Background
Plasma‐derived (pd) or recombinant (r) therapeutic factor VIII proteins (FVIIIs) are infused to arrest/prevent bleeding in patients with hemophilia A (PWHA). However, FVIIIs are ...neutralized if anti‐FVIII‐antibodies (inhibitors) develop. Accumulating evidence suggests that pdFVIIIs with von Willebrand factor (VWF) are less immunogenic than rFVIIIs and that distinct rFVIIIs are differentially immunogenic. Since inhibitor development is T‐helper‐cell‐dependent, human leukocyte antigen (HLA)‐class‐II (HLAcII) molecules constitute an important early determinant.
Objectives
Use dendritic cell (DC)‐protein processing/presentation assays with mass‐spectrometric and peptide‐proteomic analyses to quantify the DP‐bound, DQ‐bound, and DR‐bound FVIII‐derived peptides in individual HLAcII repertoires and compare the immunogenic potential of six distinct FVIIIs based on their measured peptide counts.
Patients/Methods
Monocyte‐derived DCs from normal donors and/or PWHA were cultured with either: Mix‐rFVIII, a VWF‐free equimolar mixture of a full‐length (FL)‐rFVIII Advate® (Takeda) and four distinct B‐domain‐deleted (BDD)‐rFVIIIs Xyntha® (Pfizer), NovoEight® (Novo‐Nordisk), Nuwiq® (Octapharma), and Afstyla® (CSL Behring GmBH); a pdFVIII + pdVWF Beriate® (CSL Behring GmBH); Advate ± pdVWF; Afstyla ± pdVWF; and Xyntha + pdVWF.
Results
We showed that (i) Beriate had a significantly lower immunogenic potential than Advate ± pdVWF, Afstyla − pdVWF, and Mix‐rFVIII; (ii) distinct FVIIIs differed significantly in their immunogenic potential in that, in addition to (i), Afstyla + pdVWF had a significantly lower immunogenic potential than Beriate, while the immunogenic potential of Beriate was not significantly different from that of Xyntha + pdVWF; and (iii) rFVIIIs with pdVWF had significantly lower immunogenic potentials than the same rFVIIIs without pdVWF.
Conclusions
Our results provide HLAcII peptidomic level explanations for several important clinical observations/issues including the differential immunogenicity of distinct FVIIIs and the role of HLAcII genetics in inhibitor development.
The immunogenicity of protein therapeutics is an important safety and efficacy concern during drug development and regulation. Strategies to identify individuals and subpopulations at risk for an ...undesirable immune response represent an important unmet need. The major histocompatibility complex (MHC)–associated peptide proteomics (MAPPs) assay directly identifies the presence of peptides derived from a specific protein therapeutic on a donor's MHC class II (MHC-II) proteins. We applied this technique to address several questions related to the use of factor VIII (FVIII) replacement therapy in the treatment of hemophilia A (HA). Although >12 FVIII therapeutics are marketed, most fall into 3 categories: (i) human plasma-derived FVIII (pdFVIII), (ii) full-length (FL)–recombinant FVIII (rFVIII; FL-rFVIII), and (iii) B-domain–deleted rFVIII. Here, we investigated whether there are differences between the FVIII peptides found on the MHC-II proteins of the same individual when incubated with these 3 classes. Based on several observational studies and a prospective, randomized, clinical trial showing that the originally approved rFVIII products may be more immunogenic than the pdFVIII products containing von Willebrand factor (VWF) in molar excess, it has been hypothesized that the pdFVIII molecules yield/present fewer peptides (ie, potential T-cell epitopes). We have experimentally tested this hypothesis and found that dendritic cells from HA patients and healthy donors present fewer FVIII peptides when administered pdFVIII vs FL-rFVIII, despite both containing the same molar VWF excess. Our results support the hypothesis that synthesis of pdFVIII under physiological conditions could result in reduced heterogeneity and/or subtle differences in structure/conformation which, in turn, may result in reduced FVIII proteolytic processing relative to FL-rFVIII.
•MAPPs allows more accurate T-cell epitope identification as the assay needs MHC protein proteolytic processing and antigen presentation.•In a MAPPs assay, antigen-presenting cells presented more T-cell epitopes when matured with rFVIII compared with pdFVIII.
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Background: Patients with the X-linked bleeding disorder hemophilia A have impaired blood clotting due to deficient or absent factor VIII (FVIII) coagulant activity. Bleeding can be managed by ...infusions of any of several plasma-derived (pd) or recombinant (r) therapeutic FVIII proteins (tFVIIIs). The efficacy of tFVIIIs can be eliminated, however, if neutralizing anti-tFVIII-antibodies called “inhibitors” develop. Since the development of inhibitors is T-helper-cell dependent, human leukocyte antigen (HLA)-class-II (HLAcII) molecules comprise an important early determinant. Accumulating evidence suggests that the presence of the FVIII chaperon protein, von Willebrand factor (VWF), in either pdFVIII or rFVIII concentrates, decreases the immunogenicity of these tFVIIIs by reducing their uptake by antigen presenting cells, especially dendritic cells (DCs).
Objectives: Use a native (i.e., non-engineered) full-length (FL) tFVIII without ((−)) or with ((+)) pdVWF in DC-protein processing and presentation assays (PPPAs) followed by mass-spectrometric and peptide-proteomic analyses to identify and quantify the DP-, DQ-, and DR-bound/tFVIII-derived-peptides in individual HLAcII repertoires. Compare the number of peptides in the subset from any of the five globular domains (A1, A2, A3, C1 and C2) or three acidic-residue-rich connecting segments (a1, a2 and a3), which we collectively refer to as the non-B-domain (NBD) portion of a tFVIII, with the number of peptides from its non-globular “outrigger like” B-domain (BD) that contains ~80% of the N-linked glycans of a FL-FVIII molecule despite containing only 908 amino acid residues, i.e. slightly less than 40% of its 2,332 total residues.
Methods: DC-PPPAs were performed using monocyte-derived (Mo)DCs obtained from 12 healthy blood donors. The tFVIII tested was a FL-rFVIII (Advate®) used (−) or (+) pdVWF (i.e., FL-rFVIII − pdVWF and FL-rFVIII + pdVWF) and the resulting data consists of counts of tFVIII-derived peptides presented on and extracted from HLAcII molecules. Difference of proportion tests were used to compare the effect of pdVWF as well as the NBD- and BD-regions of the FL tFVIII on the peptide counts.
Results: FL-rFVIII − pdVWF yielded significantly more peptides (p<0.05) than FL-rFVIII + pdVWF from the NBD portions but not the BD. Interestingly, for the FL-rFVIII − pdVWF preparation, the NBD portions yielded significantly more peptides (p<0.05) than the BD, but this pattern was reversed for the FL-rFVIII + pdVWF preparation in that the NBD portions yielded significantly less peptides (p<0.05) than the BD.
Conclusions: The Outrigger Hypothesis posits that in the presence of VWF the heavily glycosylated BD acts as an “outrigger” and renders this portion of a FL tFVIII relatively more likely to be internalized, proteolytically processed and HLAcII-presented. However, in the absence of VWF, the N-linked glycans individually act to protect the amide bonds in the underlying peptide bond backbone of a tFVIII from proteolytic processing, as posited by the GUMB Hypothesis. Our results support both hypotheses as important determinants in the pathogenesis of inhibitor development.
Howard:Haplogenics Corporation: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Luu:Haplogenics Corporation: Employment. Hofmann:CSL Behring: Employment. Dinh:Haplogenics Corporation: Employment. Mead:CSL Behring: Employment. Powell:Haplogenics: Membership on an entity's Board of Directors or advisory committees. Escobar:Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; National Hemophilia Foundation: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Consultancy, Membership on an entity's Board of Directors or advisory committees. Eugene:CSL Behring: Employment.
The development of neutralizing antibodies-termed “inhibitors”-to infused therapeutic (t) factor VIII proteins (tFVIIIs) is the most serious obstacle to effective treatment of bleeding in Hemophilia ...A (HA) patients. As clinically significant FVIII immune responses are only initiated if dendritic cell (DC) cII-HLAs can present foreign tFVIII-derived peptides to naïve FVIII-specific T cells, we posit the “Gate Keeper” hypothesis in which the limiting determinant of inhibitor formation are patients' cII-HLA repertoires with the majority being individually distinct and each contributing slightly to the vast population level diversity of cII-HLAs. While cII-HLAs are critical at the cellular level for initiating immune responses, conflicting results from population studies have led some to describe their encoding HLA-II structural genes as weak determinants of inhibitor causation. Our main objective here is to test a hypothesis that gets at the heart of this disconnect between molecular-based expectations and population-level data by analyzing cII-HLA peptidomic data from DC-protein processing and presentation assays (PPPAs). The chief variable of DC-PPPA data is the peptide count, which we assume to be directly proportional to immunogenic potential (IP). Our working model is that inhibitor formation requires at minimum, in its initial stages, a complex between cII-HLAs and specific tFVIII-derived peptides. A testable null hypothesis under this thinking posits that a given cII-HLA allotype will have the same IP when exposed to several tFVIIIs. To test this hypothesis, we first performed model selection to determine the best set of predictor allotypes. To analyze the data, we employed a log-linear model where the peptide count is the dependent variable and allotype is a categorical independent variable consisting of 29 levels for 29 allotypes (8 DP, 10 DQ, and 11 DR allotypes). We used elastic net regression (ENR) to select the best set of allotype levels thus giving the best overall model consisting now of only four DR allotypes (Table 1). We then performed interaction analysis under the best-selected allotypes model in which we introduced as additional predictor variables, a tFVIII categorical variable consisting of five levels for five different tFVIIIs, namely full length (FL)-recombinant (r) FVIII (FL-rFVIII) ± von Willebrand Factor (VWF), B domain truncated (BDT)-rFVIII ± VWF, and plasma derived (pd) FVIII (pdFVIII) + VWF, and 12 interaction terms for the (4 - 1) × (5 - 1) possible interactions between the cII-HLA allotype and tFVIII variables. We found significant cII-HLA allotype × tFVIII interactions (Table 2). To get at the specific null hypothesis of interest, we examined within-allotype risk ratios (RRs) and their appropriately adjusted confidence intervals (CIs).1-4 It can be shown that an 84% CI is sufficient to achieve a significance level of α = 0.05 for the CI difference.2-4 Although there are 12 total interaction terms, per allotype there are only three possible CI comparisons on using the interaction term with the highest RR as a fixed reference. On constructing the adjusted CIs and correcting for multiple hypothesis testing,2 we found that two comparisons in Table 2 corresponded to significantly different RRs. We determined statistical power to detect a CI difference.1,3 As seen in Table 2, our study was extremely underpowered, which may explain why only two significant differences were found. Thus, at least for the two comparisons showing significant difference, we have refuted the null hypothesis of no difference across tFVIIIs for a given allotype, and have affirmed our working model that specific combinations of cII-HLAs and tFVIII-derived peptides are the triggering factor in inhibitor development.Schenker N, Gentleman J. On judging the significance of differences by examining the overlap between confidence intervals. Am Statistician. 2001; 55(3): 182-6.Julious S. Using confidence intervals around individual means to assess statistical significance between two means. Pharmaceut Statist. 2004; 3: 217-22.Maghsoodloo S, Huang C-Y. Comparing the overlapping of two independent confidence intervals with a single confidence interval for two normal population parameters. J Statist Plan & Infer. 2010; 140: 3295-305.Knol M, Pestman W, Grobbee D. The (mis)use of overlap of confidence intervals to assess effect modification. Eur J Epidemiol. 2011; 26(4): 253-4.
Hofmann:CSL Behring: Employment. Dinh:Haplomics Biotechnology Corporation: Employment, Equity Ownership. Escobar:Pfizer: Research Funding; Bayer, CSL Behring, Genentech, Hemabiologics, Kedrion, Novo Nordisk, Octapharma, Pfizer and Shire: Consultancy. Maraskovsky:CSL Behring: Employment. Howard:CSL Behring: Research Funding; Haplomics Biotechnology Corporation: Equity Ownership, Other: Chief Scientific Officer, Patents & Royalties: Patent applications and provisional patent applications .
Here we apply state-of-the-art statistical genetic approaches toward investigating the genetic architecture of factor VIII (FVIII) inhibitor (FEI) development in Hemophilia A (HA). A total of 442 ...North American HA patients (237 Whites and 205 Blacks; 88% severely affected) enrolled in the PATH Study were: 1) ImmunoChip genotyped at ~167,000 single nucleotide polymorphisms (SNPs) in genes previously implicated in autoimmune disease risk; 2) Evaluated by DNA sequencing and assays for the recurrent intron (I)1 and I22 inversions to identify their causative F8 mutations; and 3) Tested with the Bethesda assay to determine their FEI status. The ImmunoChip genotypes were used to construct a genetic relationship matrix (GRM), denoted by K, following our previously published method,1 and the F8 sequence data along with results from the I1 and I22 inversion assays were used to construct a shared F8-mutation matrix, denoted by F. We analyzed a dichotomous FEI variable under the statistical genetic threshold/liability model (a probit regression in the fixed effects) in conjunction with a variance components model for the FEI liability phenotypic covariance matrix, denoted by P, to model potentially important random effects. For the latter, we specifically assumed independent additive genetic, F8-mutation, and residual environmental random effects. By the independence assumption, the covariance matrix is then decomposable as a sum of the additive genetic (Va), F8-mutation (Vf), and residual environmental (Ve) variances respectively structured by K, F, and the identity matrix I. The variance component model is given as: P = K*Va + F*Vf + I*Ve. Heritability, denoted by h2, is defined as the ratio of Va to the total phenotypic variance (Vp): h2 = Va / Vp. We can further speak of the total heritability given as: h2t = h2r + h2f + h2snp, where the subscripts t, r, f, and snp respectively denote total, residual additive genetic, F8-mutation-specific, and SNP heritabilities. Using eigenstructure methods,2 we can compute power under a simpler model in which Va and Vf are combined as a single variance component. We computed power to detect genetic association as measured by SNP-specific heritability for a set of 403 SNPs in or near 14 candidate immune response genes previously implicated in FEI risk. To account for multiple hypothesis testing, power was computed at the Bonferroni-adjusted significance level of 0.05/403 = 1.2 × 10-4. Under the simplified model, we computed the statistical power to detect causal SNPs for our sample and study design for the sample FEI prevalences, denoted by Kp, for Whites (22.5%) and Blacks (45%), across a range of total heritabilities, h2t = 15%, 35%, and 55%, where the lattermost total heritability was observed for FEI liability in the current study (Figure 1). It should be noted that because the liability heritability is known to be biased upward, we applied the Dempster-Lerner correction to both the total and SNP-specific heritabilities.3 Close inspection of Figure 1 reveals that varying h2t from 15% to 35% to 55% results in slight decreases in power due to the decreasing ratio of the SNP-specific heritability to the total heritability. However, as seen in all three panels, the more important determinant of power is clearly the FEI prevalence in that the power curve for a Kp of 45% is associated with greater power than the power curve for a Kp of 22.5% across the range of total heritabilities examined. As seen in Figure 1, we have adequate power to detect SNP heritabilities as low as 5% and 6%, respectively, for a Kp of 45% and 22.5%. As noted above, we observed a FEI liability total heritability of 55% consisting of a 47% residual additive genetic heritability (p = 0.019) and 8% F8-mutation specific heritability (p = 0.005). This is the first study to use a GRM based on genotype data and a shared causal F8 mutation matrix to model additive genetic and F8-mutation specific effects.Almeida M, Peralta J, Farook V, …, Blangero J. Pedigree-based random effect tests to screen gene pathways. BMC Proc. 2014; 8(Suppl 1 Genetic Analysis Workshop): S100.Blangero J, Diego VP, Dyer T, …, Göring H. A kernel of truth: statistical advances in polygenic variance component models for complex human pedigrees. Adv Genetics. 2013; 81: 1-31.Glahn D, Williams J, McKay D, …, Blangero J. Discovering schizophrenia endophenotypes in randomly ascertained pedigrees. Biol Psychiatry. 2015; 77(1): 75-83.
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Chitlur:Baxter, Bayer, Biogen Idec, and Pfizer: Honoraria; Novo Nordisk Inc: Consultancy. Dinh:Haplomics Biotechnology Corporation: Employment, Equity Ownership. Howard:Haplomics Biotechnology Corporation: Equity Ownership, Other: Chief Scientific Officer, Patents & Royalties: Patent applications and provisional patent applications ; CSL Behring: Research Funding.
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