Design and Characterization of a Recombinant Brucella abortus RB51 Vaccine That Elicits Enhanced T Cell-Mediated Immune Response

Mahdieh Sarmadi; Azam Gheibi; Hossein Khanahmad; Mohammad Reza Khorramizadeh; Seyed Hossein Hejazi; Noushin Zahedi; Hamidreza Mianesaz; Khosrow Kashfi

doi:10.3390/vaccines10030388

Design and Characterization of a Recombinant Brucella abortus RB51 Vaccine That Elicits Enhanced T Cell-Mediated Immune Response

Vaccines (Basel). 2022 Mar 3;10(3):388. doi: 10.3390/vaccines10030388.

Authors

Mahdieh Sarmadi¹, Azam Gheibi², Hossein Khanahmad¹, Mohammad Reza Khorramizadeh^{2

3}, Seyed Hossein Hejazi⁴, Noushin Zahedi¹, Hamidreza Mianesaz¹, Khosrow Kashfi^{5

6}

Affiliations

¹ Department of Genetics and Molecular Biology, School of Medicine, Isfahan University of Medical Sciences, Isfahan 81746-73461, Iran.
² Department of Biotechnology, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences (TUMS), Tehran 14177-55469, Iran.
³ Biosensor Research Center, Endocrinology and Metabolism Molecular-Cellular Sciences Institute, Tehran University of Medical Sciences (TUMS), Tehran 14117-13139, Iran.
⁴ Department of Parasitology and Mycology, School of Medicine, Isfahan University of Medical Sciences, Isfahan 81746-73461, Iran.
⁵ Department of Molecular, Cellular, and Biomedical Sciences, Sophie Davis School of Biomedical Education, City University of New York School of Medicine, New York, NY 10031, USA.
⁶ Graduate Program in Biology, City University of New York Graduate Center, New York, NY 10016, USA.

Abstract

Brucella abortus vaccines help control bovine brucellosis. The RB51 strain is a live attenuated vaccine with low side effects compared with other live attenuated brucellosis vaccines, but it provides insufficient protective efficacy. Cell-mediated immune responses are critical in resistance against intracellular bacterial infections. Therefore, we hypothesized that the listeriolysin O (LLO) expression of Listeria monocytogenes, BAX, and SMAC apoptotic proteins in strain RB51 could enhance vaccine efficacy and safety. B. abortus RB51 was transformed separately with two broad-host-range plasmids (pbbr1ori-LLO and pBlu-mLLO-BAX-SMAC) constructed from our recent work. pbbr1ori-LLO contains LLO, and pBlu-mLLO-BAX-SMAC contains the mutant LLO and BAX-SMAC fusion gene. The murine macrophage-like cell line J774A.1 was infected with the RB51 recombinant strain containing pBlu-mLLO-BAX-SMAC, RB51 recombinant strain containing LLO, and RB51 strain. The bacterial cytotoxicity and survival and apoptosis of host cells contaminated with our two strain types-RB51 recombinants or the parental RB51-were assessed. Strain RB51 expressing mLLO and BAX-SMAC was tested in BALB/c mice and a cell line for enhanced modulation of IFN-γ production. LDH analysis showed that the RB51-mLLO-BAX-SMAC and RB51-LLO strains expressed higher cytotoxicity in J774A.1 cells than RB51. In addition, RB51 recombinants had lower macrophage survival rates and caused higher levels of apoptosis and necrosis. Mice vaccinated with the RB51 recombinant containing mLLO-BAX-SMAC showed an enhanced Th1 immune response. This enhanced immune response is primarily due to bacterial endosome escape and bacterial antigens, leading to improved apoptosis and cross-priming. This potentially enhanced TCD₈⁺- and T cell-mediated immunity leads to the increased safety and potency of the RB51 recombinant (RB51 mLLO-BAX-SMAC) as a vaccine candidate against B. abortus.

Keywords: BAX and SMAC apoptotic proteins; Brucella abortus; RB51 strain; Th1 immune response; listeriolysin O (LLO).