Immunization with a recombinant antigen composed of conserved blocks from TSA56 provides broad genotype protection against scrub typhus

Hong-Il Kima,b*, Na-Young Haa,b*, Gwanghun Kima,b, Chan-Ki Mina,b, Yuri Kima,b, Nguyen Thi Hai Yena,b, Myung-Sik Choia and Nam-Hyuk Choa,b,c

Department of Microbiology and Immunology, Seoul National University College of Medicine, Seoul, Republic of Korea; b Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, Republic of Korea; c Institute of Endemic Disease, Seoul National University Medical Research Center and Bundang Hospital, Seoul, Republic of Korea

ABSTRACT Scrub typhus is an acute febrile disease caused by Orientia tsutsugamushi infection. Despite the wide range of approaches explored during the last seventy years, an effective prophylactic vaccine is not yet available. Here, we developed a novel recombinant antigen derived from conserved regions of 56 kDa type-specific antigen (TSA56), a major outer membrane protein responsible for genetic heterogeneity and antigenicity, and evaluated it as a protective vaccine antigen. Our findings demonstrate that immunization with conserved blocks of TSA56 (cTSA56) not only provides protective immunity against lethal challenges with the homologous genotype, but also confers significantly better protection against heterologous genotypes than TSA56. Adoptive transfer of CD4+ or CD8+ T cells from immunized mice provided significantly enhanced protection against lethal challenge, whereas immune B cells failed to do so, indicating that cellular immunity against the conserved epitopes plays a protective role. Moreover, immunization with a 10-mer peptide mixture, screened from CD8+ T cell epitopes within the conserved region of TSA56, provided enhanced protection against lethal challenge with O. tsutsugamushi. Therefore, this novel recombinant antigen is a promising candidate for scrub typhus vaccine against a wide range of O. tsutsugamushi genotypes

ARTICLE HISTORY Received 14 January 2019; Revised 7 May 2019; Accepted 6 June 2019

KEYWORDS Scrub typhus; Orientia tsutaugmsushi; vaccine; TSA56; conserved blocks; CD8 T cell

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