In vitro and in vivo cytotoxicity induced by an attenuated Salmonella: relation to bacterial carrier state and resistance to tumour growth.

In vivo and in vitro parameters of tumour resistance were examined after immunization of mice with the attenuated 11RX strain of S. enteritidis. During the bacterial carrier state produced by intraperitoneal (i.p.) or intravenous (i.v.) injection of 11RX the mice were resistant to i.p. tumour growth, could destroy i.p. injected 125I- or 131I-labelled tumour cells in vivo and had non-specifically cytotoxic peritoneal cells (PC) which could lyse 51Cr-labelled tumour cells in vitro. Most of the in vivo and in vitro cytotoxic activity could be attributed to activated macrophages (La Posta et al., 1982). The predominantly local nature of 11RX-induced anti-tumour activity was indicated by the superiority of the i.p. route of infection for induction of tumour resistance and in vivo and in vitro cytotoxicity. After i.v. injection of 11RX, none of the anti-tumour effects outlasted the bacterial carrier state. However, after i.p. infection, a dichotomy was observed between in vitro and in vivo anti-tumour effects. In vitro PC cytotoxicity lasted only for the length of the 11RX carrier state (approximately 30 days), whereas resistance to i.p. tumour growth lasted for 60 to 100 day s and was correlated closely with cytotoxic activity measured in vivo. Possible reasons for this dichotomy are discussed.