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H2O2-Inactivated Salmonella typhimurium RE88 Strain as a New Cancer Vaccine Carrier: Evaluation in a Mouse Model of Cancer

Authors Fan Y, Bai T, Tian Y, Zhou B, Wang Y, Yang L

Received 20 September 2020

Accepted for publication 7 December 2020

Published 15 January 2021 Volume 2021:15 Pages 209—222


Checked for plagiarism Yes

Review by Single anonymous peer review

Peer reviewer comments 2

Editor who approved publication: Dr Tuo Deng

Yingzi Fan,1,2,* Tingting Bai,2,* Yaomei Tian,1 Bailing Zhou,1 Yuanda Wang,1 Li Yang1

1State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University and Collaborative Innovation Center, Chengdu, People’s Republic of China; 2Department of Laboratory Medicine, Clinical Medical College and the First Affiliated Hospital of Chengdu Medical College, Chengdu, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Li Yang
State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University and Collaborative Innovation Center, No. 17, People’s South Road, Chengdu 610041, People’s Republic of China
Tel +86 18628182400

Purpose: This study aimed to describe a novel cancer vaccine developed using H2O2-inactivated Salmonella typhimurium RE88 [with deletions of AroA (the first enzyme in the aromatic amino acid biosynthesis pathway) and DNA adenine methylase] as the carrier.
Methods: The pVLT33 plasmid was used to engineer an RE88 strain induced to express ovalbumin (OVA) by isopropylthiogalactoside (RE88-pVLT33-OVA). The immune responses and anticancer effects of H2O2-inactivated RE88-pVLT33-OVA were compared with those of non-inactivated RE88-pVLT33-OVA and OVA (positive control) in mice carrying OVA-expressing tumors (EG7-OVA) cells.
Results: Anti-ovalbumin IgG (immunoglobulin G) titer following vaccination with H2O2-inactivated RE88-pVLT33-OVA was higher for subcutaneous than for intragastric vaccination. When subcutaneous administration was used, H2O2-inactivated RE88-pVLT33-OVA (2 × 109 CFU (colony forming units)/mouse) achieved an anti-ovalbumin IgG titer higher than that for the same dose of RE88-pVLT33-OVA and comparable to that for 10 μg ovalbumin (positive control). The binding of mouse serum antibodies to EG7-OVA cells was stronger for H2O2-inactivated RE88-pVLT33-OVA (2 × 109 CFU/mouse) than for 10 μg ovalbumin. Furthermore, subcutaneous vaccination with H2O2-inactivated RE88-pVLT33-OVA (2 × 109 CFU/mouse) induced greater activation of splenic T cells and more extensive tumor infiltration with CD4+/CD8+ T cells compared with 10 μg ovalbumin (positive control). The mice vaccinated subcutaneously with H2O2-inactivated RE88-pVLT33-OVA at a dose of 2 × 108 or 6 × 108 CFU/mouse had smaller tumors compared with mice in the negative control groups. Tumor weight in mice vaccinated with H2O2-inactivated RE88-pVLT33-OVA at a dose of 2 × 109 CFU/mouse was significantly lower than that in both negative control groups (P < 0.05) and decreased with the increasing dose of H2O2-inactivated RE88-pVLT33-OVA. H2O2-inactivated RE88-pVLT33-OVA was potentially safer than the non-inactivated strain, could carry exogenous antigens, and had specific epitopes that could be exploited as natural adjuvants to facilitate the induction of cellular and humoral immune responses.
Conclusion: It was anticipated that H2O2-inactivated RE88-pVLT33-OVA could be used as a novel delivery system for new cancer vaccines.

Keywords: cancer vaccine, H2O2 inactivation, RE88-pVLT33-OVA, whole-cell bacterial vaccine

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