Generation and protective efficacy of a cold-adapted attenuated genotype 2b porcine epidemic diarrhea virus

Won, Hokeun; Lee, Dong-Uk; Jang, Guehwan; Noh, Yun-Hee; Lee, Seung-Chul; Choi, Hwan-Won; Yoon, In-Joong; Yoo, Han Sang; Lee, Changhee

A sow does not possess the means to transplacentally transmit maternal immunoglobulins to its fetus; hence, piglets are born without passive immune protection, being highly susceptible to a variety of infectious agents, particularly multiple enteric pathogens, such as PEDV. As a substitute, the passive immunity is dependent on the supplement of maternal-derived immune components via mammary secretions (i.e., colostrum and milk) [15, 33] . Therefore, maternal vaccination is the only crucial and effective tool to confer passive protection to newborn piglets through lactogenic immunity against PEDV infection. This objective may be accomplished by the selection of an ideal vaccine candidate, the antigenicity of which is close to that of an epidemic strain, and virulence is minimal or absent in piglets. In South Korea, several G1a PEDV-based live vaccines have been extensively employed to prevent PED for decades. However, owing to partial protection of these historical vaccines against the contemporary G2b strains prevailing since the 2013-2014 pandemic, a demand for the development of new effective vaccines based on the dominant epidemic strain has increased. Although efforts to pioneer a new G2b-based MLV vaccine have been made over the past several years, its success was delayed because of experimental hurdles such as a laborious long-term attenuation procedure in cell culture. It is acknowledged that cold adaptation of animal viruses at serially reduced temperatures for cultivation is the best method to derive a live virus vaccine line, as it is generally accompanied by loss of virulence [21] . In this study, we used a cold adaptation approach with a stepwise lowering of the cultivation temperature in vitro for PEDV attenuation and aimed to determine the immunogenicity and pathogenicity of the cold-adapted strain and its efficacy as an attenuated live vaccine candidate under experimental conditions.