These results suggest that InsB subunit vaccination may offer a protective efficacy similar to that of BCG or ESAT-6. Open in a separate window FIGURE 3 Protective efficacy of antigen immunization against Mtb K infection. memory T cells with a multifunctional capacity and may confer durable protection against the highly virulent Mtb K. (Mtb), remains a major public health Ldb2 threat worldwide as the top infectious disease in terms of morbidity and mortality P 22077 (WHO, 2017). Despite the global use of Calmette-Guerin (BCG) vaccination and available TB treatments, TB reportedly showed an incidence of 10.4 million cases and caused 1.7 million deaths in 2016 (WHO, 2017). Although the prevention of TB is the most effective control measure for reducing the incidence of TB, the protective efficacy of BCG, which is the only approved vaccine for TB (Nemes et al., 2018), is thought to be insufficient to protect against pulmonary TB and latent infection, and its highly variable results among different geographical locations indicate that Mtb genotypes with different virulence levels might be dominant in different regions (Pitt et al., 2013). To develop new prophylactic vaccines capable of replacing or improving the BCG vaccine, researchers have moved many vaccine candidates into the clinical phase (Kaufmann et al., 2017). The identification and discovery of novel antigens is the initial and important step in new vaccine development (Singh et al., 2014). Importantly, an understanding of antigenic variation and the differential virulence levels of clinically prevalent Mtb strains is one of the factors considered in TB vaccine development (Ernst, 2017; Chae and Shin, 2018; Chiner-Oms et al., 2018). In addition, studies of newly emerging strains displaying a wide spectrum of virulence and fitness have been considered as valuable for developing new vaccines, as screening vaccines with laboratory-adapted strains have been regarded as one possible limitation in the current field (Henao-Tamayo et al., 2015). In particular, the Mtb Beijing genotype is highly dominant in East Asian countries, and the rate of isolation of strains belonging to the Mtb Beijing family has increased worldwide, which indicates that the BCG vaccine might provide a relatively low level of protection against these strains (Abebe and Bjune, 2006; Kremer et al., 2009). Furthermore, epidemiological studies have suggested that extensive and continuous BCG vaccination may be one of the forces causing the emergence of the Beijing genotype (Abebe and Bjune, 2006), indicating that the global control of Mtb Beijing strains is important due to their association with drug resistance and their ability to evade BCG-conferred vaccine efficacy (Kremer et al., 2009). Furthermore, the failure of the MVA85A vaccine trial may have occurred because it was tested not against any clinical strains but only against laboratory-adapted strains without considering the prevalent local strains in the region of clinical trials even though MVA85A was extensively tested in animal settings (Groschel et al., 2017). In this context, greater attention to the varying fitness of Mtb strains P 22077 throughout the regions should be preferentially required for the development of a vaccine and testing of its efficacy. Thus, the protective efficacy of new TB vaccine candidates should be tested against the prevailing local strains, such as Mtb Beijing strains, in addition to the laboratory-adapted strains (van Soolingen et al., 1995). In this regard, we previously characterized the genetic features of the Mtb Korean Beijing strain (Mtb K) causing a high school TB outbreak in South Korea P 22077 via whole-genome sequencing (Han et al., 2015) and a comparative genomics approach to analyze the reference Mtb H37Rv strain (GenBank accession no. “type”:”entrez-nucleotide”,”attrs”:”text”:”NC_000962″,”term_id”:”448814763″,”term_text”:”NC_000962″NC_000962) and Mtb K (GenBank accession no. “type”:”entrez-nucleotide”,”attrs”:”text”:”CP007803.1″,”term_id”:”646273867″,”term_text”:”CP007803.1″CP007803.1). Interestingly, we identified MTBK_24790 (GenBank: “type”:”entrez-protein”,”attrs”:”text”:”AIB49023.1″,”term_id”:”646276343″,”term_text”:”AIB49023.1″AIB49023.1, hereafter referred to as InsB according to our previous study) (Park et al., 2014), an ESAT-6-like family protein encoded within the 5.7 kb gene cluster specifically inserted into the genome of Mtb strain K. Further analysis of sequences homologous to InsB by protein BLAST analysis1 revealed that an identical protein in the reported Mtb genome was found only in CDC1551, which was well characterized as a highly transmissible and virulent strain during TB outbreaks in the United States (Valway et al., 1998). In addition, our previous studies demonstrated that the recombinant InsB of Mtb K demonstrated a potential to improve the sensitivity of immunodiagnosis in both humans and mice (Park et al., 2014; Hur et al., 2016) by inducing an immune response differing from.