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Pyruvate kinase deficiency (PKD) is the most common cause of congenital nonspherocytic hemolytic anemia. Although recognition of the disease spectrum has recently expanded, data describing its impact on health-related quality of life (HRQoL) are limited. In this prospective international cohort of 254 patients (131 adults and 123 children) with PKD, we used validated measures to assess the impact of disease on HRQoL (EuroQol 5-Dimension Questionnaire, Pediatric Quality of Life Inventory Generic Core Scale version 4.0, and Functional Assessment of Cancer Therapy-Anemia) and fatigue (Patient Reported Outcomes Measurement Information System Fatigue and Pediatric Functional Assessment of Chronic Illness Therapy-Fatigue). Significant variability in HRQoL and fatigue was reported for adults and children, although individual scores were stable over a 2-year interval. Although adults who were regularly transfused reported worse HRQoL and fatigue compared with those who were not (EuroQol-visual analog scale, 58 vs 80; P = .01), this difference was not seen in children. Regularly transfused adults reported lower physical, emotional, and functional well-being and more anemia symptoms. HRQoL and fatigue significantly differed in children by genotype, with the worst scores in those with 2 severe PKLR mutations; this difference was not seen in adults. However, iron chelation was associated with significantly worse HRQoL scores in children and adults. Pulmonary hypertension was also associated with significantly worse HRQoL. Additionally, 59% of adults and 35% of children reported that their jaundice upset them, identifying this as an important symptom for consideration. Although current treatments for PKD are limited to supportive care, new therapies are in clinical trials. Understanding the impact of PKD on HRQoL is important to assess the utility of these treatments. This trial was registered at www.clinicaltrials.gov as #NCT02053480.

Pediatric Evans syndrome (pES) is increasingly identified as the presenting manifestation of several inborn errors of immunity. Despite an improved understanding of genetic defects in pES, the underlying immunobiology of pES is poorly defined, and characteristic diagnostic immune parameters are lacking. We describe the immune characteristics of 24 patients with pES and compared them with 22 patients with chronic immune thrombocytopenia (cITP) and 24 healthy controls (HCs). Compared with patients with cITP and HC, patients with pES had increased circulating T-follicular helper cells (cTfh), increased T-cell activation, and decreased naïve CD4+ T cells for age. Despite normal or high immunoglobulin G (IgG) in most pES at presentation, class-switched memory B cells were decreased. Within the cTfh subset, we noted features of postactivation exhaustion with upregulation of several canonical checkpoint inhibitors. T-cell receptor β chain (TCR-β) repertoire analysis of cTfh cells revealed increased oligoclonality in patients with pES compared with HCs. Among patients with pES, those without a known gene defect had a similar characteristic immune abnormality as patients with defined genetic defects. Similarly, patients with pES with normal IgG had similar T-cell abnormalities as patients with low IgG. Because genetic defects have been identified in less than half of patients with pES, our findings of similar immune abnormalities across all patients with pES help establish a common characteristic immunopathology in pES, irrespective of the underlying genetic etiology.

Purpose of review Transplant-associated thrombotic microangiopathy (TA-TMA) is a complication that can occur in both allogeneic and autologous haematopoietic cellular therapy (HCT) recipients and is associated with significant morbidity and mortality. Although TA-TMA is a complex disease, there is emerging evidence that complement activation and endothelial dysfunction play a key role in the pathophysiology of the disease. The use of eculizumab has improved survival in patients with high risk and severe disease, but mortality rates in treated patients still exceed 30%, highlighting the need for novel approaches. Recent findings There are multiple ongoing and planned clinical trials investigating novel complement agents in TA-TMA and other TMAs. Drugs vary by targets of the complement system, mechanism, and form of administration. Clinical trial designs include single arm studies that span across multiple age groups including children, and double-blind, randomized, placebo-controlled studies. These studies will provide robust data to inform the care of patients with TA-TMA in the future. In addition to multiple promising therapeutic agents, preventing TA-TMA is an emerging strategy. Agents known to protect the endothelium from damage and augment endothelial function by promoting anti-inflammatory and antithrombotic effects may have a role in preventing TA-TMA or ameliorating the severity, though additional studies are needed. Summary Novel therapeutic agents for TA-TMA inhibition of the complement system are under investigation and prophylactic strategies of endothelial protection are emerging. Further understanding of the pathophysiology of the disease may identify additional therapeutic targets. Multiinstitutional, collaborative clinical trials are needed to determine the safety and efficacy of these agents going forward.

Thrombotic thrombocytopenic purpura (TTP) is a potentially life-threatening disorder characterized by microangiopathic hemolytic anemia, thrombocytopenia, and severely reduced or absent ADAMTS13 (A disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13) activity, with varying degrees of organ dysfunction. As TTP is rare in pediatrics, most of the medical and scientific literature has largely reported on adult patients. As a result, limited data exist regarding the clinical features, comorbidities, treatment response, and long-term outcomes in pediatric patients with immune-mediated TTP.A single-center retrospective cohort study was conducted of all children and adolescents presenting to Children's Healthcare of Atlanta, Atlanta, Georgia, between the years 2001 and 2021 with immune-mediated TTP (iTTP). Clinical features, treatments, and outcomes, including long-term neurocognitive function, were analyzed.Eighteen individuals were identified, six of whom had a total of 10 relapses, amounting to 28 episodes overall. Thirty-eight percent of the patients experienced exacerbations but, ultimately, 85% achieved a clinical response and clinical remission. Only one in-hospital death occurred (mortality rate 5.5%). Seventy-three percent of analyzed patients demonstrated long-term neurocognitive abnormalities, including cognitive delay, learning difficulties, and severe depression.Children and adolescents recovering from iTTP are at high risk for neurocognitive deficits from initial and possibly ongoing microvascular disease. Due to risk for long-term neurological deficits, we recommend neuropsychological testing in addition to monitoring of other organ functions in all children with TTP, as well as long-term surveillance of ADAMTS13 activity during remission to detect and promptly treat early relapse.

Transplant-associated thrombotic microangiopathy (TA-TMA) and sickle cell disease (SCD) share features of endothelial and complement activation. Thus, we hypothesized that SCD is a risk factor for TA-TMA and that prehematopoietic cellular transplantation (HCT) markers of endothelial dysfunction and complement activation would be higher in patients with SCD. Children who underwent initial haploidentical or matched sibling donor HCT between January 2015 and June 2020 were included in this institutional review board–approved, single institution, retrospective study. Of the 115 children, 52 had SCD, and 63 underwent HCT for non-SCD indications. There was no significant difference in severe grade 3 to 4 acute graft-versus-host disease (GVHD) between recipients of HCT with or without SCD. The non-SCD cohort had significantly more cytomegalovirus-positive recipients, radiation-containing preparative regimens, and peripheral blood stem cell graft sources (P ≤ .05), all described risk factors for developing TA-TMA. Despite this, 7 of 52 patients (13%) with SCD developed TA-TMA compared with 1 of 63 patients (2%) without SCD (P = .015). Risk was highest in those who underwent haploidentical HCT (odds ratio [OR], 33; 95% confidence interval [CI], 1.4-793.2). Adjusting for HLA match, GVHD, post-HCT viral infection, stem cell source, and myeloablation, SCD remained a risk for developing TA-TMA (OR, 12.22; 95% CI, 1.15-129.6). In available pre-HCT samples, there was no difference in complement biomarkers between those with SCD and those without, though patients with SCD did have significantly higher levels of markers of endothelial activation, soluble vascular cell adhesion molecule 1, and P-selectin. In conclusion, children with SCD merit careful screening for TA-TMA after HCT, particularly those receiving a haploidentical HCT.

Although transplant-associated thrombotic microangiopathy (TA-TMA) commonly complicates pediatric hematopoietic cellular therapy (HCT), pulmonary manifestations and histology of TA-TMA (pTA-TMA) are rarely reported, with scant data available on timing, risk factors, pathogenesis, and outcomes. Pulmonary hypertension (PH) and diffuse alveolar hemorrhage (DAH) are recognized manifestations of pTA-TMA. The objective of this study was to characterize the pathologic findings, outcomes, and coincident diagnoses preceding biopsy-proven pTA-TMA. In Institutional Review Board- approved retrospective studies, available lung tissue was reviewed at 2 institutions between January 2016 and August 2021 to include those with pulmonary vascular pathology. Histologic features of pTA-TMA were present in 10 children with prior respiratory decline after an allogeneic HCT (allo-HCT; n = 9) or autologous HCT (n = 1). Pathologic lesions included muscular medialization, microthrombi, and red cell fragments, in addition to perivasculitis and intimal arteritis. Parenchymal findings included diffuse alveolar damage, organizing pneumonia, and plasmocytic infiltrates. Six children were clinically diagnosed with TA-TMA, and all were treated with eculizumab, at a median of 2.5 days after clinical diagnosis (range, 0 to 11 days). Four were identified postmortem. Coincident pulmonary infection was confirmed in 8 of the 10 patients. Five allo-HCT recipients (56%) experienced graft-versus-host disease (GVHD; 4 acute, 1 chronic) prior to the onset of respiratory symptoms. Two patients (20%) had clinically recognized DAH, although 9 (90%) had evidence of DAH on histology. Although all 10 patients underwent echocardiography at the time of symptom onset and 9 had serial echocardiograms, only 2 patients had PH detected. Treatments varied and included sildenafil (n = 3), steroids (n = 1), and eculizumab (n = 6). One patient was alive at the time of this report; the remaining 9 died, at a median of 52 days after onset of respiratory symptoms (range 4 to 440 days) and a median of 126 days post-HCT (range, 13 to 947 days). pTA-TMA is a heterogeneous histologic disease characterized by arteriolar inflammation, microthrombi, and often DAH. pTA-TMA presented with respiratory decline with systemic TA-TMA in all patients. Clinicians should maintain a high degree of suspicion for DAH in patients with TA-TMA and pulmonary symptoms. Coincident rates of GVHD and pulmonary infections were high, whereas the rate of PH identified by echocardiography was 20%. Outcomes were poor despite early use of eculizumab and other therapies. Our data merit consideration of pTA-TMA in patients with acute respiratory decline in the setting of systemic TA-TMA, GVHD, and infection. Investigation of additional therapies for pTA-TMA is needed as well. © 2022 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Transfusion of blood products is a necessary part of successful delivery of myelosuppressive regimens in pediatric cancer. There is a paucity of literature characterizing outcomes or management of pediatric patients with cancer when transfusion is declined.The objective of this paper is to describe the clinical characteristics, care, and outcomes of patients with cancer at risk for declining transfusion.A retrospective cohort of patients aged 0-21 years with cancer managed at Children's Healthcare of Atlanta between 2006 and 2020 and with ICD-9 codes indicating risk of "transfusion refusal" or Jehovah's witness (JW) religion was identified. Demographics, disease, and management were abstracted. Descriptive statistics were performed to examine associations with transfusion receipt. Among 35 eligible patients identified as at risk for declining transfusion, 89% had primary guardians who identified as JW, and 45.7% identified as Black, non-Hispanic. Only 40% of guardians actively declined transfusion. Transfusion recipients had significantly lower hemoglobin (g/dl) and platelet counts (1000/μl) at initial presentation (9.6 vs. 11.9, p .002 and 116.0 vs. 406.5, p = .001, respectively) and at nadir (5.9 vs. 8.7, p .001 and ≤ 10 vs. 154, p .001, respectively) than non-recipients. Legal intervention was required in 36.4% of those who ultimately received a transfusion.Among pediatric cancer patients whose medical record initially indicated a preference for no transfusion, 60% of guardians accepted blood products when prescribed for oncology care. Guidelines for systematic management and transfusion sparing approaches are needed to honor guardian's preferences when possible yet while maintaining equitable cancer outcomes in this population.

Background While convalescent plasma (CP) may benefit patients with COVID‐19, fundamental questions remain regarding its efficacy, including the components of CP that may contribute to its therapeutic effect. Most current serological evaluation of CP relies on examination of total immunoglobulin or IgG‐specific anti‐SARS‐CoV‐2 antibody levels. However, IgA antibodies, which also circulate and are secreted along the respiratory mucosa, represent a relatively uncharacterized component of CP. Study design and methods Residual samples from patients and CP donors were assessed for IgM, IgG, and IgA anti‐SARS‐CoV‐2 antibody titers against the receptor‐binding domain responsible for viral entry. Symptom onset was obtained by chart review. Results Increased IgA anti‐SARS‐CoV‐2 antibody levels correlated with clinical improvement and viral clearance in an infant with COVID‐19, prompting a broader examination of IgA levels among CP donors and hospitalized patients. Significant heterogeneity in IgA levels was observed among CP donors, which correlated weakly with IgG levels or the results of a commonly employed serological test. Unlike IgG and IgM, IgA levels were also more likely to be variable in hospitalized patients and this variability persisted in some patients >14 days following symptom onset. IgA levels were also less likely to be sustained than IgG levels following subsequent CP donation. Conclusions IgA levels can be very heterogenous among CP donors and hospitalized patients and do not necessarily correlate with commonly employed testing platforms. Examining isotype levels in CP and COVID‐19 patients may allow for a tailored approach when seeking to fill specific gaps in humoral immunity.

While a variety of therapeutic options continue to emerge for COVID-19 treatment, convalescent plasma (CP) has been used as a possible treatment option early in the pandemic. One of the most significant challenges with CP therapy, however, both when defining its efficacy and implementing its approach clinically, is accurately and efficiently characterizing an otherwise heterogenous therapeutic treatment. Given current limitations, our goal is to leverage a SARS antibody testing platform with a newly developed automated endpoint titer analysis program to rapidly define SARS-CoV-2 antibody levels in CP donors and hospitalized patients. A newly developed antibody detection platform was used to perform a serial dilution enzyme-linked immunosorbent assay (ELISA) for immunoglobulin (Ig)G, IgM, and IgA SARS-CoV-2 antibodies. Data were then analyzed using commercially available software, GraphPad Prism, or a newly developed program developed in Python called TiterScape, to analyze endpoint titers. Endpoint titer calculations and analysis times were then compared between the two analysis approaches. Serial dilution analysis of SARS-CoV-2 antibody levels revealed a high level of heterogeneity between individuals. Commercial platform analysis required significant time for manual data input and extrapolated endpoint titer values when the last serial dilution was above the endpoint cutoff, occasionally producing erroneously high results. By contrast, TiterScape processed 1008 samples for endpoint titer results in roughly 14 minutes compared with the 8 hours required for the commercial software program analysis. Equally important, results generated by TiterScape and Prism were highly similar, with differences averaging 1.26 ± 0.2 percent (mean ± SD). The pandemic has created unprecedented challenges when seeking to accurately test large numbers of individuals for SARS-CoV-2 antibody levels with a rapid turnaround time. ELISA platforms capable of serial dilution analysis coupled with a highly flexible software interface may provide a useful tool when seeking to define endpoint titers in a high-throughput manner. Immunohematology 2021;37:33-43.While a variety of therapeutic options continue to emerge for COVID-19 treatment, convalescent plasma (CP) has been used as a possible treatment option early in the pandemic. One of the most significant challenges with CP therapy, however, both when defining its efficacy and implementing its approach clinically, is accurately and efficiently characterizing an otherwise heterogenous therapeutic treatment. Given current limitations, our goal is to leverage a SARS antibody testing platform with a newly developed automated endpoint titer analysis program to rapidly define SARS-CoV-2 antibody levels in CP donors and hospitalized patients. A newly developed antibody detection platform was used to perform a serial dilution enzyme-linked immunosorbent assay (ELISA) for immunoglobulin (Ig)G, IgM, and IgA SARS-CoV-2 antibodies. Data were then analyzed using commercially available software, GraphPad Prism, or a newly developed program developed in Python called TiterScape, to analyze endpoint titers. Endpoint titer calculations and analysis times were then compared between the two analysis approaches. Serial dilution analysis of SARS-CoV-2 antibody levels revealed a high level of heterogeneity between individuals. Commercial platform analysis required significant time for manual data input and extrapolated endpoint titer values when the last serial dilution was above the endpoint cutoff, occasionally producing erroneously high results. By contrast, TiterScape processed 1008 samples for endpoint titer results in roughly 14 minutes compared with the 8 hours required for the commercial software program analysis. Equally important, results generated by TiterScape and Prism were highly similar, with differences averaging 1.26 ± 0.2 percent (mean ± SD). The pandemic has created unprecedented challenges when seeking to accurately test large numbers of individuals for SARS-CoV-2 antibody levels with a rapid turnaround time. ELISA platforms capable of serial dilution analysis coupled with a highly flexible software interface may provide a useful tool when seeking to define endpoint titers in a high-throughput manner. Immunohematology 2021;37:33­43.

Mutations in the CBL gene were first identified in adults with various myeloid malignancies. Some patients with juvenile myelomonocytic leukemia (JMML) were also noted to harbor mutations in CBL, but were found to have generally less aggressive disease courses compared to patients with other forms of Ras pathway-mutant JMML. Importantly, and in contrast to most reports in adults, the majority of CBL mutations in JMML patients are germline with acquired uniparental disomy occurring in affected marrow cells. Here, we systematically studied a large cohort of 33 JMML patients with CBL mutations and found that this disease is highly diverse in presentation and overall outcome. Moreover, we discovered somatically acquired CBL mutations in 15% of pediatric patients who presented with more aggressive disease. Neither clinical features nor methylation profiling were able to distinguish patients with somatic CBL mutations from those with germline CBL mutations, highlighting the need for germline testing. Overall, we demonstrate that disease courses are quite heterogeneous even among patients with germline CBL mutations. Prospective clinical trials are warranted to find ideal treatment strategies for this diverse cohort of patients.

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired clonal stem cell disease harvesting a somatic mutation in the phosphatidylinositol glycan class A (This paper will review primary data on the pharmacology, efficacy, and safety of ravulizumab in the pediatric/adolescent population gathered from literature search from PubMed, abstracts from annual meetings, and medication package inserts. Eligible clinical trials identified on the clinicaltrials.gov website are also briefly discussed.The discovery of eculizumab, a monoclonal antibody against complement protein 5, has revolutionized the PNH landscape, with decreased hemolysis and risk of thrombosis, improved quality-of-life, and has become the standard of care. Ravulizumab, a longer-acting C5-inhibitor with 4 times the half-life of eculizumab, was recently approved for pediatric patients with PNH. Ravulizumab is effective, safe, and has the potential to improve quality of life further. In addition, ongoing clinical trials using second-generation complement inhibitors may provide promising new interventions in PNH.

BACKGROUND: Alloimmunization can be a significant barrier to red blood cell (RBC) transfusion. While alloantigen matching protocols hold promise in reducing alloantibody formation, transfusion-dependent patients can still experience RBC alloimmunization and associated complications even when matching protocols are employed. As a result, complementary strategies capable of actively preventing alloantibody formation following alloantigen exposure are warranted. STUDY DESIGN AND METHODS: We examined whether pharmacological removal of macrophages using clodronate may provide an additional strategy to actively inhibit RBC alloimmunization using two preclinical models of RBC alloimmunization. To accomplish this, mice were treated with clodronate, followed by transfusion of RBCs expressing the HOD (HEL, OVA and Duffy) or KEL antigens. On days 5 and 14 post transfusion, anti-HOD or anti-KEL IgM and IgG antibodies were evaluated. RESULTS: Low dose clodronate effectively eliminated key marginal zone macrophage populations from the marginal sinus. Prior treatment with clodronate, but not empty liposomes, also significantly inhibited IgM and IgG anti-HOD alloantibody formation following transfusion of HOD RBCs. Similar exposure to clodronate inhibited IgM and IgG antibody formation following KEL RBC transfusion. CONCLUSIONS: Clodronate can inhibit anti-HOD and anti-KEL antibody formation following RBC transfusion in preclinical models. These results suggest that clodronate may provide an alternative approach to actively inhibit or prevent the development of alloantibodies following RBC transfusion, although future studies will certainly be needed to fully explore this possibility.

Mitapivat, an oral activator of pyruvate kinase (PK) in red blood cells (RBCs), has shown significant improvements in haemoglobin and haemolysis among patients with pyruvate kinase deficiency who were not receiving regular transfusions. We aimed to evaluate the efficacy and safety of mitapivat in adults with pyruvate kinase deficiency receiving regular transfusions.ACTIVATE-T was an open-label, single-arm, phase 3 trial conducted in 20 centres across Europe, North America, and Asia. Eligible participants were adults (aged ≥18 years) with a clinical laboratory confirmation of pyruvate kinase deficiency receiving regular transfusions (at least six episodes in the previous year). Participants received oral mitapivat during a 16-week dose-optimisation period (5 mg, 20 mg, 50 mg twice daily) and 24-week fixed-dose period. The primary endpoint was a reduction in transfusion burden (≥33% reduction in number of RBC units transfused during the fixed-dose period, compared with the participant's individual historical transfusion burden, standardised to 24 weeks). Efficacy and safety were assessed in all participants who received at least one dose of mitapivat. This trial is registered with ClinicalTrials.gov, NCT03559699, and is complete.Between June 26, 2018, and Feb 4, 2020, 27 participants (20 [74%] female and seven [26%] male; 20 [74%] White, three [11%] Asian, and four [15%] not reported) were enrolled and received at least one dose of mitapivat. Median duration of exposure to mitapivat was 40·3 weeks (IQR 40·0-41·3). A reduction in transfusion burden by at least 33% was found in ten (37%) participants (95% CI 19-58; p=0·0002). The most common treatment-emergent adverse events were increase in alanine aminotransferase (ten [37%] participants), headache (ten [37%]), increase in aspartate aminotransferase (five [19%]), fatigue (five [19%]), and nausea (five [19%]). Two grade 3 treatment-emergent adverse events were related to study treatment: joint swelling (one participant [4%]) and an increase in aspartate aminotransferase (one participant [4%]). Three participants had serious treatment-emergent adverse events, none related to the study treatment: increased blood triglycerides, ovarian cyst, and renal colic (each in one participant [4%]). No treatment-related deaths were observed.Mitapivat represents a novel therapy that can reduce transfusion burden in some adults with pyruvate kinase deficiency receiving regular transfusions, and is the first disease-modifying agent approved in this disease.Agios Pharmaceuticals.

Paroxysmal nocturnal hemoglobinuria is a clonal hematopoietic stem cell disorder resulting in complement-mediated hemolysis. Eculizumab, a monoclonal antibody against complement protein C5, has been shown to reduce both intravascular hemolysis and risk for thrombosis, and thereby improve the quality of life in these patients. While the infection risk from Neisseria meningitidis due to terminal complement blockade can be mitigated with appropriate immunizations and prophylactic antibiotics, these patients remain vulnerable to infections from Neisseria gonorrhoeae. Physicians and families should be aware of disseminated and severe gonococcal infections in patients receiving complement blockade, especially in this era of emerging cephalosporin and azithromycin resistance.

Thrombocytosis is common in sickle cell disease and may contribute to vaso‐occlusion. Hydroxyurea treats extreme thrombocytosis. Acquired von Willebrand disease should be considered prior to aspirin therapy.

Red blood cell (RBC) transfusion therapy is a key component in the comprehensive management of patients with sickle cell disease (SCD). Consequently, most adult SCD patients will receive at least one, and many will receive more than a hundred RBC transfusions in their lifetime. SCD patients develop RBC alloantibodies much more frequently than non-SCD transfused patients, which often make the selection of compatible RBCs extremely difficult, in addition to placing patients at significantly higher risk of suffering from delayed hemolytic transfusion reactions (DHTRs). Similar to alloimunization, DHTRs are much more common in patients with SCD compared to other heavily transfused populations, and are particularly consequential due to their propensity to cause hyperhemolysis, a life-threatening phenomenon in which both transfused RBCs in addition to the patient's own sickle-erythrocytes are destroyed. In this review, we highlight the incidence and pathophysiology of DHTRs; illustrate common presentations, appropriate evaluations and outcomes of DHTRs in patients with SCD; and discuss strategies for preventing or reducing the likelihood of DHTRs from occurring.

Background Delayed hemolytic transfusion reactions (DHTRs) are serious complications of RBC transfusion that can occur in previously alloimmunized patients. Patients who require episodic transfusions during heightened inflammatory states, such as patients with sickle cell disease (SCD), are particularly prone to alloimmunization and developing DHTRs with hyperhemolysis. While efforts to mitigate these hemolytic episodes via immunosuppressive drugs can be employed, the relative efficacy of various treatment options remains incompletely understood. Case reports In this study, we explored five patients with SCD and multiple RBC alloantibodies who received various forms of immunosuppressive therapy in an attempt to prevent or treat severe DHTRs. Results The clinical course for these five patients provides insight into the difficulty of effectively treating and preventing DHTRs in patients with SCD with currently available immunosuppressive therapies. Conclusion Based on our experience, and the current literature, it is difficult to predict the potential impact of various immunosuppressive therapies when seeking to prevent or treat DHTRs. Future mechanistic studies are needed to identify the optimal treatment options for DHTRs in the presence or absence of distinct alloantibodies in patients with SCD.

Pyruvate kinase deficiency (PKD) is a rare, autosomal recessive red blood cell enzyme disorder, which leads to lifelong hemolytic anemia and associated complications from the disease and its management.An international, multicenter registry enrolled 124 individuals younger than 18 years old with molecularly confirmed PKD from 29 centers. Retrospective and prospective clinical data were collected.There was a wide range in the age at diagnosis from 0 to 16 years. Presentation in the newborn period ranged from asymptomatic to neonatal jaundice to fulminant presentations of fetal distress, myocardial depression, and/or liver failure. Children5 years old were significantly more likely to be transfused than children12 to18 years (53% vs. 14%, p = .0006), which correlated with the timing of splenectomy. Regular transfusions were most common in children with two severe PKLR variants. In regularly transfused children, the nadir hemoglobin goal varied considerably. Impact on quality of life was a common reason for treatment with regular blood transfusions and splenectomy. Splenectomy increased the hemoglobin and decreased transfusion burden in most children but was associated with infection or sepsis (12%) and thrombosis (1.3%) even during childhood. Complication rates were high, including iron overload (48%), perinatal complications (31%), and gallstones (20%).There is a high burden of disease in children with PKD, with wide practice variation in monitoring and treatment. Clinicians must recognize the spectrum of the manifestations of PKD for early diagnostic testing, close monitoring, and management to avoid serious complications in childhood.

PurposeT cell-Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis (T cell-EBV-HLH) is prevalent in East Asia and has poor prognosis. Understanding of this disease is limited and literature regarding prevalence in North America is scarce. Herein, we summarize our experience. MethodsA retrospective analysis of T cell-EBV-HLH patients admitted to Children's Healthcare of Atlanta (GA, USA) from 2010-2020 was conducted. Additional immune studies were completed in a subset of patients. ResultsWe report 15 patients (10 months-19 years of age) diagnosed with T cell-EBV-HLH. Nine patients were Hispanic and the majority without primary HLH (p-HLH) gene defects. Soluble interleukin-2 receptor levels in T cell-EBV-HLH were significantly higher than other forms of secondary-HLH but comparable to p-HLH, and it correlated with disease severity at presentation. Natural-Killer cell function was decreased in most patients despite a negative workup for p-HLH. Depending on disease severity, initial therapy included dexamethasone or dexamethasone and etoposide. Refractory patients were managed with blended regimens that included one or more of these therapies - combination chemotherapy, alemtuzumab, emapalumab and nivolumab. Rituximab did not appreciably decrease EBV viremia in most patients. Alemtuzumab resulted in inflammation flare in 2 of the 3 patients. Two patients underwent allogeneic hematopoietic cell transplantation, with disease relapse noted in one. At a median follow-up of 3 years, 10 of the 15 patients are alive.ConclusionT cell-EBV-HLH occurs in the US among the non-Asian population, especially in those who are Hispanic. The amplitude of T cell activation noted in T cell-EBV-HLH is comparable to p-HLH.

Congenital dyserythropoietic anemias (CDAs) are characterized by ineffective erythropoiesis and distinctive erythroblast abnormalities; the diagnosis is often missed or delayed due to significant phenotypic heterogeneity. We established the CDA Registry of North America (CDAR) to study the natural history of CDA and create a biorepository to investigate the pathobiology of this heterogeneous disease. Seven of 47 patients enrolled so far on CDAR have CDA-I due to biallelic CDAN1 mutations. They all presented with perinatal anemia and required transfusions during infancy. Anemia spontaneously improved during infancy in three patients; two became transfusion-independent rapidly after starting interferon-α(2); and two remain transfusion-dependent at last follow-up at ages 5 and 30 y.o. One of the transfusion-dependent patients underwent splenectomy at 11 y.o due to misdiagnosis and returned to medical attention at 27 y.o with severe hemolytic anemia and pulmonary hypertension. All patients developed iron overload even without transfusions; four were treated with chelation. Genetic testing allowed for more rapid and accurate diagnosis; the median age of confirmed diagnosis in our cohort was 3 y.o compared to 17.3 y.o historically. In conclusion, CDAR provides an organized research network for multidisciplinary clinical and research collaboration to conduct natural history and biologic studies in CDA.

Objectives Pyruvate kinase (PK) deficiency is caused by PKLR gene mutations, leading to defective red blood cell glycolysis and hemolytic anemia. Rates of comorbidities and complications by transfusion history and relative to the general population remain poorly quantified. Methods Data for patients aged ≥ 18 years with two confirmed PKLR mutations were obtained from the PK deficiency Natural History Study (NCT02053480). Frequencies of select conditions were compared with an age‐ and sex‐matched cohort from a general insured US population without PK deficiency. Results Compared with the matched population (n = 1220), patients with PK deficiency (n = 122) had significantly higher lifetime rates of osteoporosis, liver cirrhosis, and pulmonary hypertension; splenectomy and cholecystectomy rates were also significantly higher in the 8 years before the index date. Sixty‐five (53.3%) patients with PK deficiency were classified as regularly transfused, 30 (24.6%) as occasionally transfused, and 27 (22.1%) as never transfused. Regularly transfused patients were significantly more likely than never transfused patients to have had splenectomy, cholecystectomy, and/or thrombosis. Liver iron overload was reported in 62% of patients and occurred regardless of transfusion cohort. Conclusions Even never transfused patients with PK deficiency had higher rates of select comorbidities and complications than individuals without PK deficiency.

PURPOSE OF REVIEW: The purpose of this review is to summarize the role of complement in regulating the removal of a target alloantigen following an incompatible red blood cell (RBC) transfusion, the formation of alloantibodies following RBC alloantigen exposure, and the development of hyperhemolysis in patients with sickle cell anemia. RECENT FINDINGS: Recent studies demonstrate that complement can accelerate alloantibody-mediated removal of target alloantigens from the RBC surface following incompatible transfusion. Complement also influences alloantigen availability during developing alloimmune responses and serves as a unique mediator of CD4 T cell-independent alloantibody formation following RBC alloantigen exposure. Finally, alternative complement activation appears to play a key role in the development of acute hemolytic episodes in patients with sickle cell anemia, providing a potential druggable target to prevent acute complications in patients with this disease SUMMARY: Recent studies suggest that complement can regulate a wide variety of processes germane to hematology, from transfusion complications to baseline hemolysis in patients with sickle cell anemia. As the role of complement in various disease processes becomes more fully understood, the ability to leverage recently developed complement modulating drugs will only continue to enhance provider’s ability to favorable intervene on many hematological diseases.

Red blood cell (RBC) transfusions can result in alloimmunization toward RBC alloantigens that can increase the probability of complications following subsequent transfusion. An improved understanding of the immune mechanisms that underlie RBC alloimmunization is critical if future strategies capable of preventing or even reducing this process are to be realized. Using the HOD (hen egg lysozyme [HEL] and ovalbumin [OVA] fused with the human RBC antigen Duffy) model system, we aimed to identify initiating immune factors that may govern early anti-HOD alloantibody formation. Our findings demonstrate that HOD RBCs continuously localize to the marginal sinus following transfusion, where they colocalize with marginal zone (MZ) B cells. Depletion of MZ B cells inhibited immunoglobulin M (IgM) and IgG anti-HOD antibody formation, whereas CD4 T-cell depletion only prevented IgG anti-HOD antibody development. HOD-specific CD4 T cells displayed similar proliferation and activation following transfusion of HOD RBCs into wild-type or MZ B-cell–deficient recipients, suggesting that IgG formation is not dependent on MZ B-cell–mediated CD4 T-cell activation. Moreover, depletion of follicular B cells failed to substantially impact the anti-HOD antibody response, and no increase in antigen-specific germinal center B cells was detected following HOD RBC transfusion, suggesting that antibody formation is not dependent on the splenic follicle. Despite this, anti-HOD antibodies persisted for several months following HOD RBC transfusion. Overall, these data suggest that MZ B cells can initiate and then contribute to RBC alloantibody formation, highlighting a unique immune pathway that can be engaged following RBC transfusion.

In humans, red blood cells (RBCs) make up a quarter of all cells in the body. Around two billion new RBCs are produced daily. Each RBC survives for about 120 days in the circulation (Shemin and Rittenberg, J Biol Chem. 166:627–636, 1946). Hemolysis is therefore defined as reduced survival of circulating RBCs due to premature destruction. Under steady state conditions, the rate of RBC production equals the rate of RBC loss. As a compensatory mechanism for hemolysis, increased erythropoiesis occurs in the bone marrow, with resultant increase in the reticulocyte count. Hemolytic anemia manifests when this compensatory mechanism cannot keep up with the increased destruction of erythrocytes. Hemolysis can result from intrinsic red cell abnormalities, extrinsic factors, or both. This chapter will discuss extrinsic or extracorpuscular causes of hemolytic anemia, which includes both immune and nonimmune-mediated mechanisms. RBC disorders secondary to intrinsic membrane protein defects, enzyme dysfunction, or hemoglobinopathy are covered in separate chapters. This chapter consists of the pathophysiology, clinical manifestations, and diagnosis and, finally, discusses treatment options for extrinsic causes of hemolytic anemia.