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

Abstract

Background aims

Dendritic cell (DC)-based vaccines hold promise as a safe therapy for prostate cancer (PCa), and prostate-specific membrane antigen (PSMA) fulfils 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 PSMA₇₁₁ (ALFDIESKV), PSMA₂₇ (VLAGGFFLL) and PSMA₆₆₃ (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 (CD83⁺ CCR7⁺) mDC were pulsed with fluorescein (FL)-conjugated peptides and an anti-HLA-A2 monoclonal antibody (MAb) and analyzed.

Results

Flow cytometry analysis showed best binding efficiency to be by PSMA_27. Confocal microscopy confirmed coincident fluorescence emission of HLA-A2 MAb and FL–PSMA₂₇. Virtual co-localization of PSMA₂₇ and HLA class I molecules was supported further by fluorescence resonance energy transfer (FRET) analysis. The clinical relevance of our findings has to be validated in vivo.

Conclusions

The present report is the first to score selected PSMA peptides based on their detectable binding to mDC. It identifies PSMA₂₇ as the choice candidate among other PSMA peptides and it should be included in developing DC vaccine protocols for HLA-A2 PCa patients.

Keywords:

• Antigenic peptides
• dendritic cells
• prostate cancer
• prostate-specific membrane antigen
• vaccines

Acknowledgments

This work was supported by grants from the Italian Ministry of University, Regione Piemonte (Oncology project), CERMS/COES project funded by the Compagnia di San Paolo di Torino/FIRMS (to LM), Compagnia di San Paolo di Genova (to LM), Fondazione Cassa di Risparmio di Torino (to LM), Fondazione Cariverona (to LM) and Fondazione Guido Berlucchi di Brescia (to FB). SG is a recipient of a fellowship from Fondazione Banca Popolare Di Novara. DB is recipient of a fellowship from Compagnia di San Paolo.

Disclosure of interest: The authors have no conflicts of interest to declare.