The approach relies on the use of a device called the SonoPrep that temporarily increases the permeability of the skin, making it possible for vaccine antigens to penetrate into the dermal layer. Once there, they can stimulate the host immune response, just as they would by needle delivery, according to the company.
The preliminary results from the 20 patient study, conducted by Daniel Libraty at the University of Massachusetts Medical School, evaluated the immune response induced by using the SonoPrep device to allow the transdermal delivery of tetanus toxoid and Candida albicans, a form of yeast that can act as a pathogen in humans.
The SonoPrep device consists of a battery operated power and control unit, a hand piece containing the ultrasonic horn and the disposable coupling medium cartridge, and a return electrode. A clinician performs a skin permeation treatment by applying the ultrasonic hand piece to the patient's skin. The hand piece is pushed down on the patient's skin to activate the ultrasonic horn, and the patient holds the return electrode so that the device automatically shuts itself off, based on a drop in skin impedance (as measured by current moving through the return electrode) once the proper level of skin permeation is achieved.
In this study, 10 patients in the treatment group first received a fast (10-30 seconds) SonoPrep skin pretreatment on their forearm creating an imperceptible window for drug delivery through the skin. Then the tetanus toxoid and C albicans were applied topically to the treated skin sites. A 10-patient control group received the standard intradermal injection of the same antigenic proteins.
The immune responses induced by these antigenic proteins were evaluated by measuring the extent and duration of the skin reaction, known at the delayed-type hypersensitivity response (DTH). A DTH skin immune response was induced in 90 per cent of the SonoPrep treated patients and the duration of the DTH skin reaction was similar in the treatment group versus the control group.
"I think this is an innovative technology with interesting potential in vaccinology and modulation of immune responses to infectious pathogens," said Dr Libraty.
Flu shortage puts brake on development
Following the completion of this first study, Sontra had initially planned to complete a second human study at the University of Massachusetts Medical School using SonoPrep to facilitate the transdermal delivery of an influenza vaccine. But due to the current shortage of flu vaccines and concern by public health officials, Sontra has decided to donate its existing supply of flu vaccine to the medical school's clinical partner, UMass Memorial Health Care and will instead commence a second vaccine study later this fall with a hepatitis A vaccine.
Shikha Barman, director of transdermal drug development at Sontra, explained that SonoPrep allows an immune response to be induced by activating the Langerhan cells in the epidermis.
"To date the majority of vaccines are delivered by needle injection. Not only does SonoPrep have the potential to improve the efficacy of vaccines, transdermal vaccines also eliminate the risk of inadvertent needle generated disease transmission."