Abstract
Telomerase reverse transcriptase (TERT) is a classic tumor-associated antigen overexpressed in majority of tumors. Several TERT-based cancer vaccines are currently in clinical trials, but immune correlates of their antitumor activity remain largely unknown. Here, we characterized fine specificity and lytic potential of immune response against rat TERT in mice. BALB/c mice were primed with plasmids encoding expression-optimized hemagglutinin-tagged or nontagged TERT or empty vector and boosted with same DNA mixed with plasmid encoding firefly luciferase (Luc DNA). Injections were followed by electroporation. Photon emission from booster sites was assessed by in vivo bioluminescent imaging. Two weeks post boost, mice were sacrificed and assessed for IFN-γ, interleukin-2 (IL-2), and tumor necrosis factor alpha (TNF-α) production by T-cells upon their stimulation with TERT peptides and for anti-TERT antibodies. All TERT DNA-immunized mice developed cellular and antibody response against epitopes at the N-terminus and reverse transcriptase domain (rtTERT) of TERT. Photon emission from mice boosted with TERT/TERT-HA+Luc DNA was 100 times lower than from vector+Luc DNA-boosted controls. Bioluminescence loss correlated with percent of IFN-γ/IL-2/TNF-α producing CD8+ and CD4+ T-cells specific to rtTERT, indicating immune clearance of TERT/Luc-coexpressing cells. We made murine adenocarcinoma 4T1luc2 cells to express rtTERT by lentiviral transduction. Expression of rtTERT significantly reduced the capacity of 4T1luc2 to form tumors and metastasize in mice, while not affecting in vitro growth. Mice which rejected the tumors developed T-cell response against rtTERT and low/no response to the autoepitope of TERT. This advances rtTERT as key component of TERT-based therapeutic vaccines against cancer.
Highlights
Cancer immunotherapies fall in two major categories: passive that includes blockade of immune checkpoints and adoptive immunotherapy and active that includes therapeutic vaccination and immuno/chemotherapy combinations [1]
Mice were assessed in two independent runs, taking two mice from each cluster. Their splenocytes were tested for the capacity to produce IFN-γ, IL-2, and TNF-α in response to stimulation with TERT6 and TERT8, which we have shown to be recognized by T cells of mice DNA-immunized with rat Telomerase reverse transcriptase (TERT) (TERT7 was excluded as it partially overlapped TERT8) and against epitopes of TERT lying outside rtTERT: TERT1 as an epitope inducing T cell response in DNA-immunized mice and TERT2 as an autoepitope of TERT
Our study indicates that these B-cell epitopes may be localized at aa 888–929 of TERT within rtTERT domain
Summary
Cancer immunotherapies fall in two major categories: passive that includes blockade of immune checkpoints and adoptive immunotherapy and active that includes therapeutic vaccination and immuno/chemotherapy combinations [1]. Active immunotherapies based on TAAs presented by the patient autologous tumor cells or dendritic cells (DCs) as well as chimeric antigen receptor T cell immunotherapy (CAR-T) are effective, if combined with surgery and radioand/or chemotherapy [4,5,6]. Straightforward active tumor immunotherapy implying immunization with TAA-based vaccines is still underdeveloped. The first successful therapeutic DNA vaccine reported to cause recession of cervical neoplasia based on the consensus tumor antigens of HPV16 [15] is currently in two Phase III clinical trials (NCT03185013 and NCT03721978)
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