Recombinant vaccinia viruses derived from strain Praha, clone P13, and strain MVA were used for intratumoral delivery and expression of IL12 genes in tumors induced by HPV16 E6+E7 oncogenes in mice. Intratumoral injection of 103 PFU of P13-IL12 virus resulted in an increase of intra-tumoral IL12 on days 6-13, while only low levels of IL12 were found in sera. After the inoculation of 106 PFU of MVA-IL12, the same levels of IL12 were found as in animals injected with control virus. The intratumoral inoculation of 103 PFU P13-IL12 resulted in only approximately 30% of the tumors being virus positive, which was a consequence of reduced multiplication of the recombinant virus in vivo. The number of virus-positive tumors was not increased by repeated inoculations on three consecutive days. Intratumoral therapy with a dose of 103 PFU of P13-IL12 slowed down the growth of TC1 tumors, but never caused their regression. When local P13-IL12 treatment was combined with antigen-specific, DNA-vaccination therapy, no synergy between the two treatments was observed. The treatment with IL12-expressing virus retarded tumor growth to some degree, but did not change the number of regressing tumors. The highest efficacy of intra-tumoral P13-IL12 therapy was observed when the TC-1/A9 cell subline, with downregulated MHC class I expression, was used. TC-1/A9 tumors are less refractory to treatment with 103 P13-IL12/EL than are parental TC-1 cells.

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