Helios gene gun system instruction manual

Gold particles (Bio-Rad Laboratories, Hercules, CA 94547, USA) were used as microcarriers for the high-helium-pressure delivery of DNA vaccination. Microcarrier loading quantity (MLQ), the amount of Gold particles, was set to 0.5 mg per target according to the manufacturer’s recommendation for in vivo delivery. The amount of DNA loaded per mg of microcarriers is referred to as the DNA loading ratio (DLR), was set to 1 μg/mg DNA/Gold particles, giving 0.5 mg of Gold particles and 0.5 μg of DNA per cartridge. Cartridge preparation was conducted according to the manufacturer’s protocol (BIO-RAD Helios gene gun system instruction manual, #165–2431 and #165–243). Briefly, spermidine, CaCl₂, polyvinylpyrrolidone solutions and Gold particles were added to the purified DNA (at a concentration of 500 ng/μl) to bind it to the Gold particles. The DNA-gold mixture was injected to plastic tubes and dried using a gentle stream of nitrogen gas. Gold-DNA coated tubes were cut into 1 cm-long cartridges. Cartridges were stored in a desiccator at 4 °C until use.