Abstract 5562: Development of a TERT-specific peptide/adjuvant vaccine in C57BL/6 mice

Abstract Telomerase plays a vital role in cell senescence and cellular replication and has been described as a leading regulator in several human cancers, including prostate, thyroid, breast, colon, and bladder cancer. Telomerase is responsible for elongating telomere length and prolonging cellular lifespan as well as acting as a transcriptional modulator in cancer signaling pathways. Because of its enhanced expression in primary tumor cells as well as incipient tumor-initiating stem cells and with limited distribution in normal somatic cells, the catalytic component of telomerase, TERT (telomerase reverse transcriptase), is regarded as a high-impact target for immunotherapeutic agents and vaccines. In order to derive a mouse TERT (mTERT)-specific vaccine which could be useful in a preventive approach, we implemented an epitope-mapping stratagem by which pools of 30-mer peptides overlapping by 5 spanning the entire mTERT sequence were used to immunize C57BL/6 mice. Several immunogenic peptides were identified by matrixed peptide pool IFN-ɣ ELISPOT screening in a 2-part process that first identified positive pools, then identified individual peptides. 15-mer and 31-mer versions of the top 7 immunogenic mTERT peptides were synthesized and used as a peptide pool combined separately with several adjuvants to optimize immunogenicity. Results suggested a peptide sequence-specific preference for TLR3-mediated Hiltonol versus TLR9-mediated CpG-based adjuvants. In addition, the majority of T cell responses specific to the TERT peptides was identified through flow cytometry as belonging to the CD4 compartment, although one class I-restricted epitope was also identified. Multifunctional CD4+ T cells expressing IFN-ɣ, TNF-α, IL-2, and CD107a were identified specific to several mTERT peptides. In vivo cytotoxic effects exerted on TERT peptide pool-loaded target cells were also uncovered that were specific to a CpG-adjuvanted version of the vaccine. Finally, multiple versions of the mTERT peptide/adjuvant vaccine with highest immunogenicity scores are being tested in a syngeneic graft mouse model using subcutaneous implantation of lung cancer-derived SPON10 cells expressing mTERT. If proven efficacious, these results will support the feasibility of a TERT peptide/adjuvant approach for prophylactically engendering broad antitumor immunity to TERT-expressing cancers. Funded by NCI Contract No. HHSN261200800001E Citation Format: Jason D. Marshall, Yurong Song, Hamid Zarkesh, Rebecca L. Matthews, Chelsea Sanders, Simone Difilippantonio, Ligia A. Pinto, Shizuko Sei, Robert H. Shoemaker. Development of a TERT-specific peptide/adjuvant vaccine in C57BL/6 mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5562.