Maturation and persistence of the anti-SARS-CoV-2 memory B cell response.

Memory B cells play a fundamental role in host defenses against viruses, but to date, their role has been relatively unsettled in the context of SARS-CoV-2. We report here a longitudinal single-cell and repertoire profiling of the B cell response up to 6 months in mild and severe COVID-19 patients. Distinct SARS-CoV-2 spike-specific activated B cell clones fueled an early antibody-secreting cell burst as well as a durable synchronous germinal center response. While highly mutated memory B cells, including pre-existing cross-reactive seasonal Betacoronavirus-specific clones, were recruited early in the response, neutralizing SARS-CoV-2 RBD-specific clones accumulated with time and largely contributed to the late, remarkably stable, memory B cell pool. Highlighting germinal center maturation, these cells displayed clear accumulation of somatic mutations in their variable region genes over time. Overall, these findings demonstrate that an antigen-driven activation persisted and matured up to 6 months after SARS-CoV-2 infection and may provide long-term protection.

SARS-CoV-2 Omicron BA.1 breakthrough infection drives late remodeling of the memory B cell repertoire in vaccinated individuals.

How infection by a viral variant showing antigenic drift impacts a preformed mature human memory B cell (MBC) repertoire remains an open question. Here, we studied the MBC response up to 6 months after SARS-CoV-2 Omicron BA.1 breakthrough infection in individuals previously vaccinated with three doses of the COVID-19 mRNA vaccine. Longitudinal analysis, using single-cell multi-omics and functional analysis of monoclonal antibodies from RBD-specific MBCs, revealed that a BA.1 breakthrough infection mostly recruited pre-existing cross-reactive MBCs with limited de novo response against BA.1-restricted epitopes. Reorganization of clonal hierarchy and new rounds of germinal center reactions, however, combined to maintain diversity and induce progressive maturation of the MBC repertoire against common Hu-1 and BA.1, but not BA.5-restricted, SARS-CoV-2 Spike RBD epitopes. Such remodeling was further associated with a marked improvement in overall neutralizing breadth and potency. These findings have fundamental implications for the design of future vaccination booster strategies.

Analysis of mRNA vaccination-elicited RBD-specific memory B cells reveals strong but incomplete immune escape of the SARS-CoV-2 Omicron variant.

The SARS-CoV-2 Omicron variant can escape neutralization by vaccine-elicited and convalescent antibodies. Memory B cells (MBCs) represent another layer of protection against SARS-CoV-2, as they persist after infection and vaccination and improve their affinity. Whether MBCs elicited by mRNA vaccines can recognize the Omicron variant remains unclear. We assessed the affinity and neutralization potency against the Omicron variant of several hundred naturally expressed MBC-derived monoclonal IgG antibodies from vaccinated COVID-19-recovered and -naive individuals. Compared with other variants of concern, Omicron evaded recognition by a larger proportion of MBC-derived antibodies, with only 30% retaining high affinity against the Omicron RBD, and the reduction in neutralization potency was even more pronounced. Nonetheless, neutralizing MBC clones could be found in all the analyzed individuals. Therefore, despite the strong immune escape potential of the Omicron variant, these results suggest that the MBC repertoire generated by mRNA vaccines still provides some protection against the Omicron variant in vaccinated individuals.

mRNA vaccination of naive and COVID-19-recovered individuals elicits potent memory B cells that recognize SARS-CoV-2 variants.

In addition to serum immunoglobulins, memory B cell (MBC) generation against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is another layer of immune protection, but the quality of MBC responses in naive and coronavirus disease 2019 (COVID-19)-recovered individuals after vaccination remains ill defined. We studied longitudinal cohorts of naive and disease-recovered individuals for up to 2 months after SARS-CoV-2 mRNA vaccination. We assessed the quality of the memory response by analysis of antibody repertoires, affinity, and neutralization against variants of concern (VOCs) using unbiased cultures of 2,452 MBCs. Upon boosting, the MBC pool of recovered individuals expanded selectively, matured further, and harbored potent neutralizers against VOCs. Although naive individuals had weaker neutralizing serum responses, half of their RBD-specific MBCs displayed high affinity toward multiple VOCs, including delta (B.1.617.2), and one-third retained neutralizing potency against beta (B.1.351). Our data suggest that an additional challenge in naive vaccinees could recall such affinity-matured MBCs and allow them to respond efficiently to VOCs.

An oral carbon monoxide-releasing molecule protects against acute hyperhemolysis in sickle cell disease.

ABSTRACT: Acute hyperhemolysis is a severe life-threatening complication in patients with sickle cell disease (SCD) that may occur during delayed hemolytic transfusion reaction (DHTR), or vaso-occlusive crises associated with multiorgan failure. Here, we developed in vitro and in vivo animal models to mimic endothelial damage during the early phase of hyperhemolysis in SCD. We then used the carbon monoxide (CO)-releasing molecule CORM-401 and examined its effects against endothelial activation, damage, and inflammation inflicted by hemolysates containing red blood cell membrane-derived particles. The in vitro results revealed that CORM-401: (1) prevented the upregulation of relevant proinflammatory and proadhesion markers controlled by the NF-κB enhancer of activated B cells, and (2) abolished the expression of the nuclear factor erythroid-2-related factor 2 (Nrf2) that regulates the inducible antioxidant cell machinery. We also show in SCD mice that CORM-401 protects against hemolysate-induced acute damage of target organs such as the lung, liver, and kidney through modulation of NF-κB proinflammatory and Nrf2 antioxidant pathways. Our data demonstrate the efficacy of CORM-401 as a novel therapeutic agent to counteract hemolysate-induced organ damage during hyperhemolysis in SCD. This approach might be considered as possible preventive treatment in high-risk situations such as patients with SCD with history of DHTR.

Delayed haemolytic transfusion reaction in paediatric patients with sickle cell disease: A retrospective study in a French national reference centre.

Delayed haemolytic transfusion reaction (DHTR) is a life-threatening haemolytic anaemia following red blood cell transfusion in patients with sickle cell disease, with only scarce data in children. We retrospectively analysed 41 cases of DHTR in children treated between 2006 and 2020 in a French university hospital. DHTR manifested at a median age of 10.5 years, symptoms occurred a median of 8 days after transfusion performed for an acute event (63%), before surgery (20%) or in a chronic transfusion programme (17%). In all, 93% of patients had painful crisis. Profound anaemia (median 49 g/L), low reticulocyte count (median 140 ×109 /L) and increased lactate dehydrogenase (median 2239 IU/L) were observed. Antibody screening was positive in 51% of patients, and more frequent when there was a history of alloimmunisation. Although no deaths were reported, significant complications occurred in 51% of patients: acute chest syndrome (12 patients), cholestasis (five patients), stroke (two patients) and kidney failure (two patients). A further transfusion was required in 23 patients and corticosteroids were used in 21 to reduce the risk of additional haemolysis. In all, 13 patients subsequently received further transfusions with recurrence of DHTR in only two. The study affords a better overview of DHTR and highlights the need to establish guidelines for its management in children.

Platelet EVs contain an active proteasome involved in protein processing for antigen presentation via MHC-I molecules.

In addition to their hemostatic role, platelets play a significant role in immunity. Once activated, platelets release extracellular vesicles (EVs) formed by the budding of their cytoplasmic membranes. Because of their heterogeneity, platelet EVs (PEVs) are thought to perform diverse functions. It is unknown, however, whether the proteasome is transferred from platelets to PEVs or whether its function is retained. We hypothesized that functional protein processing and antigen presentation machinery are transferred to PEVs by activated platelets. Using molecular and functional assays, we found that the active 20S proteasome was enriched in PEVs, along with major histocompatibility complex class I (MHC-I) and lymphocyte costimulatory molecules (CD40L and OX40L). Proteasome-containing PEVs were identified in healthy donor blood, but did not increase in platelet concentrates that caused adverse transfusion reactions. They were augmented, however, after immune complex injections in mice. The complete biodistribution of murine PEVs after injection into mice revealed that they principally reached lymphoid organs, such as spleen and lymph nodes, in addition to the bone marrow, and to a lesser extent, liver and lungs. The PEV proteasome processed exogenous ovalbumin (OVA) and loaded its antigenic peptide onto MHC-I molecules, which promoted OVA-specific CD8+ T-lymphocyte proliferation. These results suggest that PEVs contribute to adaptive immunity through cross-presentation of antigens and have privileged access to immune cells through the lymphatic system, a tissue location that is inaccessible to platelets.

Red blood cell alloimmunisation in sickle cell disease patients in the Democratic Republic of the Congo.

OBJECTIVES: To determine the prevalence of red blood cell (RBC) alloimmunisation and alloantibody specificity in sickle cell disease (SCD) patients in Kisangani, Democratic Republic of Congo (DRC) in comparison with those followed at the Centre Hospitalier Régional (CHR) de la Citadelle of Liège (Belgium). BACKGROUND: Data regarding RBC alloimmunisation (immune response of the organism to foreign erythrocyte antigens, antigens that lack on its own RBC) in SCD patients are scarce in sub-Saharan Africa. METHODS: We conducted a multi-site-based cross-sectional study among 125 SCD patients at Kisangani and 136 at the CHR de la Citadelle of Liège. The diagnosis of SCD was confirmed by high-performance liquid chromatography. Alloantibodies were screened using the agglutination technique on gel cards and their specificity determined using 11 and/or 16 cell panels. Statistical analyses were carried out using SPSS. RESULTS: The prevalence of RBC alloimmunisation was 9.6% among SCD patients in Kisangani versus 22.8% in those of Liège. At Kisangani as well as at Liège, the median age of alloimmunised patients was higher than that of non-alloimmunised patients, 15.5 years (IQR:4.8-19.8) and 24 years (IQR:14-31) versus 10 years (IQR: 6.5-17) and 17 years (IQR:12-24), respectively. The median number of blood units was higher in both Kisangani and Liège immunised patients compared to non-immunised patients, 8 (IQR:5-11) versus 5 (IQR:3-13) and 41(IQR:6-93) versus 6.5(3-37) respectively. At Kisangani (N = 14), the most frequent antibodies were anti-D (28.6%) and anti-C versus anti-E (13.6%), anti-S (13.6%) and anti-Lea (11.4%) at Liège (N = 44). CONCLUSIONS: These findings stated that alloimmunisation is a common complication in SCD patients in the DRC. In the resource-limited setting of this country, blood transfusion with minimal ABO, D, C and E antigen matching in addition to the use of compatibility test could significantly reduce the incidence of this complication.

Convalescent plasma therapy for B-cell-depleted patients with protracted COVID-19.

Anti-CD20 monoclonal antibodies are widely used for the treatment of hematological malignancies or autoimmune disease but may be responsible for a secondary humoral deficiency. In the context of COVID-19 infection, this may prevent the elicitation of a specific SARS-CoV-2 antibody response. We report a series of 17 consecutive patients with profound B-cell lymphopenia and prolonged COVID-19 symptoms, negative immunoglobulin G (IgG)-IgM SARS-CoV-2 serology, and positive RNAemia measured by digital polymerase chain reaction who were treated with 4 units of COVID-19 convalescent plasma. Within 48 hours of transfusion, all but 1 patient experienced an improvement of clinical symptoms. The inflammatory syndrome abated within a week. Only 1 patient who needed mechanical ventilation for severe COVID-19 disease died of bacterial pneumonia. SARS-CoV-2 RNAemia decreased to below the sensitivity threshold in all 9 evaluated patients. In 3 patients, virus-specific T-cell responses were analyzed using T-cell enzyme-linked immunospot assay before convalescent plasma transfusion. All showed a maintained SARS-CoV-2 T-cell response and poor cross-response to other coronaviruses. No adverse event was reported. Convalescent plasma with anti-SARS-CoV-2 antibodies appears to be a very promising approach in the context of protracted COVID-19 symptoms in patients unable to mount a specific humoral response to SARS-CoV-2.

Anti-CD38 monoclonal antibody interference with blood compatibility testing: Differentiating isatuximab and daratumumab via functional epitope mapping.

BACKGROUND: There are two FDA-approved anti-CD38 monoclonal antibodies for treatment of multiple myeloma: isatuximab and daratumumab. Owing to expression of CD38 on reagent red blood cells (RBCs), these antibodies interfere with indirect antiglobulin tests (IATs). We sought to understand differences in such interference by performing binding experiments. STUDY DESIGN AND METHODS: In vitro experiments to compare the binding to RBCs of isatuximab and daratumumab alone or in the presence of a mouse anti-human CD38 antibody (HB-7 or AT13/5) or a nicotinamide adenine dinucleotide-analog CD38 inhibitor were performed and quantified by flow cytometry, imaging, mass spectrometry, surface plasmon resonance, and LigandTracer technologies. Serologic testing was performed on plasma samples spiked with isatuximab or daratumumab. RESULTS: CD38 expressed on RBCs can be directly bound by daratumumab, whereas isatuximab requires a co-factor, such as HB-7, AT13/5, or a CD38 inhibitor, suggesting that the isatuximab epitope on RBCs is masked in vitro. Daratumumab samples more frequently showed interference and had stronger reactions than isatuximab samples. Dithiothreitol treatment was equally effective in mitigating the interference caused by either drug. DISCUSSION: Both isatuximab and daratumumab interfere with IATs but at different magnitudes, reflecting distinct binding to CD38 on RBCs. From the binding studies, we conclude that the isatuximab epitope on RBCs is masked in vitro and binding requires a certain CD38 conformation or co-factor. This circumstance may explain why interference is seen only in a subset of patients receiving isatuximab when compared with interference seen in most patients on daratumumab therapy.

The transfusion of non-prophylactically RH-KEL1 antigen-matched red blood cells is feasible in selected myelodysplastic syndrome and acute myeloid leukaemia patients.

BACKGROUND AND OBJECTIVES: Most myelodysplastic syndromes (MDS) patients become red blood cell (RBC) transfusion-dependent. Transfusing MDS patients with prophylactically RH-KEL1 antigen-matched (PAM) RBC units is recommended to avoid RBC allo-immunization. D+C-E-c+e+, D+C-E+c+e- and D+C+E-c-e+ phenotypes are infrequent among French blood donors. To preserve infrequent phenotype RBC units for patients other than MDS, and to manage frequent phenotype RBC unit stocks, we let, for 1 year, higher-risk non-immunized chronically transfused MDS and acute myeloid leukaemia (AML) patients receive RBC transfusions matched only for D. Our objectives were to evaluate the impact of non-PAM transfusions on the transfusion policy (which would be modified in case of RBC allo-immunization) for frequent and infrequent phenotypes patients and to estimate the number of infrequent phenotypes RBC units that could be redistributed to other patients. RESULTS: Ninety patients were enrolled. Thirty-five patients had infrequent phenotypes, nine received only PAM RBC (143 units) and 26 PAM and non-PAM RBC (415 and 532, respectively): none developed allo-immunization. Fifty-five patients had frequent RBC phenotypes, 34 received only PAM RBC (561 units) and three developed antibodies (2 non-RH-KEL1 and one anti-E); 21 received PAM and non-PAM RBC (436 and 109, respectively) and one developed allo-immunization (unknown specificity). Our strategy enabled us to preserve 532 infrequent phenotypes RBC units: 216 D+C-E-c+e+, 33 D+C-E+c+e- and 283 D+C+E-c-e+ units, representing 48.8% of the total number of RBC units received by infrequent phenotypes patients during the study period. CONCLUSION: Allowing the transfusion of non-PAM RBC in selected chronically transfused MDS and AML patients was feasible and enabled to redistribute infrequent phenotypes RBC units to other patients in need.

Emerging RNA-Dependent RNA Polymerase Mutation in a Remdesivir-Treated B-cell Immunodeficient Patient With Protracted Coronavirus Disease 2019.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a newly discovered virus for which remdesivir is the only antiviral available. We report the occurrence of a mutation in RdRP (D484Y) following treatment with remdesivir in a 76-year-old female with post-rituximab B-cell immunodeficiency and persistent SARS-CoV-2 viremia. A cure was achieved after supplementation with convalescent plasma.

Blood microparticles are a component of immune modulation in red blood cell transfusion.

Patients may display alloimmunization following transfusion. Microparticles (MPs) released into the blood are present in transfusion products. We show that MPs can modulate the immune system, CD4+ T-cell, and humoral responses, through their concentration, cellular origin and phenotype, and should therefore be considered to reduce the immune impact of transfusion.

Efficacy, safety and immunological profile of combining rituximab with belimumab for adults with persistent or chronic immune thrombocytopenia: results from a prospective phase 2b trial.

B-cell activating factor may be involved in the failure of B-cell depleting therapy with rituximab in immune thrombocytopenia (ITP) by promoting the emergence of splenic long-lived plasma cells. From results obtained in mouse models, we hypothesized that combining rituximab with sequential injections of belimumab could increase the rate of response at one year in patients with persistent or chronic ITP by preventing the emergence of these long-lived plasma cells. The study was a single-center, single arm, prospective phase 2b trial (RITUX-PLUS, NCT03154385) investigating the safety and efficacy of rituximab given at a fixed dose of 1,000 mg, two weeks apart, combined with five infusions of belimumab, 10 mg/kg at week 0 (W0)+2 days, W2+2 days, W4, W8 and W12 for adults with primary persistent or chronic ITP. The primary endpoint was the total number of patients achieving an overall response (complete response + response) at W52 according to a standard definition. In total, 15 non-splenectomized adults, nine (60%) with persistent IPT and six (40%) with chronic ITP, were included. No severe adverse event, infection, or severe hypogammaglobulinemia was observed. Thirteen patients achieved an initial overall response. At W52, 12 (80%) patients achieved an overall response, including ten (66.7%) with complete response. When compared with a cohort of patients receiving rituximab alone, the kinetics of B-cell repopulation appeared similar, but the number of circulating T follicular helper cells was significantly decreased with belimumab combination therapy. Combining rituximab and belimumab seems a promising strategy in ITP, with high efficacy and acceptable safety.

HLA molecule expression on the surface of cells and microparticles in platelet concentrates.

BACKGROUND: Platelet (PLT) transfusions are an essential treatment for bleeding disorders. However, immunologic complications can occur, including alloantibody production against Class I HLA molecules. The principal source of HLA molecules in PLT concentrates (PCs) is the PLTs themselves. However, extracellular microparticles (MPs) present in PCs may express HLA molecules. STUDY DESIGN AND METHODS: We used nanoscale flow cytometry to explore the expression of HLA-A2, HLA-B7, and HLA-B57 on the surface of cells, PLT-derived MPs (PMPs), lymphocyte-derived MPs (LMPs), and monocyte-derived MPs (MMPs) present in PCs. Expression was studied during 7 days of storage. RESULTS: Platelets were not the only source of HLA molecules in PCs. HLA molecules were present on PMPs, LMPs, and MMPs. The level of HLA Class I molecule expression varied between haplotypes and MPs of different origins and during storage. CONCLUSION: Platelets or residual cells remaining after leukoreduction are not the only source of HLA Class I molecules in PCs, highlighting the contribution of MPs to alloimmunization mechanisms. These data may be relevant for the development of new transfusion guidelines.

Insights into anti-D formation in carriers of RhD variants through studies of 3D intraprotein interactions.

BACKGROUND: Many RhD variants associated with anti-D formation (partial D) in carriers exposed to the conventional D antigen carry mutations affecting extracellular loop residues. Surprisingly, some carry mutations affecting transmembrane or intracellular domains, positions not thought likely to have a major impact on D epitopes. STUDY DESIGN AND METHODS: A wild-type Rh trimer (RhD1 RhAG2 ) was modeled by comparative modeling with the human RhCG structure. Taking trimer conformation, residue accessibility, and position relative to the lipid bilayer into account, we redefine the domains of the RhD protein. We generated models for RhD variants carrying one or two amino acid substitutions associated with anti-D formation in published articles (25 variants) or abstracts (12 variants) and for RHD*weak D type 38. We determined the extracellular substitutions and compared the interactions of the variants with those of the standard RhD. RESULTS: The findings of the three-dimensional (3D) analysis were correlated with anti-D formation for 76% of RhD variants: 15 substitutions associated with anti-D formation concerned extracellular residues, and structural differences in intraprotein interactions relative to standard RhD were observed in the others. We discuss the mechanisms by which D epitopes may be modified in variants in which the extracellular residues are identical to those of standard RhD and provide arguments for the benignity of p.T379M (RHD*DAU0) and p.G278D (RHD*weak D type 38) in transfusion medicine. CONCLUSION: The study of RhD intraprotein interactions and the precise redefinition of residue accessibility provide insight into the mechanisms through which RhD point mutations may lead to anti-D formation in carriers.

ABO blood group and COVID-19: a review on behalf of the ISBT COVID-19 Working Group.

Growing evidence suggests that ABO blood group may play a role in the immunopathogenesis of SARS-CoV-2 infection, with group O individuals less likely to test positive and group A conferring a higher susceptibility to infection and propensity to severe disease. The level of evidence supporting an association between ABO type and SARS-CoV-2/COVID-19 ranges from small observational studies, to genome-wide-association-analyses and country-level meta-regression analyses. ABO blood group antigens are oligosaccharides expressed on red cells and other tissues (notably endothelium). There are several hypotheses to explain the differences in SARS-CoV-2 infection by ABO type. For example, anti-A and/or anti-B antibodies (e.g. present in group O individuals) could bind to corresponding antigens on the viral envelope and contribute to viral neutralization, thereby preventing target cell infection. The SARS-CoV-2 virus and SARS-CoV spike (S) proteins may be bound by anti-A isoagglutinins (e.g. present in group O and group B individuals), which may block interactions between virus and angiotensin-converting-enzyme-2-receptor, thereby preventing entry into lung epithelial cells. ABO type-associated variations in angiotensin-converting enzyme-1 activity and levels of von Willebrand factor (VWF) and factor VIII could also influence adverse outcomes, notably in group A individuals who express high VWF levels. In conclusion, group O may be associated with a lower risk of SARS-CoV-2 infection and group A may be associated with a higher risk of SARS-CoV-2 infection along with severe disease. However, prospective and mechanistic studies are needed to verify several of the proposed associations. Based on the strength of available studies, there are insufficient data for guiding policy in this regard.

Donor-targeted serotherapy as a rescue therapy for steroid-resistant acute GVHD after HLA-mismatched kidney transplantation.

Acute graft-versus-host disease (GVHD) is a rare but frequently lethal complication after solid organ transplantation. GVHD occurs in unduly immunocompromised hosts but requires the escalation of immunosuppression, which does not discriminate between host and donor cells. In contrast, donor-targeted therapy would ideally mitigate graft-versus-host reactivity while sparing recipient immune functions. We report two children with end-stage renal disease and severe primary immune deficiency (Schimke syndrome) who developed severe steroid-resistant acute GVHD along with full and sustained donor T cell chimerism after isolated kidney transplantation. Facing a therapeutic dead end, we used a novel strategy based on the adoptive transfer of anti-HLA donor-specific antibodies (DSAs) through the transfusion of highly selected plasma. After approval by the appropriate regulatory authority, an urgent nationwide search was launched among more than 3800 registered blood donors with known anti-HLA sensitization. Adoptively transferred DSAs bound to and selectively depleted circulating donor T cells. The administration of DSA-rich plasma was well tolerated and notably did not induce antibody-mediated rejection of the renal allografts. Acute GVHD symptoms promptly resolved in one child. This report provides a proof of concept for a highly targeted novel therapeutic approach for solid organ transplantation-associated GVHD.

How I safely transfuse patients with sickle-cell disease and manage delayed hemolytic transfusion reactions.

Transfusions can be a life-saving treatment of patients with sickle-cell disease (SCD). However, availability of matched units can be limiting because of distinctive blood group polymorphisms in patients of African descent. Development of antibodies against the transfused red blood cells (RBCs), resulting in delayed hemolytic transfusion reactions (DHTRs), can be life-threatening and pose unique challenges for this population with regard to treatment strategies and transfusion management protocols. In cases where the transfused cells and the patient's own RBCs are destroyed, diagnosis of DHTR can be difficult because symptoms may mimic vaso-occlusive crisis, and frequently, antibodies are undetectable. Guidelines are needed for early diagnosis of DHTR because treatment may need to include temporarily withholding any new transfusions to avoid further hemolysis. Also needed are case-control studies to optimally tailor treatments based on the severity of DHTR and develop preventive transfusion strategies for patients at DHTR risk. Here, we will review gaps in knowledge and describe through case studies our recommended approach to prevent alloimmunization and to diagnose and treat symptomatic DHTRs for which complementary mechanistic studies to understand their pathogenesis are sorely needed.

Cytokine changes in sickle-cell disease patients as markers predictive of the onset of delayed hemolytic transfusion reactions.

BACKGROUND: Changes in cytokine production are known to contribute to the pathogenesis of sickle-cell disease (SCD), particularly in painful acute complications (crises) and episodes of post-transfusion hemolysis. Little is known about cytokine profiles in patients with these complications. STUDY DESIGN AND METHODS: We investigated possible associations between cytokine profile and the onset of delayed hemolytic transfusion reactions (DHTRs), particularly during acute-phase episodes, to improve characterization of the biological parameters predictive of such events. We included SCD patients with severe acute symptoms (n = 36) or steady-state disease (n = 31), both possibly leading to a DHTR (n = 18) event. Luminex® technology was used to determine the plasma concentrations of 23 cytokines. RESULTS: Regardless of clinical context, the concentrations of interleukin (IL)-6, IL-10, inducible protein-10, and macrophage inflammatory protein-1ß were higher in plasma samples from SCD patients than in those from healthy controls. IL-6 and IL-10 concentrations were even higher in acute-phase plasma samples from SCD patients. In addition, IL-27 and TNFα levels were higher, and IL-6 and RANTES levels were lower in acute-phase SCD patients just before the onset of DHTR than in patients experiencing painful occlusive episodes. CONCLUSION: In addition to reporting the plasma cytokine profiles of SCD patients in various clinical phases of the disease, we provide the first evidence of a significant association between low plasma TNFα concentration, high plasma IP-10 concentration and the onset of DHTR in SCD patients.