Table 4 Summary of advantages and disadvantages of physical delivery strategies used in DNA vaccination

Electroporation

• High levels of transgene expression

• Invasive

• Long-lasting gene expression

• Need for specialist equipment and training

• Safety demonstrated in numerous clinical trials

• Potential for tissue damage

• Commercially available delivery devices

• Two-step delivery process

Gene Gun

• High levels of transgene expression

• Invasive

• Long-lasting gene expression

• Limited DNA carrying capacity

• Safety demonstrated in clinical trials

• Need for specialist equipment and training

• Commercially available delivery devices

• Often need for multiple administrations

• One-step delivery process

• Low tissue penetration

Ultrasound

• Non-invasive

• Low levels of transgene expression

• Can be targeted to specific organs easily

• Need for specialist equipment and training

• Two-step delivery process

• Safety not yet widely demonstrated in gene therapy clinical trials