SummaryDetailed knowledge of dengue virus (DENV) cell-mediated immunity is limited. In this study we characterize CD8 + T lymphocytes recognizing three novel and two known non-structural protein 3 peptide epitopes in DENVinfected dendritic cells. Three epitopes displayed high conservation (75-100%), compared to the others (0-50%). A hierarchy ranking based on magnitude and polyfunctionality of the antigen-specific response showed that dominant epitopes were both highly conserved and cross-reactive against multiple DENV serotypes. These results are relevant to DENV pathogenesis and vaccine design. Dengue virus (DENV) is a major global health threat [1] and the cause of severe haemorrhagic fever (DHF), a lifethreatening disease when not addressed correctly [2]. DENV exists as four distinct serological types and DHF occurs at increased frequency after exposure to different (heterotypic) DENV serological types from the one that was first encountered [3,4]. Cross-reactive, CD8
Keywords+ cytotoxic T lymphocytes (CTL), together with other factors, are important in the aetiology of DHF, but their role is still unclear [5][6][7][8][9][10]. Disappointing results from a dengue vaccine in a recent paediatric clinical trial [11] also suggest that, in addition to high titre neutralizing antibodies specific for structural proteins, CTL directed to nonstructural viral proteins are likely to be important correlates of protection.T cell responses to the four DENV serotypes are quantitatively and qualitatively different [7,[12][13][14][15]. DENV crossreactive, memory CTL have reduced killing activity and are more prone to apoptosis upon encounter with novel DENV epitope variants encoded by the heterotypic serotype [16,17], although recent evidence has challenged this model [10]. Also, virus variants that result in diminished or abolished binding of DENV CTL epitopes to major histocompatibility complex (MHC)-I could result in the higher degree of mortality within epidemics [18].Two recent detailed analyses [10,19] have considerably expanded the existing knowledge [8] of DENV-specific T cell epitopes. There is still, however, a relative paucity of information regarding which DENV CTL epitopes correlate with protection or disease. DENV is translated as a single polyprotein that is subsequently processed into 10 mature, non-structural and structural proteins each containing CTL epitopes [8]. However, non-structural protein 3 (NS3) contains more epitopes (31% of the total) compared to the other nine DENV proteins and is also the most immunogenic, followed by NS5 (22% of the total) [7,8,10,19].Characterization of DENV CTL epitopes has so far relied almost exclusively on the use of synthetic peptides with sequences obtained from MHC-I binding prediction algorithms [10] or from testing pools of longer, overlapping peptides organized in matrices which are then deconvoluted. Even more importantly, few, if any, studies have confirmed the expression of these epitopes in DENVinfected cells and/or have determined the optimal length of the CTL e...