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eJhaem

Published by Wiley and British Society for Haematology

Online ISSN: 2688-6146

Disciplines: Hematology

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26 reads in the past 30 days

What is the origin of the normal ranges of blood cell counts? An evolutionary perspective

December 2024

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66 Reads

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Laetitia Largeaud

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Background The normal values of the complete blood count are part of the foundational medical knowledge that is seldom questioned due to their well‐established nature. These normal values are critical for optimal physiological function while minimizing the harmful consequences of an excessive number of blood cells. Thus, they represent an evolutionary trade‐off likely shaped by natural selection if they significantly influence individual fitness and exhibit heritability. Methods On the basis of the analysis of normal blood count values of 94 mammalian species, we discovered that certain parameters are strongly associated with diet, habitat, and lifespan. Results Carnivorous mammals had higher hemoglobin levels than vegetarians, and aquatic mammals displayed red blood cell parameters probably selected to enhance for the diving capacities. Body weight influenced platelet counts and innate immune cells, with lighter animals having higher platelet counts and larger animals showing elevated monocytes and neutrophils. Conclusions By treating the history of life as an experiment, we have discerned some evolutionary constraints likely contributing to the selection for optimal trade‐offs in blood cell count.

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21 reads in the past 30 days

The association of donor and recipient sex on sepsis rates and hemoglobin increment among critically ill patients receiving red cell transfusions in a retrospective study

January 2025

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22 Reads

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Kayla J. Lucier

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[...]

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Background Existing research presents conflicting results on the influence of blood donor sex on hemoglobin (Hb) change and transfusion‐associated infection and mortality in transfusion recipients. Aim This retrospective study explored the association between donor and recipient sex on hospital‐onset sepsis (HO‐sepsis) and Hb changes in critically ill patients receiving red blood cell (RBC) transfusions. Methods Data from 2010–2020 were extracted from an academic hospital's clinical database and a blood supplier's donor database. HO‐sepsis was determined based on the International Classification of Diseases and Related Health Problems 10th Revision (ICD‐10) diagnostic codes without requiring a microbiology test within the first 48 h of admission. Hb increments were determined by comparing the last Hb result in the 24‐h period prior to RBC unit issue and the first Hb result within 4–24 h after RBC unit issued for transfusion. Results 25,585 critically ill patients received one or more RBC transfusions; 3,410 were included in the HO‐sepsis and 3,487 in the Hb increment analysis. There was no significant differences in the HO‐sepsis rate among the four groups, but female recipients were more prone to HO‐sepsis than males (OR 1.48, p = 0.04). Multivariate analysis found that the number of RBC unit transfused ( p = 0.001) and recipient age ( p = 0.03), but not recipient sex ( p = 0.63), were significant contributors to HO‐sepsis. Male blood was associated with higher Hb than female blood in female recipients ( p = 0.007), but not in male recipients ( p = 0.75). Variables such as donor Hb levels and recipient Hb level influenced Hb increments. Conclusion Blood donor sex was not associated with HO‐sepsis in critically ill patients receiving RBC transfusion. Male to female transfusions were associated with a higher Hb increment in recipients. Further exploration of the impact of sex mis‐matched transfusion on recipient outcomes is warranted.

Aims and scope


eJHaem is a Gold Open Access (OA), sound science journal of the British Society for Haematology and Wiley publishing haematology practice and research applicable to a worldwide readership.
We offer rapid publication and fast decision times with an average of 7 days to first decision. By publishing OA, your research will be free to read and share, with author copyright retention. Now accepted into PubMed, we offer greater reach to your OA research.
We accept direct submissions as well as content that is transferred from top quartile journals the British Journal of Haematology and the American Journal of Hematology.

Recent articles


Elimination of residual adult T‐cell leukaemia clones by Tax‐targeted dendritic cell vaccine
  • Article
  • Full-text available

February 2025

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3 Reads

Background A pilot clinical study of a Tax peptide‐pulsed dendritic cell (DC) vaccine for adult T‐cell leukaemia/lymphoma (ATL) indicated favourable clinical outcomes. Methods We investigated its anti‐tumour effect by T cell receptor (TCR) repertoire analysis in samples from an enrolled ATL patient who achieved a 10‐year complete remission after DC vaccination. Results In this patient, the dominant residual ATL clones that had persisted following previous treatment entirely disappeared within 3 years after DC vaccination. Additionally, the DC vaccine restored TCR repertoire diversity of normal T cells and newly induced functional Tax‐specific CD8 ⁺ T cell clones. Conclusions The recovery of normal T cell immunity mediated by the DC vaccine may contribute to this long‐lasting remission.


Longitudinal assessment of cerebral infarcts and small vessel disease using magnetic resonance imaging in antiphospholipid syndrome: A single‐centre retrospective study

February 2025

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1 Read

Introduction Stroke is the most frequent arterial thrombosis in antiphospholipid syndrome (APS) with high rates of recurrence. Methods and patients A retrospective, single‐centre 10‐year review of patients with APS having sequential cerebral magnetic resonance imaging (MRI) was performed to describe ischaemic features in APS and associated disease risk factors and progression over time. Results A total of 120 patients and 307 scans were included with 67% of patients receiving vitamin K antagonists (VKA). Note that 65% of patients had baseline ischaemic features with white matter hyperintensities (WMH), as a feature of small vessel disease (SVD), seen in 79% of abnormal scans. Fifteen percent of patients had progressive ischaemic changes with 83% demonstrating progressive WMH and 33% new infarcts (predominantly lacunar) on sequential scans. Progression‐free survival for progressive ischaemia was 88% at 5 years. Multivariate analysis showed longer follow‐up was a risk for developing progressive ischaemia (odds ratio [OR] 1.43, 95% confidence interval [CI] 1.13–1.86, p = 0.005). Hypertension (56% vs. 30%, p = 0.04) and ischaemic heart disease (22% vs. 6%, p = 0.04) were more prevalent with progressive ischaemia. There was no difference in progression or bleeding events according to VKA therapeutic intensity. Discussion These results show SVD is a common feature of APS using MRI with progressive changes despite anticoagulation. Traditional risk factors for cerebrovascular disease were associated with progression.


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The prognostic value of POD24 in relapsed/refractory follicular lymphoma—A SCHOLAR‐5 analysis

February 2025

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5 Reads

Introduction Follicular lymphoma (FL) has a heterogeneous prognosis. Progression within 24 months of starting front‐line therapy (POD24) is prognostic of overall survival (OS). Despite its prognostic value in early lines, the role of POD24 in relapsed/refractory (R/R) patients initiating later lines of therapy (LoTs) is unknown. Methods We analyzed the SCHOLAR‐5 real‐world cohort to investigate whether POD24 is prognostic in patients with R/R FL initiating ≥3rd LoT. Results Among the 128 SCHOLAR‐5 patients, 34 patients experienced POD24. POD24 patients received their ≥3 LoT after a shorter time compared with non‐POD24 patients (median 42.0 months [range: 8.8‒17.8] vs. 109.9 months [range: 29.6‒310.2]). Using a time‐dependent multivariate Cox model, POD24 was predictive of shorter OS from initiation of ≥3rd LoT with a hazard ratio (HR) of 2.44 (95% confidence interval [CI]: 1.20‒4.96). For progression‐free survival, using a multivariate repeated‐measures Cox model, the effect was similar but not statistically significant (HR: 1.45; 95% CI: 0.94‒2.11). Conclusion This study demonstrates that among patients with R/R FL initiating a ≥3rd LoT, POD24 patients reach these LoTs sooner after diagnosis and POD24 remains prognostic of subsequent OS. This suggests that POD24 status can inform clinical decision making in this population.


Patient characteristics.
Real‐World Data on Lymphoma in Adolescents and Young Adults (AYA)—Report From the Lymphoma and Related Diseases Registry (LaRDR)

January 2025

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9 Reads

Introduction Lymphoma is a common malignancy among adolescents and young adults (AYAs) which is generally defined as 15–39 years. Relative to other age groups, lymphoma in AYAs remains understudied with heterogeneous treatment options. Methods We performed a retrospective review of patients aged 18–60 years in the Australasian Lymphoma and Related Diseases Registry (LaRDR) with new diagnoses of the common subtypes of lymphoma in AYAs between January 2016 and April 2023. The subtypes are classic Hodgkin lymphoma (cHL), diffuse large B‐cell lymphoma (DLBCL), primary mediastinal B‐cell lymphoma (PMBCL) and Burkitt lymphoma (BL). Patient demographics, disease characteristics, treatment and outcome data were collected, and comparisons were made between AYAs (18–39 years) and older adults (OAs) (aged 40–60). Results AYAs had higher rates of cHL and PMBCL whereas OAs presented more frequently with DLBCL. AYAs with cHL and PMBCL had higher rates of early‐stage and low‐risk disease than OAs. In contrast, both AYAs and OAs were more likely to present with advanced‐stage DLBCL and BL. AYAs with cHL were more likely to be treated with BEACOPP as compared to OAs who were more commonly treated with ABVD. There was no significant difference in treatment regimens for DLBCL, PMBCL or BL between AYAs and OAs. AYAs with cHL had better overall survival (OS) compared to OAs; specifically, cHL AYAs had better OS and DLBCL AYAs had better progression‐free survival (PFS) and OS compared to OAs. Conclusion The study provides valuable data on patient and disease characteristics, treatments used and outcomes in AYA compared to OA aged 40–60 years. Registry data such as from LaRDR can help improve treatment standardisation and AYA patient outcomes. Trial Registration The authors have confirmed clinical trial registration is not needed for this submission


Abbreviations: CR, Complete remission/Complete remission with incomplete hematologic recovery; DLI, donor lymphocyte infusions; MRD, minimal residual disease; SCT, stem cell transplantation.
Relapsed Philadelphia chromosome‐positive B‐cell acute lymphoblastic leukaemia responds well to a combination of modified hyper‐CVAD, blinatumomab and tyrosine kinase inhibitor

January 2025

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15 Reads

Introduction Adults with relapsed or refractory Philadelphia chromosome‐positive B‐cell precursor acute lymphoblastic leukaemia (R/R Ph+ BCP‐ALL) have a dismal outcome. Blinatumomab as a single agent has shown activity in R/R Ph‐ BCP‐ALL, and second or third‐generation tyrosine kinase inhibitors (TKIs) can produce high remission rates in Ph+ leukaemias. We aimed to assess the activity of blinatumomab and TKI in combination with intensive chemotherapy in the relapsed or refractory setting. Methods Ten patients with R/R Ph+ BCP‐ALL were treated with the combination of a modified hyper‐CVAD (mHCVAD) regimen (cyclophosphamide, vincristine, adriamycin, dexamethasone), blinatumomab and TKI (mainly ponatinib). Results Complete remission (CR) was achieved in 10/10 patients, with deep molecular responses, and 6/10 were alive in remission after a median follow‐up of 19.4 months. Three major cardiovascular events were noted. Conclusion These preliminary data, suggest that the mHCVAD‐blinatumomab‐TKI (mainly ponatinib) regimen may achieve a high rate of CR with undetectable measurable residual disease in adults with R/R Ph+ BCP‐ALL and could be proposed to such patients, but cardiovascular or infectious complications should be warning, especially in older or frail patients.


Angioimmunoblastic T‐cell lymphoma: Characterization of clonal T and B cells and a patient‐derived xenograft study of coexisting T‐ and B‐cell proliferation

January 2025

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3 Reads

Introduction Angioimmunoblastic T‐cell lymphoma (AITL) is a rare and aggressive lymphoma with a poor prognosis. AITL is associated with Epstein–Barr virus (EBV)‐positive B cells in most cases, suggesting a possible role for the virus in the pathobiology of AITL. Cell lines from AITL patients do not exist and models of human AITL are needed. We aim to establish such a model and use it for preclinical therapeutic evaluation. Methods Primary lymph node tissue from an AITL patient was used for tumor cell isolation and injection to NSG mice. The established patient‐derived xenograft (PDX) model was characterized by immunophenotyping, whole‐exome sequencing (WES), and T/B‐cell receptor gene rearrangement studies. In vivo AITL PDX trials were performed with elotuzumab, romidepsin, and rituximab. Results An AITL PDX mouse model that includes a coexisting EBV+ B‐cell proliferation was established. We confirmed clonal identity of the engrafted T cells with the primary T‐lymphoma cells. WES on DNA from xenografted sorted T and B cells identified eight and three mutations previously reported in the COSMIC database, respectively. Primary tumor cells could be passaged serially in NSG mice with an increasing percentage of monoclonal B cells that mimic the human condition in which the clonal B‐cell component in some cases may mask an underling T‐cell lymphoma. In this PDX mouse study, single agent elotuzumab or rituximab significantly improved mice survival. Survival was further improved when elotuzumab or romidepsin was combined with rituximab. Conclusion To our knowledge, this is the first molecular characterization of AITL model coexisting with associated EBV+ B cells, and use of such a PDX model for therapeutic evaluation of agents targeting both malignant T cells and B cells simultaneously.


FIGURE 1 Absolute neutrophil count (ANC) trend in relation to intravenous immunoglobulin (IVIG) administration. (A) ANC trend over a 6-month period, showing pre-and post-IVIG administration neutrophil counts for six cycles of IVIG administration (demarcated by alternating shading of blue and white). ANC drawn before each IVIG administration is noted in red. The neutrophil count drops each cycle on the day after IVIG administration (purple dot), except for Cycle 3 when the patient experienced a coronavirus disease 2019 (COVID-19) infection with an appropriate neutrophil response (denoted by a yellow dot on day 42 of the graph). The blue dots on days 8 and 15 represent the ANC from more frequent weekly draws during Cycle 1, and this cycle is further expanded in (B). The median ANC pre-IVIG is 1.1×103/µL. The median ANC post-IVIG is 0.3×103/µL. (B) An expanded graph showing the ANC trend over the 21 days after IVIG administration (this corresponds to days 1-21 of A). The pre-IVIG ANC is 0.8×103/µL (day 0), dropping to 0.4×103/µL on day 1, with a nadir at 0.3×103/µL on day 8, rising back to 0.8×103/µL by day 15.
Chronic Severe Neutropenia Associated With Intravenous Immunoglobulin for Multifocal Motor Neuropathy

January 2025

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10 Reads

Intravenous immunoglobulin (IVIG) is an immunomodulatory therapy derived from pooled donor immunoglobulins and used for treatment of various autoimmune conditions. Here we report the diagnosis and management of IVIG‐induced chronic severe neutropenia with absolute neutrophil count <0.5×10 ³ /µL in a patient with multifocal motor neuropathy. Serial blood count showed a cyclical pattern of neutropenia: worsening 24–48 h post‐IVIG, then gradually improving before the next infusion. IVIG‐induced neutropenia is rare, with previous reports of predominantly mild transient neutropenia. Our case describes chronic severe neutropenia that developed years after starting IVIG. We summarize available evidence and management strategies for IVIG‐associated neutropenia.


FIGURE 1 X-ray of multiple lytic lesions in the skull in AP view.
FIGURE 2 X-ray of multiple lytic lesions in the skull in Lateral view.
Shows hypercalcemia and hyperphosphatemia.
Shows Proteinuria.
A Complex Presentation of Multiple Myeloma With Renal Complications in a Young Female: Diagnostic Challenges and Treatment Approach

A previously healthy 30‐year‐old woman experienced worsening back pain, fatigue, weakness, loss of appetite, and facial puffiness. After 18 months of these symptoms, she was diagnosed with multiple myeloma, which was also damaging her kidneys. The treatment involved a combination of medications and blood transfusions, leading to improved kidney function. Despite the challenges of managing her condition as a mother of young children, she remains hopeful. This case emphasizes the need for awareness of multiple myeloma in younger patients and the importance of early diagnosis and multidisciplinary care for managing this chronic illness. Trial Registration : The authors have confirmed clinical trial registration is not needed for this submission


A novel TERT variant associated with a telomere biology disorder and challenges in variant classification

January 2025

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16 Reads

Telomere biology disorders (TBDs) are inherited conditions associated with multisystem manifestations. We describe clinical and functional characterisation of a novel TERT variant. Whole‐genome sequencing was performed along with single telomere length analysis ( STELA ). Telomerase activity and processivity were assessed. A novel TERT variant (K710R) was detected in a patient with classic TBD features showing reduced telomerase activity and processivity. Despite clinical and functional evidence, the variant was classified as a variant of uncertain significance. We have described a novel TERT variant and highlighted the need for further refinement of variant classification specific for TBDs.


Defibrotide for the Treatment of Veno‐Occlusive Disease/Sinusoidal Obstruction Syndrome in Paediatric Patients Who Did Not Receive Haematopoietic Stem Cell Transplantation: Case Reports of Patients From a German Academic Hospital

January 2025

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5 Reads

Introduction Veno‐occlusive disease/sinusoidal obstruction syndrome (VOD/SOS) is a potentially life‐threatening condition characterised by obstruction of the small veins of the liver. Although typically associated with haematopoietic stem cell transplantation, VOD/SOS may also occur following intensive multimodal chemotherapy regimens. In children, symptoms of VOD/SOS are refractory thrombocytopaenia, weight gain, hepatomegaly, ascites and fluid retention, hyperbilirubinaemia and sometimes right upper quadrant pain. Methods Here, we present a case series of six paediatric patients with acute lymphoblastic leukaemia who developed severe VOD/SOS while receiving standard AIEOP‐BFM ALL protocol treatment. Results/Conclusions All patients responded promptly to defibrotide treatment and exhibited favourable clinical outcomes. Trial Registration The authors have confirmed clinical trial registration is not needed for this submission


Combined Proteasome and Autophagy Inhibition in Relapsed/Refractory Multiple Myeloma—A Phase I Trial of Hydroxychloroquine, Carfilzomib, and Dexamethasone

January 2025

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6 Reads

Multiple myeloma is characterized by malignant cells which produce high amounts of monoclonal immunoglobulin. Myeloma cells are, therefore, dependent on effective protein degradation. Proteasomal protein degradation is targeted by proteasome inhibitors in routine care. Autophagic protein degradation is currently not targeted in myeloma treatment. This Phase I trial showed that the combination of the proteasome inhibitor carfilzomib and the autophagy inhibitor hydroxychloroquine was well tolerated in patients with relapsed/refractory multiple myeloma. Adverse events were mostly Grades 1 and 2. An overall response rate of 44% indicates a meaningful clinical efficacy of this combination. Trial Registration : The study was registered at clinicaltrials.gov # NCT04163107.



HLA‐matched related peripheral blood stem cell and bone marrow transplantation with RIC regimens yield comparable outcomes for adult AML

January 2025

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9 Reads

Introduction Understanding differences in clinical outcomes between PBSCT and BMT is important, and this study compared outcomes of HLA‐matched related PBSCT and BMT using reduced‐intensity conditioning (RIC) in adult acute myeloid leukemia (AML) patients. Methods Data from 402 patients who underwent either PBSCT ( n = 294) or BMT ( n = 108) between 2000 and 2022 were analyzed using the Japanese nationwide registry database. The primary endpoint was overall survival (OS), and secondary endpoints included disease‐free survival (DFS), non‐relapse mortality (NRM), and GVHD. Results Results indicated no significant difference in 3‐year OS (44.6% for PBSCT vs. 46.9% for BMT, HR 1.173, P = 0.299) and DFS (42.1% vs. 41.8%, HR 1.073, P = 0.639). PBSCT was more beneficial for avoiding relapse (20.3% vs. 12.4%, HR, 0.715, P = 0.059). However, PBSCT was associated with higher NRM (20.3% vs. 12.4%, HR 1.801, P = 0.025) due to more frequent, chronic GVHD (HR 1.889, P = 0.035). Subgroup analysis did not reveal specific patient groups that benefited more from PBSCT or BMT. Incidence of extensive chronic GVHD and NRM has improved in PBSCT recipients in recent years (2014–2022). Conclusions We conclude that related PBSCT with RIC regimens offers comparable prognosis to BMT for adult AML patients. Further optimization of prophylactic strategies for chronic GVHD is required to improve outcomes after PBSCT.


Erythrocytapheresis as a strategy to manage anemia and iron overload in nondeletional hemoglobin H disease

Hemoglobin H (HbH) disease is associated with anemia, ineffective erythropoiesis, and iron overload. We report a case of a patient with HbH/Hb Constant Spring disease, who was maintained on chronic transfusions as an adult due to symptomatic anemia. Over time, he developed iron overload and was started on chelation therapy but did not have an adequate response to chelation. We then added erythrocytapheresis to chelation therapy and were able to successfully decrease his iron burden while managing his anemia. Therapeutic erythrocytapheresis may be an effective treatment strategy for iron overload in HbH disease that is refractory to chelation.






The association of donor and recipient sex on sepsis rates and hemoglobin increment among critically ill patients receiving red cell transfusions in a retrospective study

January 2025

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22 Reads

Background Existing research presents conflicting results on the influence of blood donor sex on hemoglobin (Hb) change and transfusion‐associated infection and mortality in transfusion recipients. Aim This retrospective study explored the association between donor and recipient sex on hospital‐onset sepsis (HO‐sepsis) and Hb changes in critically ill patients receiving red blood cell (RBC) transfusions. Methods Data from 2010–2020 were extracted from an academic hospital's clinical database and a blood supplier's donor database. HO‐sepsis was determined based on the International Classification of Diseases and Related Health Problems 10th Revision (ICD‐10) diagnostic codes without requiring a microbiology test within the first 48 h of admission. Hb increments were determined by comparing the last Hb result in the 24‐h period prior to RBC unit issue and the first Hb result within 4–24 h after RBC unit issued for transfusion. Results 25,585 critically ill patients received one or more RBC transfusions; 3,410 were included in the HO‐sepsis and 3,487 in the Hb increment analysis. There was no significant differences in the HO‐sepsis rate among the four groups, but female recipients were more prone to HO‐sepsis than males (OR 1.48, p = 0.04). Multivariate analysis found that the number of RBC unit transfused ( p = 0.001) and recipient age ( p = 0.03), but not recipient sex ( p = 0.63), were significant contributors to HO‐sepsis. Male blood was associated with higher Hb than female blood in female recipients ( p = 0.007), but not in male recipients ( p = 0.75). Variables such as donor Hb levels and recipient Hb level influenced Hb increments. Conclusion Blood donor sex was not associated with HO‐sepsis in critically ill patients receiving RBC transfusion. Male to female transfusions were associated with a higher Hb increment in recipients. Further exploration of the impact of sex mis‐matched transfusion on recipient outcomes is warranted.




Uptake of the first to fifth doses of coronavirus disease 2019 vaccine in individuals with chronic lymphocytic leukaemia: A nationwide cohort study in Sweden

January 2025

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3 Reads

Objectives Patients with chronic lymphocytic leukaemia (CLL) have an increased risk of severe coronavirus disease 2019 (COVID‐19) as well as impaired responses to COVID‐19 vaccination, which may be overcome by repeated booster vaccinations. Our objective was to explore the uptake of the COVID‐19 vaccine in this population since records of this are scarce. Methods In this nationwide cohort study, we used multiple population‐based health and sociodemographic registries to study COVID‐19 vaccine uptake in individuals with CLL in Sweden, from 27 December 2020 to 28 February 2023. Results A total of 6304 individuals were included. The cumulative incidence (95% confidence interval) at the end of the study period was 95%, 94%, 88%, 78% and 56% for the first, second, third, fourth and fifth doses, respectively. The uptake was significantly higher compared with the age‐standardized nationwide uptake. However, there were large disparities, especially for the fourth and fifth doses, across different age groups, birth regions, and income quartiles. These differences were especially pronounced in intersectional analyses, where individuals born abroad in the lowest income quartile had a vaccine uptake of only 49% and 24% for the fourth and fifth doses, respectively. Conclusions Even though uptake was generally high in individuals with CLL, it seems to be declining from dose three and onwards, and there are significant sociodemographic disparities in vaccine uptake.



CD58 expression does not impact response to inotuzumab ozogamicin in patients with B-cell acute lymphoblastic leukemia

December 2024

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8 Reads

Background CD58 loss has been described as a mechanism of resistance to blinatumomab and chimeric antigen receptor T‐cell therapy, functioning as a modulator of response to T‐cell activation. Methods Using flow cytometry, we evaluated the impact of CD58 mean fluorescence intensity (MFI) on the probability of achieving measurable residual disease (MRD) negativity in patients with B‐cell acute lymphoblastic leukemia treated with inotuzumab ozogamicin (InO). Results The odds ratio of achieving MRD negativity was 1.03 for every 1000 unit increase in CD58 MFI. Conclusion Our results suggest that MRD negativity rates after InO are high, regardless of the intensity of CD58 expression.


What is the origin of the normal ranges of blood cell counts? An evolutionary perspective

December 2024

·

66 Reads

Background The normal values of the complete blood count are part of the foundational medical knowledge that is seldom questioned due to their well‐established nature. These normal values are critical for optimal physiological function while minimizing the harmful consequences of an excessive number of blood cells. Thus, they represent an evolutionary trade‐off likely shaped by natural selection if they significantly influence individual fitness and exhibit heritability. Methods On the basis of the analysis of normal blood count values of 94 mammalian species, we discovered that certain parameters are strongly associated with diet, habitat, and lifespan. Results Carnivorous mammals had higher hemoglobin levels than vegetarians, and aquatic mammals displayed red blood cell parameters probably selected to enhance for the diving capacities. Body weight influenced platelet counts and innate immune cells, with lighter animals having higher platelet counts and larger animals showing elevated monocytes and neutrophils. Conclusions By treating the history of life as an experiment, we have discerned some evolutionary constraints likely contributing to the selection for optimal trade‐offs in blood cell count.


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