Robert C Carlisle

Alternatives are needed to remove the pain, injury, cross‐infection, and hazardous waste associated with needle and syringe (N+S)‐based vaccination. Reported here is the use of novel ultrasound‐responsive protein cavitation nuclei (pCaN), formed using the model antigen bovine serum albumin (BSA), to achieve effective transcutaneous delivery. Upon exposure to ultrasound (US), these pCaN instigate cavitation events which propel themselves and co‐located DNA vectors into the skin. US parameters as well as pCaN and DNA concentration are refined to achieve optimal expression of encoded luciferase transgene. Twenty‐four hours post‐treatment, luciferase expression in the skin, by IVIS imaging, was 1.67 × 10 6 ±941943, photons per sec for N+S intradermal injection and 1.49 × 10 6 ±261832 for cavitation‐mediated delivery ( p >0.05). Hence, there is no significant difference in luciferase level achieved, but improved homogeneity and reproducibility of expression are evident in mice treated using US‐mediated cavitation. Despite this equivalence in luciferase levels, a >5× higher level ( p <0.02) of anti‐luciferase antibodies is achieved when cavitation is used versus N+S injection. Antibody levels against BSA, resulting from the use of BSA pCaN, are equivalent for the two groups. PCaN can be formed from a range of antigenic proteins and DNA can encode a range of antigenic proteins, so this approach has wide‐ranging implications for needle‐free vaccination.

The promotion of anti-tumour immune responses can be an effective route to the complete remission of primary and metastatic tumours in a small proportion of patients. Hence, researchers are currently investigating various methods to further characterise and enhance such responses to achieve a beneficial impact across a wider range of patients. Due to its non-invasive, non-ionising, and targetable nature, the application of ultrasound-mediated cavitation has proven to be a popular method to enhance the delivery and activity of immune checkpoint inhibitors. However, to optimise this approach, it is important to understand the biological and physical mechanisms by which cavitation may promote anti-tumour immune responses. Here, the published literature relating to the role that cavitation may play in modulating anti-tumour immunity is therefore assessed.