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Key Clinical Message: Recommendations advise factor IX desensitization before immune tolerance induction in severe hemophilia B, supported by immunosuppression. A child with inhibitor and anaphylaxis to factor IX showed successful immunosuppression‐free immune tolerance induction using very low and slowly increasing doses of a factor IX extended‐half‐life product. Immune tolerance to factor IX based on this protocol merits further study. [ABSTRACT FROM AUTHOR]

Introduction: Surgeries are implicated in the development of anti-factor VIII (FVIII) neutralizing antibodies (inhibitors) in hemophilia A individuals with immune tolerance induction (ITI) treatment being the recommended therapy to eradicate these inhibitors. We evaluated the association of surgical procedures performed during ITI and treatment outcome. Methods: Patients were treated according to the Brazilian ITI Protocol with outcomes being defined as successful (i.e., recovered responsiveness to exogenous FVIII) and failed (i.e., unresponsiveness to exogenous FVIII thus requiring bypassing agents for bleeding control). Surgical procedures during induction therapy were managed following international recommendations. Results: Treatment success rate was 68.7 % in 163 patients; 33 (20.2 %) were submitted to 43 (96 %) minor and two major surgeries. Personal, hemophilia, inhibitor, and treatment characteristics were similar between patients submitted to surgical procedures or not while on ITI; the success rates were 72.7 % and 67.7 % (p-value = 0.577), respectively. Conclusion: No association was found between having a minor surgical procedure and ITI treatment outcome.

ABSTRACT Importance It remained unclear that the efficacy comparison between low‐dose immune tolerance induction (LD‐ITI) incorporating immunosuppressants (IS) when severe hemophilia A (SHA) patients had inhibitor‐titer ≥200 Bethesda Units (BU)/mL (LD‐ITI‐IS200 regimen) and LD‐ITI combining with IS when SHA patients had inhibitor‐titer ≥40 BU/mL (LD‐ITI‐IS40 regimen). Objective To compare the efficacy of the LD‐ITI‐IS200 regimen with that of the LD‐ITI‐IS40 regimen for SHA patients with high‐titer inhibitors. Methods A prospective cohort study on patients receiving LD‐ITI‐IS200 compared to those receiving LD‐ITI‐IS40 from January 2021 to December 2023. Both received LD‐ITI [FVIII 50 IU/kg every other day]. IS (rituximab + prednisone) was added when peak inhibitor tier ≥200 BU/mL in the LD‐ITI‐IS200 regimen and ≥40 BU/mL in the LD‐ITI‐IS40 regimen. Success is defined as a negative inhibitor plus FVIII recovery ≥66% of the expected. Results We enrolled 30 patients on LD‐ITI‐IS200 and 64 patients on LD‐ITI‐IS40, with similar baseline clinical characteristics. A lower IS‐use rate was discovered in the LD‐ITI‐IS200 regimen compared to the LD‐ITI‐IS40 regimen (30.0% vs. 62.5%). The two regimens (LD‐ITI‐IS200 vs. LD‐ITI‐IS40) had similar success rate (70.0% vs. 79.7%), median time to success (9.4 vs. 10.6 months), and annualized bleeding rate during ITI (3.7 vs. 2.8). The cost to success was lower for LD‐ITI‐IS200 than for LD‐ITI‐IS40 (2107 vs. 3256 US Dollar/kg). Among patients with peak inhibitor‐titer 40–199 BU/mL, 10 non‐IS‐using (on LD‐ITI‐IS200 regimen) and 28 IS‐using (on LD‐ITI‐IS40 regimen) had similar success rates (70.0% vs. 78.6%) and time to success (9.0 vs. 8.8 months). Interpretation In LD‐ITI, IS are not necessary for inhibitor titer

One of the well-known X-linked genetic disorders is hemophilia, which could be hemophilia A as a result of a mutation in the F8 (factor VIII) gene or hemophilia B as a result of a mutation in the F9 (factor IX) gene, leading to insufficient levels of the proteins essential for blood coagulation cascade. In patients with severe hemophilia, factor VIII or factor IX activities in the blood plasma are considerably low, estimated to be less than 1%. This is responsible for spontaneous or post-traumatic bleeding episodes, or both, leading to disease complications and death. Current treatment of hemophilia relies on the prevention of bleeding, which consists of expensive lifelong replacement infusion therapy of blood plasma clotting factors, their recombinant versions, or therapy with recombinant monoclonal antibodies. Recently emerged gene therapy approaches may be a potential game changer that could reshape the therapeutic outcomes of hemophilia A or B using a one-off vector in vivo delivery and aim to achieve long-term endogenous expression of factor VIII or IX. This review examines both traditional approaches to the treatment of hemophilia and modern methods, primarily focusing on gene therapy, to update knowledge in this area. Recent technological advances and gene therapeutics in the pipeline are critically reviewed and summarized. We consider gene therapy to be the most promising method as it may overcome the problems associated with more traditional treatments, such as the need for constant and expensive infusions and the presence of an immune response to the antibody drugs used to treat hemophilia. [ABSTRACT FROM AUTHOR]

Importance: It remained unclear that the efficacy comparison between low‐dose immune tolerance induction (LD‐ITI) incorporating immunosuppressants (IS) when severe hemophilia A (SHA) patients had inhibitor‐titer ≥200 Bethesda Units (BU)/mL (LD‐ITI‐IS200 regimen) and LD‐ITI combining with IS when SHA patients had inhibitor‐titer ≥40 BU/mL (LD‐ITI‐IS40 regimen). Objective: To compare the efficacy of the LD‐ITI‐IS200 regimen with that of the LD‐ITI‐IS40 regimen for SHA patients with high‐titer inhibitors. Methods: A prospective cohort study on patients receiving LD‐ITI‐IS200 compared to those receiving LD‐ITI‐IS40 from January 2021 to December 2023. Both received LD‐ITI [FVIII 50 IU/kg every other day]. IS (rituximab + prednisone) was added when peak inhibitor tier ≥200 BU/mL in the LD‐ITI‐IS200 regimen and ≥40 BU/mL in the LD‐ITI‐IS40 regimen. Success is defined as a negative inhibitor plus FVIII recovery ≥66% of the expected. Results: We enrolled 30 patients on LD‐ITI‐IS200 and 64 patients on LD‐ITI‐IS40, with similar baseline clinical characteristics. A lower IS‐use rate was discovered in the LD‐ITI‐IS200 regimen compared to the LD‐ITI‐IS40 regimen (30.0% vs. 62.5%). The two regimens (LD‐ITI‐IS200 vs. LD‐ITI‐IS40) had similar success rate (70.0% vs. 79.7%), median time to success (9.4 vs. 10.6 months), and annualized bleeding rate during ITI (3.7 vs. 2.8). The cost to success was lower for LD‐ITI‐IS200 than for LD‐ITI‐IS40 (2107 vs. 3256 US Dollar/kg). Among patients with peak inhibitor‐titer 40–199 BU/mL, 10 non‐IS‐using (on LD‐ITI‐IS200 regimen) and 28 IS‐using (on LD‐ITI‐IS40 regimen) had similar success rates (70.0% vs. 78.6%) and time to success (9.0 vs. 8.8 months). Interpretation: In LD‐ITI, IS are not necessary for inhibitor titer <200 BU/mL. [ABSTRACT FROM AUTHOR]

Introduction: Immune tolerance induction (ITI) is the only treatment to eradicate inhibitors in people with severe haemophilia A with inhibitors. Since the risk of inhibitor development is greater among Black and Hispanic persons, it has been hypothesized that race and ethnicity may influence ITI success. Limited studies have evaluated this hypothesis. Aim: To examine the success of ITI according to race and ethnicity. Methods: Participants who entered the Community Counts (CC) Registry between 2013 and 2017, were aged ≥3 years at study entry, and received ITI were included (n = 559). The proportion of participants with successful ITI was examined with adjusted prevalence ratios (aPRs) and corresponding 95% confidence intervals (95% CIs). Results: Among 559 participants, 56.9%, 19.1%, 18.1% and 4.3% were Non‐Hispanic (NH) White, NH Black, Hispanic and Asian, respectively, and 1.7% were coded as other or missing. Approximately 80% of Hispanic, NH Black and NH White participants had good/very good prognosis, defined as having a pre‐ITI peak inhibitor of < 200 Bethesda Units per millilitre. Nearly 60% of participants (59.7%) achieved successful ITI, 20.7% and 19.5% experienced partially successful or failed ITI, respectively. Successful ITI was non‐significantly lower in NH Black (54.2%; aPR = 0.95, 95% CI 0.62–1.44) and Hispanic (55.4%; aPR = 0.89, 95% CI 0.71–1.13) relative to NH White participants (62.6%). Conclusion: In this study, 60% of participants in the CC Registry had successful ITI, consistent with previous studies. The proportion with successful ITI was generally comparable across racial and ethnic groups with similar prognosis. These findings do not support the hypothesis that ITI response varies according to race or ethnicity. [ABSTRACT FROM AUTHOR]

• Immunogenicity is a recurring concern across all therapies for Hemophilia A. It impacts the safety and efficacy of new and old recombinant Factor VIII products, the long-acting FVIII versions, as well as other clinical options such as bypassing agents and gene-based therapies. • The risk of anti-drug antibody development for any given Hemophilia A patient remains under investigation but a multitude of factors, related to the patient's genetic mutations, health status, and treatment or product history, have been recognized. • Gene replacement and gene editing therapies for Hemophilia A represent new treatment options for generating long-term production of factor VIII in patients, but pre-existing and de novo immunity against the vector capsids and transgene products pose significant impediments in their development. The introduction and development of biologics such as therapeutic proteins, gene-, and cell-based therapy have revolutionized the scope of treatment for many diseases. However, a significant portion of the patients develop unwanted immune reactions against these novel biological modalities, referred to as immunogenicity, and no longer benefit from the treatments. In the current review, using Hemophilia A (HA) therapy as an example, we will discuss the immunogenicity issue of multiple biological modalities. Currently, the number of therapeutic modalities that are approved or recently explored to treat HA, a hereditary bleeding disorder, is increasing rapidly. These include, but are not limited to, recombinant factor VIII proteins, PEGylated FVIII, FVIII Fc fusion protein, bispecific monoclonal antibodies, gene replacement therapy, gene editing therapy, and cell-based therapy. They offer the patients a broader range of more advanced and effective treatment options, yet immunogenicity remains the most critical complication in the management of this disorder. Recent advances in strategies to manage and mitigate immunogenicity will also be reviewed. [ABSTRACT FROM AUTHOR]

Abstract Background Haemophilia A is a bleeding disorder caused by deficiency of coagulation factor VIII (FVIII) which leads to severe and repeated bleedings. There is a need to understand the optimal treatment pathway for FVIII inhibitors with the use of immune tolerance induction (ITI) and the role of haemostatic ‘bypassing’ agents (BPA) on-demand (OD) or prophylactically (Px). The aim of this study was to gain a better understanding of the real-world use of BPA therapy administered prophylactically or on-demand concomitant with ITI, for the treatment of an inhibitor to FVIII replacement therapy in patients with severe haemophilia A. Methods Retrospective observational data were used to capture disease management information for patients who were aged 16 or under and had received ITI and BPA treatment for their most recent inhibitor from Jan-2015 to Jan-2019, for 47 patients in the UK and Germany. Descriptive comparisons of the clinical effectiveness and resource utilisation of Px and OD BPA therapy during ITI were conducted. Results During ITI and BPA treatment, for an inhibitor, bleeding events averaged 1.5 and 1.2 for Px and OD treatment respectively. Compared to only BPA therapy we see 3.4 and 1.4 bleeding events for Px and OD respectively during an inhibitor. Conclusion Baseline disease characteristics differed between BPA therapy cohorts and this resulted in higher clinical effectiveness of ITI treatment alongside BPA Px than BPA OD during an inhibitor.

The predictors of immune tolerance induction (ITI) outcomes in hemophilia A (HA) patients with the same F8 genetic background have not yet been evaluated, although the F8 genotype is strongly associated with ITI response. This study aims to explore the predictors of ITI outcomes in the same F8 genetic background by focusing on intron 22 inversion (Inv22) patients with high-responding inhibitors. HA children with Inv22 and high-responding inhibitors who received low-dose ITI therapy over 24 months were included in this study. ITI outcomes were centrally assessed at the 24th month of treatment. The predictive ability of clinical variables to identify ITI success was determined using the receiver operating characteristic (ROC) curve, and the predictor of ITI outcomes was analyzed on the multivariable Cox model. Among the 32 patients investigated, 23 (71.9 %) achieved success. In univariate analysis, interval time from inhibitor diagnosis to ITI start (interval-time) was significantly associated with ITI success (P = 0.001); however, inhibitor titers showed no significance (P > 0.05). The interval-time demonstrated a good predictive value for ITI success with the area under the ROC curve of 0.855 (P = 0.002), and the cutoff value was 25.8 months (sensitivity, 87.0 %; specificity, 88.9 %). In the multivariable Cox model which considered success rate and time to success, interval-time was the only independent predictor (<25.8 months vs. ≥25.8 months, P = 0.002). The interval-time was first identified as a unique predictor of ITI outcomes in HA patients with high-responding inhibitors under the same F8 genetic background (Inv22). An interval-time of <25.8 months was associated with increased ITI success and reduced time to success. • Predictor of ITI outcomes in the same F8 gene background is unclear. • Inv22 children with high-responding inhibitors were included and analyzed. • Interval time from inhibitor diagnosis to ITI start (interval-time) was first identified as a unique predictor of ITI outcomes. • Interval-time of <25.8 months was associated with improved ITI outcomes. [ABSTRACT FROM AUTHOR]

Shorter interval-time from inhibitor detection to starting immune tolerance induction (ITI) might predict better ITI outcomes for severe Hemophilia A (SHA) patients with high-risk-inhibitors. However, the prediction-impact of interval-time for these patients on low-dose ITI strategy remained unclear. To explore the relationship between interval-time and low-dose ITI outcomes in Chinese SHA children with high-risk-inhibitors. This was a single-center, retrospective study on SHA children with high-risk-inhibitors (each with immediate pre-ITI inhibitor titer>10 Bethesda Units/mL) undergoing low-dose ITI strategy for ≥24 months. ITI outcomes and their predictive factors were evaluated at the 24th month treatment for each patient. The predictive ability of interval-time on ITI success was determined using receiver operating characteristic (ROC) curve. Among 47 patients investigated, 34 (72.3 %) achieved success. Independent predictor for ITI-outcome on multivariate analysis included the interval-time (p = 0.007) and peak inhibitor-titer (p = 0.011). Shorter interval-time predicted ITI success [cut-off value = 22.3 months, area under ROC-curve (AUC) = 0.701] and early-ITI success within 12 month (cut-off value = 9.4 months AUC = 0.704). Linear regression analysis suggested each month interval-time delay delayed success by 0.1552 month. Unlike the interval-time, peak inhibitor-titer had no success-predictive value in high-peak inhibitor-titer patients on ITI with immunosuppressants. Interval-time represented a strong predictive value for outcomes in our low-dose ITI strategy for SHA patients with high-risk-inhibitors. Shorter interval-time was associated with higher success rate and earlier success achievement. The respective interval-time cut-off values were 22.3 months for ITI success and 9.4 months for early-success. • The interval-time is the time from inhibitor detection to starting ITI. • Interval-time for predicting low-dose ITI outcomes remained unclear, for high-risk-inhibitors patients. • Interval-time had a strong predictive value for outcomes in our low-dose ITI strategy. • Interval-time cut-off values were 22.3 for success and 9.4 months for early-success. [ABSTRACT FROM AUTHOR]

• Refractoriness was inability to achieve negative inhibitor titer over at least 12 months period taking LD-ITI+Rituximab-IS. • There is therefore a need to explore rescue-regimen(s) for refractory patients. • MMF might exert T-cell immunosuppression not covered by Rituximab which focuses on B-cell suppression. • The sequential MMF-rescue-regimen had efficacy in the patients refractory to our initial LD-ITI+Rituximab-IS regimen. [ABSTRACT FROM AUTHOR]

Background: Haemophilia A is a bleeding disorder caused by deficiency of coagulation factor VIII (FVIII) which leads to severe and repeated bleedings. There is a need to understand the optimal treatment pathway for FVIII inhibitors with the use of immune tolerance induction (ITI) and the role of haemostatic 'bypassing' agents (BPA) on-demand (OD) or prophylactically (Px). The aim of this study was to gain a better understanding of the real-world use of BPA therapy administered prophylactically or on-demand concomitant with ITI, for the treatment of an inhibitor to FVIII replacement therapy in patients with severe haemophilia A. Methods: Retrospective observational data were used to capture disease management information for patients who were aged 16 or under and had received ITI and BPA treatment for their most recent inhibitor from Jan-2015 to Jan-2019, for 47 patients in the UK and Germany. Descriptive comparisons of the clinical effectiveness and resource utilisation of Px and OD BPA therapy during ITI were conducted. Results: During ITI and BPA treatment, for an inhibitor, bleeding events averaged 1.5 and 1.2 for Px and OD treatment respectively. Compared to only BPA therapy we see 3.4 and 1.4 bleeding events for Px and OD respectively during an inhibitor. Conclusion: Baseline disease characteristics differed between BPA therapy cohorts and this resulted in higher clinical effectiveness of ITI treatment alongside BPA Px than BPA OD during an inhibitor. [ABSTRACT FROM AUTHOR]

This study aimed to measure the cost-effectiveness of prophylaxis with emicizumab in PsHAhri on ITI in Brazil. A cost-effectiveness modeling analysis was used to estimate the costs per PsHAhri on ITI and the number of prevented bleedings from undertaking one intervention (prophylaxis with BpA) over another (prophylaxis with emicizumab), based on the Brazilian Ministry of Health perspective. Costs of ITI with recombinant FVIII, prophylaxis with BpA or emicizumab, and treated bleeding episodes with BpA costs were evaluated for PsHAhri who had ITI success or failure. This study was conducted with the perspective of the Brazilian Ministry of Health (payer). During ITI, prophylaxis with BpA cost US $924 666/PsHAhri/ITI, whereas prophylaxis with emicizumab cost US $488 785/PsHAhri/ITI. During ITI, there was an average of 9.32 bleeding episodes/PsHAhri/ITI when BpA were used as prophylaxis and 0.67 bleeding/PsHAhri/ITI when emicizumab was used. By univariate deterministic sensitivity analysis, emicizumab remained dominant whichever variable was modified. In this study, prophylaxis with emicizumab during ITI is a dominant option compared with prophylaxis with BpA during ITI. • The development of anti-factor VIII antibodies (inhibitor) is related to worse outcomes of treatment of people with severe hemophilia A (PsHA). • Immune tolerance induction (ITI) is the treatment of choice to eradicate inhibitors in PsHA and high-responding inhibitors (PsHAhri). The effectiveness of bypassing agents for preventing bleeding during ITI is already known. Assuming the same effectiveness of emicizumab in preventing bleeding in PsHAhri not under ITI, we evaluated the cost-effectiveness of emicizumab for PsHAhri undergoing ITI according to the Brazilian ITI protocol. • By univariate deterministic and probabilistic sensitivity analyses, emicizumab remained dominant whichever variable was modified. [ABSTRACT FROM AUTHOR]

Enzyme replacement therapy (ERT) is the current standard treatment for Pompe disease, a lysosomal storage disorder caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). ERT has shown to be lifesaving in patients with classic infantile Pompe disease. However, a major drawback is the development of neutralizing antibodies against ERT. Hematopoietic stem and progenitor cell-mediated lentiviral gene therapy (HSPC-LVGT) provides a novel, potential lifelong therapy with a single intervention and may induce immune tolerance. Here, we investigated whether ERT can be safely applied as additional or alternative therapy following HSPC-LVGT in a murine model of Pompe disease. We found that lentiviral expression at subtherapeutic dose was sufficient to induce tolerance to the transgene product, as well as to subsequently administered ERT. Immune tolerance was established within 4–6 weeks after gene therapy. The mice tolerated ERT doses up to 100 mg/kg, allowing ERT to eliminate glycogen accumulation in cardiac and skeletal muscle and normalizing locomotor function. The presence of HSPC-derived cells expressing GAA in the thymus suggested the establishment of central immune tolerance. These findings demonstrate that lentiviral gene therapy in murine Pompe disease induced robust and long-term immune tolerance to GAA either expressed by a transgene or supplied as ERT.

Abstract Background Classic infantile onset of Pompe disease (c-IOPD) leads to hypotonia and hypertrophic cardiomyopathy within the first days to weeks of life and, without treatment, patients die of cardiorespiratory failure in their first 1–2 years of life. Enzymatic replacement therapy (ERT) with alglucosidase alfa is the only available treatment, but adverse immune reactions can reduce ERT’s effectiveness and safety. It is therefore very important to identify strategies to prevent and manage these complications. Several articles have been written on this disease over the last 10 years, but no univocal indications have been established. Methods Our study presents a review of the current literature on management of immune responses to ERT in c-IOPD as considered by an Italian study group of pediatric metabolists and immunologists in light of our shared patient experience. Results We summarize the protocols for the management of adverse reactions to ERT, analyzing their advantages and disadvantages, and provide expert recommendations for their optimal management, to the best of current knowledge. However, further studies are needed to improve actual management protocols, which still have several limitations.

Introduction: The development of inhibitors against factor FIX (FIX) is the most serious complication of FIX replacement therapy in haemophilia B (HB) patients. Currently, only few cohorts of HB inhibitor patients have been reported worldwide. Aim: This Chinese nationwide study of HB inhibitor patients explored their risk factors for FIX inhibitor development and experience on their management. Methods: We retrospectively analysed patient characteristics, F9 genotypes, treatment strategies and outcomes of HB inhibitor patients registered to the Chinese National Registry and Patient Organization Registry. Results: Forty‐four unique HB inhibitor patients were identified in 4485 unique HB patients registered by year 2021 to the two Registries. Inhibitor diagnosis were usually delayed and the low prevalence (.98%) may suggest some inhibitor patients were not identified. Their median age at inhibitor diagnosis was 7.5 (IQR, 3.0–14.8) years. Most patients (95.5%) had high‐titre inhibitors. Allergic/Anaphylactic reactions occurred in 59.1% patients. Large deletions and nonsense mutations were the most common F9 mutation types in our FIX inhibitor patients. Patients with large F9 gene deletions were more likely to develop inhibitors (p =.0002), while those with missense mutations had a low risk (p <.0001). Thirteen (29.5%) patients received immune tolerance induction (ITI) therapy using low‐dose prothrombin complex concentrate regimens. Twelve completed ITI with three (25.0%) achieving success. Nephrotic syndrome developed in two (16.7%) patients during ITI. Conclusion: This study reports the largest Chinese cohort of HB inhibitor patients. Large deletions were most significantly associated with inhibitor development. Low‐dose ITI might be feasible for FIX inhibitor eradication. [ABSTRACT FROM AUTHOR]

Introduction: The development of inhibitors with factor VIII (FVIII) replacement therapy is one of the most common and challenging complications of haemophilia A (HA) treatment, jeopardising treatment efficacy and predisposing patients to high risks of morbidity and mortality. The management of patients with inhibitors is particularly challenging in countries where resources are limited. Aim: To provide a comprehensive summary of the management of HA with inhibitors while focusing on differences in practice between Western and non‐Western countries and how resource scarcity can impact HA management, leading to suboptimal outcomes in patients with inhibitors. Methods: Summary of key evidence and regional expert opinion. Results: We address, particularly, the diagnosis of and testing for inhibitors, as well as the epidemiology of inhibitors, including incidence, prevalence and disease burden. Secondly, we provide an overview of the current treatment landscape in HA with inhibitors regarding the eradication of inhibitors with immune tolerance induction and the treatment and prevention of bleeding with bypassing agents, non‐factor replacement agents and other experimental therapies. This is complemented with insights from the authors around the applicability of, and challenges associated with, such therapies in their settings of practice. Conclusions: We conclude by proposing some key steps towards bridging the gaps in the management of HA with inhibitors in resource‐limited countries, including: (1) the collection of quality data that can inform healthcare reforms and policies; (2) improving disease knowledge among healthcare practitioners and patients with the aim of standardising disease management across centres and (3) working towards promoting equal access to HA care and therapies for everyone. [ABSTRACT FROM AUTHOR]

The development of inhibitory antibodies (inhibitors) in persons with hemophilia B (PwHB) causes significant morbidity. Data on the impact of the F9 variant and immune tolerance induction (ITI) outcome are limited. The aim of this study was to investigate the presence of neutralizing and non-neutralizing antibodies (NNA) in severe hemophilia B (HB) and to evaluate ITI outcome and complications in relation to the pathogenic F9 variant. Persons with severe HB in the Nordic countries were enrolled and information on F9 variants, inhibitors, ITI and complications were collected. Analyses of anti-FIX antibodies with a fluorescence-immunoassay (xFLI) and an ELISA method were conducted. Seventy-nine PwHB were enrolled. Null variants were seen in 33 (42 %) PwHB and 12 (15 %) had a current or former inhibitor. Eleven (92 %) of the inhibitor patients had experienced allergic manifestations and three (25 %) nephrotic syndrome. Of 10 PwHB with at least one ITI attempt, eight (80 %) were considered tolerant at enrolment. Immunosuppression was included in seven of eight successful or partially successful attempts. Five PwHB had at least one ITI failure before a successful or partially successful ITI. No NNA could be identified. A high proportion of severe F9 gene defects among persons with severe HB in the Nordic countries may explain the observed relatively high prevalence of inhibitors. ITI success was independent of the F9 variant and attained despite allergic manifestations and previous ITI failures. Inclusion of immunosuppression tentatively enhances the chances of ITI success. No NNA were observed. [ABSTRACT FROM AUTHOR]

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system with no cure yet. Here, we report genetic engineering of hematopoietic stem cells (HSCs) to express myelin oligodendrocyte glycoprotein (MOG), specifically in platelets, as a means of intervention to induce immune tolerance in experimental autoimmune encephalomyelitis (EAE), the mouse model of MS. The platelet-specific αIIb promoter was used to drive either a full-length or truncated MOG expression cassette. Platelet-MOG expression was introduced by lentivirus transduction of HSCs followed by transplantation. MOG protein was detected on the cell surface of platelets only in full-length MOG-transduced recipients, but MOG was detected in transmembrane-domain-less MOG1-157-transduced platelets intracellularly. We found that targeting MOG expression to platelets could prevent EAE development and attenuate disease severity, including the loss of bladder control in transduced recipients. Elimination of the transmembrane domains of MOG significantly enhanced the clinical efficacy in preventing the onset and development of the disease and induced CD4+Foxp3+ Treg cells in the EAE model. Together, our data demonstrated that targeting transmembrane domain-deleted MOG expression to platelets is an effective strategy to induce immune tolerance in EAE, which could be a promising approach for the treatment of patients with MS autoimmune disease.

Abstract Background No studies evaluated the role of F8 mutations in outcomes for low‐dose immune tolerance induction (ITI) in people with severe hemophilia A (SHA) with high‐titer inhibitors. Objectives To explore the association between F8 mutation types and low‐dose ITI outcomes in children with SHA with high‐titer inhibitors. Methods Children SHA with high‐titer inhibitors who received low‐dose ITI therapy at least for 1 year were included in this study. Based on the risk of inhibitor development, F8 mutations were classified into a high‐risk group and a non–high‐risk group. Rapid tolerance and the final ITI outcomes were assessed at the 12th and 24th month of treatment, respectively, and the predictor of outcomes was analyzed. Results Of 104 children included, 101 had F8 mutations identified. The children with non–high‐risk mutations presented a higher rate of rapid tolerance than those with high‐risk mutations (61.0% vs. 29.2%; p = 0.006). Among 72 children beyond 24 months of ITI, 55 children (76.4%) achieved success, 3 (4.2%) achieved partial success, and 14 (19.4%) failed. The children in the non–high‐risk group showed a higher success rate (86.8% vs. 43.8%; p = 0.001) and a shorter time to success (mean time, 9.3 months vs. 13.2 months; p = 0.04) compared to those in the high‐risk group. In multivariable logistic regression, F8 mutations were an independent predictor of ITI success (non–high‐risk group vs. high‐risk group, adjusted odds ratio [OR], 20.3; 95% confidence interval [CI], 3.5–117.8), as was the interval from inhibitor diagnosis to ITI start (adjusted OR, 0.95; 95% CI, 0.90–0.99). They remained the significant predictors when success time was taken into account in a Cox model. Conclusions Types of F8 mutation were a key predictor of outcomes for low‐dose ITI in children with SHA with high‐titer inhibitors. It can help to stratify the prognosis and guide clinical decisions.

Infantile-onset Pompe disease (IOPD) is a rare, severe disorder of lysosomal storage of glycogen that leads to progressive cardiac and skeletal myopathy. IOPD is a fatal disease in childhood unless treated with enzyme replacement therapy (ERT) from an early age. Sickle cell anemia (SCA) is a relatively common hemoglobinopathy caused by a specific variant in the hemoglobin beta-chain. Here we report a case of a male newborn of African ancestry diagnosed and treated for IOPD and SCA. Molecular testing confirmed two GAA variants, NM_000152.5: c.842G>C, p.(Arg281Pro) and NM_000152.5: c.2560C>T, p.(Arg854*) in trans, and homozygosity for the HBB variant causative of SCA, consistent with his diagnosis. An acute neonatal presentation of hypotonia and cardiomyopathy required ERT with alglucosidase alfa infusions preceded by immune tolerance induction (ITI), as well as chronic red blood cell transfusions and penicillin V potassium prophylaxis for treatment of IOPD and SCA. Clinical course was further complicated by multiple respiratory infections. We review the current guidelines and interventions taken to optimize his care and the pitfalls of those guidelines when treating patients with concomitant conditions. To the best of our knowledge, no other case reports of the concomitance of these two disorders was found. This report emphasizes the importance of newborn screening, early intervention, and treatment considerations for this complex patient presentation of IOPD and SCA.

Hemophilia A is an inherited bleeding disorder caused by pathogenic variants in the factor VIII gene (F8), which leads to factor VIII (FVIII) deficiency. Immune tolerance induction (ITI) is a therapeutic approach to eradicate alloantibodies (inhibitors) against exogenous FVIII in people with inherited hemophilia A. Few studies have evaluated the role of F8 variants on ITI outcome. We included people with severe hemophilia A (FVIII ˂ 1 international units/dL) and high-responding inhibitors (≥ 5 Bethesda units/mL lifelong) who underwent a first course of ITI. Socio-demographic, clinical and laboratory data were collected. ITI outcomes were defined as total, partial successes, and failure. Detection of intron 1 and 22 inversions was performed by polymerase-chain reaction, followed by F8 sequencing. We included 168 people with inherited hemophilia A and high-responding inhibitors, median age 6 years at ITI start. Intron 22 inversion was the most prevalent variant (53.6 %), followed by nonsense (16.1 %), small insertion/deletion (11.3 %), and large deletion (10.7 %). In comparison with intron 22 inversion, the odds of ITI failure were 15.5 times higher (odds ratio [OR] 15.50; 95 % confidence interval [95 % CI] 4.59–71.30) and 4.25 times higher (95 % CI, 1.53–12.3) among carriers of F8 large deletions and small insertions and deletions, respectively. F8 large deletions and small insertions/deletions predicted ITI failure after a first course of ITI in patients with severe hemophilia A and high-responding inhibitors. This is the first study to show F8 large deletions and small insertions/deletions as predictors of ITI failure. [Display omitted] • The role of F8 variants in immune tolerance induction (ITI) outcome has not been fully explored. • We assessed the F8 genotype in 168 people with severe hemophilia A and high-responding inhibitors. • Compared to Int22inv, ITI failure was ~15 times higher among carriers of F8 large deletions. • Compared to Int22inv, ITI failure was ~4 times higher among carriers of F8 small insertions/deletions. • F8 large deletions and small insertion/deletion are predictors of ITI failure in severe hemophilia A. [ABSTRACT FROM AUTHOR]

Hemophilia B is an X-linked inherited bleeding disorder caused by either the absence or reduced biosynthesis of clotting factor IX (FIX). This disorder affects approximately 1 in 30,000 male individuals worldwide. Patients with severe form (FIX

Introduction: Development of haemophilia B inhibitors (HBI) results in the ineffectiveness of FIX replacement therapy. Inhibitor eradication by immune tolerance induction (ITI) is therefore necessary. In HBI, ITI even at high FIX dose is less effective and has a higher risk of severe complications. Aim: To characterize clinical features and outcome of ITI on HBI. Methods: This retrospective study was conducted in Haemophilia Paediatric Comprehensive Care Centre of China. We used low‐dose ITI (25–50 FIX IU/kg/three‐times‐weekly to every‐other‐day) with domestic prothrombin complex concentrate (PCC), combined with two successive immunosuppressive (IS) regimens. Results: Sixteen HBI children, representing 5.7% of all and 14.4% of our severe registered HB patients, were enroled. Seven cases reported allergic reactions (ARs) proximal to inhibitor development. The historic peak inhibitor titre was median 54.2 (range 4.7–512) BU, and 15 (93.8%) had high‐titre inhibitors. Twelve patients adherent to ITI were analysable. Of the nine ITI patients who received rituximab/prednisone (IS Regimen‐1), four achieved tolerization in 1.4–43.3 months. Two subsequently relapsed but re‐tolerized after a second course of IS Regimen‐1. During ITI, the median treated bleed was.39/month (82.7% reduction from before ITI), and the incidence of AR and nephrotic syndrome (NS) complications was each at 22% (2/9). Three ITI patients received modified 'Beutel' protocol (IS Regimen‐2) using multiple‐IS‐drugs, and two had rapid tolerization (.8 and 1.8 months). Conclusions: Inhibitor eradication could be achieved by low‐dose ITI protocol using PCC combined with IS. Larger studies are needed to confirm if ITI with IS Regimen‐2 is more effective with less complications. [ABSTRACT FROM AUTHOR]

While platelet-specific gene therapy is effective in inducing immune tolerance to a targeted protein, how the reactivity of pre-existing immunity affects the efficacy, and whether CD8 T cells were involved in tolerization, is unclear. In this study, ovalbumin (OVA) was used as a surrogate protein. Platelet-OVA expression was introduced by 2bOVA lentivirus transduction of Sca-1+ cells from either wild-type (WT)/CD45.2 or OT-II/CD45.2 donors followed by transplantation into OVA-primed WT/CD45.1 recipients preconditioned with 6.6 Gy of irradiation. Sustained platelet-OVA expression was achieved in >85% of OVA-primed recipients but abolished in animals with high-reactive pre-existing immunity. As confirmed by OVA rechallenge and skin graft transplantation, immune tolerance was achieved in 2bOVA-transduced recipients. We found that there is a negative correlation between platelet-OVA expression and the percentage of OVA-specific CD4 T cells and a positive correlation with the OVA-specific regulatory T (Treg) cells. Using the OT-I/WT model, we showed that antigen-specific CD8 T cells were partially deleted in recipients after platelet-targeted gene transfer. Taken together, our studies demonstrate that robust antigen-specific immune tolerance can be achieved through platelet-specific gene therapy via peripheral clonal deletion of antigen-specific CD4 and CD8 T effector cells and induction of antigen-specific Treg cells. There is an antagonistic dynamic process between immune responses and immune tolerance after platelet-targeted gene therapy.

BACKGROUND: Immune tolerance induction (ITI) is the gold standard approach for eradicating inhibitors and increasing patient tolerance to factor VIII. The success rate of ITI may vary depending on patient variables and factors relating to the pattern of treatment for the induction of immune tolerance. Children with recently diagnosed inhibitors are the best candidates for ITI, and those with favourable expected results should be offered ITI as soon as inhibitors are identified. Recombinant factor VIII Fc fusion protein has proved a therapeutic advantage in patients with high factor VIII inhibitor titers AIMS AND OBJECTIVES: To evaluate the clinical characteristics and outcomes of ten hemophilic pediatric patients who underwent ITI therapies to eliminate FVIII inhibitors at Tawam Hospital, UAE MATERIALS AND METHODS: The data of ten hemophilia A children aged 2–7 years with high inhibitor titers who underwent ITI therapy at Tawam Hospital, UAE, were retrospectively collected for this case series. A comparison of bleeds before and after the ITI therapy was also made. Patients with either failed or partially successful primary ITI therapy underwent rescue ITI therapy. Data analysis was performed using SPSS version 26. RESULTS: Full success was achieved in 60% (6/10) of the patients, 10% (1/10) achieved partial success, whereas 30% (3/10) failed the primary ITI therapy. The rescue ITI therapy was successful in 50% (2/4) of the patients and the remaining 50% (2/4) achieved partial success [Table 2]. The rescue ITI was successful in 66% (2/3) of those patients who received Elocta and partially successful in 33% (1/3) CONCLUSION: ITI therapy is the gold standard for the eradication of antibodies against FVIII. The patients with good expected outcomes should be offered ITI as soon as the inhibitors are confirmed. The use of extended half life rFVIIIFc demonstrated therapeutic benefit, particularly in challenging ITI patients with high inhibitor titers [ABSTRACT FROM AUTHOR]

Background: Classic infantile onset of Pompe disease (c-IOPD) leads to hypotonia and hypertrophic cardiomyopathy within the first days to weeks of life and, without treatment, patients die of cardiorespiratory failure in their first 1–2 years of life. Enzymatic replacement therapy (ERT) with alglucosidase alfa is the only available treatment, but adverse immune reactions can reduce ERT's effectiveness and safety. It is therefore very important to identify strategies to prevent and manage these complications. Several articles have been written on this disease over the last 10 years, but no univocal indications have been established. Methods: Our study presents a review of the current literature on management of immune responses to ERT in c-IOPD as considered by an Italian study group of pediatric metabolists and immunologists in light of our shared patient experience. Results: We summarize the protocols for the management of adverse reactions to ERT, analyzing their advantages and disadvantages, and provide expert recommendations for their optimal management, to the best of current knowledge. However, further studies are needed to improve actual management protocols, which still have several limitations. [ABSTRACT FROM AUTHOR]

Introduction: The development of inhibitory antibodies is a severe complication of clotting factor replacement therapy in patients with severe haemophilia A (HA). Current World Federation of Hemophilia (WFH) guidelines for haemophilia care indicate that eradication of inhibitors is best achieved through immune tolerance induction (ITI) therapy. Aim: The European Collaborative Haemophilia Network conducted a survey to determine whether ITI is still used in the routine management of patients with HA, and whether the availability of emicizumab prophylaxis has influenced treatment decisions. Methods: The survey was conducted in late 2020/early 2021 in 18 centres representing 17 countries in the Europe/Middle East region treating a total of 4955 patients, and included sections specific to patient and centre demographics, treatment protocols (both ITI and prophylactic), inhibitor development and initiation of ITI, treatment success, and the incidence of adverse events. Results: While our results indicate that ITI can still be considered a mainstay of treatment for patients with HA with inhibitors, less than daily dosing of ITI in combination with emicizumab prophylaxis is becoming commonplace across the spectrum of disease severity, with initiation being guided by bleeding patterns. The most frequently cited reasons for not initiating emicizumab prophylaxis were availability or reimbursement issues. Conclusion: ITI remains a mainstay for haemophilia treatment of patients with HA with inhibitors, but emicizumab has become a preferred first‐line approach to protect against bleeds and represents an alternative to burdensome ITI in certain patient groups. [ABSTRACT FROM AUTHOR]

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Introduction: In good risk patients (historic inhibitor peak < 200BU), the International Immune Tolerance Study demonstrated equal efficacy to induce tolerance between high (200iu/kg/day) and low dose (50iu/kg ×3 times/week) immune tolerance induction (ITI) regimens. However, the trial stopped early on account of the excessive bleed rate in the low dose ITI arm. Methods: United Kingdom Haemophilia Centre Doctors' Organization (UKHCDO) Paediatric and Inhibitor working parties considered available ITI data alongside the bi‐phenotypic antibody emicizumab (Hemlibra®) efficacy and safety data to develop a consensus guideline for the future UK ITI guideline. Results: This revision of UKHCDO ITI guidance incorporates the recommendation to use emicizumab as a prophylaxis haemostatic agent to reduce bleeding rates and to facilitate low dose and reduced frequency of FVIII CFC for ITI in the majority of children. Conclusion: This consensus protocol will facilitate future evaluation of ITI outcomes in the evolving landscape of haemophilia therapeutics and ITI strategies. [ABSTRACT FROM AUTHOR]

Classic infantile Pompe disease (IPD) is a rare lysosomal storage disorder characterized by severe hypertrophic cardiomyopathy and profound muscle weakness. Without treatment, death occurs within the first 2 years of life. Although enzyme replacement therapy (ERT) with alglucosidase alfa has improved survival, treatment outcome is not good in many cases and is largely dependent on age at initiation. The objective of the study was (a) to analyse the different stages in the diagnosis and specific treatment initiation procedure in IPD patients, and (b) to compare clinical and biochemical outcomes depending on age at ERT initiation (<1 month of age vs. <3 months of age). Here, we show satisfactory clinical and biochemical outcomes in two IPD patients after early treatment initiation before 3 months of life with immunomodulatory therapy in the ERT-naïve setting, with a high ERT dose from the beginning. Despite the overall good evolution, the patient who initiated treatment <1 month of life presented even better outcomes than the patient who started treatment <3 months of life, with an earlier normalization of hypertrophic cardiomyopathy, along with CK normalization, highlighting the importance of early treatment initiation in this progressive disease before irreversible muscle damage has occurred. [ABSTRACT FROM AUTHOR]

Introduction: Inhibitors develop less frequently in haemophilia B (HB) than haemophilia A (HA). However, when present, the success of tolerization by immune tolerance induction (ITI) therapy is lower and the risk of complications higher. Aim: To evaluate the use and outcome of ITI in patients with HB and inhibitors. Methods: Subjects include singletons or siblings with a current/history of inhibitors enrolled in B‐Natural—an observational study designed to increase understanding of clinical management of patients with HB. Patients were followed for 6 months and information on demographics, medical and social history, and treatment were recorded. Results: Twenty‐nine patients with severe HB and inhibitors were enrolled in 24 centres. Twenty‐two underwent one or more courses of ITI with or without immune suppression. Eight patients (36.4%) were successfully tolerized after the first course of ITI. One of these successes (12.5%) experienced allergic manifestations, whereas the corresponding number for the 10 treatment failures was five (50%). One of seven (14.2%) patients with large deletions and three of eight (37.5%) with nonsense mutations were tolerized at the first attempt, and all patients experiencing nephrosis either failed or were on‐going. At study end, 11 (50%) were considered successfully tolerized after one or more ITI courses, three were unsuccessful, and eight were still undergoing treatment. Conclusion: Our data underscore the possibilities and difficulties of achieving tolerization in patients with HB with inhibitors. The type of mutation and complications appear to correlate with ITI outcome, but more accurate definitions of successful ITI are warranted. [ABSTRACT FROM AUTHOR]

Hemophilia B is an X-linked inherited bleeding disorder caused by either the absence or reduced biosynthesis of clotting factor IX (FIX). This disorder affects approximately 1 in 30,000 male individuals worldwide. Patients with severe form (FIX <1%) account for 30%–45% of hemophilia B cases and usually report of spontaneous bleeds. Treatment includes FIX replacement prophylactically to prevent complications. However, the patient may develop inhibitors against FIX, which is rare and a serious complication, reported to occur in 1.5%–3% of hemophilia B patients. Immune tolerance induction is a therapeutic strategy to eliminate inhibitors. We report a 14-month-old-male child with severe hemophilia B on primary prophylaxis, presented with right knee swelling. He developed anaphylactic reaction while receiving recombinant FIX concentrate. Investigation revealed that FIX inhibitor titers were 1.0 Bethesda Units. He was managed with immune tolerance induction successfully. [ABSTRACT FROM AUTHOR]

Abstract Background Immune tolerance induction (ITI) therapy is currently unaffordable in China. Management of hemophilia A children with high‐titer inhibitor is therefore a challenge. Aim To describe the ITI strategy using plasma‐derived factor VIII/von Willebrand factor concentrate (pdFVIII/VWF) +/− immunosuppression and to report its efficacy in children with hemophilia A having poor‐risk status for ITI success. Methods A prospective pilot study on children with hemophilia A having poor‐risk status (all with at least inhibitor titer > 10 BU pre‐ITI initiation). Patients received ~50 IU/kg FVIII every other day using domestic intermediate purity pdFVIII/VWF products, either alone or in combination with rituximab +/− prednisone. Results Sixteen patients with median age 2.9 (range, 2.2‐13.2) years and median pre‐ITI inhibitor titer 30.7 (range, 10.4‐128) BU were enrolled. Analysis at median 14.7 (range, 12.4‐22.6) months’ follow‐up showed a total response rate of 87.5%. This included success (achieving inhibitor 0.6BU) in 1 (6.3%). Compared to the pre‐ITI period, the mean bleeds/month during ITI was 0.51 (64.0% reduction), and joint bleeds/month was 0.34 (64.3% reduction). This low‐dose ITI strategy cost less by 70% to 87% than that for the high‐dose FVIII regimen. No severe adverse events were observed. Conclusion This low‐dose ITI strategy of pdFVIII/VWF +/− immunosuppression achieved relatively satisfactory outcomes in children with hemophilia A inhibitor having poor‐risk status. This low‐dose regimen showed economic advantages and is therefore suitable for using in China. However, further study in a larger cohort with a longer follow‐up time is needed.

Abstract Background In developing countries, children with hemophilia A (HA) with high‐titer inhibitor and poor immune tolerance induction (ITI) prognostic risk(s) cannot afford the recommended high‐ or intermediate‐dose ITI. Objectives To determine the efficacy of low‐dose ITI (plasma‐derived factor VIII [FVIII]/von Willebrand factor at 50 FVIII IU/kg every other day) by itself (ITI‐alone) or combined with immunosuppressants rituximab and prednisone (ITI‐IS) in children with HA with high‐titer inhibitor. Methods All enrolled patients had pre‐ITI inhibitor ≥10 BU. We used ITI‐alone if inhibitor titer was

Neutralizing anti-FVIII IgG5 and FVIII-specific CD4+ T cells6 have been detected in some patients after successful ITI; this suggests that active FVIII-specific tolerance is mediated by anti-idiotypic antibodies5 and probably regulatory T cells, rather than resulting from the mere elimination of FVIII-specific immune effectors. Keywords: emicizumab; FVIII inhibitor; haemophilia A; immune tolerance induction EN emicizumab FVIII inhibitor haemophilia A immune tolerance induction e581 e584 4 07/21/21 20210701 NES 210701 ACKNOWLEDGEMENTS We acknowledge Sadyo Darame for her technical assistance. However, around 30% of patients develop neutralizing antibodies against FVIII (also known as "inhibitors"), and those with high inhibitor titres become resistant to FVIII replacement therapy. In high-titre inhibitor-positive patients, however, the cautious use of FVIII bypassing agents in conjunction with emicizumab therapy is the only option.2 The availability of emicizumab raises several questions, particularly concerning FVIII prophylaxis after successful ITI. [Extracted from the article]

Standard treatment of haemophilia A is based on replacing the missing coagulation factor VIII (FVIII) to treat and prevent bleeding episodes. The most challenging complication of FVIII therapy is the development of neutralizing antibodies (inhibitors) that can render treatment ineffective. Eradication of the inhibitor through immune tolerance induction (ITI) remains the most effective strategy for managing these patients. Bypassing agents can be used to help restore haemostasis in inhibitor patients. Several novel agents have recently been developed, such as the FVIII mimetic agent emicizumab, which has been effective in reducing the annualized bleeding rate in haemophilia A patients with inhibitors. When coadministered with repetitive high doses of activated prothrombin complex concentrate (ie >100 U/kg/d for ≥24 hours), emicizumab was associated with thrombotic microangiopathy and thrombosis events. As a consequence the United Kingdom Haemophilia Centres Doctors' Organisation (UKHCDO) issued the first guidance on the treatment of bleeding episodes in patients receiving emicizumab. To build on and extend this work, a panel of German haemophilia specialists met to discuss the UK guidance, review current evidence and provide additional guidance for German healthcare professionals on how to optimize the management of patients with haemophilia A receiving emicizumab. Recommendations are provided on the use of bypassing and other agents to manage breakthrough bleeding, ITI in the emicizumab era, haemostatic support during surgery and issues relating to laboratory monitoring. [ABSTRACT FROM AUTHOR]

Summary: The development of alloantibodies (inhibitors) against coagulation factor VIII (FVIII) is the most serious complication of FVIII replacement therapy in patients with haemophilia A (HA). We carried out a nationwide study focussing on patients with HA with inhibitors in China to evaluate the condition and management of this population. The study retrospectively analysed patient characteristics, clinical history, manifestation, treatment strategy as well as individual haemophilia care of 493 patients with inhibitors (466 with severe HA and 27 with non‐severe HA) registered all over China. The median (interquartile range) age at diagnosis of FVIII inhibitors was 13 (5–28) years in patients with severe HA and 24 (10·5–39·5) years in patients with non‐severe HA. Most patients (85%) had high‐titre inhibitors. Prothrombin complex concentrate and recombinant activated coagulation factor VII were used respectively in 76·2% and 29·2% of patients for acute bleeding. Only 22·3% of patients underwent immune tolerance induction (ITI) treatment, of whom 64·9% achieved negative inhibitor titre. In patients who did not undergo ITI, the inhibitors turned negative in 17·7%, and patients with low peak inhibitor titre were more likely to acquire negative titre spontaneously (odds ratio 11·524, 95% confidence interval 5·222–25·432; P = 0·000). We recorded that 3·2% of the patients died from haemophilia‐related life‐threatening bleeding. [ABSTRACT FROM AUTHOR]

Emicizumab is a bispecific antibody that recognizes FIX(a)/FX, and mimics FVIIIa cofactor activity. Due to its unique characteristics including longer half‐life and subcutaneous injectability, treatment for haemophilia A dramatically improved regardless of the presence of FVIII inhibitor. Protection from pathological change in joints, avoidance of inhibitor development and intra‐cranial haemorrhage could be expected by introduction of emicizumab in early childhood. Applications in mild/moderate patients should be also considered. Clinical assessment tool should be standardized; however, since there are limitations to conventional ABR‐based assessment. Laboratory monitoring is another practical issue due to the mode of action of emicizumab. Chromogenic assays and global assays could be utilized. The other emicizumab‐related practical issue is immune tolerance induction for the inhibitor patients, since ITI remains the only effective means to inhibitor eradication. With the recently introduced Atlanta protocol, emicizumab prophylaxis is given in combination with 50‐100 IU/kg FVIII three times a week. A single manuscript has been published, and multiple clinical trials are open to address the efficacy of this strategy. Whether the Atlanta protocol will be fully embraced is yet to be seen, but there is widespread consensus about attempts to tolerize every haemophilia A patient with an inhibitor. [ABSTRACT FROM AUTHOR]

Immune tolerance induction (ITI) with a short-course of rituximab, methotrexate, and/or IVIG in the enzyme replacement therapy (ERT)-naïve setting has prolonged survival and improved clinical outcomes in patients with infantile Pompe disease (IPD) lacking endogenous acid-alpha glucosidase (GAA), known as cross-reactive immunologic material (CRIM)-negative. In the context of cancer therapy, rituximab administration results in sustained B-cell depletion in 83% of patients for up to 26–39 weeks with B-cell reconstitution beginning at approximately 26 weeks post-treatment. The impact of rituximab on serum immunoglobulin levels is not well studied, available data suggest that rituximab can cause persistently low immunoglobulin levels and adversely impact vaccine responses. Data on a cohort of IPD patients who received a short-course of ITI with rituximab, methotrexate, and IVIG in the ERT-naïve setting and had ≥6 months of follow-up were retrospectively studied. B-cell quantitation, ANC, AST, ALT, immunization history, and vaccine titers after B-cell reconstitution were reviewed. Data were collected for 34 IPD patients (25 CRIM-negative and 9 CRIM-positive) with a median age at ERT initiation of 3.5 months (0.1–11.0 months). B-cell reconstitution, as measured by normalization of CD19%, was seen in all patients (n = 33) at a median time of 17 weeks range (11–55 weeks) post-rituximab. All maintained normal CD19% with the longest follow-up being 248 weeks post-rituximab. 30/34 (88%) maintained negative/low anti-rhGAA antibody titers, even with complete B-cell reconstitution. Infections during immunosuppression were reported in five CRIM-negative IPD patients, all resolved satisfactorily on antibiotics. There were no serious sequelae or deaths. Of the 31 evaluable patients, 27 were up to date on age-appropriate immunizations. Vaccine titers were available for 12 patients after B-cell reconstitution and adequate humoral response was observed in all except an inadequate response to the Pneumococcal vaccine (n = 2). These data show the benefits of short-course prophylactic ITI in IPD both in terms of safety and efficacy. Data presented here are from the youngest cohort of patients treated with rituximab and expands the evidence of its safety in the pediatric population.

In humans, maternal IgGs are transferred to the fetus from the second trimester of pregnancy onwards. The transplacental delivery of maternal IgG is mediated by its binding to the neonatal Fc receptor (FcRn) after endocytosis by the syncytiotrophoblast. IgGs present in the maternal milk are also transferred to the newborn through the digestive epithelium upon binding to the FcRn. Importantly, the binding of IgGs to the FcRn is also responsible for the recycling of circulating IgGs that confers them with a long half-life. Maternally delivered IgG provides passive immunity to the newborn, for instance by conferring protective anti-flu or anti-pertussis toxin IgGs. It may, however, lead to the development of autoimmune manifestations when pathological autoantibodies from the mother cross the placenta and reach the circulation of the fetus. In recent years, strategies that exploit the transplacental delivery of antigen/IgG complexes or of Fc-fused proteins have been validated in mouse models of human diseases to impose antigen-specific tolerance, particularly in the case of Fc-fused factor VIII (FVIII) domains in hemophilia A mice or pre-pro-insulin (PPI) in the case of preclinical models of type 1 diabetes (T1D). The present review summarizes the mechanisms underlying the FcRn-mediated transcytosis of IgGs, the physiopathological relevance of this phenomenon, and the repercussion for drug delivery and shaping of the immune system during its ontogeny.

Replacement therapy with coagulation factor VIII (FVIII) represents the current clinical treatment for patients affected by hemophilia A (HA). This treatment while effective is, however, hampered by the formation of antibodies which inhibit the activity of infused FVIII in up to 30% of treated patients. Immune tolerance induction (ITI) protocols, which envisage frequent infusions of high doses of FVIII to confront this side effect, dramatically increase the already high costs associated to a patient's therapy and are not always effective in all treated patients. Therefore, there are clear unmet needs that must be addressed in order to improve the outcome of these treatments for HA patients. Taking advantage of preclinical mouse models of hemophilia, several strategies have been proposed in recent years to prevent inhibitor formation and eradicate the pre-existing immunity to FVIII inhibitor positive patients. Herein, we will review some of the most promising strategies developed to avoid and eradicate inhibitors, including the use of immunomodulatory drugs or molecules, oral or transplacental delivery as well as cell and gene therapy approaches. The goal is to improve and potentiate the current ITI protocols and eventually make them obsolete.

Keywords: retrospective chart review; haemophilia A; immune tolerance induction; inhibitor; recombinant factor VIII Fc fusion protein; rescue therapy EN retrospective chart review haemophilia A immune tolerance induction inhibitor recombinant factor VIII Fc fusion protein rescue therapy 19 25 7 02/04/21 20210101 NES 210101 Dear Editor, Prophylactic factor VIII (FVIII) replacement is the current standard of care for severe haemophilia A but approximately 25%-40% of patients develop inhibitors against exogenous FVIII, rendering FVIII replacement therapy ineffective.1 Eradication of high-titre inhibitors involves immune tolerance induction (ITI): repeated, long-term administration of high-dose FVIII.1 Recombinant FVIII Fc fusion protein (rFVIIIFc [ELOCTATE SP ® sp , Sanofi, Waltham, MA]) is the first extended half-life FVIII approved for haemophilia A.2 Case reports and an initial retrospective chart review suggest that rFVIIIFc ITI may lead to faster tolerization than ITI with standard FVIII concentrates.3,4 This letter reports final clinical outcomes of 29 patients (19 included in the initial analysis) with severe haemophilia A undergoing ITI with rFVIIIFc in a real-world setting.4 We performed a retrospective review of patient charts at 13 sites across the United States and Canada, using previously published methods.4 Briefly, de-identified clinical data were collected from patients with severe haemophilia A and historical high-titre inhibitors, who began first-time or rescue ITI with rFVIIIFc between July 2014 and February 2018 and had >=3 months of exposure to rFVIIIFc ITI. Tolerization was defined as a negative Bethesda titre (<0.6 BU/mL), normal FVIII recovery (>=66% of expected) and rFVIIIFc half-life >=6 hours.5 Altogether, 29 rFVIIIFc ITI patients were identified: 10 first-time (Table 1) and 19 rescue patients (Table 2). [Extracted from the article]