Scientific discussion of trial results
Overall, 100% of the study participants (18 of 18) reported antibody positivity to at least two vaccine antigens, and 94% (17 of 18) reported positivity to three antigens; 56% (10 of 18) were positive to all four antigens.
Similarly, a deeper ELISpot analysis of the T-cell immune data showed that 78% (14 of 18) subjects showed T-cell responses to at least one vaccine antigen, 72% (13 of 18) responded to at least two antigens, and 50% (9 of 18) responded to all four antigens. Moreover, analysis of T-cell immune data 24 weeks after the last immunization showed that the responses were still detectable in 86% of evaluable patients, indicating that T-cell responses, in addition to antibody responses, persist for at least 6 months after the final immunization at month 3.
The investigators also undertook a more detailed analysis of antigen specific cytotoxic T-lymphocyte (CTL/killer T-cell) activity in the CD8+ T-cells from the high dose cohort of vaccinated subjects by measuring the expression of biologic markers like granzyme B and perforin (proteins that are known to be important in killing) as well as the direct killing of cells displaying HPV antigens on their surface through the release of granzyme B from the CTLs. Results presented in the paper show that these patients showed a significant increase in the amount of granzyme B and perforin found within their CTLs, and direct killing by CTLs was observed in all vaccinated subjects (6 of 6) in the high dose cohort. These results suggest that immunization with VGX-3100 generated CD8+ T-cells that were capable of making granzyme B and perforin upon seeing HPV antigens, and that these CD8+ T-cells were able to effectively use the granzyme B and perforin to kill cells displaying HPV antigens on their surface - a clear indication of the presence of a functional CTL/killer T-cell response.