Vaccinia virus-infected C-C36 colon tumor cell lysates stimulate cellular responses in vitro and protect syngeneic Balb/c mice from tumor cell challenge.

Vaccinia virus (VV) was used to infect and lyse the Balb/c colon tumor line C-C36 to prepare oncolysate (VCO) with augmented immunogenicity. Mice treated with VCO and challenged with C-C36 were significantly protected against tumor growth as compared to untreated controls (P less than 0.001) and mice treated with CO (P less than 0.01). Moreover, protection induced by VCO was specific when growth inhibition of C-C36 was compared to that of meth-A (P = 0.027). Splenocytes from mice stimulated with VCO in vitro showed greater proliferation than splenocytes stimulated with CO alone or VV alone, suggesting induction of a unique VCO component. Additional evidence for a specific response was suggested by the observation that splenocytes stimulated with VCO in vitro demonstrated augmented cytolysis of C-C36 but did not show cytolytic activity against unrelated target cells. However, augmented cytolysis of the natural killer (NK)-sensitive YAC-1 by VCO-stimulated splenocytes was also observed. These results suggest that in vivo resistance to tumor challenge induced by VCO treatment may result from stimulation of both specific and nonspecific effector cells.