Immunization with truncated sequence of Telomerase Reverse Transcriptase induces a specific antitumor response in vivo

Abstract

To select the MHC-I-binding epitope-rich sequence of mice telomerase reverse transcriptase (mTERT) and study the antitumor immune response induced by truncated TERT through mRNA-transfected dendritic cells (DCs) immunization in mice. The MHC-I-binding epitopes of TERT were predicted using bioinformatics software. The selected sequence of TERT (Truncated mTERT, TERT^t, mTERT cDNA 1776 bp-2942 bp encoding 584 aa-969 aa) was cloned from B16 mouse melanoma cells and inserted into pBluescriptIIKS(+) plasmid downstream of the T7 promoter. TERT^t RNA was prepared through in vitro transcription. Bone marrow-derived DCs were electroporated with TERT^t RNA and used to immunize syngeneic naïve mice. The quantity and cytotoxic activity of TERT-specific cytotoxic T lymphocytes (CTLs) in mice spleen were evaluated using IFN-γ enzyme-linked immunospot (ELISPOT) and Lactate dehydrogenase release assay. The immunoprophylactic effects against TERT positive tumor induced by TERT^t RNA transfected DC in vivo were evaluated through an immunized-challenged mouse model. TERT^t was cloned and in vitro transcribed into TERT^t mRNA. As shown in FCM analysis, the efficiency of DC electroporation is 35.1% (29.7–41.2%). After electroporation, a subtle increase of costimulator and MHC-II molecules were expressed on the cell surface. Immunization of TERT^t mRNA transfected DCs induced IFN-γ-secreting CTLs which manifested specific cytotoxic activity against TERT-positive target cells. In a cancer mouse model, vaccination of TERT^t mRNA-transfected DCs suppressed the growth of TERT positive tumors (p=0.001) and prolong the survival time of tumor-bearing animals (p=0.029). TERT^t evokes an antitumor immune response in vivo which is targeted to TERT. TERT^t can be used as an antigeneic sequence to produce anti-TERT tumor vaccine.