Alloantibodies to factor VIII in haemophilia

Abstract

Up to one-third of haemophilia A patients develop factor VIII (FVIII) alloantibodies (inhibitors). The Bethesda assay detects inhibitors but is relatively insensitive. Recently, a new fluorescence-based immunoassay (FLI) was developed for antibody detection. The aim of this study was to assess the prevalence of inhibitors as measured by FLI. Assays of FVIII, FVIII inhibitor by Bethesda assay with Nijmegen modification, and FVIII inhibitor by FLI were performed on adult patients with haemophilia A. Data were complete for 46 patients (median age 39), of whom 72% were severe, 7% moderate and 22% mild. The Bethesda assay was positive in only two patients (4%), while FLI was positive in 23 of 46 patients (50%), with values ranging from 0.4 to 33.7 nm (median 3.5 nm). FLI titres exceeded 7.0 nm in 19.5% of patients, all but one of whom had severe haemophilia. FLI antibody-positive patients were less likely to be HIV positive (30% vs. 70%, P = 0.02). The use of a prophylaxis regimen was associated with a lower incidence of antibody; only two of 23 patients with detectable antibody and none of those with antibody >7 nm were on a prophylaxis regimen, while nine of 23 patients without antibody were on prophylaxis, (P = 0.03). There was no difference in inhibitor presence in patients using recombinant versus plasma-derived factor. Antibodies detected by FLI are frequent in patients with haemophilia A, but are less common in those who are HIV positive or are receiving regular FVIII prophylaxis.

Distinct characteristics of antibody responses against factor VIII in healthy individuals and in different cohorts of hemophilia A patients

“…40 In contrast to our study which only included patients with severe hemophilia A (FVIII activity Ͻ 1%), the studies presented by Krudysz-Amblo et al, Lebreton et al, and Zakarija et al included patients with all severities of hemophilia A. 12,13,39 We believe that discrepancies in results for the prevalence of FVIII-binding antibodies between the various studies might be because of differences in the patient populations investigated and different assay formats. The study by Lebreton et al presented findings indicating that FVIII-binding antibodies found in patients without inhibitors are directed against light chain, heavy chain, or B-domain, with a clear dominance of antibodies directed against the heavy chain.…”

“…For comparison, 3 recent studies using bead-based assays reported a prevalence of 50% (23 of 46), 33% (13 of 39), and 18% (28 of 210) for FVIII-binding antibodies in hemophilia A patients without inhibitors. 12,13,39 Another study which used an ELISA-based approach found a prevalence of 12% (6 of 49). 40 In contrast to our study which only included patients with severe hemophilia A (FVIII activity Ͻ 1%), the studies presented by Krudysz-Amblo et al, Lebreton et al, and Zakarija et al included patients with all severities of hemophilia A.…”

Nonneutralizing antibodies against factor VIII and risk of inhibitor development in severe hemophilia A

“…[13][14][15][16][17][18][19][20][21][22]24,25,29,30 Several factors, particularly that all previous studies predominantly included patients with multiple transfusions, explain this large variation and the gaps in knowledge about their potential clinical role. For instance, the intron 22 inversion of FVIII mutation was associated with an increased frequency of NNAs in patients who had had multiple transfusions in 1 study 29 that was not confirmed in another study.…”

“…Their prevalence is approximately 2% to 3% in healthy individuals, 16,18,21,24 but estimates in patients who have hemophilia with different degrees of severity vary widely from 12% to 54%. [13][14][15][16][17][18][19][20][21][22]24,25,[29][30][31] Although NNAs and inhibitors cannot be distinguished on the basis of their isotypes, clonality, and epitopes, 32 recent data published by Hofbauer et al 16 indicate that anti-FVIII immunoglobulin G (IgG) with inhibitory activity has an up to 100-fold higher affinity for FVIII than IgG without inhibitory activity. On the basis of cross-reactivity studies, it has also been suggested that FVIII inhibitors in hemophilia A patients originate from the expansion of a natural anti-FVIII clone of B lymphocytes that exists before any treatment with FVIII and secretes anti-FVIII antibodies similar to the natural antibodies found in healthy individuals.…”

Hemophilia Inhibitors Prevalence, Causes and Diagnosis

“…The ELISA provides rapid screening that could be available well in advance of inhibitor confirmation by the Bethesda assay (77,78). Recently developed a new fluorescence-based immunoassay (FLI) was found to be much more sensitive for detecting especially low titre inhibitors (79).…”