Folia Biologica
Journal of Cellular and Molecular Biology, Charles University 

We have investigated the capacity of cellular vaccines based on dendritic cells loaded with human HPV16 E6/E7 oncoprotein-derived peptides to induce immune responses in vitro and to elicit protective immunity in a murine experimental model mimicking human HPV16-associated carcinomas. Dendritic cells loaded with the HPV16 E6/E7 peptides exhibiting CTL or Th epitopes (E6_41-50, E6_81-90, E6_98-107, E6_130-137, E7_49-57, and E7_44-62) were able to stimulate in vitro DNA synthesis in syngeneic H-2^b spleen cells. The priming capacity of peptide-loaded BMDC and peptide-loaded dendritic cell lines DC2.4 and JAWS II was compared. It has been found that both peptide-loaded BMDC and established dendritic cell lines can activate the syngeneic responder cells, but the priming capacity of BMDC was substantially higher. In the second set of experiments, we have examined the cytolytic activity of syngeneic spleen cells after repeated activation in vitro with BMDC loaded with HPV16 synthetic peptides containing CTL epitopes. Significant cytotoxic responses against HPV16 E6/E7 antigen-expressing TC-1 targets have been found after repeated in vitro activation with all peptides containing the CTL epitopes. In contrast, peptide E7_44-62 harbouring both Th and CTL epitopes induced significant cytotoxic responses already after single in vitro activation. This cytotoxic effect could be enhanced with admixture of the E7_49-57 peptide. Experiments with MHC class I proficient (TC-1, MK16-IFNγ) and deficient (MK16) target cells revealed that the dendritic cells loaded with the E6/E7 HPV16 peptides activated CTLs in vitro, but not the other cytolytic effector mechanisms. The effectiveness of the peptide-loaded BMDC-based cellular vaccines was also investigated in vivo. C57BL/6 (H-2^b) mice were immunized with various peptide-loaded BMDC and subsequently challenged with TC-1 cells. The strongest protective effect was achieved with the BMDC loaded with the peptide E7_44-62 harbouring both CTL and Th epitopes. Mice immunized with the E7_44-62 peptide remained tumour-free after s.c. transplantation of the TC-1 cells and exhibited long-lasting protective immunity, whereas the mice immunized with E6_81-90 and E7_49-57 peptides did not remain tumour-free and exhibited only partial inhibition of tumour growth detectable as depression of the tumour growth curves.

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