Haemophiliacs with factor VIII inhibitors in Finland: prevalence, incidence and outcome

Management of haemophilia A with inhibitors: A regional cross-talk

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.

Prevalence of factor VIII inhibitors among Afghan patients with hemophilia A: a first report

: Prevalence of inhibitors in Afghan hemophilia patients has not been reported previously. Our aim was to determine the prevalence of factor VIII inhibitors among hemophilia A patients from the Kabul province of Afghanistan to identify and characterize the pattern of inhibitor formation. Clinical information and blood samples were collected from three hemophilia centers in Kabul, Afghanistan. Plasma samples were obtained from 62 patients with severe (80.5%) and 15 patients with moderate hemophilia A (19.5%) in this cross-sectional study design. All the patients were receiving on-demand treatment. The Nijmegen modification of the Bethesda assay was used to detect inhibitors. Multiplex PCR, inverse-PCR, Multiplex ligation-dependent probe amplification and direct sequencing were performed for genotyping. Inhibitor activity was detected in one out of 15 (6.7%) patients with moderate hemophilia and in six out of 62 (9.7%) with severe disease. Apart from the intron 22 inversion, five different mutations including one missense, two large and two small deletions were detected. This is the first report showing that the prevalence of inhibitors in Afghan hemophilia A patients is much lower than in other populations.

Factor VIII products and inhibitor development in previously treated patients with severe or moderately severe hemophilia A: a systematic review

Essentials Data on product-related immunogenicity in previously treated haemophilia A patients is scarce. A systematic review and meta-analysis of all currently available evidence was conducted. The overall incidence rate was 2.06 per 1000 person-years (95% confidence interval: 1.06-4.01). Some recombinant factor VIII products were associated with increased immunogenicity.

SUMMARY

Background Patients with severe hemophilia A who have been treated extensively with factor VIII products have a low but potentially serious risk of inhibitor development. It is unknown why these patients develop inhibitors, and data on product-related immunogenicity are scarce. Aims To summarize the currently available evidence on the relationship between inhibitor development and recombinant FVIII product type in previously treated patients (PTPs) with severe hemophilia A. Methods Longitudinal studies were included that reported on de novo inhibitor formation in patients with baseline FVIII activity levels of < 0.02 IU mL-1 who had been treated with FVIII for at least 50 days. Pooled incidence rates of inhibitor development according to product types were calculated with a random intercept Poisson regression model. Results Forty-one independent cohorts were included; 39 patients developed de novo inhibitors during 19 157 person-years of observation. The overall incidence rate was 2.06 per 1000 person-years, with a 95% confidence interval (CI) of 1.06-4.01. According to product type, the pooled incidence rates were 0.99 (95% CI 0.37-2.70) per 1000 person-years for patients treated with Advate, 5.86 (95% CI 0.25-134.92) per 1000 person-years for those treated with Kogenate/Helixate, 1.35 (95% CI 0.66-2.77) per 1000 person-years for those treated with Kogenate FS/Helixate NexGen, 12.05 (95% CI 1.53-94.78) per 1000 person-years for those treated with Refacto, and 4.64 (95% CI 0.82-26.43) per 1000 person-years for those treated with Refacto AF. Conclusion These results suggest that some products may be associated with increased immunogenicity. However, the low incidence of inhibitors in PTPs and the differences in study design may cause significant variation in estimates of risk.

Inhibitor development in previously untreated patients with severe haemophilia A: a nationwide multicentre study in Finland

INTRODUCTION

Currently the most serious treatment complication of haemophilia is the inhibitor development (ID), i.e. neutralizing antibody development.

AIM

This nationwide multicentre study in Finland evaluated the incidence and risk factors of ID in previously untreated patients (PUPs) with severe haemophilia A (FVIII:C < 0.01 IU mL(-1) ).

METHODS

We enrolled all PUPs (N = 62) born between June 1994 and May 2013 with at least 75 exposure days (EDs) to screen ID during follow-up extending to September 2013.

RESULTS

Thirteen ID (21% of 62) occurred; 10 (16% of 62) with high titre. Fifty-one patients (82%) were on primary prophylaxis (regular prophylaxis before the age of 2 and before the first joint bleed) from the median age of 11.4 months, 90% via a central venous access device. The initial product was rFVIII in 63% and pd-FVIII in 37%, moreover in 24% pd-FVIII was switched to rFVIII concentrate during the 75 EDs. Non-transient inhibitors developed in 9/51 (17.6%; 13.7% high titre) children with primary and in 4/11 (36.4%; 27.3% high titre) patients with secondary prophylaxis (P = 0.24). Overall, 74% had a high-risk genotype similarly distributed among the prophylaxis groups. The history of a major bleed enhanced ID (aHR, 4.0; 95% CI, 1.2-13.7), whereas FVIII treatment intensity or source and early implantation of ports did not increase ID risk.

CONCLUSION

The cumulative incidence of ID was low notwithstanding prevalent high-risk mutations. Despite patient-related risk factors, our management involving early intensive primary prophylaxis via ports helps to prevent bleeds and lower the incidence of inhibitors.

Inhibitor development and mortality in non-severe hemophilia A

BACKGROUND

The life expectancy of non-severe hemophilia A (HA) patients equals the life expectancy of the non-hemophilic population. However, data on the effect of inhibitor development on mortality and on hemophilia-related causes of death are scarce. The development of neutralizing factor VIII antibodies in non-severe HA patients may dramatically change their clinical outcome due to severe bleeding complications.

OBJECTIVES

We assessed the association between the occurrence of inhibitors and mortality in patients with non-severe HA.

METHODS

In this retrospective cohort study, clinical data and vital status were collected for 2709 non-severe HA patients (107 with inhibitors) who were treated between 1980 and 2011 in 34 European and Australian centers. Mortality rates for patients with and without inhibitors were compared.

RESULTS

During 64,200 patient-years of follow-up, 148 patients died (mortality rate, 2.30 per 1000 person-years; 95% confidence interval (CI), 1.96-2.70) at a median age of 64 years (interquartile range [IQR], 49-76). In 62 patients (42%) the cause of death was hemophilia related. Sixteen inhibitor patients died at a median age of 71 years (IQR, 60-81). In ten patients the inhibitor was present at time of death; seven of them died of severe bleeding complications. The all-cause mortality rate in inhibitor patients was > 5 times increased compared with that for those without inhibitors (age-adjusted mortality rate ratio, 5.6).

CONCLUSION

Inhibitor development in non-severe hemophilia is associated with increased mortality. High rates of hemophilia-related mortality in this study indicate that non-severe hemophilia is not mild at all and stress the importance of close follow-up for these patients.

Impact of inhibitors on hemophilia A mortality in the United States

The previously published mortality studies are limited in hemophilia populations but suggest that there is no increased risk of mortality in factor VIII inhibitor patients. This retrospective study analyzed surveillance data collected on 7,386 males with severe hemophilia A over a 13-year period to assess the association between a current inhibitor and death. During the study period, 432 participants died, among whom 48 were patients with an inhibitor. Clinical characteristics most strongly associated with death were increased number of reported bleeds, signs of liver disease, infection with either HIV or HCV, and the presence of inhibitor. Patients who underwent successful tolerization were not considered inhibitor patients in our analysis. In a multivariable analysis, the odds of death were 70% higher among patients with a current inhibitor compared to those without an inhibitor (P < 0.01). Deaths among patients with inhibitors were much more likely to be attributed to bleeding complications than those among patients without an inhibitor (42 vs. 12%, P < 0.0001). We conclude that males with severe hemophilia A and a current inhibitor are at increased risk of death.

A study of variations in the reported haemophilia A prevalence around the world

The objectives of this paper were to study the reported haemophilia A prevalence (per 100 000 males) on a country-by-country basis and address the following: Does the reported prevalence of haemophilia A vary by national economies? We collected prevalence data for 106 countries from the World Federation of Hemophilia (WFH) annual global surveys and the literature. We found that the reported haemophilia A prevalence varied considerably among countries, even among the wealthiest of countries. The prevalence (per 100 000 males) for high income countries was 12.8 +/- 6.0 (mean +/- SD) whereas it was 6.6 +/- 4.8 for the rest of the world. Within a country, there was a strong trend of increasing prevalence over time--the prevalence for Canada ranged from 10.2 in 1989 to 14.2 in 2008 (R = 0.94 and P < 0.001) and for the United Kingdom it ranged from 9.3 in 1974 to 21.6 in 2006 (R = 0.94 and P < 0.001). Prevalence data reported from the WFH compared well with prevalence data from the literature. Patient registries generally provided the highest quality of prevalence data. The lack of accurate country-specific prevalence data has constrained planning efforts for the treatment and care of people with haemophilia A. With improved information, healthcare agencies can assess budgetary needs to develop better diagnostic and treatment facilities for affected patients and families and work to ensure adequate supplies of factor VIII concentrates for treatment. In addition, this information can help manufacturers plan the production of concentrates and prevent future shortages.

The epidemiology of factor VIII inhibitors

Risk factors for inhibitor development include specific factor VIII (FVIII) genotypes, a family history of inhibitor development amongst first-degree relatives, certain HLA haplotypes and non-caucasian ethnicity. Patients with major FVIII deletions or rearrangements have a higher risk of inhibitor development than those with small deletions or missense mutations. Studies of HLA-DR amongst northern European patients with the intron 22 inversion indicate that certain HLA haplotypes may also confer either increased or decreased inhibitor risk. However, although brothers of patients with inhibitor have a high risk of inhibitor development, concordance is not 100%, and other constitutional factors must also operate. Disputed risk factors for inhibitor development include early age at first FVIII exposure, the use of recombinant rather than plasma-derived FVIII and product switching. Two studies suggest that inhibitor risk is increased by very early FVIII exposure (P = 0.03), but this is disputed by a third study; larger studies addressing the question are ongoing. Studies investigating the relative inhibitor risk of plasma-derived vs. recombinant FVIII have been similarly inconclusive and will be reviewed. Other environmental or treatment variables such as concomitant infection or vaccination are suspected to influence inhibitor risk but have not yet been fully investigated.

Incidence of inhibitors in a cohort of 838 males with hemophilia A previously treated with factor VIII concentrates

BACKGROUND

Development of an inhibitory antibody to factor VIII is currently the most serious complication of hemophilia A treatment. The rate of inhibitor development in those that have been previously treated with factor concentrates is poorly defined. Understanding the baseline rate of inhibitor development in the population of previously treated patients (PTPs) is important when evaluating the effect of exposure to new factor replacement products on inhibitor formation.

OBJECTIVES

To determine the rate of inhibitor development in PTPs with hemophilia A.

METHODS

A cohort of males with hemophilia A who had data collected on four or more occasions prior to 30 March 2003, as part of the Center for Disease Control and Prevention's Universal Data Collection Project, were eligible for inclusion in the cohort. Patients were included in the cohort if they had at least two Bethesda assay measurements and did not have an inhibitor prior to or at the start of the study period. The overall incidence rate was estimated as the number of verified incident inhibitor cases divided by the total follow-up time in years multiplied by 1000 (cases per 1000 person-years).

RESULTS

A total of 838 patients were included in the study. The overall incidence rate was calculated to be 2.14 cases per 1000 person years. All incident cases had more than 50 exposure days prior to inhibitor development.

CONCLUSIONS

Given the low rate of inhibitor development in PTPs with hemophilia A, small, non-randomized studies are inadequate to determine the rate of inhibitor development after exposure to novel products. Ongoing, standardized, postmarketing surveillance is needed to determine if novel factor products pose an increased risk of inhibitor development.

The incidence of factor VIII and factor IX inhibitors in the hemophilia population of the UK and their effect on subsequent mortality, 1977-99

BACKGROUND

Previous studies of the development of inhibitors and their impact on mortality have been small.

OBJECTIVES

To examine the development of inhibitors in people with hemophilia in the UK and their effect on subsequent mortality.

PATIENTS

6078 males with hemophilia A and 1172 males with hemophilia B registered in the UK Haemophilia Centre Doctors' Organisation database, 1977-98.

RESULTS

In severe hemophilia A inhibitors developed at rates of 34.4, 5.2 and 3.8 per 1000 years at ages <5, 5-14 and 15+years; cumulative risks at ages 5 and 75 were 16% and 36%. In hemophilia A the rate of inhibitor development decreased during 1977-90, but increased during the 1990s. In severe hemophilia B inhibitors developed at rates of 13.3 and 0.2 per 1000 years at ages <5 and 5+ and cumulative risks at ages 5 and 75 were 6% and 8%. With HIV, inhibitor development did not increase mortality. In severe hemophilia without HIV, inhibitor development doubled mortality during 1977-92, but during 1993-99 mortality was identical with and without inhibitors. In severe hemophilia without HIV but with inhibitors, mortality from causes involving bleeding decreased during 1977-99 (P = 0.001) as did mortality involving intracranial hemorrhage (P = 0.007).

CONCLUSIONS

These data provide estimates of the rate of inhibitor development in hemophilia A and hemophilia B, and they show that the rate of inhibitor development has varied over time, although the reasons for this remain unclear. They also show that in severe hemophilia the substantial increase in mortality previously associated with inhibitors is no longer present.

The epidemiology of inhibitors in haemophilia A: a systematic review

This paper emphasizes the importance of distinguishing between the prevalence, incidence and cumulative incidence of inhibitors in haemophilia A. Incidence and cumulative incidence data will include patients with transient inhibitors or whose inhibitors have been eliminated by treatment. As these will not be included in prevalence data, prevalence studies will tend to give rise to lower figures than incidence studies. As a result, the most accurate estimates of the true risk of inhibitor development comes from prospective studies of newly diagnosed haemophiliacs who are tested regularly for the presence of inhibitors. This paper reports a systematic review of the best available evidence relating to the epidemiology of inhibitors in haemophilia A. Cohort studies, registry data reporting incidence or prevalence of inhibitors in patients with haemophilia A, and prospective studies of factor VIII (FVIII) in the treatment of previously untreated patients which reported the development of inhibitors as an outcome, were included in the review. The overall prevalence of inhibitors in unselected haemophiliac populations was found to be 5-7%. The cumulative risk of inhibitor development varied (0-39%). Incidence and prevalence were substantially higher in patients with severe haemophilia. Studies of patients using a single plasma-derived FVIII (pdFVIII) preparation reported lower inhibitor incidence than those using multiple pdFVIII preparations or single recombinant FVIII preparations. Incidence data should be used to estimate the likely demand for treatments aimed at eliminating inhibitors, whereas the best estimates of the overall burden to the National Health Service (NHS) of treating bleeding episodes in patients with continuing inhibitors will come from prevalence studies.

Influence of human immunodeficiency virus infection on the course of hepatitis C virus infection: a meta-analysis

Studies have shown that rates of liver disease are higher in persons who are coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV) than they are in persons with HCV alone, but estimates of risk vary widely and are based on data for dissimilar patient populations. We performed a meta-analysis to quantify the effect of HIV coinfection on progressive liver disease in persons with HCV. Eight studies were identified that included outcomes of histological cirrhosis or decompensated liver disease. These studies yielded a combined adjusted relative risk (RR) of 2.92 (95% confidence interval [CI], 1.70-5.01). Of note, studies that examined decompensated liver disease had a combined RR of 6.14 (95% CI, 2.86-13.20), whereas studies that examined histological cirrhosis had a pooled RR of 2.07 (95% CI, 1.40-3.07). There is a significantly elevated RR of severe liver disease in persons who are coinfected with HIV and HCV. This has important implications for timely diagnosis and consideration of treatment in coinfected persons.

Immune tolerance treatment in haemophilia patients with inhibitors: the Spanish Registry

We present a retrospective study of immune tolerance treatment (ITT) carried out in 42 Spanish haemophiliac patients. Most of the patients were high responders (39/42), with a median maximum titre of 67 Bethesda units (BU) (range 6-2984). The median inhibitor titre at the start the ITT was 11 BU (range 1-256 BU) and the median age of the patients was 7 years (range 0-57). The mean factor dosage was 140 IU kg bodyweight(-1) day(-1) (range 25-500). In most of the ITTs, plasma-derived factor concentrate of intermediate and high purity was used. The inhibitor was eradicated in 26/38 (68%) of the patients who completed the treatment and two patients changed their status from high to low responders. Multivariate logistic regression analysis showed that three significant variables were associated with the highest probability of success: (i) the use of low factor doses for ITT (< or = 100 IU kg(-1) day(-1); P = 0.0106; 95% CI 0.000289-0.342); (ii) a titre of < 10 BU at start of ITT (P = 0.0286; 95% CI 0.00253-0.7189) and (iii) a lower maximum titre (P = 0.0214; 95% CI 0.98-0.9994).

Immune tolerance induction in hemophilia patients with inhibitors: costly can be cheaper

The development of inhibitory antibodies to factor VIII (FVIII) occurs in approximately 30% to 40% of patients with severe hemophilia A. Management options for patients with inhibitor include eradicating it via immune tolerance induction (ITI) or treating bleeding episodes with large quantities of hemostatic agents. ITI is costly, approaching $1 million for the average 5-year-old, but if successful results in improved clinical outcomes. We constructed a decision analysis using the Markov process to model expected clinical outcomes and costs over a lifetime for a typical 5-year-old hemophiliac with high inhibitor levels. Estimates of relevant variables were based on a thorough review of the medical literature. Outcomes modeled included total lifetime costs as well as life expectancy. The decision analytic model revealed that the ITI strategy was associated with an increase in projected life expectancy of 4.6 years. Total estimated lifetime costs for the ITI strategy were approximately $1.7 million less per patient. Sensitivity analyses over clinically and economically reasonable ranges did not change these findings. The insight that ITI can achieve an improved clinical outcome while being cost-saving is not reflected in many current treatment regimens. This example also illustrates that expensive therapy for patients with a chronic disease may be cost effective when analyzed from a societal perspective over the patient's lifetime. This finding has important policy implications for medical decision makers at many levels and reinforces the need to undertake pharmacoeconomic analyses and choose therapies from a long-term, societal perspective.

Immune tolerance induction in hemophilia patients with inhibitors: costly can be cheaper

The development of inhibitory antibodies to factor VIII (FVIII) occurs in approximately 30% to 40% of patients with severe hemophilia A. Management options for patients with inhibitor include eradicating it via immune tolerance induction (ITI) or treating bleeding episodes with large quantities of hemostatic agents. ITI is costly, approaching $1 million for the average 5-year-old, but if successful results in improved clinical outcomes. We constructed a decision analysis using the Markov process to model expected clinical outcomes and costs over a lifetime for a typical 5-year-old hemophiliac with high inhibitor levels. Estimates of relevant variables were based on a thorough review of the medical literature. Outcomes modeled included total lifetime costs as well as life expectancy. The decision analytic model revealed that the ITI strategy was associated with an increase in projected life expectancy of 4.6 years. Total estimated lifetime costs for the ITI strategy were approximately $1.7 million less per patient. Sensitivity analyses over clinically and economically reasonable ranges did not change these findings. The insight that ITI can achieve an improved clinical outcome while being cost-saving is not reflected in many current treatment regimens. This example also illustrates that expensive therapy for patients with a chronic disease may be cost effective when analyzed from a societal perspective over the patient's lifetime. This finding has important policy implications for medical decision makers at many levels and reinforces the need to undertake pharmacoeconomic analyses and choose therapies from a long-term, societal perspective.

[The young hemophiliac, inhibitors and immune tolerance]

The occurrence of inhibitor in a hemophilic patient is the greatest therapeutic complication in 1999. The inhibitor incidence is higher in hemophilia A (20-30%) than in hemophilia B (3%). At the moment, the best management is immune tolerance induction. This consists in frequent infusion of antihemophilic factor (every day or every other day). The risk of inhibitor development is higher in a young child than in an adult. Consequently, a venous access device is essential for this treatment although not devoid of complications in the young boy. Moreover, the probability of inhibitor disappearance is higher in a child (recent inhibitor) than in an adult ("old" inhibitor).

Incidence of inhibitors in haemophilia A patients--a review of recent studies of recombinant and plasma-derived factor VIII concentrates

The development of inhibitors to factor VIII or IX is the most serious complication of haemophilia therapy. While early surveys revealed inhibitor prevalences of 3.6-25%, recent studies, especially those using recombinant DNA-derived products, have prompted speculation as to whether ultrapurified products may cause a higher incidence of inhibitors. Although studies of ultrapure rFVIII in previously treated patients have not shown an increased inhibitor risk, in previously untreated patients (PUPs) with severe haemophilia A (factor VIII < 2%), cumulative incidences of approximately 30% have been reported. The majority of these inhibitors are low responders; many have disappeared spontaneously despite continued treatment with the study product (i.e. transient inhibitors), and were most probably detected as a consequence of frequent inhibitor testing. The mutation causing haemophilia has recently been shown to be a significant risk factor for developing an inhibitor; mutations leading to the absence of endogenous factor VIII protein (for example, large multidomain deletions, nonsense mutations, isochromosomal intron 22 inversions) are associated with the highest risk of inhibitor development. Furthermore, recent prospective studies of plasma-derived products reveal inhibitor incidences (i.e. 21-52%) that are comparable to those obtained with recombinant products. When comparing the incidences of high-responder inhibitors (> 10 BU) among recent prospectively studied severe haemophilia A cohorts (i.e. 11-41%), differences between plasma-derived and recombinant products cannot be discerned. New studies of either recombinant or plasma-derived products should consider all known parameters influencing inhibitor formation, thereby facilitating meaningful comparisons of inhibitor risk.

Causes of death in Canadians with haemophilia 1980-1995. Association of Hemophilia Clinic Directors of Canada

The life expectancy of individuals with haemophilia was close to that of the general population in the early 1980s. Since then, life expectancy has decreased, due to transfusion-transmitted virus infections. Deaths in individuals with haemophilia were investigated by analysing 2450 records from the Canadian Hemophilia Registry, for the years 1980-1995. Deaths were tabulated by age, year and cause, and compared with that of the Canadian male population by calculating standardized mortality ratios (SMRs). The median life expectancy at 1 year of age was calculated for various subpopulations and the impact of various population characteristics was assessed by survival regression modelling. There were 359 deaths and the annual number of deaths increased significantly after 1986. Risk factors were seropositivity to human immunodeficiency virus (relative risk 16.7, 95% CI 11.1-25.1), severe haemophilia (1.9, 1.3-2.7) and moderate haemophilia (1.8, 1.2-2.6). In HIV antibody negative individuals, the overall death rate was not increased (SMR 0.9, 95% CI 0.7-1.1) and only haemorrhage was significantly increased. In HIV antibody positive individuals, causes of death which were significantly increased were acquired immunodeficiency syndrome, liver failure, haemorrhage, lymphoma, liver cancer, nonspecific infections, and trauma or violence. Deaths due to the acquired immunodeficiency syndrome accounted for only 66% of the excess deaths in individuals who were HIV antibody positive. Life expectancy has markedly decreased since the onset of the HIV epidemic. The impact of HIV is underestimated by considering only deaths due to the acquired immunodeficiency syndrome; other HIV-linked causes need also to be considered.

Zero incidence of inhibitor development in previously treated haemophilia A, HIV-negative patients upon exposure to a plasma-derived high-purity and double viral inactivated factor VIII concentrate

Thirty-six haemophilia A, HIV-negative, previously treated patients were changed therapy to a highpurity and double-inactivated (solvent/detergent and dry-heating) previously unused factor VIII concentrate. The mean age of these patients was 27 years at the time of the change. Twenty-three patients were severe haemophiliacs (FVIII:C < 0.02 IU mL-1), seven moderate (FVIII:C between 0.02 and 0.05 IU mL-1) and six mild (FVIII:C > 0.05 IU mL-1). The mean follow-up with this single product was 16 months, with 82 accumulated exposure days and the mean consumption was 117,300 IU of FVIII corresponding to a mean of six batches per patient. No patient developed FVIII inhibitors (upper limit of the CI95: 7.98%), resulting in an incidence rate of 0/48 patient-years (upper limit of the CI95: 77/1000 patient-years). The change in therapy to this new factor VIII concentrate was not associated with the appearance of inhibitors.

The incidence of factor VIII inhibitors in patients with severe hemophilia A

1. Many factors must be considered when retrospective studies are compared, for the intensity of F.VIII treatment and the frequency of inhibitor evaluation have a marked effect on inhibitor incidence. 2. The incidence of F.VIII inhibitors in patients treated with cryoprecipitate and/or intermediate purity concentrates varies greatly in different studies, with cumulative risks of 7-32% after 10-15 years of follow-up. 3. The rate of inhibitor development appears to be higher for patients treated with recombinant F.VIII, but the cumulative incidence is not greater. This may change, however, when there has been an equivalent follow-up period for the patients receiving recombinant F.VIII. 4. Cumulative risk figures may inappropriately overstate the magnitude of the problem since some inhibitors disappear after short periods of time. 5. Only prospective, long-term studies will provide more satisfactory incidence and prevalence data.

Inhibitors in hemophilia patients: current status and management

The development of inhibitor antibodies is a long-standing, well-documented complication of coagulation factor replacement therapy and is difficult to treat. Previous estimates of 5-15% of patients developing inhibitors may be low, since newer data suggest a wider range of occurrence. Factors that appear to affect inhibitor development include the severity of hemophilia, age, genetics, and, possibly, the type of replacement therapy administered. Recent studies raise the concern that recombinant factor therapies may be associated with more rapid development and higher levels of inhibitors in previously untreated patients. However, results of different studies are often difficult to compare owing to differences in methodology and populations studied. Further studies standardized in design and methods are clearly needed. Management of patients with inhibitors involves control of acute bleeding episodes and, over the long term, induction of immune tolerance for the coagulation replacement therapy. Many with low or moderate levels of inhibitors may be treated simply by administering higher doses of clotting factor. Other therapies appropriate for those with high levels of inhibitors include porcine F VIII and factor VIII "bypassing" agents, such as recombinant factor VIIa. Long-term immune tolerance has been achieved through the high-dose "Bonn" regimen and immunosuppressive regimens such as the "Malmö" method. Although management of inhibitor patients has improved, it still represents a major challenge. Further research is needed to identify which patients will develop inhibitors and tolerance, as well as to develop better methods to manage, reduce, or eliminate inhibitors from these patients.

Screening of F.VIII:C antibodies by an enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (Elisa) method was developed in order to examine prevalence and titer of antibodies directed against the factor VIII coagulant protein (F.VIII:C) in hemophilia A and nonhemophilia A patients. Highly purified F.VIII:C was used as immunosorbent on microtiter plates with a peroxidase-conjugated goat anti human IgG antibody for F.VIII:C antibody detection. Results determined by Elisa were compared with measurements according to the Bethesda method. Initially 24 plasma samples containing an F.VIII:C inhibitory activity ranging from 0 to 7,700 Bethesda units (BU) were analysed. At plasma dilutions of 1:128 the optical density determined by our Elisa measurement and the corresponding BU showed a logarithmic correlation. The coefficient of correlation was r = 0.92 with a standard deviation of 0.002 from the regression curve. Plasma samples were analysed from 53 hemophilia A patients, from 21 nonhemophilia patients with acquired F.VIII:C antibodies and from 460 randomly selected nonhemophilia patients presenting for routine preoperative coagulation examination. F.VIII:C antibody-positive Elisa results and positive BU were found in 7 hemophilia A patients and the 2 patients with a history of acquired F.VIII:C antibodies. Positive Elisa results and negative BU were found in 1 hemophilia A patient and 25 out of 460 nonhemophilia A patients (5.43%) suggesting F.VIII:C antibodies without inhibitory potency on F.VIII:C in these cases.(ABSTRACT TRUNCATED AT 250 WORDS)

[Risk of the appearance of inhibitors linked to the administration of factors VIII and IX. Review of the literature]

Factors VIII and IX administration exposes haemophiliac patients to the risk of inhibitor development which reduces treatment efficacy. Methods and results of 17 studies (transversal and longitudinal) and of one clinical trial dealing with haemophilia A and of 3 studies dealing with haemophilia B were reviewed. Besides differences in study design, lack of method standardisation complicates comparison between studies. In patients with haemophilia A, prevalence of inhibitors ranges from 4 to 18% (5 studies), and incidence between 3 and 39/1,000 person-years (7 studies). Cumulative age incidence is above or equal to 20% after 6 years of age (4 studies). Cumulative incidence by exposure days is estimated at 22% at 100 exposure days in a retrospective cohort observed between 1975 and 1992, and above or equal to 36% at 25 exposure days in two prospective cohorts of patients receiving recombinant factor VIII products. The new European regulation dealing with stable blood products will make the evaluation of new products by clinical trials mandatory. With The National therapeutic Follow up of Haemophiliacs which begun in October 1994, following a decision by the French Minister of Health, the adverse effects in patients receiving factor VIII and IX which have been approved for sales will be evaluated.

Loss of high-responder inhibitors in patients with severe hemophilia A and human immunodeficiency virus type 1 infection: a report from the Multi-Center Hemophilia Cohort Study

To evaluate the effects of human immunodeficiency virus type 1 (HIV-1) infection on the loss of factor VIII alloantibodies, we identified 77 patients with a history of inhibitors from among a large cohort of HIV-1-infected participants enrolled in a natural history study of HIV-1 infection in hemophilia. Fifty-six patients were high responders with inhibitors titers greater than 5 Bethesda Units (BU) measured on at least one occasion. From May 1985 to December 1989, 13 of the high-responder patients were rechallenged with factor VIII concentrates after several years of treatment with other plasma products. All exhibited excellent hemostasis upon reinstitution of factor VIII. Seven of the 13 patients (11.3-46.3 years of age) were in the advanced stages of HIV-1 infection at the time of rechallenge. Inhibitor titers measured subsequent to the reinstitution of factor VIII were consistently less than 1 BU in five of these seven patients. The remaining six patients (6.1-57.5 years of age) had mild to moderate CD4+ lymphocyte depletion (absolute CD4+ cells: 262-935/mm3) at the time of factor VIII rechallenge. Follow-up inhibitor titers were negative 7-42 months after consistent factor VIII use in these six patients. The lack of anamnestic response to factor VIII in all 13 patients who were rechallenged indicates that HIV-1-infected patients who have a history of high-responder inhibitors frequently benefit from the reintroduction of factor VIII use for the control of bleeding, regardless of their stage of HIV-1 disease.

Recombinant factor VIII for the treatment of previously untreated patients with hemophilia A. Safety, efficacy, and development of inhibitors. Kogenate Previously Untreated Patient Study Group

BACKGROUND

Although methods of viral attenuation in plasma-derived clotting-factor concentrates have improved, there is still a possibility that such concentrates may transmit certain blood-borne viruses. For this reason, the use of recombinant DNA-derived factor VIII (which is virus-free) to treat hemophilia A has generated considerable interest.

METHODS

We conducted a multicenter trial in previously untreated children with hemophilia A. They received recombinant factor VIII for all treatment or for prophylaxis and were evaluated at their respective clinics at intervals of no more than three months.

RESULTS

Between January 1, 1989, and July 1, 1992, 95 patients who could be evaluated received recombinant factor VIII. By September 1, 1992, they had received the concentrate exclusively for 2.4 months to 3.5 years (median, 1.5 years). All responded well, with no treatment failures. A total of 3315 infusions were administered; there were three reports of minor adverse reactions. Inhibitor antibodies to factor VIII developed in 16 of 81 patients tested for them, after a median of nine days of exposure to factor VIII treatment. Inhibitor titers were or became low in 9 of the 16 patients despite continued episodic treatment with the concentrate. Inhibitors disappeared completely in 4 patients and remained at a low level (< 10 Bethesda units) in 5 patients receiving episodic treatment.

CONCLUSIONS

Transient or low levels of inhibitor, as observed in this study, may represent part of the natural history of hemophilia in infants. In view of the transient nature and lower concentration of the inhibitors detected and the generally satisfactory response to treatment, the benefits of recombinant factor VIII for the treatment of hemophilia seem to outweigh the risks.

Incidence of development of factor VIII and factor IX inhibitors in haemophiliacs

The development of factor VIII:C inhibitors remains one of the most serious complications of repeated transfusion in patients with haemophilia A. The proportion of patients affected has been reported to range from 3.6% to 25%, but these figures have been derived mainly from retrospective data and from total numbers of known haemophiliacs instead of number at true risk. The assessment here is based on a prospective study, started in 1976, on the incidence of inhibitor development in haemophiliacs born after 1970 whose FVIII or FIX activity was 5% or less, and who had received replacement therapy at least once. 46 of 63 children with haemophilia A and 13 of 17 with haemophilia B fulfilled the enrollment criteria. Inhibitors developed only in haemophilia A patients who had previously been treated with FVIII products--inhibitor concentrations were high in 12 and low in 3. Inhibitors developed in 24% (15/63) of all haemophilia A patients, and in 52% (14/27) of those with severe disease. The incidence of inhibitor development for all haemophilia patients was 39.1 per 1000 patient-years of observation. All inhibitors were first detected when patients were aged 0.08-5.2 years. The cumulative risk was 33% at age 6 years. The findings indicate that previous reports have underestimated the risk of acquiring FVIII inhibitors. Prospective, standardised studies, especially in children, are needed for the assessment of the true risk of this complication.