Binding of prostate-specific membrane antigen to dendritic cells: a critical step in vaccine preparation

Background aims Dendritic cell (DC)-based vaccines hold promise as a safe therapy for prostate cancer (PCa), and prostate-specifi c membrane antigen (PSMA) fulfi ls the requirements for a tumor-associated antigen (TAA) to be clinically effective. We evaluated the actual binding of selected HLA-A2-restricted PSMA peptides to HLA class I molecules on ex vivo -generated mature (m) DC. Methods mDC were generated from peripheral monocytes of HLA-A2 normal donors. The PSMA peptides PSMA 711 (ALFDIESKV), PSMA 27 (VLAGGFFLL) and PSMA 663 (MMNDQLMFL) were selected based on computer-assisted prediction programs, documented CTL epitope activity or previous use in clinical trials. The model cell line T2 and the clinical grade (CD8 3 � CCR7 � ) mDC were pulsed with fl uorescein (FL)-conjugated peptides and an anti-HLA-A2 monoclonal antibody (MAb) and analyzed. Results Flow cytometry analysis showed best binding effi ciency to be by PSMA 27 . Confocal microscopy confi rmed coincident fl uorescence emission of HLA-A2 MAb and FL–PSMA 27 . Virtual co-localization of PSMA 27 and HLA class I molecules was supported further by fl uorescence resonance energy transfer (FRET) analysis. The clinical relevance of our fi ndings has to be validated in vivo .