Page 186 - Haematologica June

J. Hrdinová et al.
B
1088
tides are displayed on MHC class II following pulsing of dendritic cells with ADAMTS13. To complement our analysis of peptides eluted from MHC, we employed a bio-informatic approach to identify whether the ADAMTS13-derived peptides identified in this and a pre- vious study (Table 3)19 might be immunogenic. Firstly, we used the EpiMatrix algorithm, which assesses the poten- tial for individual peptides to bind to HLA-DR based on amino acid motifs preferred by nine “supertype” HLA-DR allele families. These HLA-DR motif families cover 95% of the human population worldwide.27 EpiMatrix assesses peptides for binding potential against a matrix of amino acid preferences for each HLA allele. This score is adjusted to a normalized (Z) score. The EpiMatrix Score of a pep- tide represents a sum of significant assessments for all of the nine-mers in a sequence, adjusted for length. An EpiMatrix Score of 40.66 was obtained for metallo-pro-
tease-derived peptide SRRQLLSLLSAGRAR (residues 266- 280); this value indicates that this peptide has a significant potential to bind to multiple HLA-DR molecules (Table 3). Also, the CUB2 domain-derived peptide FSEGFLKA- QASLRGQYW (residues 1390-1406) was predicted to bind to multiple HLA-DR alleles (Table 3). A number of other CUB1-2 domain-derived peptides were found to be potentially immunogenic, as revealed by an EpiMatrix Score higher than 10 (Table 3).
A second tool, JanusMatrix,28 was used to evaluate whether the HLA-DR-presented ADAMTS13 peptides dis- played homology to proteins from the human proteome. JanusMatrix differentiates HLA-binding peptides that are more cross-conserved at the TCR face and thus more likely tolerated (or actively tolerogenic) from those less cross-con- served that are more likely to be immunogenic.29,30 This analysis revealed that six of the peptides (Table 3 and
haematologica | 2018; 103(6)