1 μCi/106 cells of Na251CrO4 for 90 min at 37° and, where indicated, were pulsed for 45 min with 10−6 m of the different peptides at 37°. Cells were then washed,

and 4 × 103 cells were used as targets of each CTL at different effector to target ratios. The per cent specific lysis was calculated as 100 × [(c.p.m. sample)−(c.p.m. medium)/(c.p.m. Triton X-100)−(c.p.m. medium)], where c.p.m. represents counts/min. Spontaneous release was always < 20% in all cases. None of the tested peptides affected spontaneous release. Enzyme-linked immunosorbent spot-forming cell assay [ELISPOT; for interferon-γ (IFN-γ)] was carried out using commercially available kits (Becton-Dickinson, Franklin Lakes, NJ) according to the manufacturer’s instructions. buy JQ1 find more In brief, 96-well nitrocellulose plates were coated with 5 μg/ml anti-IFN-γ, and maintained at 4° overnight. The following day the plates were washed four times with PBS and blocked for 2 hr with 10% fetal bovine serum-supplemented RPMI-1640 at 37°. The CTLs were added to the wells (in triplicate) at a ratio of 10 : 1 and incubated

with target cells at 37° for 24 hr. Controls were represented by cells incubated with concanavalin A (Sigma-Aldrich, St Louis, MO; 5 μg/ml) (positive control), or with the medium alone (negative control). Spots were read using an ELISPOT reader (A.EL.VIS GmbH, Hannover, Germany). Results are expressed as net number of spot-forming units/106 cells.15 Surface expression of HLA-ABC molecules was detected by indirect immunofluorescence using anti-human HLA-ABC mouse monoclonal antibody (BD Pharmingen, San Diego, CA). Mean logarithmic fluorescence intensity was determined by FACS analysis (Bryte HS; Bio-Rad, Milan, Italy).13 It has been previously demonstrated that the HPV epitope, derived from the EBNA1 antigen (amino acid 407–417) and presented by HLA-B35 and HLA-B53 alleles of the B5 cross-reactive group, is one of the targets of EBNA1-specific Phosphatidylethanolamine N-methyltransferase CTL responses in healthy EBV-seropositive individuals.20 To identify specific responses to this epitope and to obtain HPV-specific CTL cultures for further evaluation, we investigated the presence of HPV-specific memory CTL responses in a panel of HLA-B35

healthy EBV-seropositive individuals. To this end, PBLs obtained from nine healthy HLA-B35 positive, EBV-seropositive donors (Table 1) were stimulated with the HPV peptide.24 As control, parallel stimulations were performed using the HLA-B35-presented YPL epitope derived from the EBNA3A antigen.5 The specificity of CTL cultures was tested after three stimulations using standard 51Cr-release assays against autologous PHA-blasts, pulsed or not with the relevant synthetic peptide. As shown in Fig. 1, HPV-pulsed PHA blasts were efficiently lysed by representative CTL cultures obtained from donors 5, 6, 7 and 8. Three of these donors also responded to the YPL epitope. Overall, these stimulations yielded HPV-specific CTL responses in six of the nine donors tested (Table 1).