5B). Immunization with the full length human IgG1 DNA construct appears to show high- and low-frequency responder populations. The high-frequency population have

an average avidity of 1.4×10−10 M and the low frequency population has an average avidity of 8.1×10−11 M (Fig. 5C). Despite the disparity in frequency, the avidity of these two populations is not significantly different (p=0.14). The avidity of the responses from mice immunized with the construct lacking the Fc region demonstrate an average avidity of 3.7×10−9 M (Fig. 5C). The avidity of TRP2-specific responses in mice immunized with the full length construct is significantly enhanced for both the high and low frequency responders when compared to the Fab fragment immunized mice (p=0.016 and p=0.0007, respectively). These results suggest that the targeting of the high affinity FcR, FcγR1, plays a role in the generation of efficient immune responses. NVP-BGJ398 order This was further confirmed by RG7420 clinical trial the immunization of Fcγ−/− mice. WT and Fcγ−/− mice show high frequency. However, analysis of the avidity of these responses reveals that Fcγ−/− mice generate lower avidity (2.1×10−11 M) responses than WT mice (1.9×10−13 M) (p=0.0001) (Fig. 5D). This is emphasized by comparison

of the TRP2-specific responses at low peptide concentration in WT and Fcγ−/− mice which shows a significantly lower response in Fcγ−/− mice (p=0.0005) (Fig. 5E). This response is comparable to that induced by a construct lacking Fc region in WT mice. In contrast, analysis of the helper peptide-specific response shows no significant difference between

WT and Fcγ−/− mice when Fc region is present or absent. The role of FcγR1 was further suggested as there was no change in responses in FcγRIIb−/− mice Rolziracetam suggesting that this inhibitory receptor plays no role in the cross-presentation of this vaccine (data not shown). Vaccination to date has been relatively unsuccessful for treatment of cancer patients with established disease. It is widely accepted that the generation of high-frequency T-cell responses is not necessarily an indication of a competent immune response. In contrast T-cell functional avidity correlates well with an efficient anti-tumor immune response 1–4. Is the failure of most vaccinations in cancer patients therefore due to an attenuated T-cell repertoire or an inability of the vaccination to generate high-avidity responses? Several studies have shown that CTL can modulate their functional avidity. Recent studies in TCR transgenic mice have shown that an individual cell can give rise to progeny with different avidities suggesting that avidity modulation at the level of an individual cell may play an important role in the CD8+ T-cell response in vivo27. We have previously demonstrated that an Ab–DNA vaccine encoding defined T-cell epitopes is an efficient means to generate CD8+ and CD4+ T-cell responses but did not assess avidity 26.