A Mutated Prostatic Acid Phosphatase (PAP) Peptide-Based Vaccine Induces PAP-Specific CD8+ T Cells with Ex Vivo Cytotoxic Capacities in HHDII/DR1 Transgenic Mice

Pauline Le Vu; Jayakumar Vadakekolathu; Sarra Idri; Holly Nicholls; Manon Cavaignac; Stephen Reeder; Masood A Khan; Dennis Christensen; Alan Graham Pockley; Stéphanie E McArdle

doi:10.3390/cancers14081970

A Mutated Prostatic Acid Phosphatase (PAP) Peptide-Based Vaccine Induces PAP-Specific CD8⁺ T Cells with Ex Vivo Cytotoxic Capacities in HHDII/DR1 Transgenic Mice

Cancers (Basel). 2022 Apr 13;14(8):1970. doi: 10.3390/cancers14081970.

Authors

Affiliations

¹ The John van Geest Cancer Research Centre, School of Science and Technology, Nottingham Trent University, Nottingham NG11 8NS, UK.
² Centre for Health, Ageing and Understanding Disease (CHAUD), School of Science and Technology, Nottingham Trent University, Nottingham NG11 8NS, UK.
³ Department of Urology, University Hospitals of Leicester NHS Trust, Leicester LE1 5WW, UK.
⁴ Center for Vaccine Research, Statens Serum Institute, DK-2300 Copenhagen, Denmark.

Abstract

Background: Current treatments for castrate (hormone)-resistant prostate cancer (CRPC) remain limited and are not curative, with a median survival from diagnosis of 23 months. The PAP-specific Sipuleucel-T vaccine, which was approved by the FDA in 2010, increases the Overall Survival (OS) by 4 months, but is extremely expensive. We have previously shown that a 15 amino accid (AA) PAP sequence-derived peptide could induce strong immune responses and delay the growth of murine TRAMP-C1 prostate tumors. We have now substituted one amino acid and elongated the sequence to include epitopes predicted to bind to several additional HLA haplotypes. Herein, we present the immunological properties of this 42mer-mutated PAP-derived sequence (MutPAP42mer).

Methods: The presence of PAP-135-143 epitope-specific CD8⁺ T cells in the blood of patients with prostate cancer (PCa) was assessed by flow cytometry using Dextramer™ technology. HHDII/DR1 transgenic mice were immunized with mutated and non-mutated PAP-derived 42mer peptides in the presence of CAF^®09 or CpG ODN1826 (TLR-9 agonist) adjuvants. Vaccine-induced immune responses were measured by assessing the proportion and functionality of splenic PAP-specific T cells in vitro.

Results: PAP-135-143 epitope-specific CD8⁺ T cells were detected in the blood of patients with PCa and stimulation of PBMCs from patients with PCa with mutPAP42mer enhanced their capacity to kill human LNCaP PCa target cells expressing PAP. The MutPAP42mer peptide was significantly more immunogenic in HHDII/DR1 mice than the wild type sequence, and immunogenicity was further enhanced when combined with the CAF^®09 adjuvant. The vaccine induced secretory (IFNγ and TNFα) and cytotoxic CD8⁺ T cells and effector memory splenic T cells.

Conclusions: The periphery of patients with PCa exhibits immune responsiveness to the MutPAP42mer peptide and immunization of mice induces/expands T cell-driven, wild-type PAP immunity, and therefore, has the potential to drive protective anti-tumor immunity in patients with PCa.

Keywords: CAF®09; Dextramer™; HHDII/DR1 mice; PBMC; castrate (hormone)-resistant PCa (CRPC); immunotherapy; prostate cancer; prostatic acid phosphatase (PAP).