Immune Thrombocytopenia Cohort Research Articles

MicroRNA-199a-5p may be a diagnostic biomarker of primary ITP.

There is no diagnostic test for primary immune thrombocytopenia (ITP). Certain microRNAs have shown to have diagnostic potential in ITP. We validated 12 microRNAs identified from two previous studies to find a diagnostic biomarker. The study included two ITP cohorts (n = 61) and healthy controls (n = 28). The first ITP cohort involved 24 patients from the Prolong study, patients with newly diagnosed/persistent ITP (<1 year) treated with corticosteroids ± IVIG but relapsed/failed to respond. The second cohort comprised 37 patients from ITP biobank, Østfold Hospital, Norway, patients had different disease stages and therapies. Twelve microRNAs were measured: miR-199a-5p, miR-33a-5p, miR-195-5p, miR-130a-3p, miR-144-3p, miR-146a-5p, miR-222-3p, miR-374b-5p, miR-486-5p, miR-1341-5p, miR-766-3p and miR-409-3p. miR-199a-5p, miR-33a-5p, miR-374b-5p, miR-146a-5p and miR-409-3p were expressed differentially in the entire ITP cohort compared to controls; of those only miR-199a-5p showed good discriminative ability between ITP and controls with area under the curve (AUC) of 0.718 (95% CI: 0.599-0.836). In the Prolong cohort (ITP < 1 year), miR-199a-5p and miR-374b-5p showed very good discriminative ability between ITP and controls with AUC of 0.824 (0.708-0.940) and 0.806 (0.688-0.924) respectively. This study confirmed that miR-199a-5p has good discriminative ability between primary ITP and healthy controls, thus may be a diagnostic biomarker of ITP.

Identification and validation of key regulating circRNAs in Immune Thrombocytopenia by circRNAs sequencing

Dysfunction of T cells is a causative factor in Immune Thrombocytopenia (ITP), an autoimmune disorder. Circular RNAs (circRNAs), which have been associated with the pathophysiology of various immunological conditions, are of particular interest. Our study aimed to identify pivotal regulatory circRNAs within the peripheral T cells of ITP patients. We utilized circRNA sequencing to discern differences in circRNA expression between the ITP cohort and healthy controls. We identified 606 upregulated and 719 downregulated circRNAs. Subsequent Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were conducted to scrutinize the parent genes of these differentially expressed circRNAs, revealing their significant involvement in metabolic processes and T cell receptor signaling pathways. Following a rigorous selection process that included DEG analysis, KEGG, and GO pathways analysis, along with an assessment of the potential roles of their parent genes, five top differentially expressed circRNAs were subjected to further validation via quantitative Polymerase Chain Reaction (RT-qPCR). Specifically, in the peripheral T cells of ITP patients, hsa_circ_0008866 (TAOK1), hsa_circ_0006856 (MAP3K5), and hsa_circ_0007444 (RHOBTB3) emerged as key regulatory circRNAs. The potential miRNA targets of these circRNAs were predicted employing miRanda, RNAhybrid, and TargetScan algorithms.

Genetic Variants in Canonical Wnt Signaling Pathway Associated with Pediatric ITP

Introduction : Pediatric immune thrombocytopenia (ITP) is thought to develop when a triggering event inappropriately activates an autoimmune anti-platelet response in the context of predisposing genetic factors. Inborn errors of immunity are increasingly being identified in cases of chronic, refractory autoimmune cytopenias. We sought to identify genetic variants associated with predisposition to 1) primary or secondary pediatric ITP of any disease duration versus healthy controls and 2) chronic ITP (cITP) versus disease that spontaneously resolves in &amp;lt; 1 year (sr-ITP). Methods : DNA and clinical data were derived from 8 sites from the Pediatric ITP Consortium of North America's (ICON) biorepository. Samples were genotyped using the Illumina Global Screening Array BeadChip. Genotypes were imputed using the Michigan Imputation Server HRC reference panel. Genetic variants that passed standard quality metrics and had a MAF ≥1% were retained. Control samples (n=8,372) were obtained from the National Longitudinal Study of Adolescent to Adult Health (Add Health) cohort. Logistic regression models were used to estimate adjusted odds ratios (aORs) comparing (1) ITP and control cohorts and (2) cITP and sr-ITP cohorts. Models assumed additive allelic effects and accounted for the top 3 principal components. Genome-wide significance was defined as P &amp;lt;5 × 10 -8 and suggestive of genome-wide significance, P &amp;lt;1 x 10 -5. Results : Six-hundred ten unique patient samples were genotyped. Nineteen (3.1%) did not pass quality control, leaving 591 for analysis. This cohort included 307 (52.0%) cITP patients, 209 (35.4%) sr-ITP patients, and 75 (12.7%) individuals without complete follow-up data to allow for classification of cITP or sr-ITP. The ITP cohort was 50.1% male, 50.1% non-Hispanic (NH) white, 29.4% Hispanic, 6.1% NH Black, 3.1% NH Asian, and 11.3% Other/Unknown. Compared with healthy controls, we identified 6 loci associated with ITP at genome-wide significance (Figure 1). Located within the intronic region of SLC24A4 rs75650997 was associated with an increased risk of ITP compared with controls (aOR: 2.38, P=3.9x10 -8). An intronic variant, rs2165798, in NAV2 was inversely associated with ITP (aOR: 0.52, P=3.2x10 -11). A variant in NKD1 rs4785216, was inversely associated with ITP (aOR: 0.43, P=8.86x10 -15).Another intergenic variant, rs4785426, in close proximity to NKD1 was also inversely associated with ITP (aOR: 0.48, P=1.84x10 -16) . An additional 20 variants met suggestive of genome-wide significance. When comparing sr-ITP and cITP patients, no SNVs (single nucleotide variant) reached genome-wide significance, but one variant, rs117609649, in ABCC4 met suggestive of genome-wide significance (aOR: 0.26, P=4.49x10 -7). Discussion : This is the largest, unbiased genetic study of pediatric ITP patients. The analysis comparing ITP versus healthy controls identified 20 suggestive SNVs and 6 which met genome-wide significance. Several of the top SNVs identified in this study affect Wnt/β-catenin signaling. Wnt-signaling impacts the development and regulation of immune cell populations including dendritic cells, macrophages, NK cells, B cells, and T cells. NAV2 activates Wnt/β-catenin signaling. NAV2 variants have been implicated in autoimmune conditions including Celiac disease and rheumatoid arthritis. NKD1 inhibits the canonical Wnt/β-catenin signaling pathway. The cumulative impact of these variants on Wnt activity in ITP should be evaluated in the future. No genetic variants met genome-wide significance in a comparison of sr-ITP and cITP patients. Collectively, these findings suggest there may be genetic variants implicated in ITP risk, but those genetic features are not specific to sr-ITP or cITP. A focused analysis of 632 genes that cause inborn errors of immunity (IEI) is ongoing. This includes gene burden testing and analysis of pathogenic variants within this gene subset. Variants in IEI genes will also be evaluated in a sub-population of patients with Evans syndrome. Conclusion : ITP is highly heterogenous in its presentation, disease course, and response to therapy. Mirroring its clinical behavior, the genetic contribution to ITP development is complex. This study identified potential SNVs associated with ITP, but not specific to sr-ITP or cITP. Variants in genes that affect the canonical Wnt-signaling pathway may play a role in ITP risk.

Validation of Differentially Expressed Micrornas in Primary Immune Thrombocytopenia Suggests Mir-199a-5p Is a Potential Diagnostic Biomarker

Introduction Currently, there is no specific diagnostic test for immune thrombocytopenia (ITP). MicroRNAs (miRNA) are small, noncoding RNAs involved in the post-transcriptional regulation of gene expression. Aberrant expression of miRNAs has been suggested to have potential diagnostic value. Previous explorative studies have identified several differentially expressed miRNAs in ITP with potential diagnostic value; however, such findings are usually difficult to reproduce. Therefore, we aimed to validate some of these miRNAs in a larger ITP cohort. Methods Based on previous studies in ITP, we selected 12 miRNAs for validation in patients with primary ITP. The following miRNA were selected: miR-199a-5p, miR-33a-5p, miR-195-5p, miR-130a-3p, miR-144-3p, miR-146a-5p, miR-222-3p, miR-374-5p, miR-486-5p, miR-1341-5p, miR-766-3p, miR-409-3p. Blood samples (n=61) were obtained from 2 cohorts of primary ITP and healthy controls. The first cohort included samples from 24 patients with newly diagnosed or persistent ITP from the PROLONG study (NCT00344149); all patients had been treated with corticosteroids +/- IVIG but relapsed or failed to respond. The second cohort included 37 samples obtained from the ITP biobank at Østfold Hospital, Norway; patients had different disease phases and had received different therapies. In addition, 28 samples were obtained from healthy controls. The miRNAs were quantified in citrated plasma using droplet digital PCR (Bio-Rad). Results The mean age of the ITP patients was 51 years (62% female) and of the controls 47 years (64% female). The mean platelet count for all patients was 48.8 ·10 9/L. PROLONG patients had a lower mean platelet count (33 ·10 9/L) than patients from ITP biobank (59 ·10 9/L). Mann-Whitney test showed that miR-199a-5p (p=0.001), miR-33a-5p (p=0.010), miR-374-5p (p=0.009) and miR-146a-5p (p=0.026) were significantly differentially expressed (downregulated) in ITP compared with controls. Subgroup analysis of PROLONG patients showed that 3 additional miRNAs (7 of the 12 miRNAs) were significantly differentially expressed (downregulated) in these ITP patients: miR-130a-3p (p=0.005), miR-766-3p (p=0.010) and miR-409-3p (p=0.001). ROC curve analysis showed good discrimination for miR-199a-5p in all patients with an AUC of 0.718 (95% CI 0.599-0.836), and satisfactory for miR-33a-5p with an AUC of 0.671 (CI 0.549-0.793), 0.673 (CI 0.554-0.792) for miR-374-5p and 0.632 (CI 0.505-0.759) for miR-409-3p (Figure A). Subgroup analysis for each of the two cohorts separately showed higher AUC in PROLONG patients for miR-199a-5p (AUC=0.824; 95% CI 0.708-0.940), miR-374-5p (AUC=0.806; 95% CI 0.688-0.924), and for miR-33a-5p (AUC=0.732; 95% CI 0.597-0.868). The combination of all three miRNAs: miR-199a-5p, miR-33a-5p and miR-374-5p in PROLONG patients resulted in a slight improvement of the AUC to 0.865 (CI 0.767-0.962) (Figure B). Conclusions This study confirms that miR-199a-5p, miR-33a-5p, miR-374-5p and miR-146a-5p are differentially expressed in primary ITP compared with healthy controls. miR-199a-5p shows a good ability to discriminate primary ITP patients from healthy controls. In the PROLONG cohort, both miR-199a-5p and miR-374-5p showed a very good discrimination, probably due to the fact that these patients had early ITP. These findings should be further validated in a prospective cohort of newly diagnosed ITP patients and in patients with other types of thrombocytopenia to explore their potential diagnostic value. Some of these miRNAs have important regulatory functions, particularly in inflammation and apoptosis, so it is essential to evaluate their function and role in the pathogenesis of ITP and their potential use as therapeutic targets.

Health Related Quality of Life in Patients with Primary ITP Compared with Population Norms: A Multicenter Retrospective Analysis of Data from Norwegian ITP Registry

Introduction: Immune thrombocytopenia (ITP) is characterized by thrombocytopenia and varying grades of bleeding manifestations. Many patients develop a fear of bleeding, which can impact their health-related quality of life (HRQoL). In addition, often necessary lifestyle adjustments as well as treatment-related side effects may further reduce HRQoL. Aims: to estimate HRQoL in adult patients diagnosed with ITP and to compare their HRQoL to that of the general population using the EuroQol-5 Dimensions-3 Levels (EQ-5D-3L) questionnaire. Methods: Data from the Norwegian ITP (NOR-ITP) Registry was used. Adult ITP patients registered in NOR-ITP from Dec 2016 to May 2023 were included in this study. Patients included in NOR-ITP complete the EQ-5D-3L questionnaire, when included in the registry and then annually as part of their scheduled follow-up. In patients who had completed several EQ-5D-3L questionnaires, the most recent one was used. The age-adjusted Norwegian EQ-5D-3L populations norms were used as reference values for Index and VAS scores. Missing data were replaced using multiple imputation. Results: Median (IQR) age of 247 patients was 57 years (34); M:F ratio = 1:1.5. ITP was newly diagnosed in 18 (7%), persistent in 14 (6%), and chronic in 215 (87%) patients. Platelet count was &amp;gt;50*10 9/L in 166 (67%) patients, between 31 and 50*10 9/L in 15 (6%), and &amp;lt; 30*10 9/L in 18 (7%), unknown for 19% (48). Thirty-nine (16%) patients were never treated for ITP, 80 (32%) patients had remission induced by glucocorticoids +/- IVIGs, and 128 (52%) were treated with second-line agents. Ongoing treatment was an immunosuppressive agent (i.e. glucocorticoids +/- IVIGs, rituximab (received during the last 3 months), azathioprine, cyclosporine-A, mycophenolate mofetil) in 43 (17%) patients, a thrombopoietin receptor agonist in 42 (17%) patients, while 162 (66%) were off-ttraetment. Median time from diagnosis of ITP to most recent EQ-5D questionnaire was 4 (10) years. Figure1a displays the frequency of reported problems (levels 2 and 3) in ITP patients compared to the population norms. ITP patients reported significantly more problems in 4 out of 5 domains. EQ-5D index score was significantly lower in ITP patients compared to the general population [Mean (SD) = 0.790 (0.23) vs 0.830 ([0.041); p-value 0.007]. Likewise, we found VAS to be significantly lower in ITP patients compared to the general population [Mean (SD) = 70.82 (21.09) vs 77.32 (5.554); p-value 0.0001). Within the ITP cohort, we found significantly lower VAS scores in ITP patients receiving ongoing treatment compared to those off treatment (p-value 0.01), as shown in figure1b. However, no significant difference was found concerning Index scores when comparing patients with ongoing to off-treatment. Comparing index scores and VAS according to platelet count category (&amp;lt;30; 31-50; &amp;gt;50*109/L) and the phase of ITP did not reveal any significant differences. Conclusion: This study is the first to evaluate HR-QoL using EQ-5D in a well-characterized cohort of patients with ITP. In line with existing evidence, using other HRQoL instruments, we found significantly reduced HRQoL in ITP patients compared to the general population. ITP patients receiving ongoing treatment had worse HRQoL compared to those off-treatment. Limitations of this study are the the long time period between diagnosis and completing the questionnaire, the observational and retrospective study design, and the lack of predictors for HRQoL.

Initial Report of Povetacicept, an Enhanced Dual BAFF/APRIL Antagonist, in Autoimmune Cytopenias: The RUBY-4 Study

Introduction: BAFF and APRIL are cytokines with key roles in B cell development, survival, differentiation into antibody-secreting cells (ASCs; plasmablasts and plasma cells), and production of antibodies, making them promising targets for the treatment of autoantibody-associated diseases such as immune thrombocytopenia (ITP), warm autoimmune hemolytic anemia (wAIHA), and cold agglutinin disease (CAD). Patients with ITP or AIHA have elevated serum BAFF and APRIL levels and belimumab, a BAFF inhibitor, has exhibited encouraging efficacy in the treatment of lupus-associated ITP as well as alone or in combination with rituximab for the treatment of primary ITP. Due to their overlapping but non-redundant roles, inhibition of both BAFF and APRIL may be required for optimal efficacy in autoimmune cytopenias. In preclinical studies, dual BAFF/APRIL inhibition achieved superior suppression of ASCs and immunoglobulin levels vs inhibitors of BAFF or APRIL alone or an anti-CD20 antibody, suggesting the potential of this novel mechanism to modify the underlying pathogenesis of autoimmune cytopenias. Povetacicept (ALPN-303) is a TACI-Fc fusion protein engineered for potent dual BAFF/APRIL inhibition. In a mouse model of AIHA, povetacicept suppressed anti-erythrocyte autoantibodies and increased hematocrit (ASH 2022 abstract #3763). In a first-in-human study in healthy volunteers, povetacicept was well tolerated and reduced levels of circulating ASCs and immunoglobulins. This is an initial report of an open-label study of povetacicept in autoimmune cytopenias (RUBY-4; NCT05757570). Methods: RUBY-4 is a phase 1b, group-sequential, parallel-cohort study evaluating povetacicept in participants aged ≥18 years with a documented diagnosis of primary ITP, wAIHA, or CAD of ≥12 weeks in duration (Figure). Eligible participants must have sustained thrombocytopenia (ITP cohort) or sustained symptomatic anemia (wAIHA/CAD cohorts)-i.e., platelet count &amp;lt;30 × 10 9/L or hemoglobin ≤10 g/dL on 2 occasions ≥7 days apart during screening-and a history of failure or relapse on ≥2 prior treatments (including a thrombopoietin receptor agonist for the ITP cohort). Background therapy, including corticosteroids, is allowed but must remain at stable doses for the durations specified in the protocol. Participants receive povetacicept 240 mg subcutaneously once every 4 weeks for 24 weeks, with an optional 24-week treatment extension, followed by an 8-week off-treatment follow-up period. The primary objective is safety and tolerability; secondary objectives include pharmacokinetics, pharmacodynamics, immunogenicity, and efficacy. Results: As of 31 July 2023, 1 participant with ITP has enrolled and received 2 doses of povetacicept 240 mg without incident. Initial, preliminary observations include expected reductions in B cells and immunoglobulin levels. The RUBY-4 study continues to enroll in the US, Canada, Australia, and Turkey. At the time of presentation, available data including safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy (e.g., platelet or hemoglobin response rate, duration of response, and time to response) findings will be reported. Conclusions: To our knowledge, povetacicept is the first dual BAFF/APRIL inhibitor to be evaluated for the treatment of autoimmune cytopenias. Previous preclinical and healthy volunteer studies suggest the potential of povetacicept for suppression of the pathogenic autoimmunity that mediates platelet/erythrocyte destruction in ITP, wAIHA, and CAD, which may lead to more durable responses and improved outcomes for patients.

Clinical and immunological characterisation of patients with common variable immunodeficiency related immune thrombocytopenia

Primary Immune thrombocytopenia (ITP) is an autoimmune disease. Secondary ITP occurs in patients with underlying diseases such as common variable immunodeficiency (CVID). CVID is one of the most common symptomatic primary immunodeficiencies in adults, characterised by infectious and non-infectious symptoms. Amongst CVID patients, ITP is the most frequent autoimmune manifestation. In this single-centre study, we performed a clinical and immunological characterisation of 20 patients with CVID-related ITP and 20 ITP patients without CVID to compare severity and remission rates. We found that patients with CVID-related ITP had a higher WHO Bleeding Scale at initial diagnosis yet showed higher remission rates and required less treatment. Patients with ITP needed up to seven therapy options and were often treated with second-line drug therapy, whilst only one CVID-related ITP patient required second-line drug therapy. Therefore, we show that the course of thrombocytopenia in patients with CVID-related ITP is milder. Furthermore, we show that soluble interleukin-2 receptor (sIL-2R, CD25) was higher in CVID-related ITP compared to ITP patients and could accurately classify patient cohorts with an Area Under the Receiver Operating Characteristic of 0.92. Whilst none of the ITP patients had a history of immunodeficiency, we found immunological abnormalities in 12 out of 18 patients. Therefore, we recommend screening ITP patients for CVID and other immunodeficiencies to detect immune abnormalities early, as we found patients with reduced immunoglobulin levels as well as severe lymphocytopenia in our ITP cohort.

The Impact of Human Platelet Antigen Allele on Antiplatelet Antibodies and Cryoglobulins in Patients with Primary Immune Thrombocytopenia and Hepatitis C Virus-Associated Immune Thrombocytopenia.

Human platelet antigens (HPAs) are alloantigens associated with antiplatelet alloantibodies and the risk of immune thrombocytopenia (ITP). However, few studies have investigated associations among HPAs, antiplatelet autoantibodies, and cryoglobulins. We enrolled 43 patients with primary ITP, 47 with hepatitis C virus-associated ITP (HCV-ITP), 21 with hepatitis B virus-associated ITP (HBV-ITP), 25 controls with HCV, and 1013 normal controls. We analyzed HPA allele frequencies, including HPA1-6 and 15, antiplatelet antibodies binding to platelet glycoprotein (GP) IIb/IIIa, Ia/IIa, Ib/IX, IV, human leukocyte antigen class I, cryoglobulin IgG/A/M, and their associations with thrombocytopenia. In the ITP cohort, HPA2ab, rather than HPA2aa, predicted a low platelet count. HPA2b was associated with the risk of developing ITP. HPA15b was correlated with multiple antiplatelet antibodies. In HCV-ITP patients, HPA3b was correlated with anti-GPIIb/IIIa antibodies. HCV-ITP patients with anti-GPIIb/IIIa antibodies had a higher positive rate of cryoglobulin IgG and IgA compared with those without anti-GPIIb/IIIa antibodies. Overlapping detection was also found among other antiplatelet antibodies and cryoglobulins. Like the antiplatelet antibodies, cryoglobulins were associated with clinical thrombocytopenia, implying their close relationship. Finally, we extracted cryoglobulins to confirm the exhibition of cryoglobulin-like antiplatelet antibodies. In contrast, in primary ITP patients, HPA3b was correlated with cryoglobulin IgG/A/M rather than anti-GPIIb/IIIa antibodies. HPA alleles were associated with antiplatelet autoantibodies and had different impacts in primary ITP and HCV-ITP patients. HCV-ITP was considered to be a symptom of mixed cryoglobulinemia in HCV patients. The pathophysiology may differ between these two groups.

Immune Thrombocytopenia Onset and Relapse During the COVID-19 Pandemic. A Monocenter Study.

Several infections and vaccinations can provoke immune thrombocytopenia (ITP) onset or relapse. Information on ITP epidemiology and management during the Covid-19 pandemic is scarce. In a large monocenter ITP cohort, we assessed the incidence and risk factors for: 1) ITP onset/relapse after Covid19 vaccination/infection; 2) Covid19 infection. Information on the date/type of anti-Covid-19 vaccine, platelet count before and within 30 days from the vaccine, and date/grade of Covid-19 was collected via phone call or during hematological visits. ITP relapse was defined as a drop in PLT count within 30 days from vaccination, compared to PLT count before vaccination that required a rescue therapy OR a dose increase of an ongoing therapy OR a PLT count <30 ×109/L with ≥20% decrease from baseline. Between February 2020 and January 2022, 60 new ITP diagnoses were observed (30% related to Covid-19 infection or vaccination). Younger and older ages were associated with a higher probability of ITP related to Covid19 infection (p=0.02) and vaccination (p=0.04), respectively. Compared to Covid-19-unrelated ITP, Infection- and vaccine-related ITP had lower response rates (p=0.03) and required more prolonged therapy (p=0.04), respectively. Among the 382 patients with known ITP at the pandemic start, 18.1% relapsed; relapse was attributed to Covid-19 infection/vaccine in 52.2%. The risk of relapse was higher in patients with active disease (p<0.001) and previous vaccine-related relapse (p=0.006). Overall, 18.3% of ITP patients acquired Covid19 (severe in 9.9%); risk was higher in unvaccinated patients (p<0.001). All ITP patients should receive ≥1 vaccine dose and laboratory follow-up after vaccination, with a case-by-case evaluation of completion of the vaccine program if vaccine-related ITP onset/relapse and with tempest initiation of antiviral therapy in unvaccinated patients.

Risk of Immune Thrombocytopenia Relapse and Onset Related to Sars-Cov-2 Infection and Vaccination

New diagnoses and relapses of primary immune thrombocytopenia (ITP) have been reported following SARS-CoV-2 infection and vaccination. In a large monocenter cohort, we assessed: 1) incidence, risk factors and outcome of newly diagnosed ITP and ITP relapses after SARS-CoV-2 infection/vaccination; 2) incidence and risk factors for SARS-CoV-2 infection in the ITP cohort. After IRB approval, 1142 ITP patients (pts) followed at our Hematology Center from 1982 to Feb 2022 were registered in an electronic database. Between Feb 2020 (pandemic start) and Feb 2022, 60 pts were newly diagnosed with ITP. Among the 1082 pts with ITP diagnosis prior to Feb 2020, 297 (27.4%) were deceased before the pandemic start and 403 (37.2%) were untraceable. Taken together, 442 ITP (60 newly and 382 previously diagnosed) pts were included in this study. Information on SARS-CoV-2 infection/vaccination, platelet (PLT) count, and ITP therapy, was collected via phone call/e-mail or during routine medical visits. Laboratory data were verified through health electronic records. Risk factors for ITP relapse included sex, age, vaccine type, previous splenectomy, comorbidities (CCI), active disease (ongoing ITP therapy and/or PLT <100 x109/L), other immune diseases and ITP relapse to previous vaccine doses. Newly diagnosed ITP was considered infection-related (inf-ITP) or vaccine-related (vax-ITP) if the onset occurred <30 days from infection or vaccination, respectively. ITP relapse (rel-ITP) was defined as a drop in PLT count (<30 days from vaccination/infection) that required a rescue therapy OR a dose increase of an ongoing therapy OR a PLT count <30 x109/L with ≥20% decrease from baseline. Eighteen (30%) out of 60 newly diagnosed pts had SARS-CoV-2-related ITP. Inf-ITP was diagnosed in 5 pts (8.3%). Compared to the 55 pts whose ITP was not related to Sars-CoV-2 infection, Inf-ITP pts were younger (median, 41.9 vs 70.2 yrs, p=0.02). ITP outcome was comparable in inf-ITP and other newly diagnosed pts, in terms of response to fist-line steroids (p=0.09), no. of therapeutic lines (p=0.9), and no. of pts still on therapy (p=0.9) at 6 months from diagnosis. Vax-ITP was diagnosed in 13 (21.7%) pts after the first (no.4, 30.8%), second (no.4, 30.8%) or third vaccine dose (no.5, 38.4%). Vaccines were: Comirnaty (53.8%), Vaxzervria (23.1%) or Spikevax (23.1%). Compared to the 47 pts whose ITP was not related to Sars-CoV-2 vaccine, Vax-ITP pts were older (median, 74 vs 55 yrs, p=0.04). ITP treatment duration was longer in Vax-ITP pts (median, 150 days vs 54 days in no Vax-ITP pts, p=0.04); 53.8% of vax-ITP pts were still on therapy 6 months after diagnosis (vs 23.4%, p=0.03). Between Feb 2020 and Feb 2022, 69/382 (18.1%) had a relapse of ITP. In 36/69 pts (52.2%), relapse was related to SARS-CoV-2 infection (1 case) or vaccination (35 cases out of 360 pts who received ≥1 vaccine dose, 9.7%). Ten pts experienced multiple relapses (46 total cases). Post-vaccine relapse occurred in 3.3%, 4.7%, and 5.4% of these 35 pts after the 1st, 2nd, and booster dose, respectively (p=0.65). In multivariate analysis (MVA), active disease at the time of the 1st and the 2nd vaccine dose was associated with Rel-ITP (Odds ratio, OR 10.81, p=0.002; OR 6.88, p=0.001, respectively). After booster, active disease (OR 9.90, p<0.001) and previous Rel-ITP (OR 5.33, p=0.007) was associated with relapse (Fig.1). No major bleeding occurred in newly diagnosed and relapsed pts. Overall, 89/442 (20.1%) ITP pts had a SARS-CoV-2 infection (g≥3 in 10.1%). In MVA with death as competing risk, ≥2 vaccine doses (SHR 0.18; p<0.001) was associated with a lower risk of SARS-CoV-2 infection. SARS-CoV-2 is a risk factor for ITP onset, with 30% of new diagnoses being related to infection/vaccination. In older pts, the risk of vax-ITP is higher, and ITP requires more prolonged therapy, suggesting closer hematological monitoring. Also, >50% of total ITP relapses were related to SARS-CoV-2, mainly occurring after vaccination and regardless of vaccine dose. Thus, strict hematological monitoring may be recommended after all doses. In pts with active disease at vaccination and/or previous ITP relapse after vaccine, the completion of the vaccine program and subsequent laboratory follow-up should be personalized. Notably, vaccination confirmed to be the most protective factor against SARS-CoV-2 infection also in ITP pts. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

P1640: SINGLE NUCLEOTIDE POLYMORPHISMS OF THE HIF1A GENE ARE ASSOCIATED WITH SENSITIVITY OF GLUCOCORTICOID TREATMENT IN PEDIATRIC ITP PATIENTS

Background: Hypoxia-inducible factor-1α (HIF-1α) plays a crucial role in both innate and adaptive immunity. Emerging evidence indicates that HIF-1α is associated with the inflammation and pathologic activities of autoimmune diseases，suggesting that HIF1α may be involved in immune dysregulation in patients with immune thrombocytopenia (ITP). Aims: The purpose of this study was to evaluate whether single nucleotide polymorphisms (SNPs) of the HIF1A gene are associated with susceptibility to ITP and its clinical prognosis including incidence of chronic immune thrombocytopenia (CITP) and glucocorticoid sensitivity. Methods: This study involved 197 Chinese ITP pediatric patients (discovery cohort) and 220 healthy controls. The Sequenom MassArray system (Sequenom, San Diego, CA) was used to detect three SNPs genotypes in the HIF1A gene: rs11549465, rs1957757 and rs2057482. We also employed another ITP cohort (N = 127) to validate the significant results of SNPs found in the discovery cohort. Results: The frequencies of the three SNPs did not show any significant differences between the ITP and healthy control groups. The CT genotype at rs11549465 was significantly higher in ITP patients sensitive to glucocorticoid-treatment than in those insensitive to glucocorticoid-treatment (P = .025). These results were validated using another ITP cohort (N =127, P = .033). Moreover, the CC genotype was a risk factor for insensitive to GT the OR (95% confidence interval) was 5.96(5.23-6.69) in standard prednisone (PDN) (P=.0069) and 6.35(5.33-7.37) in high-dose dexamethasone (HDD) (P=.04). Summary/Conclusion: Although HIF1A gene polymorphisms were not associated with susceptibility to ITP, the CT genotype at rs11549465 was associated with the sensitivity to glucocorticoid-treatment of ITP patients, suggesting that the rs11549465 SNP may contribute to the sensitivity of glucocorticoid treatment in pediatric ITP patients.

SARS-CoV-2 vaccination in pediatric patients with immune thrombocytopenia.

SARS-CoV-2 vaccination in pediatric patients with immune thrombocytopenia.

Single Nucleotide Polymorphisms of the HIF1A Gene are Associated With Sensitivity of Glucocorticoid Treatment in Pediatric ITP Patients.

Hypoxia-inducible factor-1α (HIF-1α) plays a crucial role in both innate and adaptive immunity. Emerging evidence indicates that HIF-1α is associated with the inflammation and pathologic activities of autoimmune diseases, suggesting that HIF1α may be involved in immune dysregulation in patients with immune thrombocytopenia (ITP). The purpose of this study was to evaluate whether single nucleotide polymorphisms (SNPs) of the HIF1A gene are associated with susceptibility to ITP and its clinical prognosis including incidence of chronic ITP and glucocorticoid sensitivity. This study involved 197 Chinese ITP pediatric patients (discovery cohort) and 220 healthy controls. The Sequenom MassArray system (Sequenom, San Diego, CA) was used to detect 3 SNPs genotypes in the HIF1A gene: rs11549465, rs1957757, and rs2057482. We also used another ITP cohort (N=127) to validate the significant results of SNPs found in the discovery cohort. The frequencies of the three SNPs did not show any significant differences between the ITP and healthy control groups. The CT genotype at rs11549465 was significantly higher in ITP patients sensitive to glucocorticoid treatment than in those insensitive to glucocorticoid treatment ( P =0.025). These results were validated using another ITP cohort (N=127, P =0.033). Moreover, the CC genotype was a risk factor for insensitive to GT the odds ratio (95% confidence interval) was 5.96 (5.23-6.69) in standard prednisone ( P =0.0069) and 6.35 (5.33-7.37) in high-dose dexamethasone ( P =0.04). Although HIF1A gene polymorphisms were not associated with susceptibility to ITP, the CT genotype at rs11549465 was associated with the sensitivity to glucocorticoid treatment of ITP patients, suggesting that the rs11549465 SNP may contribute to the sensitivity of glucocorticoid treatment in pediatric ITP patients.

Contribution of Next Generation Flow (NGF) Cytometry in Primary Immune Thrombocytopenia (ITP): Utility for the Differential Diagnosis with Myelodysplastic Syndromes

Background: Primary immune thrombocytopenia (ITP) is an immune-mediated acquired disorder characterized by impaired production and increased destruction of platelets with an elevated risk of bleeding. At present, diagnosis of primary ITP still remains one of exclusion with a need to discard other causes of isolated thrombocytopenia, in the absence of robust and accurate clinical and laboratory diagnostic criteria. For the diagnosis of ITP, a bone marrow (BM) study may be useful to differentiate between ITP and other diseases, such as myelodysplastic syndromes (MDS). Next generation flow (NGF) has emerged as a potential useful tool in these settings.Aim: In this study (FCR-PTI-2017-01) we prospectively evaluated the potential utility of NGF analysis of BM and peripheral blood (PB) for more accurate diagnosis of ITP vs MDS.Methods: 62 patients presenting with isolated thrombocytopenia and classified as ITP (n=20), MDS (n= 11) or inconclusive, i.e. unclassifiable, (n= 25) by BM cytomorphology, were studied. PB (n=47) and BM (n=62) analysis by NGF was blindly performed in parallel for the ITP, MDS and unclassifiable patient groups using the EuroFlow 8-colour AML/MDS classification antibody panel followed by automated analysis against pre-existing flow cytometry databases of normal healthy donor PB and BM immunophenotypic profiles. NGF BM and PB results were then compared with the BM cytomorphological diagnosis. In parallel, epidemiological data from patients were recorded in an electronic case report form (eCRF) and analyzed afterwards.Results: By cytomorphology, expert hematologists were able to conclude an ITP or MDS diagnosis in only 31 cases (55.3%). 62 BM and 48 PB samples with isolated thrombocytopenia were evaluated by NGF. Our 62 patients were allocated in 4 immunophenotypic groups attending to different BM variables observed: maturation blockades, abnormal antigen expression and cross lineage markers. Thus, we observed normal phenotype cases (n=10), isolated (unilineage) alterations (n=24), mild multilineage (>1) alterations (n=20) and severe multilineage (MDS-like) phenotypes (n=8). Cytomorphology diagnosed our cases as ITP, MDS or unclassifiable with a median number of alterations observed by BM NGF of 4 (IQR, 3-6), 2 (IQR, 1-6) and 4 (IQR, 3-5) respectively. For ITP cytomorphology group, NGF demonstrated numerous BM alterations being monocytic alterations (n=17, 94%) the most frequent finding observed. MDS presumed cases were also associated with monocytic alterations (50%) with a frequent decrease in neutrophil precursors (40%). On the contrary, when cytomorphology was not capable to establish a diagnosis, NGF showed a mixture of alterations with no clear predominance of none of them (table 1). Similarly to our work with BM NGF, we looked into a potential correlation of cytomorphology with PB NGF phenotypes. Thus, we observed a median number of alterations of 4 (IQR, 3-5), 4 (IQR, 2-4) and 4 (IQR, 3-5) in ITP, MDS and inconclusive cytomorphology groups. Increased platelet size and upregulated CD41, CD61 and CD63 glycoprotein (GP) expression were the most characteristic findings of ITP cohort. MDS subtype depicted an increased platelet size and overexpression of CD41. Downregulation of GP was restricted to patients with MDS-like phenotypes. (table 2). Nearly statistical significant differences at significance level of 90% were observed between cytomorphology and BM NGF results (p=0.179) (table 3), between platelet score and BM NGF findings (p=0.118) and also, among morphology, BM NGF and platelet score (p=0.179). Nevertheless, cytomorphology and PB NGF showed no statistical differences between them (p=0.206) (table 4).Conclusions: Limitations of BM cytomorphology when facing an isolated thrombocytopenia were demonstrated here. However, normal or unilineage BM NGF alterations may lead us to an ITP diagnosis while mild or severe multilineage BM phenotypes may correlate good with MDS. PB platelet GP expression allowed us to classify our patients in six groups (Gonzalez-Lopez/Matarraz platelet score) which may help ITP diagnosis when this score is low. Comparison of BM cytomorphology, BM NGF and PB NGF techniques at diagnosis showed statistically nearly comparable results (p=0.179), with a bigger amount of patients needed to confirm this trend. All these NGF findings may lead us to better address ITP at diagnosis. [Display omitted] DisclosuresGonzalez-Lopez: Novartis: Other: Advisoryboard and speakers honoraria, Research Funding; Amgen: Other: Advisory board and speakers honoraria, Research Funding; Sobi: Other: Advisory board honoraria; Grifols: Other: Advisory board honoraria.

Proteomic analysis and microRNA expression profiling of plasma‐derived exosomes in primary immune thrombocytopenia

Exosomes are released into extracellular fluids and have emerged as vital biological mediators in autoimmune diseases. Plasma-derived exosomes have been reported to take part in the pathogenesis of primary immune thrombocytopenia (ITP), but the protein and miRNA cargoes have not been entirely elucidated. Via proteomic analysis and RNA sequencing on plasma-derived exosomes from ITP patients and healthy controls, we found one upregulated exosomal protein (apolipoprotein E, ApoE), six downregulated exosomal miRNAs (miR-584-5p, miR-4433a-5p, miR-4433b-3p, miR-6842-3p, miR-130b-5p and miR-222-3p), and 10 upregulated exosomal miRNAs (miR-29a-3p, miR-142-5p, miR-16-2-3p, miR-29b-3p, miR-501-3p, miR-144-5p, miR-192-5p, miR-182-5p, miR-363-3p and miR-96-5p) in ITP patients. The elevated exosomal protein candidate ApoE in the ITP cohort was further validated using western blot. Via quantitative real-time polymerase chain reaction assays, three differentially expressed miRNAs (miR-584-5p, miR-142-5p and miR-29b-3p) were identified. This study provides direct evidence for a restricted signature of exosomal protein and miRNAs which distinguishes ITP from healthy controls. The results require further validation in larger independent ITP cohorts, which will provide insights into the potential pathophysiological significance of circulating exosomes in ITP.

Platelet function and bleeding at different phases of childhood immune thrombocytopenia

Immune thrombocytopenia (ITP) is believed to be associated with platelet function defects. However, their mechanisms are poorly understood, in particular with regard to differences between ITP phases, patient age, and therapy. We investigated platelet function and bleeding in children with either persistent or chronic ITP, with or without romiplostim therapy. The study included 151 children with ITP, of whom 56 had disease duration less than 12 months (grouped together as acute/persistent) and 95 were chronic. Samples of 57 healthy children were used as controls, while 5 patients with leukemia, 5 with aplastic anemia, 4 with MYH9-associated thrombocytopenia, and 7 with Wiskott-Aldrich syndrome were used as non-ITP thrombocytopenia controls. Whole blood flow cytometry revealed that platelets in both acute/persistent and chronic ITP were increased in size compared with healthy donors. They were also pre-activated as assessed by PAC1, CD62p, cytosolic calcium, and procoagulant platelet levels. This pattern was not observed in other childhood thrombocytopenias. Pre-activation by CD62p was higher in the bleeding group in the chronic ITP cohort only. Romiplostim treatment decreased size and pre-activation of the patient platelets, but not calcium. Our data suggest that increased size, pre-activation, and cytosolic calcium are common for all ITP platelets, but their association with bleeding could depend on the disease phase.

Antimicrobial prophylaxis in patients with immune thrombocytopenia treated with rituximab: a retrospective multicenter analysis.

The primary aim of this study was to describe the use of primary anti-infective prophylaxis (AP) in common clinical practice in patients affected by immune thrombocytopenia (ITP) and treated with RTX. Population studied consisted of patients affected by ITP (age ≥ 18years) who had received at least one dose of RTX from January 2008 to June 2018. Five Italian haematology centres participated in the current study. Data were retrospectively collected: demographic data (age, gender), concomitant comorbidities and previous therapies for ITP, characteristics of AP, the occurrence of infections and their management. The ITP cohort consisted of 67 patients sub-grouped into two categories according to the administration of AP: (1) treated with AP (N= 34; 51%) and (2) not treated with AP (N=33, 49%). AP consisted of combined trimethoprim/sulfamethoxazole (TMP/SMX) and acyclovir (AC) in half of patients. TPM/SMX as a single agent was adopted in 32% patients and one patient received only AC. Overall, infections were experienced in 15% of patients during follow-up with a similar proportion in the 2 groups (treated and not treated) of patients (14.7% vs 15%). Clinical course of infections was however, less severe in patients treated with AP, where all infections were grade 2 and did not require hospitalization. In neither group of patients was reported Pneumocystis pneumonia. In conclusion, despite the absence of clear evidence, our analysis shows that AP in patients with ITP receiving RTX is frequently adopted, even if in the absence of well-defined criteria. Prophylaxis administration is quite consistent within the same haematological Center; thus, it seems related to clinicians' experience.

Immunoglobulin Levels As Predictors of the Development of Chronic Disease in Pediatric Immune Thrombocytopenia

Background: Immune thrombocytopenia (ITP) is the most common acquired bleeding disorder in children. Although ~75% of these patients will go on to have spontaneous resolution of disease, up to 25% will develop chronic ITP, with significant and prolonged bleeding symptomatology and impaired quality of life. At this time, there is no definitive method to predict the development of chronic disease at the time of ITP diagnosis. Aims: We aim to identify clinical biomarkers predictive of the development of chronic ITP at the time of diagnosis among pediatric ITP patients. Methods: The clinical records of 280 pediatric ITP patients enrolled in a biological banking study at a large pediatric tertiary care referral center from July 1, 2015 to July 1, 2019 were reviewed in accordance with IRB-approved protocols. ITP diagnosis and chronicity of disease (vs. spontaneous resolution within 1 year of diagnosis) was confirmed by a pediatric hematologist, as defined by current international expert committee standards (Neunert et al, Blood, 2011;117(16):4190-207; Provan et al, Blood, 2010;115(2):168-186). Patients with non-classical ITP were excluded (1 child with drug-induced ITP in the setting of acyclovir therapy, and 1 neonate with passive ITP in the setting of maternal lupus); and patients who were lost to follow-up or had ongoing disease of &amp;lt;1 year duration were subsequently excluded. Patient characteristics including age, gender, ethnicity, presence of concurrent autoimmune disease, and time to resolution were collected. Pertinent biomarkers including immunoglobulin levels (IgG, IgA, and IgM), anti-nuclear antibody (ANA), C-reactive protein (CRP), and immature platelet fraction (IPF) which were obtained at the time of diagnosis were documented, if if obtained prior to the administration of any ITP-directed therapy, and within 2 weeks of diagnosis. Chi-squared test or Fisher's exact test was utilized to compare nonparametric categorical data. Mann-Whitney U test was used to compare nonparametric continuous data. A multivariate backwards logistic regression model was conducted to determine independent associations with the development of chronic ITP. Statistical analyses were performed using SPSS Statistics 26 (IBM, Armonk, New York). A Bonferroni correction was applied to correct for multiple comparisons. A p value &amp;lt; 0.05 was defined as statistically significant. Results: We identified 251 pediatric ITP patients with sufficient length of follow-up to define acute (&amp;lt;1 year) vs. chronic (&amp;gt;1 year) disease within our 4-year study period. This included 132 patients with acute ITP (53%) and 119 patients who went on to develop chronic ITP (47%). Mean age of diagnosis among those with acute ITP was 5.5 years, while mean age of diagnosis among those with chronic ITP was 7.7 years. Within the entire cohort, 126 (50%) were male, and 124 (49%) were of Hispanic ethnicity. Fifty-eight had ITP attributable to systemic autoimmune disease - 17% within the Acute ITP group, and 30% within the Chronic ITP group. Among all patients (n=251), 188 with evaluable biomarkers (immunoglobulin levels, ANA, CRP, or IPF) at the time of diagnosis were identified. These included 174 patients with Ig levels at diagnosis, 43 patients with ANA titers at diagnosis, 25 patients with CRP levels at diagnosis, and 78 patients with IPF at diagnosis. By univariate analysis, we found that abnormalities in immunoglobulin levels at diagnosis were significantly associated with the development of chronic ITP. Low IgG levels (p = 0.015) were more prevalent in chronic (10.3%) vs. acute ITP (1.9%). High IgG levels (p = 0.015) were more prevalent in chronic (6.7%) vs. acute ITP (1.9%). High IgM levels (p = 0.03) were more prevalent in chronic (26.5%) vs. acute ITP (13.3%). Of note, the presence of Evans syndrome (p = 0.0005) and other systemic autoimmune disease (p = 0.011) were also significantly associated with the development of chronic ITP. Subsequent multivariate analysis identified low IgG level at diagnosis to be independently predictive of chronic ITP (p = 0.043, with an odds ratio of 5.7). Conclusion: Although further study is needed within a larger international pediatric ITP cohort, the findings from this institutional study indicate that biomarkers obtained in routine clinical care at the time of ITP diagnosis, specifically immunoglobulin levels, can be utilized to help predict development of chronic disease among pediatric ITP patients. Disclosures Despotovic: Amgen: Research Funding; Dova: Honoraria; Novartis: Research Funding.

Long‐term remission rates after splenectomy in adults with Evans syndrome compared to immune thrombocytopenia: A single‐center retrospective study

Evans syndrome, the combination of immune thrombocytopenia (ITP) and autoimmune hemolytic anemia (AIHA) or autoimmune neutropenia, is associated with a high rate of relapsed/refractory disease. There are limited data on the efficacy of splenectomy for this condition. We reviewed patient outcomes after splenectomy for Evans syndrome compared to ITP at our institution. We performed a retrospective analysis of patients who underwent splenectomy for autoimmune cytopenias over a 23-year period with the intention of comparing disease relapse rates after splenectomy in patients with Evans syndrome and in those with ITP. During the study period, 77 patients underwent splenectomy for ITP and seven underwent splenectomy for Evans syndrome. In the Evans cohort, splenectomy led to an 85.7% initial response rate with a 42.8% rate of relapse within one year and a long-term (one-year) response rate of 42.8%. In the ITP cohort, the initial response rate was 90.9% with a long-term response rate of 70.1%. Our data suggest that long-term remission rates after splenectomy are lower in adults with Evans syndrome compared to those with ITP, although splenectomy may still be an acceptable treatment for certain patients with Evans syndrome. Our findings underscore the need for further research and development of additional therapeutic strategies for this patient population.

Bayesian Analysis of TPO Levels in Immune Thrombocytopenia

Introduction: Thrombopoietin (TPO) is a haematopoietic growth factor that has a primary function in promoting the differentiation and maturation of megakaryocytes and the subsequent production of platelets. In patients with immune thrombocytopenia (ITP) TPO levels have been shown to be inappropriately low. The exact reasons for this are not well understood and are highly debated. The predominant hypothesis is that higher rates of platelet turnover in active ITP lead to an increased consumption of TPO through its binding to high-affinity receptors on the platelet cell membrane (the ‘sponge theory‘). To better understand the relationship between TPO and platelets in ITP we measured TPO levels in 67 patients with chronic ITP with a range of different platelet counts. For comparison we also measured TPO levels in 5 patients with aplastic anaemia as these patients are thrombocytopenic but lack direct immune-mediated platelet destruction. We used a Bayesian regression model to analyse the association between TPO and platelet counts, which has been shown to be more accurate with smaller sample sizes than classical gaussian regression models. We used this model to infer the probability distribution of TPO over a range of different platelet counts.Methods: Blood samples were collected in duplicate in sodium citrate vacutainer tubes, double spun and stored at -80°C within four hours of collection. TPO levels were measured using quantitative sandwich enzyme immunoassay technique. We used log-normalised TPO and platelet counts in a Bayesian regression model; with uninformative Gaussian prior distributions (mean 0.01, standard deviation 10). We used Gibbs sampling with 100,000 iterations to calculate posterior distributions from which we derived maximium a posteriori (MAP) estimates and 90% Bayesian Confidence intervals (BCI) for a range of platelet counts (1 to 200).Results: Of the 130 samples collected, 30 samples were excluded for failing to detect any TPO. All but 1 of these patients had a second positive sample. In the ITP group, median TPO levels was 43pg/ml (range 1.7 - 923.4pg/ml) with a median platelet count of 63 (range 3 - 328). 20% of this group were in remission at the time of sampling. In the aplastic anaemia cohort there were 9 samples with a median TPO of 1887.6pg/ml (range 9.4-4572.5pg/ml) and a median platelet count of 20 (range 4 - 102). The higher platelet counts (>35) in this aplastic group were from patients on tacrolimus therapy (n= 3). There was a clear non-linear relationship between platelet counts and TPO levels in both ITP and aplastic anaemia patients (FIGURE 1). At any given platelet count, MAP TPO estimates in our ITP cohort were approximately a tenth of that for patients with aplastic anaemia. 13% of the ITP patients were on TPO agonists, although a sensitivity analysis found this did not significantly influence model estimates. At a platelet count of 1 the MAP TPO estimate in ITP was 410pg/ml (BCI; 200-804pg/ml). This declined sharply to 100pg/ml as platelet counts increased to 10. The decline in TPO became increasingly shallow as platelet counts increased further, and at 100 it was 24pg/ml (BCI 18-29 pg/ml). In contrast, MAP TPO estimates in the aplastic anaemia group were >10000pg/ml at a platelet count of 1 and 221pg/ml (BIC 112 to 828pg/ml) at 100. This is approaching the normal range for a healthy individual (mean 120pg/ml, range 80 - 230pg/ml).Conclusion: This study shows that in patients with ITP and aplastic anaemia there is a non-linear correlation between platelet counts and TPO. The levels of TPO in patients with ITP were consistently lower than patients with aplastic anaemia at all platelet counts. This indicates that at all stages of disease activity, immune attack on platelets (and possibly megakaryocytes) in ITP and immune attack on the whole bone marrow in aplastic anaemia have differential effects on TPO levels. The findings also suggest that TPO in combination with platelet counts, when compared to modelled predictions, could be used as a diagnostic marker to differentiate between failure of platelet production and increased platelet destruction. Further work is needed to better understand the regulation of TPO in each disease. [Display omitted] DisclosuresCooper:Amgen, Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.