In the present study, the selection of the 1 M concentration of NaSCN was a conservative MLN0128 concentration choice to avoid potential artefacts associated with higher concentrations, such as the modification of antigen structural components (e.g. the disruption of conformational epitopes; or the instability of antigen attachment to the ELISA plate: see [29] in which Guanidine HCl and

NH4SCN were evaluated). The relevance of the avidity ELISA in this study was confirmed by detecting HPV16 and HPV18 L1-specific AI increases at post-Dose 3 (Month 7) compared with post-Dose 2 (Month 2). These increases were in line with a previous study of the same vaccine [10] and with the anticipated affinity maturation of vaccine-antigen specific antibodies [21] and [22]. The impact of the interval

Screening Library between Dose 1 and Dose 2 in the 2-dose schedule on the magnitude of the AI was not evaluated. Although the data suggested that HPV16 and HPV18 L1-specifc AIs were higher one month after Dose 2 in a 0, 6 month schedule than in a 0, 1 month schedule, the length of time after Dose 1 (seven months rather than two months) may have also contributed to the magnitude of the AIs [28]. The absence of strong correlations between AIs and absolute antibody concentrations concurred with other published observations, in that the magnitude and quality of the antibody response are not temporally associated [9], [10] and [11]. In one of those studies, HPV16 L1-specific AIs were only correlated with neutralisation responses at one of the several time points examined over a 36-month post-vaccination period [10]. Furthermore, although the magnitude of absolute high-avidity antibody concentrations at Month 7 appeared to vary with the age of the vaccine recipient, the AI appeared unaffected. Therefore, this suggests that antibody Terminal deoxynucleotidyl transferase quality (as measured by AI) is not highly

linked to antibody quantity. Instead, the magnitude of the AI may reflect the magnitude of certain aspects of the T cell response including the involvement of TFH cells in the clonal selection of B-cell populations, such as B-memory cells and plasma cells, with high-affinity for the antigens [31]. Moreover, the induction of persistent B-memory and T cells after immunisation with HPV-16/18 vaccine has been demonstrated in several studies [11], [32] and [33]. Hence further investigations could be conducted to identify the relationship between the avidity of HPV L1-specific antibodies, their functional activity and the induction of B-memory and T cells. In the absence of clinical efficacy data in the 9–14 year olds, the assessment of the antibody concentration and quality in this population is crucial.