Plates were washed as described above, serum samples were serially diluted 3-fold down the plate, and plates left for 2 h at room temperature. Plates were washed 3 times in wash buffer and 100 μL detection antibody AZD2281 chemical structure was added to each well (for mouse samples HRP-conjugated rabbit anti-mouse IgG (Jackson Immuno Research,West Grove, PA), for non-human primate samples HRP-conjugated goat anti-monkey IgG (Abcam, Cambridge) and incubated for 1 h at room temperature. Plates were then washed 3 times in wash buffer and incubated for 10 min in

the dark with 100 μL per well of a TMB substrate solution (BD). The enzymatic reaction was stopped with 50 μL per well of 2 N H2SO4. Optical density was read immediately after adding stop solution on a Versamax plate reader (Molecular Devices, Sunnyvale, CA) at 450 nm with subtraction at 570 nm. Data analysis was done using SoftMax Pro v5.4 (Molecular Devices) and the half maximum values (EC50) determined to calculate antibody

titers for each sample. We screened candidate epitopes for in silico predicted broad HLA class II allele cross reactivity and high affinity binding using the immune epitope data base (IEDB) CD4 T cell prediction tool [24] and [25]. A chimeric TT/DT epitope was designed that fit these criteria. We hypothesized that inclusion of two epitopes that would induce a CD4 memory helper T cell response in vaccinated individuals may provide an others advantage over individual peptides.

A cathepsin cleavage site, either pmglp or kvsvr [26] was introduced between the epitopes with the prediction that it would find more provide more efficient processing when taken up by antigen presenting cells. Pmglp was designed to be a selective cathepsin S substrate whereas kvsvr is a less selective cathepsin S, B and L substrate. Individual DT (D) and TT (T) peptides were generated (Fig. 1A) as well as a chimeric TD peptide without a cathepsin cleavage site. In addition, two chimeric peptides containing the pmglp or the kvsvr cathepsin cleavage site (TpD and TkD respectively) were also generated. The predicted reactivity of individual and chimeric peptides to 25 MHC class II alleles, as well as predicted binding affinity, and allele frequency are shown in Fig. 1B. The combined frequency of this set of alleles is predicted to have greater than 99% population coverage [25]. The predicted consensus of several algorithms is shown, where a lower score is a predictor of higher affinity binding. Scores higher than ten are not shown. Both T and D epitopes are predicted to have high affinity binding primarily across HLA-DRB1, with some binding to DP and DQ alleles. Interestingly combining the two peptides with a cathepsin linker in some cases alters the predicted binding affinity, for example HLA-DQA1*0301-DQB*0302.