Application of RNA Transcribed from Viral IRES Control: Utilization of Vaccine Development for MERS-CoV Hye Won Kwak1, Ryoon Ho Kim1, Hae-Rim Park1, Hyo-Jung Park1, Hae Ri Ko1, Man Ki Song2, Jae-Ouk Kim2, Seung Rok Ryu3, Kyung Won Kang3, Sang-Myeong Lee3, Jae-Hwan Nam1* 1Department of Biotechnology, The Catholic University of Korea; 2International Vaccine Institute; 3Division of Biotechnology, Chonbuk National University
In 2015, a large outbreak of the Middle East respiratory syndrome coronavirus (MERS-CoV) occurred in Korea. Since then, a clinically available vaccine has not yet been made available. In this study, we developed a novel RNA adjuvant, i.e., RNA transcribed from plasmid (pCrPV-MERS) including MERS spike (S) gene under internal ribosome entry site (IRES) control of cricket paralysis virus (CrPV) for combinational immunization with MERS S protein. RNA transcribed from pCrPV-MERS was used to treat mouse bone marrow-derived conventional dendritic cells and human peripheral blood mononuclear cells. This showed that the changes in transcriptome and cytokines by RNA treatment were similar to those by poly I:C treatment as positive control, which means that it is possible to use RNA-containing CrPV-IRES as adjuvant. To confirm this in vivo, MERS S protein is intramuscularly immunized to mouse with/without alum and RNA transcribed from pCrPV-MERS as adjuvant. The RNA adjuvant immunized group showed higher neutralizing antibody and IgG2a (indicated Th1-oriented response) levels against MERS S compared with the mouse group immunized with S protein without RNA from pCrPV-MERS. Furthermore, the population of T cells secreting IFN- (indicated cytotoxic T lymphocyte, CTL, response) from splenocytes of RNA adjuvant-immunized group is higher than that of MERS S protein immunized group after priming with S protein and peptide. However, both groups showed a protection effect against the MERS-CoV challenge. All data indicated that RNA transcribed from IRES of CrPV as adjuvant can trigger Th1 and CTL immune responses, which means that a RNA adjuvant including a gene of interest (GOI) under CrPV-IRES can induce a specific cellular immune response against GOI. Furthermore, RNA adjuvant-immunized group induced high neutralizing antibody. Therefore, it is a good vaccine strategy because the immunization with alum-formulated protein vaccine and RNA vaccine as adjuvant together can induce both humoral immune response by protein vaccine and cellular immune response by RNA vaccine, which are mutually complementary.
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