The study of the initiation and regulation of T-cell responses to vaccine antigens is of primary importance in the rational design of mucosal adjuvants. The detection in vivo of T-cell priming following immunization can be performed by using the adoptive transfer model of naïve antigen-specific transgenic T cells into immunocompetent mice. In this work, we discuss the applications of this system for detecting in vivo the primary antigen-specific clonal expansion, the phenotype, and the effector function of transgenic T cells following mucosal immunization. OVA and the mucosal adjuvant CTB were used as a model vaccine formulation and administered by the nasal route to study T-cell priming. T helper and T cytotoxic primary proliferation and expression of activation and migration markers was observed both in draining and distal sites. This method proved to be a powerful tool to study the efficacy of mucosal adjuvants in enhancing T-cell priming.