWH had significantly more circulating MPs than controls, for MPs of all sizes originating from T lymphocytes, red blood cells, neutrophils, dendritic cells, B lymphocytes and endothelial cells. PMPs and MMPs were not more numerous in PLWH, but the immunoregulatory phenotypes of these MPs differed between PLWH and controls. These differences in immunoregulatory molecule expression profile were also observed for LMPs. PDL1, ICOSL, CCR5, TGFβ1, MHC classes I and II, TRAIL, CXCR4, OX40, DC-SIGN, CTLA4 and PDL2 were more strongly expressed on the surface of MPs from PLWH than on those from controls.ConclusionMPs are an important element in intercellular communication, making it possible to transfer phenotypes and functions to immune cells. The significantly higher numbers of MPs expressing diverse immunomodulatory molecules in PLWH may make a major contribution to the maintenance and/or the development of immune-cell activation in these individuals.

Introduction Acute hyper-hemolysis is a severe and potentially life-threatening complication that can occur during delayed hemolytic transfusion reactions (DHTR) or treatment procedures such as Extracorporeal Membrane Oxygenation (ECMO). This pathological condition leads to increased plasma hemoglobin (Hb) levels and subsequent heme release from Hb oxidation, resulting in multi-organ failure. Our previous study, using a fluidic model and a humanized sickle cell disease mouse model reproducing hyper-hemolysis onset (Nguyen et al., Blood, 2024), suggested that hemolysate suspension, in the absence of heme, could induce endothelial and organ damage. In this study, we aim to identify the mechanisms involved in this process. Materials and Methods Washed red blood cells (RBCs) were reconstituted in compatible serum at 2.5% hematocrit and then sonicated to prepare whole hemolysate, which was characterized by spectrophotometry and flow cytometry. Human Umbilical Vein Endothelial Cells (HUVECs) were exposed to serum alone or the same serum containing either whole hemolysate or various hemolysate components under flow conditions (1 dyn/cm²). In experiments requiring complement analysis, cell assays were performed under static conditions to avoid non-specific complement activation. Anti-C3 (Compstatin Cp40), and anti-C5 antibody (Eculizumab) were added in specific experiments to elucidate underlying mechanisms. Endothelial activation was assessed by measuring membrane expression of ICAM-1. Endothelial damage was evaluated by actin network staining, platelet thrombus formation, and RBC adhesion. Complement fragments and proteins was measured using Multiplex and EIA kits. Results and Discussion Hemolysate suspensions contained 522±29 µM free Hb, negligible MetHb (<0.1%), and no heme. Particles larger than 1 µm were significantly more abundant in hemolysate compared to serum (1.7-fold, p=0.002) whereas microparticles were similar in hemolysate and serum. These particles were predominantly CD235a positive (68%), with subpopulations co-expressing CD45 (3.6%), CD41 (7%), and CD31 (18%), and 65% were C3 positive. Hb binding to RBC-derived particles correlated with particle size. Centrifugation at 14,000 g effectively removed these particles. Both whole hemolysate and the 14,000 g pellet induced HUVEC activation and damage, but these effects were significantly reduced when using the supernatant of 14,000 g centrifugation or purified AA Hb at equivalent concentrations, indicating that RBC-derived particles play a critical role in endothelial activation during early hemolysis. We quantified complement components in the supernatant of HUVECs treated with hemolysate to elucidate the role of complement activation in hemolysate-induced endothelial damage. The hemolysate supernatant showed higher levels of final common pathway proteins and fragments compared to serum: C5a and sC5b9 (1.6- and 1.3-fold, p=0.06 and 0.01, respectively). Elements related to the alternative pathway, including C3, C3a, Ba, and Bb were also increased (1.2, 1.8, 1.7, and 1.6-fold, respectively, p=0.06). However, no difference was observed in the C1q, C2, C5, factor I, D, P, H, and C4a levels. Heat-induced decomplementation of serum led to a significant reduction in hemolysate-induced endothelial activation and damage. Treatment with either anti-C3 or anti-C5 Ab reduced endothelial activation associated with a diminution in the level of C5a (ANOVA vs control conditions, p=0.02 in two treatments) and sC5b9 (p=0.04 and 0.02 respectively) in a dose-dependent manner. As expected, C4a levels were unaffected by either treatment. In addition, anti-C3 Ab treatment significantly reduced the levels of alternative pathway fragments: C3a (p=0.001), Ba (p=0.001), and Bb (p=0.0008), whereas anti-C5 Ab had no impact on these fragments. Conclusions and perspectives These results suggest that, in the absence of heme, hemolysate containing RBC particles can trigger complement activation via the alternative pathway leading to endothelial activation and damage. This finding provides critical insight into the pathophysiology of acute hyper-hemolysis and highlights the importance of early treatment by complement inhibition in the onset phase. Ongoing research aims to reinforce these results and demonstrate complement deposition in cell-based or in vivo models.

The fibrotic stroma characterizing pancreatic ductal adenocarcinoma (PDAC) derives from a progressive tissue rigidification, which induces epithelial mesenchymal transition and metastatic dissemination. The aim of this study was to investigate the influence of matrix stiffness on PDAC progression by analyzing the proteome of PDAC-derived extracellular vesicles (EVs). PDAC cell lines (mPDAC and KPC) were grown on synthetic supports with a stiffness close to non-tumor (NT) or tumor tissue (T), and the protein expression levels in cell-derived EVs were analyzed by a quantitative MS E label-free mass spectrometry approach. Our analysis figured out 15 differentially expressed proteins (DEPs) in mPDAC-EVs and 20 DEPs in KPC-EVs in response to matrix rigidification. Up-regulated proteins participate to the processes of metabolism, matrix remodeling, and immune response, altogether hallmarks of PDAC progression. A multimodal network analysis revealed that the majority of DEPs are strongly related to pancreatic cancer. Interestingly, among DEPs, 11 related genes ( ACTB/ANXA7/C3/IGSF8/LAMC1/LGALS3/PCD6IP/SFN/TPM3/VARS/YWHAZ ) for mPDAC-EVs and 9 ( ACTB/ALDH2/GAPDH/HNRNPA2B/ITGA2/NEXN/PKM/RPN1/S100A6 ) for KPC-EVs were significantly overexpressed in tumor tissues according to gene expression profiling interaction analysis (GEPIA). Concerning the potential clinical relevance of these data, the cluster of ACTB, ITGA2, GAPDH and PKM genes displayed an adverse effect ( p  < 0.05) on the overall survival of PDAC patients.

TransfusionVolume 63, Issue S5 p. 153A-153A SUPPLEMENT ARTICLE P-CB-11 | Immunoregulation of CD41a+ Expressing Microvesicles Present in Platelet Concentrates M. Tamagne, M. Tamagne IMRBSearch for more papers by this authorD. Neyrinck-Leglantier, D. Neyrinck-Leglantier IMRBSearch for more papers by this authorL. Cagnet, L. Cagnet IMRBSearch for more papers by this authorA. Delorme, A. Delorme IMRBSearch for more papers by this authorA. Laguide, A. Laguide IMRBSearch for more papers by this authorL. Berradhia, L. Berradhia IMRBSearch for more papers by this authorM. Khelfa, M. Khelfa IMRBSearch for more papers by this authorS. Cleophax, S. Cleophax EFSSearch for more papers by this authorF. Pirenne, F. Pirenne IMRBSearch for more papers by this authorB. Vingert, B. Vingert EFSSearch for more papers by this author M. Tamagne, M. Tamagne IMRBSearch for more papers by this authorD. Neyrinck-Leglantier, D. Neyrinck-Leglantier IMRBSearch for more papers by this authorL. Cagnet, L. Cagnet IMRBSearch for more papers by this authorA. Delorme, A. Delorme IMRBSearch for more papers by this authorA. Laguide, A. Laguide IMRBSearch for more papers by this authorL. Berradhia, L. Berradhia IMRBSearch for more papers by this authorM. Khelfa, M. Khelfa IMRBSearch for more papers by this authorS. Cleophax, S. Cleophax EFSSearch for more papers by this authorF. Pirenne, F. Pirenne IMRBSearch for more papers by this authorB. Vingert, B. Vingert EFSSearch for more papers by this author First published: 12 October 2023 https://doi.org/10.1111/trf.194_17554Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume63, IssueS5October 2023Pages 153A-153A RelatedInformation

Introduction Aplasia and hematological malignancies are treated with platelet transfusions, which can have major immunomodulatory effects. Platelet concentrates (PCs) contain many immunomodulatory elements, including the platelets themselves, residual leukocytes, extracellular vesicles, such as microparticles (MPs), cytokines and other soluble elements. Two of these components, MPs and a soluble form of CD27 (sCD27), have been shown to play a particularly important role in immune system modulation. The loss of CD27 expression is an irreversible marker of terminal effector CD3 + T-lymphocyte (TL) differentiation, and the CD27 + MPs present in PCs may maintain CD27 expression on the surface of TLs, and, thus, the activation of these cells. Methods In this study, we phenotyped the CD27-expressing MPs present in PCs by microscale flow cytometry and investigated the interaction of these particles with CD4 + TLs. We cocultured MPs and PBMCs and determined the origin of the CD27 expressed on the surface of CD4 + TLs with the aid of two fluorochromes (BV510 for CD27 originating from MPs and BV786 for cellular CD27). Results We showed that the binding of CD27- expressing MPs involved the CD70 molecule, which was also present on these MPs. Finally, the maintenance of CD27 expression on the surface of TLs by sorted CD27 + MPs led to activation levels lower than those observed with other types of MPs. Discussion These results for CD27-expressing MPs and their CD70-mediated targeting open up new possibilities for immunotherapy based on the use of MPs to maintain a phenotype or to target immune cells, for example. Moreover, decreasing the levels of CD27-expressing MPs in transfused platelets might also increase the chances of success for anti-CD27 monoclonal immunotherapy.

Introduction:Acute myeloid leukemia (AML) is one of the commonest hematologic disorders. Due to the high frequency of disease- or treatment-related thrombocytopenia, AML requires treatment with multiple platelet transfusions, which can trigger a humoral response directed against platelets. Some, but not all, AML patients develop an anti-HLA immune response after multiple transfusions. We therefore hypothesized that different immune activation profiles might be associated with anti-HLA alloimmunization status.Methods:We tested this hypothesis, by analyzing CD4+ T lymphocyte (TL) subsets and their immune control molecules in flow cytometry and single-cell multi-omics.Results:A comparison of immunological status between anti-HLA alloimmunized and non-alloimmunized AML patients identified differences in the phenotype and function of CD4+ TLs. CD4+ TLs from alloimmunized patients displayed features of immune activation, with higher levels of CD40 and OX40 than the cells of healthy donors. However, the most notable differences were observed in non-alloimmunized patients. These patients had lower levels of CD40 and OX40 than alloimmunized patients and higher levels of PD1. Moreover, the Treg compartment of non-alloimmunized patients was larger and more functional than that in alloimmunized patients. These results were supported by a multi-omics analysis of immune response molecules in conventional CD4+ TLs, Tfh circulating cells, and Tregs.Discussion:Our results thus reveal divergent CD4+ TL characteristics correlated with anti-HLA alloimmunization status in transfused AML patients. These differences, characterizing CD4+ TLs independently of any specific antigen, should be taken into account when considering the immune responses of patients to infections, vaccinations, or transplantations.

Extracellular vesicles (EVs), which are generated by cell membrane budding in diverse cells, are present in variable numbers in the blood. An immunoregulatory role has been demonstrated principally for heterologous EVs, but the function of the EVs present naturally in blood remains unknown. We hypothesize that these autologous EVs might also modulate the phenotype and function of immune system cells, especially CD4+T lymphocytes (TLs), as previously described for heterologous EVs. Several membranes and soluble immunoregulatory molecules were studied after the treatment of CD4+TLs with autologous EVs. No direct activation was detected with autologous EVs, contrasting with the findings for heterologous EVs. However, following treatment with autologous EVs, a soluble form of CD27 (sCD27) was detected. sCD27 is strongly associated with lymphoproliferation. Autologous EVs have been shown to increase TL proliferation only after T-cell receptor (TcR) engagement due to polyclonal or specific-antigen stimulation. Our results therefore suggest that the EVs present in the blood have an immunomodulatory role different from that of heterologous EVs. These findings should be taken into account in future studies, particularly those focusing on infectious diseases, autotransfusion or doping practices.

Limiter les réactions transfusionnelles hémolytiques est essentiel chez les patients polytransfusés. La prévention de l’allo-immunisation, et surtout de la restimulation, est un objectif majeur, en particulier chez les patients drépanocytaires. Le statut d’immunisation antérieur de ces patients n’est pas toujours connu. Les lymphocytes T CD4+ (LT), en particulier les LT Tfh circulants, pourraient permettre de différencier le statut d’allo-immunisation des patients drépanocytaires. Nous avons testé cette hypothèse, en étudiant le phénotype des LT CXCR5 + PD1+ dans le sang total. Pour ce faire, nous avons, chez des patients drépanocytaires polytransfusés, exploré le phénotype des LT CXCR5 + PD1+ issus du sang total. Nos résultats suggèrent que des niveaux élevés de LT CXCR5 + PD1+ dans le sang total peuvent être une caractéristique des patients non allo-immunisés. Cependant, ces cellules ne présentaient pas les caractéristiques phénotypiques des cellules Tfh actives. Au contraire, une diminution des niveaux de cellules Tfh quiescentes dans le sang a été observée chez les patients polytransfusés non allo-immunisés. Les niveaux élevés de LT CXCR5 + PD1+ pourraient être associés à des fonctions de signalisation inhibitrices des LT, comme le reflètent les faibles niveaux de LT PD1 + ICOS+ dans le groupe de polytransfusés non allo-immunisés. La description de ces phénotypes particuliers, et leur comparaison entre les groupes de patients, répondeurs et non-répondeurs, suggère que de nouvelles composantes immunologiques devraient être prises en compte pour comprendre l’allo-immunisation post-transfusionnelle, et permettre de différencier le statut d’immunisé du statut de non répondeur.

Après transfusion, les patients peuvent présenter une immunomodulation, et notamment développer des allo-immunisations dirigés contre antigènes apportés par les produits sanguins labiles. Nous faisons l'hypothèse que les vésicules extracellulaires (EV) sont impliquées dans cette immunomodulation. Les EVs sont libérées dans le sang après une activation cellulaire. Quelques études ont déjà montré les effets des EVs sur le système immunitaire, mais sans en considérer les EVs lymphocytaires (LEV). Nous avons évalué la capacité des LEVs et des EVs totales présentes dans les produits transfusionnels à moduler le système immunitaire en fonction de leur concentration, de leur origine cellulaire et de leur phénotype. Nous avons analysé par cytométrie en flux la co-expression des marqueurs d'immunomodulation sur les LEVs. Les EVs totales et les LEVs ont également été purifiées par cytométrie en flux afin d'étudier leur fonctionnalité sur le système immunitaire. Ainsi, nous avons pu étudier le contenu en cytokines des LEVs et leur fonctionnalité in vitro sur les Treg et Tfh, ainsi qu'in vivo dans un modèle murin. Les marqueurs d'immunomodulation sont présents sur les LEVs. L'expression de certains marqueurs sur les LEVs est associée à un plus grand contenu en cytokines et à une lymphoprolifération plus élevée que les EVs totales. Les EVs facilitent également les réponses humorales in vitro et in vivo. Cette immunomodulation est également dépendante de la quantité d'EVs. L'origine cellulaire des EVs, leurs marqueurs d'activation, leurs contenus et leurs concentrations pourraient être pris en compte pour réduire l'impact de la transfusion sur l'immunité des patients.