P059 Analysis of HLAcII peptidomes presented by dendritic cells (DCs) from healthy donors and hemophilia-A (HA) patients with or without factor VIII (FVIII) inhibitors after ex vivo administration of different therapeutic FVIII proteins (tFVIIIs)

Aim T cells specific for tFVIIIs in HA patients can induce neutralizing FVIII antibodies called inhibitors. DCs that present tFVIII derived peptides in their HLAcII repertoire may activate T cells. We employed DC protein processing and presentation assays (DCAs) to quantify tFVIII peptides in HLAcII peptidomes and used these as measures of the immunogenic potential (IP) of tFVIIIs as a function of their associated HLAcII/tFVIII peptide density. Methods We used DCs from 28 healthy donors and 5 HA patients [2 inhibitor (Inh) positive and 3 Inh negative] in 3 DCAs. In DCA 1, DCs from healthy donors 1–12 were given an equimolar mix of 5 recombinant (r) FVIIIs. In DCA 2, DCs from healthy donors 13–24 were given a plasma derived (pd) FVIII + vWF or 1 of 2 rFVIIIs (BDT or FL) ± vWF. In DCA 3, DCs from healthy donors 25–28 and HA patients 1–5 were incubated with pdFVIII or FL, BDD, or BDT rFVIII, all + vWF (Fig. 1A). After DC lysis and DR, DQ and DP isolation, we identified tFVIII peptides by LC-MS/MS. We performed a log linear analysis of the DR bound tFVIII peptides to identify determinants of Inh risk (Fig. 1B-E) with random effects to control for potential donor- and DCA-clustering. Space limits prevent description of the DQ and DP peptides. Results The IP of tFVIIIs was greater in HA patients than in healthy donors and in Inh positive than in Inh negative patients (Fig. 1B-E). We found that BDT + vWF and FL ± vWF had lesser and greater IP, respectively, than pdFVIII + vWF; the IP of BDD + vWF was comparable to that of pdFVIII + vWF. The rFVIII mix had the greatest IP. The higher IP in HA patients versus healthy donors and in Inh positive vs Inh negative patients reflect significant correlations of 0.91 and 0.52 with the presence/absence of the FVIII Inh risk allele DRB1*15:01. Download : Download high-res image (400KB) Download : Download full-size image Conclusions DC protein processing and presentation is affected by HLAcII repertoires but not by HA patient or FVIII Inh status after accounting for correlation with DRB1*15:01. Relative to pdFVIII, rFVIIIs have different IP with BDT and FL being significantly less and greater, respectively. T.E. Howard: 4. Scientific/Medical Advisor; Company/Organization; Haplomics Biotechnology. M. Hofmann: 5. Employee; Company/Organization; CSL Behring. L.V. Dinh: 5. Employee; Company/Organization; Haplomics Biotechnology. J. Powell: 5. Employee; Company/Organization; CSL Behring. E. Maraskovsky: 5. Employee; Company/Organization; CSL Limited.