0001) (Fig. 2C). The establishment of functional T-cell memory is vital for the success of an immunization protocol. To assess if functional CTL responses could be generated by a single immunization or if a prime boost regime Selleck Saracatinib were required, C57BL/6 mice were given single or multiple immunizations with TRP2/HepB human IgG1 DNA. No epitope-specific responses were detectable 20 days after a single immunization with TRP2/HepB human IgG1 DNA, but high-frequency responses were detectable after two immunizations (p=0.026) which increased further

with another immunization (p<0.0001) (Fig. 2D). The avidity of responses after two or three immunizations was analyzed. The responses induced in mice receiving two or three DNA immunizations were of high avidity (1.4×10−12 M and 1.8×10−12 M,

respectively). There is no significant difference in avidity between these two groups (p=0.89) (Fig. 2E). As both the frequency and avidity of the CTL response appear enhanced, the question “was avidity related to frequency?” arose. Over 80 mice were immunized with TRP2/HepB human IgG1 DNA and the frequency and avidity of responses measured. The avidity of the TRP2-specific responses ranged from 5×10−8 M to 5×10−13 M peptide. No significant correlation find more between avidity and frequency of TRP2 peptide-specific responses was identified, suggesting they are independent events (Fig. 3A). It is possible that xenogeneic human Fc influences the frequency and avidity of responses induced. Comparison of responses from immunization with human IgG1 or an equivalent murine IgG2a construct reveals similar frequency and avidity (Fig. 3B), suggesting that the xenogeneic human Fc was not influencing the response. Synthetic peptides have short half lives in vivo and are poor immunogens as they

have no ability to specifically target professional Ag presenting cells such as DC. Current therapies are showing DC pulsed with peptide induce an efficient immune response. TRP2/HepB human IgG1 DNA immunization was compared to DC pulsed with HepB/TRP-2 linked peptide. TRP2/HepB human IgG1 DNA demonstrated similar frequency responses compared to those also elicited by peptide-pulsed DC, both of which were superior to peptide immunization (p=0.0051 and p=0.0053) (Fig. 4A). Analysis of the avidity of responses reveals that the avidity in TRP2/HepB human IgG1 DNA immunized mice is 10-fold higher than with peptide-pulsed DC (p=0.01) (Fig. 4B). The TRP2 specific responses were analyzed for ability to kill the B16F10 melanoma cell line in vitro. Figure 4C shows that although responses from peptide and peptide-pulsed DC immunized mice demonstrate a good peptide-specific lysis, mice immunized with TRP2/HepB human IgG1 DNA showed better killing of the B16 melanoma cells (p=0.003). The enhancement of avidity could be related to direct presentation of the epitopes by the Ab–DNA vaccine and similar responses may be elicited by a DNA vaccine incorporating the native TRP2 Ag.