Epitope Mapping Of Pd-L1 Primary Antibodies (28-8, Sp142, Sp263 E1l3n).

3028Background: Currently, programmed death-ligand 1 (PD-L1) immunohistochemistry (IHC) assays received approval in combination with an anti-PD-1 or anti-PD-L1 compounds. However, the FDA blueprint and other publications revealed differences in staining pattern between PD-L1 IHC assays. More precisely the SP142 assay detects less tumor cells (TC), but more immune cells (IC), while the 28-8 assay is more sensitive for TC and less appropriate for IC detection. SP263 stains TC and IC equally well. E1L3N IHC reveals IC and slightly more TC staining than SP142. This study investigates whether these staining discrepancies can be partly explained by specific epitope recognition. Methods: Linear epitope mapping was performed for PD-L1 antibody clones 28-8, E1L3N, SP142 and SP263. In brief, the PD-L1 sequence (Q9NZQ7, Uniprot) was split into 15 amino acid (AA) peptides with a peptide overlap of 14 AA . Each peptide was printed in duplicate on the PD-L1 microarray. The microarray was exposed to different concentrat...