Publications by authors named "John G Kelton"

70 Publications

Platelet-activating immune complexes identified in critically ill COVID-19 patients suspected of heparin-induced thrombocytopenia.

J Thromb Haemost 2021 Feb 27. Epub 2021 Feb 27.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada.

Background: Thrombocytopenia and thrombosis are prominent in coronavirus disease 2019 (COVID-19), particularly among critically ill patients; however, the mechanism is unclear. Such critically ill COVID-19 patients may be suspected of heparin-induced thrombocytopenia (HIT), given similar clinical features.

Objectives: We investigated the presence of platelet-activating anti-platelet-factor 4 (PF4)/heparin antibodies in critically ill COVID-19 patients suspected of HIT.

Patients/methods: We tested 10 critically ill COVID-19 patients suspected of HIT for anti-PF4/heparin antibodies and functional platelet activation in the serotonin release assay (SRA). Anti-human CD32 antibody (IV.3) was added to the SRA to confirm FcγRIIA involvement. Additionally, SARS-CoV-2 antibodies were measured using an in-house ELISA. Finally, von Willebrand factor (VWF) antigen and activity were measured along with A Disintegrin And Metalloprotease with ThromboSpondin-13 Domain (ADAMTS13) activity and the presence of anti-ADAMTS13 antibodies.

Results: Heparin-induced thrombocytopenia was excluded in all samples based on anti-PF4/heparin antibody and SRA results. Notably, six COVID-19 patients demonstrated platelet activation by the SRA that was inhibited by FcγRIIA receptor blockade, confirming an immune complex (IC)-mediated reaction. Platelet activation was independent of heparin but inhibited by both therapeutic and high dose heparin. All six samples were positive for antibodies targeting the receptor binding domain (RBD) or the spike protein of the SARS-CoV-2 virus. These samples also featured significantly increased VWF antigen and activity, which was not statistically different from the four COVID-19 samples without platelet activation. ADAMTS13 activity was not severely reduced, and ADAMTS13 inhibitors were not present, thus ruling out a primary thrombotic microangiopathy.

Conclusions: Our study identifies platelet-activating ICs as a novel mechanism that contributes to critically ill COVID-19.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/jth.15283DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8014456PMC
February 2021

A comparative study of platelet factor 4-enhanced platelet activation assays for the diagnosis of heparin-induced thrombocytopenia.

J Thromb Haemost 2021 Apr 19;19(4):1096-1102. Epub 2021 Feb 19.

Department of Medicine, Michael G. DeGroote School of Medicine, Hamilton, ON, Canada.

Background: Functional platelet activation assays, such as the serotonin release assay (SRA), are the gold standard for the diagnosis of heparin-induced thrombocytopenia (HIT). Recently, platelet activation assays using added platelet factor 4 (PF4) have been described and suggest improved sensitivity. Direct comparisons of these assays have not been performed.

Objective: We compare the performance characteristics of three PF4-enhanced platelet activation assays, the PF4/heparin-SRA (PF4/hep-SRA), the PF4-SRA, and the P-selectin expression assay (PEA), at a single reference laboratory.

Methods: Serum samples from two cohorts of patients were used. The referral cohort (n = 84) included samples that had previously undergone routine diagnostic testing for HIT and tested positive or negative using the SRA. The clinical cohort (n = 101) consisted of samples from patients with clinically confirmed HIT whose serum contained platelet-activating antibodies. We simultaneously tested all samples in PF4-enhanced SRA-based assays (PF4/hep-SRA, PF4-SRA) and the flow cytometry-based PEA.

Results: In the referral cohort, the three PF4-enhanced assays identified all samples that were previously determined to be positive in the SRA. However, specificity of the PF4/hep-SRA was 96.6%, the PF4-SRA was 84.7%, and the PEA was 67.8%. In the clinical cohort of samples, all SRA-based assays displayed high performance characteristics (>92.1% sensitivity, >98.4% specificity). Sensitivity and specificity of the PEA was the lowest, 65.8% and 63.5%, respectively; but improved to 92.1% and 96.8% using preselected platelet donors.

Conclusions: All PF4-enhanced assays demonstrated good performance characteristics when platelet donors were preselected. Further comparisons across multiple laboratories should be conducted for consensus on optimal HIT diagnostic testing.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/jth.15233DOI Listing
April 2021

Perioperative oral eltrombopag versus intravenous immunoglobulin in patients with immune thrombocytopenia: a non-inferiority, multicentre, randomised trial.

Lancet Haematol 2020 Sep;7(9):e640-e648

Michael G DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada; McMaster Centre for Transfusion Research, Department of Medicine, McMaster University, Hamilton, ON, Canada; Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada.

Background: Patients with immune thrombocytopenia are at risk of bleeding during surgery, and intravenous immunoglobulin is commonly used to increase the platelet count. We aimed to establish whether perioperative eltrombopag was non-inferior to intravenous immunoglobulin.

Methods: We did a randomised, open-label trial in eight academic hospitals in Canada. Patients were aged at least 18 years, with primary or secondary immune thrombocytopenia and platelet counts less than 100 × 10 cells per L before major surgery or less than 50 × 10 cells per L before minor surgery. Previous intravenous immunoglobulin within 2 weeks or thrombopoietin receptor agonists within 4 weeks before randomisation were not permitted. Patients were randomly assigned to receive oral daily eltrombopag 50 mg from 21 days preoperatively to postoperative day 7 or intravenous immunoglobulin 1 g/kg or 2 g/kg 7 days before surgery. Eltrombopag dose adjustments were allowed weekly based on platelet counts. The randomisation sequence was generated by a computerised random number generator, concealed and stratified by centre and surgery type (major or minor). The central study statistician was masked to treatment allocation. The primary outcome was achievement of perioperative platelet count targets (90 × 10 cells per L before major surgery or 45 × 10 cells per L before minor surgery) without rescue treatment. We did intention-to-treat and per-protocol analyses using an absolute non-inferiority margin of -10%. This trial is registered with ClinicalTrials.gov, NCT01621204.

Findings: Between June 5, 2013, and March 7, 2019, 92 patients with immune thrombocytopenia were screened, of whom 74 (80%) were randomly assigned: 38 to eltrombopag and 36 to intravenous immunoglobulin. Median follow-up was 50 days (IQR 49-55). By intention-to-treat analysis, perioperative platelet targets were achieved for 30 (79%) of 38 patients assigned to eltrombopag and 22 (61%) of 36 patients assigned to intravenous immunoglobulin (absolute risk difference 17·8%, one-sided lower limit of the 95% CI 0·4%; p=0·005). In the per-protocol analysis, perioperative platelet targets were achieved for 29 (78%) of 37 patients in the eltrombopag group and 20 (63%) of 32 in the intravenous immunoglobulin group (absolute risk difference 15·9%, one-sided lower limit of the 95% CI -2·1%; p=0·009). Two serious adverse events occurred in the eltrombopag group: one treatment-related pulmonary embolism and one vertigo. Five serious adverse events occurred in the intravenous immunoglobulin group (atrial fibrillation, pancreatitis, vulvar pain, chest tube malfunction and conversion to open splenectomy); all were related to complications of surgery. No treatment-related deaths occurred.

Interpretation: Eltrombopag is an effective alternative to intravenous immunoglobulin for perioperative treatment of immune thrombocytopenia. However, treatment with eltrombopag might increase risk of thrombosis. The decision to choose one treatment over the other will depend on patient preference, resource limitations, cost, and individual risk profiles.

Funding: GlaxoSmithKline and Novartis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/S2352-3026(20)30227-1DOI Listing
September 2020

The role of fluid-phase immune complexes in the pathogenesis of heparin-induced thrombocytopenia.

Thromb Res 2020 10 6;194:135-141. Epub 2020 Jun 6.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada; McMaster Centre for Transfusion Research, Hamilton, Ontario, Canada. Electronic address:

Immune complexes assemble on the platelet surface and cause Fc-mediated platelet activation in heparin-induced thrombocytopenia (HIT); however, it is not known if fluid-phase immune complexes contribute to HIT. The objective of this study was to understand the role of fluid-phase immune complexes in platelet activation and HIT. Binding of wild-type and 15 platelet factor 4 (PF4) mutants to platelets was measured using flow cytometry. Platelet activation was measured using the PF4-dependent C-serotonin release assay (PF4-SRA) with KKO and a HIT-patient plasma in the presence of wild-type or PF4 mutants. To activate platelets, we found that a minimal level of wild-type PF4 is required to bind the platelet surface in the presence of KKO (2.67 relative MFI) or HIT-patient plasma (1.71 relative MFI). Only a subset of PF4 mutants was able to support platelet activation, despite having lower surface binding than the minimum binding required of wild-type PF4 (9 mutants with KKO and 2 mutants with HIT-patient plasma). Using individual PF4 mutants, we identified that HIT immune complexes can be formed in fluid-phase and induce platelet activation. Further studies are required to investigate the role of fluid-phase HIT immune complexes in the development of thrombocytopenia and thrombosis associated with clinical HIT.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.thromres.2020.06.012DOI Listing
October 2020

Platelet autoantibodies in the bone marrow of patients with immune thrombocytopenia.

Blood Adv 2020 07;4(13):2962-2966

Department of Medicine, Michael G. DeGroot School of Medicine and.

Autoantibodies cause platelet destruction in patients with immune thrombocytopenia (ITP); yet only 50% to 60% of patients have detectable platelet autoantibodies in peripheral blood. We hypothesized that in some ITP patients, platelet autoantibodies are sequestered in the bone marrow where pathological immune reactions target megakaryocytes or newly formed platelets. In this study, we modified the platelet glycoprotein-specific assay to test bone marrow aspiration samples for free platelet autoantibodies or antibodies bound to bone marrow cells in aspirate fluid from patients with ITP (n = 18), patients with nonimmune thrombocytopenia (n = 3), and healthy donors (n = 6). We found that 10 (56%) of 18 patients with ITP had autoantibodies in the bone marrow, including 5 (50%) of 10 with autoantibodies in bone marrow only, and 5 (50%) of 10 with autoantibodies in bone marrow and peripheral blood. In comparison, 6 (33%) of 18 ITP patients had autoantibodies in peripheral blood, most of whom (5 [83%] of 6) also had autoantibodies in bone marrow. Bone marrow autoantibodies were not detected in patients with nonimmune thrombocytopenia or healthy donors; however, peripheral blood autoantibodies were detectable in 1 (33%) of 3 patients with nonimmune thrombocytopenia. The sensitivity of platelet autoantibodies for the diagnosis of ITP increased from 60% (peripheral blood testing) to 72% (peripheral blood and bone marrow testing). Immune reactions limited to the bone marrow may be characteristic of certain subsets of ITP patients.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1182/bloodadvances.2020001846DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7362381PMC
July 2020

Increased cytotoxic potential of CD8 T cells in immune thrombocytopenia.

Br J Haematol 2020 03 18;188(5):e72-e76. Epub 2019 Dec 18.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/bjh.16334DOI Listing
March 2020

Serotonin-release assay-negative heparin-induced thrombocytopenia.

Am J Hematol 2020 01 6;95(1):38-47. Epub 2019 Nov 6.

Department of Medicine, Michael G. DeGroote School of Medicine, Hamilton, Ontario, Canada.

Heparin-induced thrombocytopenia (HIT) is a prothrombotic drug reaction caused by platelet-activating anti-platelet factor 4 (PF4)/heparin antibodies. Pathogenic HIT antibodies can be detected by the serotonin-release assay (SRA), a platelet activation test. We have regarded the SRA performed in our medical community ("McMaster" SRA) as having high sensitivity and specificity. Recently, the concept of "SRA-negative HIT" has been proposed for enzyme-immunoassay (EIA)-positive/SRA-negative patients with a HIT-compatible clinical picture, who test positive in a PF4-enhanced platelet activation assay. After identifying an index case of SRA-negative HIT, we estimated the frequency of this condition by performing the "PF4-SRA" (modified SRA using high concentrations of added PF4 rather than heparin) in EIA-positive patients from a cohort study evaluating clinical and laboratory diagnosis of HIT. We defined SRA-negative HIT as patients meeting three criteria: clinical picture compatible with HIT (4Ts ≥ 4 points); EIA-positive (≥1.00 units); and PF4-SRA-positive. Among 430 patients, 35 were EIA-positive/SRA-positive and 27 were EIA-positive/SRA-negative. Among these 27 SRA-negative patients, three were found to have subthreshold levels of platelet-activating antibodies by PF4-SRA, of whom one met clinical criteria for SRA-negative HIT. Thus, based on identifying one patient with SRA-negative HIT within a cohort study that found 35 SRA-positive HIT patients, we estimate the sensitivity of the McMaster SRA for diagnosis of HIT to be 35/36 (97.2%; 95% CI, 85.8-99.9%). Although the McMaster SRA is highly sensitive for HIT, occasional SRA-negative but EIA-positive patients strongly suspected of having HIT can have this diagnosis supported by a PF4-enhanced activation assay such as the PF4-SRA.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ajh.25660DOI Listing
January 2020

The sensitivity and specificity of platelet autoantibody testing in immune thrombocytopenia: a systematic review and meta-analysis of a diagnostic test.

J Thromb Haemost 2019 05 20;17(5):787-794. Epub 2019 Mar 20.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.

Essentials The diagnosis of ITP is based on a platelet count < 100 × 10  L and exclusion of other causes. There are no standard tests or biomarkers to diagnose ITP. The sensitivity of platelet autoantibody testing is low (53%). The specificity is high (> 90%). A positive autoantibody test can be useful to rule in ITP but a negative does not rule out ITP. SUMMARY: Background Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count and an increased risk of bleeding. The sensitivity and specificity of platelet autoantibody tests is variable and their utility is uncertain. Objective The purpose of this study was to perform a systematic review and meta-analysis of platelet autoantibody tests in the diagnosis of ITP. Methods Ovid Medline, PubMed, and Web of Science were searched from inception until 31 May 2018. Two reviewers independently assessed studies for eligibility and extracted data. Studies that reported testing results for antiplatelet autoantibodies on platelets (direct tests) or in plasma/serum (indirect tests) for 20 or more ITP patients were included. Results Pooled estimates for sensitivity and specificity were calculated using a random effects model. Pooled estimates for the sensitivity and specificity of direct anti-platelet autoantibody testing for either anti-glycoprotein IIbIIIa or anti-glycoprotein IbIX were 53% (95% confidence interval [CI], 44-61%) and 93% (95% CI, 81-99%), respectively. For indirect testing, the pooled estimates for the sensitivity and specificity were 18% (95% CI, 12-24%) and 96% (95% CI, 87-100%), respectively. Conclusions Autoantibody testing in ITP patients has a high specificity but low sensitivity. A positive autoantibody test can be useful for ruling in ITP, but a negative test does not rule out ITP.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/jth.14419DOI Listing
May 2019

A platelet viability assay (PVA) for the diagnosis of heparin-induced thrombocytopenia.

Platelets 2019 29;30(8):1017-1021. Epub 2019 Jan 29.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University , Hamilton , Ontario , Canada.

Diagnosing heparin-induced thrombocytopenia (HIT) requires functional assays measuring platelet activation as they are highly specific and sensitive. A useful functional test for diagnosing HIT is the serotonin release assay (SRA), but this assay is technically demanding and requires a radioactive marker. We describe an alternate functional HIT assay, the platelet viability assay (PVA), that overcomes the need for a radioactive marker by using a viability dye endpoint to measure platelet activation. We compared the performance characteristics of the PVA to the SRA. Serum samples from 76 patients with suspected HIT were tested in both the PVA and the SRA. The PVA uses calcein-AM as a marker of platelet viability, with decreases in fluorescence and cell size as surrogate markers for platelet activation. A significant linear correlation (Spearman correlation, r = -0.78, P < 0.0001) was observed between the PVA and SRA. Calcein-AM fluorescence decreased in a negative linear relationship with platelet activation as measured by C-serotonin release. The PVA detected all positive SRA samples, with an overall sensitivity of 100% and a specificity of 97% in comparison to the SRA. The measurement of platelet viability using the PVA provided similar results to the SRA when testing suspected HIT patient samples.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/09537104.2018.1562169DOI Listing
February 2020

Peri-Operative Eltrombopag or Immune Globulin for Patients with Immune Thrombocytopaenia (The Bridging ITP Trial): Methods and Rationale.

Thromb Haemost 2019 Mar 27;119(3):500-507. Epub 2019 Jan 27.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.

Background:  The Bridging ITP Trial is an open-label randomized trial designed to compare the oral thrombopoietin receptor agonist eltrombopag and intravenous immune globulin (IVIG) for patients with immune thrombocytopaenia (ITP) who require an increase in platelet count before elective surgery. Here, we report the study methods and rationale.

Methods:  We designed a multi-centre, non-inferiority randomized trial comparing daily oral eltrombopag starting 3 weeks pre-operatively, and IVIG administered 1 week pre-operatively for patients with ITP requiring a platelet count increase prior to surgery. Starting dose of eltrombopag is 50 mg daily with a weekly pre-operative dose titration schedule, and treatment is continued for 1 week after surgical haemostasis is achieved. IVIG is administered at a dose of 1 to 2 g/kg 1 week pre-operatively with the allowance for a second dose within 1 week after surgical haemostasis. The objective of the study is to demonstrate non-inferiority of eltrombopag for the primary endpoint of achieving the pre-operative platelet count threshold (50 × 10/L for minor surgery; or 100 × 10/L for major surgery) and sustaining platelet count levels above the threshold for 1 week after surgical haemostasis is achieved, without the use of rescue treatment. Secondary endpoints include thrombosis, bleeding and patient satisfaction.

Conclusion:  The Bridging ITP Trial will evaluate the efficacy and safety of eltrombopag as an alternative to IVIG in the peri-operative setting for patients with ITP. The protocol was designed to provide a management strategy that can be applied in clinical practice. CLINICALTRIALS.

Gov Identifier:  NCT01621204.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1055/s-0038-1677531DOI Listing
March 2019

Characterization of platelet factor 4 amino acids that bind pathogenic antibodies in heparin-induced thrombocytopenia.

J Thromb Haemost 2019 02;17(2):389-399

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.

Essentials Many patients produce antibodies but few lead to heparin-induced thrombocytopenia (HIT). Pathogenic epitopes are difficult to identify as HIT antibodies are polyclonal and polyspecific. KKO binding to platelet factor 4 (PF4) depends on 13 amino acids, three of which are newly observed. Five amino acids in PF4 can help distinguish pathogenic from non-pathogenic antibodies. SUMMARY: Background Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction that results in thrombocytopenia and, in some patients, thrombotic complications. HIT is mediated by antibodies that bind to complexes of platelet factor 4 (PF4) and heparin. The antigenic epitopes of these anti-PF4/heparin antibodies have not yet been precisely defined, because of the polyspecific immune response that characterizes HIT. Objectives To identify PF4 amino acids essential for binding pathogenic HIT antibodies. Methods Alanine scanning mutagenesis was utilized to produce 70 single point mutations of PF4. Each PF4 mutant was used in an enzyme immunoassay (EIA) to test their capacity to bind a platelet-activating murine monoclonal anti-PF4/heparin antibody (KKO) and HIT patient sera (n = 9). Results and Conclusions We identified 13 amino acids that were essential for binding KKO because they directly affected either the binding site or the antigenic conformation of PF4. We also identified 10 amino acids that were required for the binding of HIT patient sera and five of these amino acids were required for binding both KKO and the HIT patient sera. The 10 amino acids required for binding HIT sera were further tested to differentiate pathogenic HIT antibodies (platelet activating, n = 45) and non-pathogenic antibodies (EIA-positive but not platelet activating, n = 28). We identified five mutations of PF4 that were recognized to be essential for binding pathogenic HIT antibodies. Using alanine scanning mutagenesis, we characterized possible binding sites of pathogenic HIT antibodies on PF4.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/jth.14369DOI Listing
February 2019

How do we diagnose immune thrombocytopenia in 2018?

Hematology Am Soc Hematol Educ Program 2018 11;2018(1):561-567

Michael G. DeGroote School of Medicine, Department of Medicine and Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada.

In this report, we will review the various clinical and laboratory approaches to diagnosing immune thrombocytopenia (ITP), with a focus on its laboratory diagnosis. We will also summarize the results from a number of laboratories that have applied techniques to detect anti-platelet autoantibodies as diagnostic tests for ITP. Although there is considerable variability in methods among laboratories, there is general agreement that platelet autoantibody testing has a high specificity but low sensitivity. This suggests several possibilities: (1) the ideal test for ITP has yet to be developed, (2) current test methods need to be improved, or (3) ITP is the clinical expression of a variety of thrombocytopenic disorders with different underlying mechanisms. Even the clinical diagnosis of ITP is complex, and experienced clinicians do not always agree on whether a particular patient has ITP. Improvements in the diagnostic approach to ITP are necessary to improve the management of this disorder.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1182/asheducation-2018.1.561DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6245958PMC
November 2018

Managing antithrombotic therapy in immune thrombocytopenia: development of the TH2 risk assessment score.

Blood 2018 12 8;132(25):2684-2686. Epub 2018 Nov 8.

Department of Medicine, Michael G. DeGroote School of Medicine, and.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1182/blood-2018-08-868406DOI Listing
December 2018

Megakaryocyte apoptosis in immune thrombocytopenia.

Platelets 2018 Nov 22;29(7):729-732. Epub 2018 May 22.

a Department of Medicine, Michael G. DeGroote School of Medicine , McMaster University , Hamilton , Canada.

The mechanisms of platelet underproduction in immune thrombocytopenia (ITP) remain unknown. While the number of megakaryocytes is normal or increased in ITP bone marrow, further studies of megakaryocyte integrity are needed. Megakaryocytes are responsible for the production of platelets in the bone marrow, and they are possible targets of immune-mediated injury in ITP. Since the biological process of megakaryocyte apoptosis impacts platelet production, we investigated megakaryocyte DNA fragmentation as a marker of apoptosis from ITP bone marrow biopsies. Archived bone marrow biopsy specimens from ITP patients, bone marrow specimens from controls with normal platelet counts, and bone marrow specimens from thrombocytopenic controls with myelodysplastic syndrome (MDS) were evaluated. Sections were stained with anti-CD61 for megakaryocyte enumeration, and terminal deoxynucleotidyl transferase dUTP nick-end labeling was used as an apoptotic indicator. In ITP patients, megakaryocyte apoptosis was reduced compared to nonthrombocytopenic controls. Megakaryocyte apoptosis was similarly reduced in thrombocytopenic patients with MDS. These results suggest a link between megakaryocyte apoptosis and platelet production.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/09537104.2018.1475637DOI Listing
November 2018

Autoantibodies to thrombopoietin and the thrombopoietin receptor in patients with immune thrombocytopenia.

Br J Haematol 2018 04 13;181(2):234-241. Epub 2018 Mar 13.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada.

Autoantibodies to thrombopoietin (TPO, also termed THPO) or the TPO receptor (cMpl, also termed MPL) could play a pathological role in immune thrombocytopenia (ITP). In this study, we tested for autoantibodies against TPO, cMpl, or the TPO/cMpl complex in ITP and other thrombocytopenic disorders. Using an inhibition step with excess TPO in fluid-phase to improve binding specificity, the prevalence of anti-TPO autoantibodies was: active ITP: 9/32 (28%); remission ITP: 0/14 (0%); non-immune thrombocytopenias: 1/10 (10%); and healthy controls: 1/11 (9%). Similarly, using an inhibition step with excess cMpl, the prevalence of specific anti-cMpl autoantibodies was: active ITP: 7/32 (22%); remission ITP: 1/14 (7%); non-immune thrombocytopenias: 3/10 (30%); and healthy controls: 0/11 (0%). Two active ITP patients had autoantibodies against the TPO/cMpl complex, but not against TPO or cMpl alone. Anti-TPO or anti-cMpl autoantibodies were found in 44% of ITP patients, and in 40% of patients with other thrombocytopenic disorders. These autoantibodies did not correlate with ITP disease severity or number of ITP treatments received; however, in this cohort, 3 patients failed to respond to TPO receptor agonist medications, and of those, 2 had anti-TPO autoantibodies. This suggests that anti-TPO and anti-cMpl autoantibodies are associated with thrombocytopenia, and may be clinically relevant in a subset of ITP patients.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/bjh.15165DOI Listing
April 2018

Platelet-Activating Antibodies Are Detectable at the Earliest Onset of Heparin-Induced Thrombocytopenia, With Implications for the Operating Characteristics of the Serotonin-Release Assay.

Chest 2018 06 8;153(6):1396-1404. Epub 2018 Jan 8.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada; McMaster Centre for Transfusion Research, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada.

Background: Heparin-induced thrombocytopenia (HIT) is a prothrombotic drug reaction caused by platelet-activating antibodies that recognize platelet factor 4 (PF4)/heparin complexes. It is unknown whether platelet-activating antibodies are detectable at the onset of the HIT-related platelet count fall.

Methods: Available blood samples from 18 patients obtained at onset of HIT were tested using the serotonin-release assay (SRA), a test for platelet-activating antibodies, and a PF4-dependent enzyme-linked immunosorbent assay (ELISA). Patient samples showing a delay of > 2 days between ELISA and SRA seroconversion were tested for subthreshold levels of platelet-activating antibodies using two modifications of the SRA that amplify detection of HIT antibodies. We also estimated SRA sensitivity and specificity in two postorthopedic surgery clinical trials (633 samples), including assessing whether a positive SRA influenced platelet count recovery in the absence of thrombocytopenia.

Results: Platelet-activating HIT antibodies were detected in all 18 patients at the beginning of the HIT-related platelet count fall. Although ELISA seroconversion usually preceded SRA seroconversion by only 1 day (median), subthreshold levels of platelet-activating antibodies were detected in both patients who exhibited a lag between ELISA and SRA seroconversion. SRA sensitivity was 100% (18/18), and its specificity was 97% (597/615). Nonthrombocytopenic SRA-positive patients with ongoing heparin treatment exhibited blunted platelet count recovery vs control subjects, suggesting even higher SRA specificity for detecting abnormal platelet count profiles.

Conclusions: Platelet-activating HIT antibodies are detectable at the onset of the HIT-related platelet count fall. The SRA has high sensitivity and specificity for HIT, and indicates that presence of HIT antibodies can blunt postoperative platelet count recovery.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.chest.2018.01.001DOI Listing
June 2018

Misdiagnosis of primary immune thrombocytopenia and frequency of bleeding: lessons from the McMaster ITP Registry.

Blood Adv 2017 Nov 28;1(25):2414-2420. Epub 2017 Nov 28.

Department of Medicine, Michael G. DeGroote School of Medicine, and.

Nonspecific diagnostic criteria and uncertain estimates of severe bleeding events are fundamental gaps in knowledge of primary immune thrombocytopenia (ITP). To address these issues, we created the McMaster ITP Registry. In this report, we describe the methodology of the registry, the process for arriving at the diagnosis, and the frequency of bleeding. Consecutive patients with platelets <150 × 10/L from a tertiary hematology clinic in Canada were eligible. Patients completed a panel of investigations and were managed per clinical need. Two hematologists initially determined the cause of the thrombocytopenia using standard criteria and reevaluated the diagnosis over time, which was adjudicated at regular team meetings. Bleeding was graded from 0 (none) to 2 (severe) prospectively using an ITP-specific tool. Data were validated by duplicate chart review and source verification. Between 2010 and 2016, 614 patients were enrolled. Median follow-up for patients with >1 visit was 1.7 years (interquartile range, 0.8-3.4). At registration, 295 patients were initially diagnosed with primary ITP; of those, 36 (12.2%) were reclassified as having a different diagnosis during follow-up. At registration, 319 patients were initially diagnosed with another thrombocytopenic condition; of those, 10 (3.1%) were ultimately reclassified as having primary ITP. Of 269 patients with a final diagnosis of primary ITP, 56.5% (95% confidence interval [CI], 50.4-62.5] experienced grade 2 bleeding at 1 or more anatomical site, and 2.2% (95% CI, 0.8-4.8) had intracranial hemorrhage. Nearly 1 in 7 patients with primary ITP were misdiagnosed. Grade 2 bleeding was common. Registry data can help improve the clinical and laboratory classification of patients with ITP.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1182/bloodadvances.2017010942DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5729626PMC
November 2017

Development of a high-yield expression and purification system for platelet factor 4.

Platelets 2018 May 27;29(3):249-256. Epub 2017 Nov 27.

a Department of Medicine , Michael G. DeGroote School of Medicine, McMaster University , Hamilton , Ontario , Canada.

Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction characterized by IgG antibodies bound to complexes of platelet factor 4 (PF4) and heparin. The majority of diagnostic tests for HIT rely on an exogenous source of PF4 to identify anti-PF4/heparin antibodies. These include the PF4-dependent enhanced serotonin release assay (PF4-SRA) among others. Using a bacterial expression system, we developed a novel and efficient method of producing recombinant human PF4 (rhPF4) that is biochemically and antigenically similar to platelet-derived human PF4. rhPF4 was produced using the pET expression system in the BL21(DE3) strain of Escherichia coli. The system was optimized for protein expression using isopropyl β-D-1-thiogalactopyranoside at different induction temperatures and incubation times. rhPF4 solubility was improved by using different detergents during cell lysis and by purifying with heparin affinity and ion exchange chromatography. Biochemical characteristics of rhPF4 were investigated using mass spectrometry, SDS-PAGE analysis, and gel filtration chromatography and compared to platelet-derived PF4. Antigenic and functional characteristics of rhPF4 were studied using the anti-PF4/heparin EIA and the PF4-SRA. Using this method, we could produce 11.4 ± 0.6 mg of pure rhPF4 per liter of bacterial culture. Absorbance readings from the anti-PF4/heparin EIA using platelet-derived and rhPF4 were highly correlated (n = 194; r = 0.9545, p < 0.0001); and functional release of serotonin in the PF4-SRA induced by anti-PF4/heparin antibodies was similar to either platelet-derived or rhPF4 and heparin (r = 0.9597, p < 0.0001). Our method of rhPF4 production is efficient and does not rely on a source of platelets. The rhPF4 purification method described produces greater yields at a lower cost than other current methods. The application of this method can improve the efficiency of biochemical investigations and HIT diagnostic testing by supplying sufficient amounts of PF4.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/09537104.2017.1378808DOI Listing
May 2018

The effect of rituximab on anti-platelet autoantibody levels in patients with immune thrombocytopenia.

Br J Haematol 2017 07 25;178(2):302-307. Epub 2017 Apr 25.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.

Rituximab is an effective therapy resulting in a platelet count improvement in 60% of patients with immune thrombocytopenia (ITP). Rituximab depletes B cells; thus, a reduction in platelet autoantibody levels would be anticipated in patients who achieve a clinical response to this treatment. The objectives of this study were to determine whether rituximab was associated with a reduction in platelet autoantibody levels, and to correlate the loss of autoantibodies with the achievement of a treatment response. We performed a case-control study nested within a previous randomized controlled trial of standard therapy plus adjuvant rituximab or placebo. We measured platelet-bound anti-glycoprotein (GP) IIbIIIa and anti-GPIbIX using the antigen capture test. Of 55 evaluable patients, 25 (45%) had a detectable platelet autoantibody at baseline. Rituximab was associated with a significant reduction in anti-GPIIbIIIa levels (P = 0·02) but not anti-GPIbIX levels (P = 0·51) compared with placebo. Neither the presence of an autoantibody at baseline nor the loss of the autoantibody after treatment was associated with a response to rituximab. The subset of patients with persistent autoantibodies after treatment failed to achieve a platelet count response, suggesting that persistence of platelet autoantibodies can be a marker of disease severity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/bjh.14664DOI Listing
July 2017

High-dose dexamethasone compared with prednisone for previously untreated primary immune thrombocytopenia: a systematic review and meta-analysis.

Lancet Haematol 2016 Oct 16;3(10):e489-e496. Epub 2016 Sep 16.

McMaster Centre for Transfusion Research, McMaster University, Hamilton, ON, Canada; Department of Medicine, Michael G DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada; Canadian Blood Services, Hamilton, ON, Canada. Electronic address:

Background: Whether high-dose dexamethasone has long-term efficacy and safety in previously untreated patients with immune thrombocytopenia is unclear. We did a systematic review and a meta-analysis of randomised trials to establish the effect of high-dose dexamethasone compared with prednisone for long-term platelet count response.

Methods: We searched MEDLINE, Embase, Cumulative Index of Nursing and Allied Health Literature, and the Cochrane Library Database for papers published from 1970 to July, 2016, and abstracts from American Society of Hematology annual meetings published from 2004 to 2015 for randomised trials comparing different corticosteroid regimens for patients with previously untreated immune thrombocytopenia who achieved a platelet count response. Trials that compared corticosteroids exclusively with other interventions were excluded. The primary endpoint was overall (platelets >30 × 10/L) and complete (platelets >100 × 10/L) platelet count response at 6 months with high-dose dexamethasone compared with standard-dose prednisone. Children and adults were analysed separately. Estimates of effect were pooled with a random-effects model.

Findings: Nine randomised trials (n=1138) were included. Of those, five (n=533) compared one to three cycles of dexamethasone (40 mg per day for 4 days) with prednisone (1 mg per kg) for 14-28 days followed by dose tapering in adults. We found no difference in overall platelet count response at 6 months (pooled proportions 54% vs 43%, relative risk [RR] 1·16, 95% CI 0·79-1·71; p=0·44). At 14 days, overall platelet count response was higher with dexamethasone (79% vs 59%, RR 1·22, 95% CI 1·00-1·49; p=0·048). The dexamethasone group had fewer reported toxicities. Long-term response rates were similar when the data were analysed by cumulative corticosteroid dose over the course of treatment. No difference in initial platelet count response was observed with different high-dose corticosteroid regimens in children.

Interpretation: In adults with previously untreated immune thrombocytopenia, high-dose dexamethasone did not improve durable platelet count responses compared with standard-dose prednisone. High-dose dexamethasone might be preferred over prednisone for patients with severe immune thrombocytopenia who require a rapid rise in platelet count.

Funding: Canadian Institutes of Health Research, and Canadian Blood Services, and Health Canada.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/S2352-3026(16)30109-0DOI Listing
October 2016

Difficulties in establishing the diagnosis of immune thrombocytopenia: An agreement study.

Am J Hematol 2016 08 1;91(8):E327-9. Epub 2016 Jun 1.

Department of Medicine, Michael G. DeGroote School of Medicine, Hamilton, Ontario, Canada.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ajh.24404DOI Listing
August 2016

Producing megakaryocytes from a human peripheral blood source.

Transfusion 2016 05 12;56(5):1066-74. Epub 2016 Jan 12.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario.

Background: Cultured megakaryocytes could prove useful in the study of human diseases, but it is difficult to produce sufficient numbers for study. We describe and evaluate the use of an expansion process to develop mature megakaryocytes from peripheral blood-derived human hematopoietic stem and progenitor cells (HSPCs).

Study Design And Methods: HSPCs (CD34+) were isolated from peripheral blood by positive selection and expanded using an optimal CD34+ expansion supplement. We evaluated megakaryocyte growth, maturation, and morphology in response to thrombopoietin (TPO) stimulation using flow cytometry and electron microscopy. TPO demonstrated a dose-dependent stimulatory effect on both megakaryocyte number and maturation.

Results: From 90 to 120 mL of unmanipulated peripheral blood, we isolated a mean of 1.5 × 10(5) HSPCs (1.5 × 10(3) cells/mL of whole blood). HSPCs expanded nine-fold after a 4-day culture using an expansion supplement. Expanded cells were cultured for an additional 8 days with TPO (20 ng/mL), which resulted in a 2.9-fold increase in megakaryocytic cells where 83% of live cells expressed CD41a+, a marker of megakaryocyte commitment, and 50% expressed CD42b+, a marker for megakaryocyte maturation. The expanded HSPCs responded to TPO stimulation to yield more than 1.0 × 10(6) megakaryocytes. This cell number was sufficient for morphologic studies that demonstrated these expanded HSPCs produced mature polyploid megakaryocytes capable of forming proplatelet extensions.

Conclusions: Peripheral blood HSPCs can be expanded and differentiated into functional, mature megakaryocytes, a finding that supports the use of this process to study inherent platelet (PLT) production disorders as well as study factors that impair normal PLT production.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/trf.13461DOI Listing
May 2016

Rituximab plus standard of care for treatment of primary immune thrombocytopenia: a systematic review and meta-analysis.

Lancet Haematol 2015 Feb 5;2(2):e75-81. Epub 2015 Feb 5.

Department of Medicine, Michael G DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada; Canadian Blood Services, Hamilton, ON, Canada. Electronic address:

Background: Rituximab is commonly used as a treatment for primary immune thrombocytopenia to induce and maintain remission. The benefit of adding rituximab to standard-of-care treatment is uncertain.

Methods: We did a systematic review and meta-analysis of randomised controlled trials assessing the efficacy and safety of rituximab for treatment of adults with primary immune thrombocytopenia. We searched Medline, Embase, and the Cochrane database in duplicate and independently from inception up to July 31, 2014, for relevant studies. Primary outcomes were the proportion of patients achieving a complete platelet count response and a partial platelet count response (as defined in primary studies) that was maintained until the end of follow-up. We also assessed bleeding, infection, and infusion reactions.

Findings: Our database search returned 468 abstracts, of which five trials (with total of 463 patients) were eligible for analysis. No patients had splenectomy at the time of enrolment. Median follow-up was 6 months (IQR 6-12). Complete response (>100 × 10(9) platelets per L without rescue therapy) was more common with rituximab than with standard of care (weighted proportions: 46·8% vs 32·5%; relative risk [RR] 1·42, 95% CI 1·13-1·77; p=0·0020). Partial response was not significantly different between groups (57·6% vs 46·7%; RR 1·26, 95% CI 0·95-1·67; p=0·11). Rituximab was not associated with a reduction in bleeding (9·2% vs 5·2%; RR 1·34, 95% CI 0·63-2·87; p=0·44) or an increase in infections (20·1% vs 12·1%; RR 1·40, 95% CI 0·87-2·26; p=0·17).

Interpretation: Rituximab can improve complete platelet count responses by 6 months in patients with immune thrombocytopenia. Evidence for sustained responses beyond 6-12 months is limited. Clinicians must consider the goals of treatment before prescribing rituximab.

Funding: None.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/S2352-3026(15)00003-4DOI Listing
February 2015

Effect of a thrombopoietin receptor agonist on use of intravenous immune globulin in patients with immune thrombocytopenia.

Transfusion 2016 Jan 24;56(1):73-9. Epub 2015 Sep 24.

Department of Medicine Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario.

Background: Thrombopoietin receptor agonists are new treatments for patients with chronic immune thrombocytopenia (ITP). How one of these agent, romiplostim, has impacted practice patterns, especially the use of intravenous immune globulin (IVIG), has not been evaluated outside of clinical trials.

Study Design And Methods: This was a retrospective cohort study of adult ITP patients treated with romiplostim in four Canadian centers. Patients had primary or secondary ITP and were followed for 1 year before starting weekly romiplostim treatment. We compared IVIG use, clinical outcomes, and cost before and after romiplostim.

Results: Twenty-nine patients with ITP received romiplostim. Median age was 54 years (interquartile range [IQR], 45-63 years) and patients had a median of two prior ITP treatments (IQR, 1-4) including splenectomy (n = 7). Median platelet (PLT) count was 23 × 10(9) before and 124 × 10(9) after romiplostim. Median duration of romiplostim treatment was 3.7 months. Patients used a median of two IVIG infusions per year before and 0.7 per year after starting romiplostim (p = 0.16). For patients who received weekly romiplostim for at least 1 month (n = 19), IVIG infusions were three (IQR, 1-5) per year before and 0.7 (IQR, 0.4-1.6) per year after romiplostim. Results were squewed by two high IVIG users. Nineteen (66%) patients discontinued romiplostim treatment during follow-up because of lack of response (n = 8), sustained response (n = 5), toxicities (n = 4), or response to splenectomy (n = 2). Overall health care costs were similar before and after romiplostim when concomitant treatments, nursing resources, and hospitalizations were considered.

Conclusions: Romiplostim was associated with improved PLT counts and fewer IVIG infusions for most ITP patients. In practice, romiplostim was generally not continued long term and was cost neutral for overall ITP management.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/trf.13336DOI Listing
January 2016

A phase-II sequential case-series study of all patients presenting to four plasma exchange centres with presumed relapsed/refractory thrombotic thrombocytopenic purpura treated with rituximab.

Br J Haematol 2015 Jul 8;170(2):208-17. Epub 2015 Apr 8.

Division of Clinical Pathology, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada.

The primary objective of this phase II study was to evaluate the efficacy of rituximab in the management of adult patients with physician-diagnosed presumed thrombotic thrombocytopenic purpura (TTP); relapsed or refractory. We conducted a multicentre study in four Canadian hospital-based apheresis units. Forty patients with presumed TTP (20 refractory and 20 relapsing) were sequentially enrolled and all received rituximab in a standardized manner. A complete response was documented in 14 of 19 refractory patients by week 8 and 15/16 were alive and in remission at 52 weeks (one patient was lost to follow-up, one was a non-responder, and three died). Among relapsing patients, 16/18 had a complete response at week 8 and 18/18 at week 52 (one patient lost to follow-up and one withdrew). At 1 year, all relapsing and 85% of refractory patients survived. Of 38/40 patients who had ADMATS13 testing at study entry, 13/19 refractory and 10/19 relapsing patients had ADAMTS13 < 10% (typical TTP); whereas 6/19 refractory and 9/19 relapsing cases had ADAMTS13 > 10% (other thrombotic microangiopathy; TMA). Refractory-typical TTP in contrast to refractory-other TMA and all relapsing patients treated with plasma exchange and rituximab, were less likely to be responsive and more likely to die or relapse.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/bjh.13408DOI Listing
July 2015

Pitfalls in the diagnosis of heparin-Induced thrombocytopenia: A 6-year experience from a reference laboratory.

Am J Hematol 2015 Jul 3;90(7):629-33. Epub 2015 May 3.

Department of Medicine. Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.

Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating antibodies against complexes of platelet factor 4 (PF4) and heparin. The diagnosis of HIT is contingent on accurate and timely laboratory testing. Recently, alternative anticoagulants for the treatment of HIT have been introduced along with algorithms for better HIT diagnosis. However, the increased reliance on immunoassays for the diagnosis of HIT may have harmful consequences due to the high rate of false positive results. To compare trends and implications of current HIT testing approaches, we analyzed results over a six-year period from the McMaster University Platelet Immunology Reference Laboratory. From 2008 to 2013, 8,546 samples were investigated for HIT using both an in-house IgG-specific anti-PF4/heparin enzyme immunoassay (EIA) and the serotonin-release assay (SRA). Of 8,546 samples tested, 13.4% were true-positives (positive in both assays); 65.6% were true-negatives (negative in both assays); 20.9% were presumed false positive for HIT (EIA-positive/SRA-negative); and 0.2% were EIA-negative/SRA-positive. The frequency of EIA-positive/SRA-negative results increased over time (from 12.9% in 2008 to 22.9% in 2013). We found that the number of SRA-negative samples was reduced from referring centers that used an immunoassay as an initial screen; however, 41% of those samples tested negative in the immunoassay and in the SRA at the reference laboratory. The suspicion of HIT continues at a high rate and the agreement between the EIA and SRA test results remains problematic.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ajh.24025DOI Listing
July 2015

The platelet serotonin-release assay.

Am J Hematol 2015 Jun 3;90(6):564-72. Epub 2015 May 3.

Department of Pathology and Molecular Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.

Few laboratory tests are as clinically useful as The platelet serotonin-release assay (SRA): a positive SRA in the appropriate clinical context is virtually diagnostic of heparin-induced thrombocytopenia (HIT), a life- and limb-threatening prothrombotic disorder caused by anti-platelet factor 4 (PF4)/heparin antibodies that activate platelets, thereby triggering serotonin-release. The SRA's performance characteristics include high sensitivity and specificity, although caveats include indeterminate reaction profiles (observed in ∼4% of test sera) and potential for false-positive reactions. As only a subset of anti-PF4/heparin antibodies detectable by enzyme-immunoassay (EIA) are additionally platelet-activating, the SRA has far greater diagnostic specificity than the EIA. However, requiring a positive EIA, either as an initial screening test or as an SRA adjunct, will reduce risk of a false-positive SRA (since a negative EIA in a patient with a "positive" SRA should prompt critical evaluation of the SRA reaction profile). The SRA also provides useful information on whether a HIT serum produces strong platelet activation even in the absence of heparin: such heparin-"independent" platelet activation is a marker of unusually severe HIT, including delayed-onset HIT and severe HIT complicated by consumptive coagulopathy with risk for microvascular thrombosis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ajh.24006DOI Listing
June 2015

Antibody binding to megakaryocytes in vivo in patients with immune thrombocytopenia.

Eur J Haematol 2015 Dec 13;95(6):532-7. Epub 2015 Mar 13.

Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.

Objectives: Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder caused by increased platelet destruction and impaired platelet production. Antibody binding to megakaryocytes may occur in ITP, but in vivo evidence of this phenomenon is lacking.

Methods: We determined the proportion of megakaryocytes bound with immunoglobulin G (IgG) in bone marrow samples from primary patients with ITP (n = 17), normal controls (n = 13) and thrombocytopenic patients with myelodysplastic syndrome (MDS; n = 10). Serial histological sections from archived bone marrow biopsies were stained for CD61 and IgG. IgG binding and the number of bone marrow megakaryocytes were determined morphologically by a hematopathologist with four assessors after a calibration exercise to ensure consistency.

Results: The proportion of ITP patients with high IgG binding (>50% of bone marrow megakaryocytes) was increased compared with normal controls [12/17 (71%) vs. 3/13 (23%), P = 0.03]. However, the proportion of ITP patients with high IgG binding was no different than thrombocytopenic patients with MDS [12/17 (71%) vs. 7/10 (70%), P = 1.00]. IgG binding was associated with increased megakaryocyte numbers. Like platelet-associated IgG, megakaryocyte-associated IgG is related to thrombocytopenia but may not be specific for ITP.

Conclusion: Mechanistic studies in ITP should focus on antibody specificity and include thrombocytopenic control patients.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/ejh.12528DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4851549PMC
December 2015

Novel treatments for immune thrombocytopenia.

Presse Med 2014 Apr 20;43(4 Pt 2):e87-95. Epub 2014 Mar 20.

McMaster University, Department of Medicine, Hamilton, Ontario, Canada; Canadian Blood Services, Hamilton, Ontario, Canada. Electronic address:

Primary immune thrombocytopenia (ITP) is caused by platelet autoantibodies and T-cell dysregulation. Both platelets and their precursor megakaryocytes may be targeted leading to platelet destruction and underproduction. Current treatments for ITP are inadequate since they do not reverse the disease process and generally do not result in durable remissions. In addition, many treatments are limited by side effects including infection and potentially thrombosis. Novel agents that are currently in development target certain key steps in the disease process, including: (1) the interaction between T-cell and antigen presenting cells (CD40-CD154 interaction); (2) the binding of the Fc portion of platelet autoantibodies to Fc-receptors on macrophages (soluble Fc-RIIb); and (3) the signaling pathways leading to platelet phagocytosis by macrophages (Syk inhibition). Other strategies have been to augment platelet production by simulating thrombopoiesis or by neutralizing physiological inhibitors of megakaryopoiesis. Targeted therapies in ITP have the potential to improve disease morbidity and mortality while limiting systemic side effects. Before these agents can be used in practice, additional clinical studies are needed with rational study outcomes including platelet count, bleeding and quality of life. An individualized treatment strategy is needed for patients since ITP is a distinctly heterogeneous disease.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.lpm.2014.02.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4880474PMC
April 2014

The effect of rituximab on vaccine responses in patients with immune thrombocytopenia.

Blood 2013 Sep 12;122(11):1946-53. Epub 2013 Jul 12.

Department of Medicine and.

B-cell depletion may impair vaccine responses and increase infection risk in patients with immune thrombocytopenia (ITP). We investigated the effects of rituximab on antibody and cellular responses to Streptococcus pneumoniae polysaccharide and Haemophilus influenzae type b (Hib) vaccines in ITP patients. Of 60 patients in the main trial, 24 patients received both vaccines 6 months after rituximab (n = 17) or placebo (n = 7). Among 20 evaluable patients, 3 of 14 (21%) in the rituximab group and 4 of 6 (67%) in the placebo group achieved a fourfold increase in anti-pneumococcal antibodies (P = .12). For anti-Hib antibodies, 4 of 14 (29%) and 5 of 6 (83%), respectively, achieved a fourfold increase (P < .05). Fewer patients in the rituximab group demonstrated Hib killing (2 of 14 [14%], 5 of 6 [83%], P < .05). Three of 14 rituximab-treated patients failed to respond to vaccines by any criteria. After vaccinations, preplasma cell blasts and interferon-γ-secreting T cells were reduced in rituximab-treated patients. Antibody responses were impaired for at least 6 months after rituximab. Cellular immunity was reduced in parallel with depleted B-cell pools. These findings have implications for the timing of vaccinations and the mechanism of infection after rituximab in ITP patients.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1182/blood-2013-04-494096DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3773242PMC
September 2013