Dry tetanus toxoid (TTx) patches were formulated without any adjuvant, with excipients to impart antigen stabilization and to enhance skin delivery. The booster effects of the TTx patches were assessed using a guinea pig model. The study revealed significant rises in TTx IgG titers induced by the TTx patches after a low-dose subcutaneous (s.c.) prime with TTx adsorbed to aluminum hydroxide. The TTx patch can therefore be considered an effective alternative to a subcutaneous booster.T ranscutaneous immunization (TCI), using a topically applied needle-free patch, allows the delivery of an antigen and/or adjuvant into the skin, providing a powerful and effective alternative to traditional immunization (1). By taking advantage of antigen-presenting cells in the skin, TCI has been shown to induce robust immune responses to a wide variety of protein antigens, including those derived from bacterial and viral pathogens (2).In this communication, we describe a research study to develop a nonadjuvanted, monovalent tetanus toxoid (TTx) booster vaccine patch to deliver TTx antigen into the skin and induce adequate serum anti-TTx IgG responses. We envision that a transcutaneous TTx patch may be conveniently used to reduce maternal and neonatal tetanus cases, observed mostly in developing countries, and as a booster vaccination for the adult/at-risk population, which includes those who have not received a tetanus booster in the preceding 10 years, as well as those persons who are exposed to hot, damp climates with soil rich in organic matter.The main goal of our study was to compare the booster effect (i.e., immunogenicity) offered by the TTx patch versus that of a subcutaneous (s.c.) booster injection of aluminum hydroxide-adsorbed TTx in primed guinea pigs. Our study model was based on the European Pharmacopoeia (Ph. Eur.) section 2.7.8, in which standard methods (i.e., methods A to C) are described and used to determine the potency of a tetanus vaccine (3). For our study, we used a modified version to measure serum (enzyme-linked immunosorbent assay [ELISA]) anti-TTx IgG antibodies induced in s.c. immunized guinea pigs; instead of determining IU/ml for the serum samples, we calculated the half-maximum titer (50% effective concentration [EC 50 ]). It is also worth mentioning that the guinea pig is the preclinical model of choice to evaluate TCI, since the skin properties (e.g., stratum corneum thickness, presence and concentration of skin immune cells, etc.) of this animal are similar to those of humans (4).We utilized our patch technology (5) to prepare dry 3-cm 2 nonwoven patches containing TTx antigen (Statens Serum Institut, Denmark) at two doses, i.e., 18 (45 g) and 100 (250 g) Lf (limit of flocculation) units. The dry patches were formulated with a proprietary mixture of GRAS (generally regarded as safe) excipients (a mixture of carbohydrates and surface active substances) for antigen stabilization (maintaining a noncrystalline, amorphous phase and minimizing denaturation/aggregation) and to facilitate a uniform coat...
