Introduction
Zika virus (ZIKV), first identified in 1947 from a rhesus monkey in Uganda [1, 2], is a mosquito-borne virus belonging to the genus Flavivirus. In 2015, outbreaks of ZIKV were reported in Brazil, and infection was associated with microcephaly, central nervous system malformations and Guillain–Barré syndrome (GBS) [3]. On 1 February 2016, the World Health Organization (WHO) declared ZIKV a ‘public health emergency of international concern’. Moreover, ZIKV disease was listed as a ”Disease X” by the WHO in the ”Research and Development (R&D) Blueprint for Action to Prevent Epidemics” [4]. As of July 2019, cases of ZIKV had been reported worldwide, including 87 countries and territories, according to a WHO report [5]. To date, no accepted therapies or vaccines are available for ZIKV, and the WHO has made ZIKV vaccine development a top priority [6]. Substantial progress has been made on developing vaccines, which are essential to control the spread of ZIKV. Moreover, new vaccine search efforts are needed because of the complexity of ZIKV immunity and pathogenesis [7-9]. Neutralizing antibody epitopes exist on the surface of the ZIKV E protein [10, 11], and precursor membrane (prM) protein complexes with the E protein are usually ideal candidates for vaccine development.
The gram-positive enhancer matrix-protein anchor (GEM-PA) is a new bacterial surface display system [12]. GEM is a peptidoglycan skeleton of the cell wall obtained by the acid boiling of gram-positive bacteria (food-grade non-gene-modified L. lactis ). PA is the C-terminal domain of the AcmA protein (an important peptidoglycan hydrolase inL. lactis ). PA contains a lysin motif (LysM), which can noncovalently bind to peptidoglycan, thus anchoring to the cell wall of GEM [13]. GEM and PA are the vectors and carrier proteins of the system, respectively. Target proteins fused to PA can be anchored on the surface of GEM, namely GEM surface display system. In this study, the GEM-PA display system was used to display ZIKV prM-E glycoproteins on the GEM surface and study their immunogenicity.