ALBERT

Description: Abstract 3071 Background: Prognosis of relapse after first allogeneic hematopoietic stem cell transplantation (allo-HSCT) is poor, and no standard treatment is available. Second HSCT (HSCT2) is a valuable treatment option for selected patients. Change of donor for HSCT2 is a frequently used strategy to enhance the graft-versus leukemia-activity, although its role for improving the outcome is still unclear. However, identification and activation of a new donor for HSCT2 is time consuming and might delay or even prevent a second transplant. In contrast, haploidentical family donors are rapidly available in the vast majority of patients and might therefore be an alternative for HSCT2, once change to a new donor is planned. Based upon these considerations, HSCT2 from haploidentical family donors was used as preferred treatment for acute leukemia relapse after allo-HSCT in our transplant center since August 2009. According to the concept of sequential therapy (as introduced by the FLAMSA-RIC regimen), patients initially received cytoreductive chemotherapy, followed, after three days of rest, by reduced intensity conditioning (RIC). Based on the Baltimore protocol for haploidentical HSCT using RIC and post-transplant cyclophosphamide for depletion of allo-reactive T-cells, individual and disease-specific modification of this regimen were used for preparation before HSCT2. Patients and Methods: Fourteen adult patients (7 male, median age: 37 years) suffering from AML (n=11) or ALL (n=3) with an ECOG score of

Description: Abstract 1115 Recombinant factor VIIa (rFVIIa) is approved to control bleeding in hemophilia A and B patients who have developed inhibitory antibodies to replacement therapy and in acquired hemophilia. rFVIIa is rapidly eliminated with a terminal half-life of approximately 2.5 hours in humans. This short half life necessitates frequent injections and considerably limits prophylactic use. A recombinant fusion protein linking activated factor VII with albumin (rVIIa-FP) was engineered to extend the half life of rFVIIa. The present studies were conducted to gather knowledge about the pharmacokinetic and pharmacodynamic (PK/PD) properties of rVIIa-FP in preclinical animals models to enable a more precise estimate of the procoagulant activity of rVIIa-FP for the future clinical use in haemophilia patients with inhibitors to FVIII and FIX. Single intravenous doses of either rVIIa-FP or the licensed rFVIIa comparator, NovoSeven® were administered to mice, rabbits and monkeys. Subsequently, plasma samples were harvested at different time-points after study drug administration and systemic levels of rVIIa-FP or NovoSeven® were assessed either by FVIIa activity measurements using the Staclot® assay system or by FVII antigen measurements using an enzyme linked immunoabsorbance assay (ELISA). When investigating dose responses or duration of hemostatic activity, rVIIa-FP and NovoSeven® were administered to mice or rabbits before tail clip or induction of venous stasis, respectively. Following a single intravenous bolus application the procoagulant activity of both study drugs was assessed in both models at different time points after administration up to 24 hours to proof prolonged procoagulant effects of rVIIa-FP compared to NovoSeven®. Intriguingly, in all animal species tested the systemic bioavailability, clearance and in addition the terminal half-life (t1/2β), of rVIIa-FP were significantly better in comparison to NovoSeven®. Based on FVIIa activity measurements in plasma samples derived from monkeys the 11 fold higher area under the curve (AUC) was accompanied with a 4-fold longer t1/2β, while in vivo recovery (IVR) of rVIIa-FP exceeded that of NovoSeven® by a 70 %. In rabbits the 20 fold higher AUC was associated with a 5-fold longer t1/2β and a 4-fold higher IVR when measuring specific FVIIa activity. In mice measurements of FVII antigen revealed a 11 fold higher AUC, while t1/2β was 4 times longer and IVR was found to be doubled in comparison to NovoSeven®. The assessment of pharmacodynamic activity after dosing based on specific FVIIa activity adjusted by the Staclot® assay revealed, that the procoagulant effect of rVIIa-FP was not different from NovoSeven®, when measuring total blood loss under acute bleeding conditions after tail clip. However, when assessing late time-points after treatment the prolonged systemic availability of rVIIa-FP translated into a longer and sustained hemostatic activity of rVIIa-FP compared to NovoSeven® in both animal models. Intriguingly, ex vivo studies in hemophilia A mice showed that the 4 fold prolonged systemic availability of rVIIa-FP in plasma translates into sustained FVIIa activity when recorded as thrombin generation activity compared to NovoSeven® at 16 hours after treatment. Furthermore in rabbits, the 5 fold longer half-life translated into a significantly greater procoagulant activity as measured by thrombus formation in both jugular veins after venous stasis. In conclusion, the recombinant albumin fusion technology was successfully applied to human recombinant FVIIa for a significantly improved of PK/PD profile as observed in different pre-clinical animal species. Future clinical studies can proof whether the observed improved PK/PD characteristics will also translate into a half-life extension and a longer hemostatic effect in hemophilia patients with inhibitors to FVIII and FIX. Allowed: The entire body of the abstract, including text and tables, must not exceed 3,800 characters. Spaces are not included in this number; title, authors' names, and affiliations are counted separately. Figures are not included in the character count. Disclosures: Zollner: CSL Behring GmbH: Employment. Schuermann:CSL Behring GmbH: Employment. Raquet:CSL Behring GmbH: Employment. Mueller-Cohrs:CSL Behring GmbH: Employment. Weimer:CSL Behring GmbH: Employment. Pragst:CSL Behring GmbH: Employment. Dickneite:CSL Behring GmbH: Employment. Schulte:CSL Behring GmbH: Employment.

Description: Abstract 1117 The recombinant fusion protein linking the human coagulation factor IX to human albumin, rIX-FP, developed by CSL Behring GmbH, is currently undergoing investigation in clinical phase II/III trials (PROLONG - 9FP) for prophylaxis and on-demand treatment of bleeding in haemophilia B patients. The present study has been conducted to evaluate the biodistribution of rIX-FP in comparison to the marketed recombinant factor IX product BeneFIX®. Therefore, [3H]-rIX-FP or [3H]-BeneFIX®, labeled at lysine or terminal NH2 residues using the N-Succinimidyl [2,3,-3H] propionate (NSP) method, were administered intravenously to male Sprague Dawley (SD) rats at a single dose leading to a radioactive dose of 400 μCi/kg. Using whole-body autoradiography (QWBA), tissue radioactivity was determined at 0.25, 1, 3, 8, 24, 72, 120 and 240 hours following [3H]-rIX-FP, and at 0.25, 1, 3 and 24 hours following [3H]-BeneFIX® administration. In addition to full body sections, the hind limbs were separately subjected to QWBA to obtain more detailed information on the product distribution within the bone marrow, articular capsule and synovial region of the knee joints. In parallel, plasma, urine and faeces were collected at pre-dose and at several sampling points throughout the 24 and 240 hour study period, respectively, to calculate excretion balance and assess physiological elimination pathways. The radioactivity associated with the purified [3H]-labelled protein was determined by quantitative radiochemical analysis (QRA) and high performance liquid chromatography (HPLC). Biological activity of [3H]-labelled rIX-FP and BeneFIX® was confirmed using a chromogenic assay for factor IX activity. The radioactivity associated with plasma, urine and faeces samples was determined by QRA. HPLC-mass spectrometry (MS) techniques were employed to further characterize individual components identified following profiling of plasma and urine samples by size exclusion chromatography (SEC). Overall, the tissue distribution of [3H]-rIX-FP and [3H]-BeneFIX® was comparable, both penetrating predominantly into well perfused tissues and organs. Both products are also rapidly present in synovial and mineralized regions of knee joint sections and seem to mostly localize to the zone of calcified cartilage within the growth plate regions of long bones. For both, the longest retention time was observed in the bone marrow and endosteum of long bones. However, whereas [3H]-rIX-FP was detectable over 120 hours after administration, [3H]-BeneFIX® signal could only be detected until 24 hours post dosing. This is also reflected in the pharmacokinetic parameters determined based on the QRA of plasma and urine samples which suggested a terminal half life of 20.4 and 6.1 hours for [3H]-rIX-FP and [3H]-BeneFIX®, respectively, following correction for total radioactivity attributable to intact product. For both proteins, the major route of elimination was urinary. In case of [3H]-rIX-FP 73% of radioactivity was recovered in urine at 240 hours, the latest sampling point investigated. Less than 5% of radioactivity was eliminated in faeces and approximately 20% of radioactivity was present in tissues after 240 hours. Plasma profiling showed that up to 8 hours, 100% of the radioactivity could be assigned to unchanged [3H]-rIX-FP. From 24 to 240 hours, increasing levels of low molecular weight components (LMW) could be observed in plasma. Intriguingly, no high molecular protein components like [3H]-rIX-FP or albumin were detected in urine. Only LMW [3H]-components were found to be renally excreted. Such LMW components could be either be free [3H]-Lysine or bigger peptide fragments derived from [3H]-rIX-FP, which occur as a result of physiological protein catabolism. An exact identification of such renally excreted fragments is currently underway using HPLC-MS. Overall, the observed data are consistent with the hypothesis, that recycling via FcRn receptor is likely to be the physiological retention route for [3H]-rIX-FP. Consequently, this study shows that rIX-FP exhibits equal biodistribution compared to other marketed recombinant factor IX products such as BeneFIX®, but clearly distinguishes itself from BeneFIX® by its extended plasma half-life allowing a reduction in dosing frequency leading to increased therapeutic convenience and compliance. Disclosures: Herzog: CSL Behring GmbH: Employment. Harris:Quotient Bioresearch Metabolic Chemistry: Commercial Research Organisation Other. McEwen:Quotient Bioresearch Metabolic Chemistry: Commercial Research Organisation Other. Pragst:CSL Behring GmbH: Employment. Dickneite:CSl Behring GmbH: Employment. Schulte:CSL Behring GmbH: Employment. Zollner:CSL Behring GmbH: Employment.

Description: Hemophilia A is an X-linked bleeding disorder caused by mutations in the gene encoding the Factor VIII coagulation protein (FVIII). Bleeding episodes in patients are reduced by prophylactic therapy or treated acutely using recombinant or plasma derived FVIII. These treatments have substantially improved the outcome of hemophilia. More recently long-acting recombinant FVIII concentrates have become available in the clinic, but hemophilia A patients still require the repeated intravenous injections frequently 2-3 times per week. Furthermore, the development of inhibitors which are associated with significant mortality and morbidity remains a serious complication for approximately 30% of patients with severe hemophilia A, highlighting the need for new FVIII products with reduced immunogenicity. The development of recombinant FVIII molecules with a lower inhibitor risk profile would present an important advance in the care of patients with hemophilia A. rVIII-SingleChain (AFSTYLATM), is the first and only single-chain molecule purposely designed to provide key features such as increased dosing intervals and high clinical efficacy. The present study has focused on evaluating the immunogenic profile of rVIII-SingleChain in comparison to other rFVIII products (both full length and B-domain-truncated/deleted). Several key characteristics have been identified: The highly pure and homogeneous rVIII-SingleChain with a covalently linked heavy chain and light chain is less likely to contain dissociated FVIII chains (or fragments thereof) that cannot bind to von Willebrand Factor (VWF) and are thus available for uptake by antigen presenting cells (APC). The high degree of sulphation of the predicted six tyrosine sulphation sites in rVIII-SingleChain (as compared to other rFVIII molecules) not only provides a basis for optimal functionality but also (with respect to Tyr1680) ensures maximal VWF binding of the majority of rVIII-SingleChain molecules. The improved binding of rVIII-SingleChain to VWF as compared to full-length rFVIII may more effectively reduce antigen uptake and processing by antigen-presenting cells. In this regard, rVIII-SingleChain pre-complexed with plasma-derived VWF, is less efficiently internalized by human monocyte-derived dendritic cells (MoDCs) as compared to several rFVIII products tested. Further, in a ProImmune ProPresent® antigen presentation assay to identify potentially immunogenic regions in rVIII-SingleChain as compared to full length rFVIII protein revealed a lower number of HLA-DR/DP/DQ-restricted epitopes derived from rVIII-SingleChain as compared to the full length rFVIII protein (33 c.f. 47 for DR; 24 c.f. 32 for DP and 26 c.f. 32 for DQ). In addition, when compared to BDD-rFVIII comparators in the ProImmune ProReveal® T cell stimulation assay, rVIII-SingleChain was found to contain fewer HLA-DR/DP/DQ-restricted epitopes derived from the linker region that triggered T-cell proliferation (15% as compared to 25-35% for the comparators). Collectively, these features should contribute to the reduced immunogenic potential of rVIII-SingleChain. Importantly, these pre-clinical studies are supported by findings from the completed rVIII-SingleChain clinical studies in previously treated patients (PTPs) in which no inhibitor development has been observed. In summary, the immunogenicity of rVIII-SingleChain has been extensively characterized in PTPs over 28,418 exposure days equivalent to more than 233 treatment years. As of 01 August 2016, no PTP subject has developed inhibitors after being exposed to rVIII-SingleChain. All available data support the hypothesis that the unique structural attributes of rVIII-SingleChain may translate into reduced immunogenicity when used for replacement therapy in patients with hemophilia A. The previously untreated patient (PUP) arm in the ongoing extension study is designed to generate data that are necessary to prove this significant clinical benefit. rVIII-SingleChain could potentially offer hemophilia A patients a recombinant product with an inhibitor risk profile that is more favorable than that of currently available products. Disclosures Maraskovsky: CSL Limited: Employment. Verhagen:CSL Limited: Employment. Huynh:CSL Limited: Employment. Baz Morelli:CSL Limited: Employment. Schmidbauer:CSL Behring: Employment. Zollner:CSL Behring: Employment. Powell:CSL Behring: Employment. St Ledger:CSL Behring: Employment. Veldman:CSL Behring: Employment. Hofmann:CSL Behring: Employment.

Description: Abstract 1524 CSL362, a novel humanized, affinity matured monoclonal antibody (mAB), is currently under development at CSL Limited. CSL362 neutralizes Interleukin-3 (IL-3) by binding to the human IL-3 receptor alpha chain (IL-3Ra/CD123). Furthermore, CSL362 has been engineered to bind to FcγRIIIa receptor (CD16) with high affinity and engages with effector cells of the innate immune system to elicit antibody-dependent cellular cytotoxicity (ADCC) against target cells expressing IL-3Ra such as AML blasts and leukemic stem cells. A non-clinical program was conducted to investigate the general safety and toxicity profile as well as the pharmacokinetic and pharmacodynamic properties of CSL362 in non-human primates. Cynomolgus monkeys (n=6 per dose cohort) were administered weekly intravenous infusions of CSL362 at doses of either 0, 3, 10, 30 or 100 mg/kg for 5 weeks with a 6 week recovery period. The potential of CSL362 to induce hypersensitivity or allergic reactions, its impact on safety pharmacology variables as well as local tolerance were assessed. Furthermore, the possible adverse effects of CSL362 on the proliferation, differentiation and maturation of bone marrow derived hematopoetic progenitors were explored. The potential for immunotoxicity of CSL362 was assessed by means of peripheral blood immunophenotyping, T cell-dependent antibody response measurements after keyhole limpet hemocyanin-immunization, measurements of natural killer cell (NK), macrophage and granulocyte function, and quantification of serum cytokine release. The ability to ablate cells expressing IL-3Ra was also determined by evaluating the numbers of basophils, plasmacytoid dendritic cells (pDCs) and monocytes in the peripheral blood. Plasma concentrations of CSL362 were determined to evaluate the pharmacokinetic characteristics. In parallel, the specific immune response against CSL362 was monitored throughout the 11 week study duration. Plasma level determination of CSL362 revealed adequate exposure and a PK profile similar to other humanized mABs. Specific anti-CSL362 antibody formation was observed in 18 % of the study animals. Treatment with CSL362 did not result in any anaphylactic or allergic reaction and had no adverse effect on systemic toxicity parameters or safety pharmacology variables measured. As predicted from in vitro and ex vivo studies, CSL362 produced a marked, dose-dependent and sustained depletion of peripheral blood basophils and pDCs which was associated with a transient decrease in NK cell numbers. No adverse effects of CSL362 on peripheral blood monocytes or pluripotent progenitor cells in the bone marrow was observed, furthermore the function of normal peripheral blood cells expressing IL-3Ra remained unaffected by CSL362. Intriguingly, a clear dose-dependent trend to NK cell recovery was observed following the final dose at week 5 during the subsequent recovery period which preceded the reappearance of basophils and pDC's. Together with the outcome of a tissue-cross reactivity study this proof of specific pharmacodynamic activity confirmed the Cynomolgus monkey as a relevant species. Overall, treatment with CSL362 was very well tolerated and 100 mg/kg, the highest tested dose, was designated the no-observed-adverse-effect-level. In conclusion, the results from this non-clinical safety program demonstrate an excellent tolerance and favorable safety profile of CSL362. This study supports the further clinical development of this mAB in the remission maintenance of patients with CD123-positive acute myeloid leukemia. Disclosures: Herzog: CSL Behring GmbH: Employment. Busfield:CSL Ltd.: Employment. Biondo:CSL Ltd.: Employment. Vairo:CSL Ltd.: Employment. DeWitte:CSL Behring: Employment. Pragst:CSL Behring GmbH: Employment. Dickneite:CSL Behring GmbH: Employment. Nash:CSL Ltd.: Employment. Zollner:CSL Behring GmbH: Employment.

Description: Abstract 2342 Background: NOX-H94, the first-in-class hepcidin inhibitor in development for treatment of anemia of chronic disease (ACD), is a PEGylated anti-hepcidin L-RNA oligonucleotide. ACD is caused by iron sequestration in the reticulo-endothelial macrophages with subsequent iron restricted erythropoiesis due to high hepcidin production and subsequent ferroportin degradation. The treatment of ACD is challenging: a significant number of ACD patients do not respond to erythropoiesis stimulating agents (ESAs), while repeated intravenous iron administrations bear a risk of iron overload. Targeting hepcidin may provide more efficacious and well tolerated treatment alternatives. Methods: This First-in-Human study investigated the safety and tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of escalating single and repeated doses of intravenous (i.v.) NOX-H94 in healthy men and women. The study protocol (ClinicalTrials.gov identifier NCT01372137) was approved by an independent ethics committee and conducted in accordance with the Declaration of Helsinki. Five successive cohorts of 8 healthy subjects, at least 3 men and women, were randomly assigned to i.v. doses of 0.3, 0.6, 1.2, 2.4, and 4.8 mg/kg of NOX-H94 (n=6) or placebo (n=2). Similarly, 2 cohorts of 8 male subjects randomly received 5 doses of either 0.6 or 1.2 mg/kg NOX-H94 or placebo every other day (q2d). Safety parameters, iron parameters, total hepcidin-25 (sum of free circulating hepcidin-25 and hepcidin-25 bound to NOX-H94), and PK were assessed during treatment and follow-up periods of ≥3 weeks. Data are given as means±SD. Results: One man, assigned to 5 i.v. doses of 0.6 mg/kg, withdrew consent after 4 administrations; all other 55 subjects completed the study as scheduled. Safety: Treatment with NOX-H94 was generally safe and well tolerated. No serious adverse event occurred; headache and fatigue were the only treatment related events that occurred more than once. Mild and transient increases in transaminases (

Description: Abstract 4593 Background NOX-A12 is a novel, potent, L-aptamer inhibitor of CXCL12/SDF-1, a chemokine which attracts and activates immune- and non-immune cells. The signaling of CXCL12 has been shown to play an important role in the pathophysiology of chronic lymphocytic leukemia (CLL), especially in the interaction of leukemic cells with their tissue microenvironment. The therapeutic concept of NOX-A12 is to inhibit such tumor-supporting pathways and thereby sensitizing the CLL cells towards chemotherapy. Methods The purpose of this phase IIa study is to evaluate the safety and efficacy of NOX-A12 in combination with background chemo-immunotherapy of bendamustine and rituximab (BR) in patients with relapsed CLL. The described study is being performed in compliance with ethical principles based on the Declaration of Helsinki and ICH-GCP guidelines. The study population was split into a pilot and expansion group. In the pilot group, 3 cohorts of 3 patients each received escalating doses of single agent NOX-A12 two weeks prior to the combined treatment of NOX-A12 and BR. Interim data from these patients are reported. Based on previous Phase I studies in healthy volunteers, pilot patients received a dose of 1, 2 or 4 mg/kg body weight (BW) single agent NOX-A12 on day -14, followed by a 2-weeks period of safety, PK and PD assessments prior to the combined treatment with NOX-A12 and BR. To date, the first cohort of the pilot group already progressed to the 2nd cycle of combined treatment. Evaluation criteria included adverse events according to CTCAE V4, flow cytometry of peripheral blood CD34+ cells and CLL cells, pharmacokinetics of NOX-A12, plasma concentration of CXCL12 and tumor response (NCI-WG 1996 criteria, updated 2008). Results To date 3 patients (age range: 58 – 65 years) have been enrolled in the pilot group of this study. They had received 1 or 2 prior therapies, but no bendamustine. Single i.v. doses of 1 mg/kg BW NOX-A12 had no clinically relevant effects on vital signs, 12-lead ECG parameters and laboratory parameters. One patient reported grade 1 pain in the lower limbs two days after treatment with NOX-A12. This event was not dose-limiting and resolved spontaneously on the same day. Flow cytometry of CD34+ cells and CLL cells (CD19+/CD5+high) showed a rapid mobilization of these cells into the peripheral blood on day 1. Interestingly, return to baseline was not complete at the last assessment on day 3 (for details see Figure 1). The NOX-A12 pharmacokinetics in these 3 patients (for concentration-time profile see Figure 2) is very comparable to healthy volunteers receiving i.v. NOX-A12, with a maximum plasma concentration of 1.52 ± 0.14 μM after 1 h (tmax) and a plasma elimination half-life of about 50 h. As seen in healthy volunteers the plasma concentration of CXCL12 increased upon NOX-A12 treatment and reached a maximum of 0.434 ± 0.076 μM at 24 to 72 h p.a. without ever approaching the plasma concentration of NOX-A12 (Figure 2). Conclusion Single i.v. doses of NOX-A12 at 1 mg/kg BW were safe and well tolerated; the maximum tolerated dose was not reached. NOX-A12 induced a long-lasting mobilization of CD34+ cells and leukemic cells in patients with relapsed CLL, consistent with a mechanism of action based on CXCL12 inhibition. Patient accrual and identification of an optimal chemosensitization regimen of NOX-A12 combined with BR is being continued. Disclosures: Vauléon: NOXXON Pharma AG: Employment. Zöllner:NOXXON Pharma AG: Employment. Dümmler:NOXXON Pharma AG: Employment. Kruschinski:NOXXON Pharma AG: Employment. Fliegert:NOXXON Pharma AG: Employment.

Description: Introduction: Factor (F)VIII immunogenicity is the main obstacle to both successfully treating hemophilia and receiving FDA approval for new therapeutics. Since immune responses to allogeneically distinct proteins require T-cell activation and proliferation, at least one foreign peptide must be liberated from FVIII that can bind with high affinity to one or more of a patient's HLA-class-II (HLA-II) isomers. Due to the complex pathogenesis of inhibitor development, which involves numerous genetic variations and both treatment and product related variables, our ability to predict which patients will become alloimmunized to FVIII remains suboptimal. The role of FVIII glycosylation in inhibitor development appears to be an important, yet not well characterized, modifying influence; defining the mechanism has been complicated by the fact that some FVIII products are highly glycosylated with thousands of potential glycoforms. Here we describe studies of the spectrum of FVIII peptides eluted from HLA-II complexes and the impact of glycosylation on the proteolysis and/or binding of these peptides to a patient's individual HLA-II isomers, i.e. to further incorporate personalized medicine in hemophilia care. Methods: Immature monocyte-derived dendritic cells (DCs) from 12 unrelated donors were generated in vitro and matured in the presence of an equimolar pool of a full length (FL) and 4 B-domain deleted (BDD) rFVIII proteins free of VWF and other proteins. Following harvest and lysis, HLA-DP, -DQ, and -DR molecules were recovered using a specific immunoaffinity step. Peptides were then eluted from these complexes and sequenced by high resolution mass spectrometry (LC/MS/MS). The bound peptides were mapped to the FVIII reference sequence. The estimated binding affinity of FVIII peptides to the HLA-II alleles found in these donors were obtained from NetMHCIIpan and compared to the peptides observed to be bound. Results: The 12 DC donors express 29 distinct HLA-II isomers (6 DP, 11 DQ, 12 DR) from an overall HLA-II gene repertoire having the following alleles: DP: 01:03/02:01, 01:03/03:01, 01:03/04:01, 01:03/04:02, 02:01/01:01, 02:02/05:01 DQ: 01:01/05:03, 01:02/06:02, 01:02/06:09, 01:03/05:01, 01:03/06:03, 01:03/06:04, 02:01/02:01, 02:01/02:02, 03:01/03:02, 03:02/03:03, 05:01/03:01 DR: 01:01, 03:01, 04:01, 04:04, 07:01, 09:01, 11:01, 11:04, 13:01, 13:02, 14:01, 15:01 These 29 HLA-II isomers were found to have 77 bound peptides that covered 1,202 of the 2,332 total amino acid residues in the NCBI reference FL-FVIII protein, whose domain structure and consensus N-linked glycosylation (NLG) sites are shown in panel A of the Figure. The HLA-II bound peptides were mapped to the FVIII regions from which they derive (panel B). One of the 20 NLG sites known to be glycosylated and 3 of the 4 known non-glycosylated NLG sites were found to be in a bound peptide. A NetMHCIIpan analysis predicted that no FVIII nonamer containing a consensus NLG site binds strongly to any of the 12 DR isomers; but, it also clearly showed that more peptides bind with weak or strong affinity as peptide length increases (data not shown). Conclusion: Despite finding 3 of FVIII's 4 non-glycosylated consensus NLG sites in the tightly bound HLA-II/peptide complexes, only 1 of the 20 glycosylated NLG sites was found among these bound peptides. The near complete absence of N-linked glycans in the presented HLA-II bound peptides is compelling, but incomplete, evidence that glycosylation influences the immunogenicity of FVIII. Potential mechanisms may include effects on internalization, proteolysis and/or HLA-II binding. Further direct studies are required to determine if these post-translational modifications affect proteolysis and/or HLA-II binding; core peptides that can be proteolyzed and/or bound in the absence of glycosylation or with alternative glycan conformations may provide more evidence that glycosylation can modulate immunogenicity. We hypothesize that HLA-II bound and unbound FVIII peptides constitute a novel immune-response-related biomarker that will improve the accuracy of inhibitor risk prediction by allowing pertinent patient-specific pharmacogenomic inputs to be analyzed in a more biologically relevant manner. References: Karosiene et al. NetMHCIIpan-3.0, a pan-specific MHC-II prediction method including all 3 human MHC-II isotypes: HLA-DR, -DP and -DQ. Immunogenetics, 2013. Disclosures Hofmann: CSL Behring: Employment. Zollner:CSL Behring: Employment. Powell:CSL Behring: Employment. Maraskovsky:CSL Behring: Employment. Howard:Baxter: Consultancy, Honoraria, Research Funding; Bayer: Consultancy, Honoraria, Research Funding; Haplomics, Inc.: Patents & Royalties; CSL Behring: Consultancy, Honoraria, Research Funding.