Preventive and therapeutic antitumor effect of tumor vaccine composed of CpG ODN class C and irradiated tumor cells is triggered through the APCs and activation of CTLs

Abstract

The present study was aimed at assessing the ability of tumor vaccine – CpG ODN class C in combination with irradiated melanoma tumor cells B16F1 to trigger the antitumor immunity in experimental tumor model in mice (i.p. B16F1) as well as at evaluating some of its mechanisms of action. A significant preventive antitumor immunity was achieved with the vaccine and two additional injections of CpG ODN (the proportion of protected mice was between 75% and 100%). In more than 80% of survivors, a long-lasting immunity was triggered. The therapy with the vaccine and two additional injections of CpG ODN significantly prolonged survival of tumor bearing mice. The rates of cured mice were 21.1% and 11.1% in mice with smaller or larger tumor masses, respectively. The mechanism of stimulation of the immune system by this kind of vaccine is likely to be through the augmentation of APC maturation (a significantly increased proportion of CD86+ CD11c+ was determined in vaccinated mice), consequent activation of T lymphocytes (the proportions of CD25+ and CD69+ splenic lymphocytes increased after the exposure to activated DCs) and establishment of memory cells. In conclusion, vaccine composed of CpG ODN class C and irradiated tumor cells powerfully triggers the immune system bringing about both preventive and therapeutic effects.