2.1 Antigen and animals
HEK293 expressing recombinant SARS-CoV-2 S1 of the original Wuhan strain
(Assession# QHD43416.1, Val 16–Arg 685) was purchased from
ACROBiosystems (Newark, DE). Female BALB/c mice (age 6-8 weeks) were
purchased from Japan SLC (Shizuoka, Japan). All animals were maintained
under specific-pathogen-free conditions. Mice were anesthetized by
intraperitoneal injection of 62.6 mg ketamine and 12.4 mg xylazine per
kg body weight before vaccination. All mice used in this study were
treated according to the Guide for the Care and Use of Laboratory
Animals (NIH Publication No. 85-23, 1996) and the study was approved by
the Animal Care Committee of Tokushima University (#T2020-65).