BACKGROUND: As robust dengue-specific CD4+ and CD8+ T cell responses are essential for protective immunity, we assessed cell-mediated immune (CMI) responses to a DENV-2-based dengue tetravalent vaccine candidate (TAK-003) in adolescents living in Panama, a dengue-endemic country. METHODS: Peripheral blood mononuclear cells were collected from a subset of 67 participants >/= 10 years old included in a phase 2 clinical trial of TAK-003 (Clinicaltrials.gov: NCT02302066). Following stimulation with dengue peptides, the frequency, magnitude, and cross-reactivity of the CD8+ and CD4+ T cell IFN-gamma, TNF-alpha and IL-2 responses were assessed by flow cytometry. RESULTS: Intracellular cytokine staining identified NS1, NS3, and NS5 as the most common non-structural (NS) targets of the CD4+ T-cell response (IFN-gamma+); NS3 and NS5 were the main NS targets of the CD8+ T cell response (IFN-gamma+). Both CD4+ and CD8+ T-cell responses were multi-functional (IFN-gamma + TNF-alpha + IL-2+) and cross-reactive against DENV-1, -3, and -4 serotypes. Similar responses were seen in all CMI assessments irrespective of participant baseline status for dengue neutralizing antibodies and T cells. CONCLUSIONS: TAK-003 elicited cross-reactive, multi-functional CD4+ and CD8+ T-cell responses, irrespective of dengue pre-exposure.