Needleless vaccine delivery using micro-shock waves

Abstract

Shock waves are one of the most efficient mechanisms of energy dissipation observed in nature. In this study, utilizing the instantaneous mechanical impulse generated behind a micro-shock wave during a controlled explosion, a novel nonintrusive needleless vaccine delivery system has been developed. It is well-known that antigens in the epidermis are efficiently presented by resident Langerhans cells, eliciting the requisite immune response, making them a good target for vaccine delivery. Unfortunately, needle-free devices for epidermal delivery have inherent problems from the perspective of the safety and comfort of the patient. The penetration depth of less than 100 μm in the skin can elicit higher immune response without any pain. Here we show the efficient utilization of our needleless device (that uses micro-shock waves) for vaccination. The production of liquid jet was confirmed by high-speed microscopy, and the penetration in acrylamide gel and mouse skin was observed by confocal microscopy. Salmonella enterica serovar Typhimurium vaccine strain pmrG-HM-D (DV-STM-07) was delivered using our device in the murine salmonellosis model, and the effectiveness of the delivery system for vaccination was compared with other routes of vaccination. Vaccination using our device elicits better protection and an IgG response even at a lower vaccine dose (10-fold less) compared to other routes of vaccination. We anticipate that our novel method can be utilized for effective, cheap, and safe vaccination in the near future.

Fig. 1.

(A) Schematic diagram of micro-shock wave generation from the polymer tube shows the initiation of ignition of the polymer tube by a spark generated by electrodes, the explosive coating undergoing combustion, the combustion flame front traveling at 2,000 m/s, and the micro-shock wave emanating from the open end of the polymer tube. (B) Sequential schlieren images of the micro-shock wave propagation from the open-end polymer tube. (C) Diagram showing pictorial views of the fluid jet delivery system before and after firing. dia, diameter. (D) Prototype model of the needleless delivery device.

Fig. 2.

Liquid jet delivery from the device. (A) Graph showing variation in pressure in the liquid inside the chamber of the device over time. (1 bar = 10⁵ Pa). (B) Microscopic image of liquid (water) jet delivered into the 4% agarose gel target merged using Adobe Photoshop. (C) Confocal images showing the penetration of fluorescent yellow-green latex beads delivered to 20% acrylamide gels using the device.

Fig. 3.

In vitro and in vivo testing of the device. (A) Gram-negative (Salmonella and E. coli) and Gram-positive (Listeria) bacterial cultures were placed in the cavity (without a discharge hole) and subjected to micro-shock waves to check the viability of bacteria using the device. The control bacterial culture was not subjected to micro-shock wave treatment. (B) Salmonella enterica serovar Typhimurium vaccine strain pmrG-HM-D (DV-STM-07) was administered to mice using the device, and the mice were sacrificed and dissected after 3 days to check the entry of bacteria in secondary lymphoid organs like mesenteric lymph nodes (MLN), spleen, and liver. In the control mice, DV-STM-07 was delivered by the oral or intraperitoneal (I.P) route. Each symbol represents the value for an individual mouse. The short black line shows the mean value for the group (5 mice in each group). (C) Confocal images (xyz scanning) showing the penetration of fluorescent beads delivered to the abdominal region of mouse skin using the device. (D) Fluorescent beads were delivered to the dorsal side of mice using the device, and a biofluorescence image showing the presence of fluorescent beads is shown. Min, minimum; Max, maximum.

Fig. 4.

Efficiency of vaccine delivery using the device. (A) S. enterica serovar Typhimurium vaccine strain pmrG-HM-D (DV-STM-07) was administered to mice using the device and by the intraperitoneal (I.P) route. The control mice were given phosphate-buffered saline (PBS) delivered using the device. Mice were infected with a lethal dose (10⁷ CFU/mouse) of virulent Salmonella orally, 5 days after the immunization. The MLN, spleen, and liver were aseptically dissected to check the Salmonella burden 4 days after the challenge. Values that are statistically significantly different (P < 0.005 by the Mann-Whitney U test) are indicated by the bracket and two asterisks. (B) Mice (6 mice per group) were infected with a lethal dose (10⁸ CFU/mouse) of virulent Salmonella orally 5 days after immunization as described for the previous experiment, and the percent survival of mice over time was determined. The values for the vaccinated mice and the control mice that were treated with PBS were significantly different (P < 0.0001 by the log rank test). (C) A single dose of DV-STM-07 was delivered using the device, orally, and by the intraperitoneal route, and the serum IgG levels were tested against Salmonella-specific lipopolysaccharide (LPS) using ELISA. Control mice were given PBS delivered using the device. Each symbol represents the value for an individual mouse. The mean value (black line) ± standard deviation (error bars) for each group of mice are shown. Values that are significantly different by Student's t test are indicated by the bracket and asterisks as follows: **, P < 0.005; ***, P < 0.0005.