Immunotherapy is another treatment modality for various cancers. There is little information on the antitumor effects of immunotherapy on implanted lung cancer mouse models. Toxoplasma gondii is able to potently induce a nonspecific stimulation of the host immune system. Therefore, this study evaluated the antitumor and antimetastatic effect of nonspecific immune stimulation by T. gondii in a Lewis lung cancer mouse model.

Femals C57BL/6 mice were injected with either Lewis lung cancer cells (1 X 10(6) per mouse) or 5 cysts from the T. gondii Me49 strain with various schedules. The number of survival days, the tumor size of the implanted muscle and the histopathological findings of each group were noted. In addition to these mice, the Toxoplasma antigen(50 micro gram per mouse) or a lymphokine (0.5ml per mouse) was added to boost the immunotherapy.

No mouse in the Toxoplasma-infected group had died, whereas the mice receiving only the cancer cells (cancer control) survived for 29.1±4.4days. Cancer cells were revealed from 1 week after cancer cell inoculation in the muscle and from 3 weeks in the lung of the cancer control, whereas cancer cells were found in both the preinfection control and coinfection control groups from 2 weeks and 4 weeks in the lung, respectively. The in the number of survival days were 32.4±3.3 in the mice receiving T. gondii 2 weeks prior to the cancer cells inoculation (preinfection control), 30.9±5.1 in mice received both simultaneously (coinfection control), and 34.9±2.9 in mice received T.gondii 2 weeks after cancer cells implantation (postinfection control). These 3 infection groups had significantly longer survival days and suppressed tumor growth than those of the cancer control. In addition to these mice, and injection with the Toxoplasma antigen alone or in combination with lymphokine resulted in a significant increase in the number of survival days.

These findings suggest that an injection with T.gondii can induce the antitumor and antimetastatic effects in Lewis lung cancer mouse models. Moreover, these effects were increased with an injection of the Toxoplasma antigen alone or in combination with lymphokine. However, this therapy can not prevent the development of cancer.