Viral RNA was detected in the sera of 19/35 mice 7 days after infection with DENV-2 NGC or DENV-2 S16803. By quantitative PCR assay with a detection limit of 1000 copies per reaction, viral titres detected in the sera of DENV-2 S16803 infected mice ranged from 1·2 × 104 to 5·7 × 107/μg of RNA at day 7 post-infection (Table 1). In mice infected with 108 PFU DENV-2 S16803 the titre peaked by day 14 and no viral RNA was detected by day 35 in any mice tested (data not shown). We next determined whether DENV-infected BLT-NSG mice generated antigen-specific T-cell responses. Seven days after infection, splenocytes from infected mice were collected and stimulated with overlapping peptide pools

(14 peptide pools containing 511 peptides; BEI Resources, Manassas, VA) that spanned the entire Staurosporine chemical structure DENV-2 genome to measure cytokine responses in an intracellular cytokine staining assay (Fig. 2a). T cells that develop in engrafted BLT-NSG ACP-196 cell line mice have the potential to be restricted

by multiple HLA alleles because they are educated on autologous thymus. Therefore experiments were performed to examine total antigen-specific T-cell responses regardless of HLA-restriction. We found that splenocytes from acutely infected mice responded to multiple peptide pools by producing IFN-γ. Five peptide pools, containing peptides from the NS2B, NS3, NS4A and NS4B proteins, significantly stimulated human CD8+ T cells from DENV-infected BLT-NSG mice to produce IFN-γ. To evaluate memory T-cell responses, DENV-2-immunized BLT-NSG mice were re-infected with DENV-2 NGC 2 months after primary infection. Seven days after a second immunization we assessed IFN-γ levels in supernatants of peptide-stimulated spleen cells by ELISA. Our not results indicate that peptide pools NS2B and NS5 pool 2 (P = 0·06) stimulated T cells to secrete IFN-γ (Fig. 2b). To determine whether CD8 T cells in BLT-NSG mice could respond to HLA-A2-restricted DENV epitopes previously identified in humans, we selected mice that were engrafted with HLA A2+ tissues. We assessed IFN-γ responses in splenocytes from BLT-NSG A2+ mice stimulated with

three HLA-A2-restricted peptides NS4B2353, NS4B2423 and NS4A2148 identified in our laboratory.22 We detected elevated frequencies of CD8+ T cells that responded to ex vivo stimulation with all three peptides by secreting IFN-γ (Fig. 3b) and a novel epitope on NS52582–2598 that was identified in screening assays by deconvoluting the NS5 pool. There were no significant differences between the frequencies of CD8 T cells that responded to HLA-A2-restricted peptides in BLT NSG A2 mice used in this study and the frequencies detected in cord-blood-engrafted NSG-A2 mice in our previous study.14 The frequencies of CD8 T cells that responded to the HLA-A2-restricted peptides in BLT-NSG mice engrafted with A2-negative tissues were low (0·09% NS4B2423, 0·04% NS4B2353 and 0·02% NS4A2148; n = 3).