COLON-CANCER CELL VACCINE PREPARED WITH REPLICATION-DEFICIENT VACCINIA VIRUSES ENCODING B7.1 AND INTERLEUKIN-2 INDUCE ANTITUMOR RESPONSE INSYNGENEIC MICE

A replication-deficient recombinant vaccinia virus, NYVAC, was develop ed by deleting 18 open reading frames in the vaccinia virus genome. Re combinant NYVAC, encoding the murine T cell co-stimulatory gene B7.1 ( CD 80) (NYVAC-B7.1) and the murine interleukin-2 gene (NYVAC-IL-2), we re prepared and the expression of B7.1 and the secretion of IL-2 were respectively confirmed in vitro. The use of these viruses to prepare a potent tumor cell vaccine was studied in a syngeneic murine CC-36 col on adenocarcinoma model, Mice were immunized on days 1 and 8 with 10(6 ) irradiated CC-36 cells that were infected with 10(7) plaque-forming units of either NYVAC-B7.1, NYVAC-IL-2 or a control virus, NYVAC-HR, w hich encodes a vaccinia virus host-range gene. These mice were then ch allenged with 10(8) viable CC-36 tumor cells on day 15. All mice (10/1 0) in a group that had received no vaccination and all mice (20/20) in a group that had received a control vaccine of CC-36/NYVAC-HR develop ed tumor 4-weeks after tumor cell challenge. Interestingly, only 16/20 mice in a group that had received CC-36/ NYVAC-B7.1 showed the develo pment of tumor after the same interval. The protection against tumor d evelopment and the reduction in tumor burden (as mean tumor diameter, 4 weeks after tumor challenge) were significant in this group when com pared to groups that were either unvaccinated or vaccinated with CC-36 /NYVAC-HR (mean tumor diameter = 6.51 +/- 3.2 mm compared to 26.5 +/- 0.9 mm or 26.2 +/- 1.8 mm respectively) (P = < 0.05). The protection a gainst tumor in a group of mice that received CC-36/ NYVAC-IL-2 vaccin ation was similar to that in the unvaccinated group or the group recei ving a CC-36/NYVAC-HR control vaccination. However, in a survival expe riment, mice that received either CC36/NYVAC-B7.1 or CC-36/ NYVAC-IL-2 vaccination on the day of tumor transplantation survived significantl y longer than mice that had not been vaccinated (median survival 60+ d ays, 60+ days or 23.5 days respectively) (P = < 0.05). Interestingly, when a therapeutic tumor vaccination was performed on day 4 after tumo r transplantation, mice that had been vaccinated with either CC36/NYVA C-B7.1 or CC-36/NYVAC-IL-2 did not show an improved survival when comp ared to mice in the control that had not been vaccinated (median survi val 28 days compared to 26 days or 25 days respectively). However, mic e that had received a therapeutic vaccination with CC-36 cells infecte d with both NYVAC-B7.1 and NYVAC-IL-2, 4 days after tumor transplantat ion, survived significantly longer than control mice that had not rece ived any vaccination (median survival 29.5 days compared to 25 days re spectively) (P<0.05). These results suggest that a replication-deficie nt recombinant NYVAC encoding the B7.1 gene and NYVAC encoding the IL- 2 gene can be used to produce an effective vaccinia-virus-augmented tu mor cell vaccine.